Are you ready to be a test pilot?

My .02

I have read with great interest this entire thread from beginning to end. F1Rocket, Tom Maxwell, Cobra, Gmcjetpilot I agree with all of you. Now that I have said that I hope everyone recognizes that each one of these distinquised gentleman represent different sides of this debate. There are several issues being discussed here not the least of which is the question of which engine to put into my RV9A project.

Here are my thoughts on this debate as I have on occasion discussed them with anyone who is within earshot of me and willing to listen. I personally agree with leeschaumberg's comments stating that:

A good modern, efficient, and powerful aircraft engine in the size needed does not exist today.

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Let me preface anything I say from here on out with this statement. I am not an engineer, heck, I am not even a mechanic, I am just your average airplane manufacturer (after all that is how the FAA sees me when I register my homebuilt RV) out there trying to build the best airplane that I can so I can enjoy the pleasures in life I have chosen for myself to enjoy.

If you want to really look at alternative engines for aircraft there are others that no one in this thread has examined. I have talked with and read articles from knowledgable individuals who say that the real issue with producing power for an aircraft has to always revolve around the amount of torque that any engine can produce. It is the torque that allows for the ability for speed, climb, cruise, everything that we want an aircraft to do (at least in the prop world, I am not a jet jockey so this could be totally different for you turbine heads out there). Well, if you want torque, and lots of it, the ideal motor is going to be an electric one. Electric motors generate darn near 100% of its energy into torque. imagine the climb characteristics of an electric motor in your aircraft.

Of course the all important problem with electric motors is feeding it all of that electricity to generate that torque. Well, I would say that the true experimental aircraft builder out there who wants to look at alternative engines should be examining the hydrogen fuel cell industry. To me that is the future of propulsion whether it be ground based or airborn in orientation.

The Subies and the Wankels are still trying to tap into the same 70+ year technology that the Lycons are doing. The only true difference I am seeing between any of the "aircraft" engines and the "auto-conversion" enginees is in the secondary systems (i.e. ignition, cooling, mixture, transmission of power to the driving force, etc.). Ok, I know there are all of these debates that discuss the beefiness of what in the auto world can be called a big block 4 cyl Lycon to a small block Subie or Wankel. The reality is that whatever house you choose to reside in these are still the same old technologies that Orville & Wilbur, RollsRoyce, Henry Ford, Mercedes or countless of the other engine forefathers of the internal combustion world devised a century ago.

There have been increases in the capabilities (metalurgy comes to mind) to creat blocks of metal that can surround and control an extremely violent explosion countless thousands of times per minute that are much better than those gentlemen could do "way back then". However you look at it though, there really isn't much difference in the design.

Outside the above discussion however, this debate over Lycon's versus autoconversions really is a matter of economics. The reason I am examining the potential of the autoconversion is the fact that I wanted an economical engine to place in my RV that would give me the performance I want. However, the real truth of the matter is I am having a very hard time chinking down 25K plus into an engine. With that idea in mind I cannot understand why a new autoconversion engine package is coming out to be equal or more in price to a Lycon package. Afterall, that is the only real reason that I am willing to turn away from the tried and true proven "technology" of the Lycons. Now, I recognize that I could go out there and purchase an auto engine myself and configure it to operate in my airplane for cheaper than the 25K plus I would pay to some of these out their selling the "plug and play" packages. Truthfully though, I can do that with a Lycon for much less than the price of a new Lycon engine also and with a lot less trouble for my efforts.

I suspect that the motivation driving those choosing Lycon packages over autoconversions is the same motivation driving me to lean that way now too. As much as I like the Eggenfelner Subaru package, and I really do like it a great deal, the reality is that I can't really afford it any more than I can afford a brand new Lycoming Mattatuck clone IO-320 with FADEC installed and constant speed prop out in front. So, I will most likely end up finding a low or mid time Lycoming engine as inexpensively as possible to put into my RV. Perhaps I will have to rebuild it to meet my requirments. If so, since I am not a mechanic, I sure bet I will learn a lot about how these massive blocks of metal make airplanes fly.

Well for what it is worth there is my .02 on the subject. As I am just beginning my research on this engine issue I welcome any and all comments concerning my input. I honestly greatly appreciate all who have contributed to this thread. It makes for very interesting reading.

RVBYSDI
Steve Ingraham
Will be adopted by an RV9A
project on 06/02/05

George,
Im playing devils advocate here- the Lyc is the engine of choice for the masses, and that is fine with me as long as they are all satisifed.

You pretty much verified the points I was trying to make concerning rotary performance. First, 21 mpg is not bad for a 200 HP engine- compare that mileage to any small v-8. My Mustang Cobra (5.0 liter, 240HP stock) regularly gives 18-22 mpg depending on how it is driven. The RX7 mileage is only bad when compared to lower output engines, not when performance is similiar. The low-rpm torque deficit is a complaint of all small displacement motors- they just have to be driven differently than a musclecar to reach their potential.

Your lyc would have terrible mileage and worse performance in a car, because its top end rpm is severely limited by a long stroke. It would have to run at full throttle most of the time, at least until it melts down. It would be fine in a tractor however .

Theory vs practical application: The 13B rotary has abt 80 cu in displacement; Im guessing your Lyc is 360 cu in?? Same power output, same fuel burn rate. You have to rebuild every 1000 hrs, right? Tracy's Mazda shows no wear at over 2000 hrs so far. I (and others) have repetedly said that fuel burn rates are mostly a function of HP produced- the engine simply converts chemical BTUs into kinetic energy, no magic extra power involved.

The RVator article aside, Tracy reports that his lightly modified 13B (1989 model) generates 185 HP, drives his RV-4 abt 220 mph, gets 6.0 gph at cruise (170 mph) and 8.2 gph at 202 mph, TBO is 2000 hrs so far and counting (costs only $600 for a full rebuild), and his is a little lighter, but not significantly so, than a Lyc. Im pretty sure he uses a fixed prop too, but I could be wrong there.

The basic, first generation rotary is a close replacement for the much more expensive Lycoming- same weight, same performance, same fuel use, better reliability, lower initial and rebuild costs over its lifetime. The only argument I see FOR a Lyc is that everyone else has one and it is a little easier install. Remember, my criteria is durability/reliability, performance, then cost.

FWIW, Id probably pick a Subaru over a Lyc as well, because they run so much smoother and cost less over their lifetime as well. I feel the Rotary is the best option of the three, but a small cheap turbine engine would force me to reconsider.

Steve,
It is easier to generate big torque numbers by running high rpms through a transmission.

Do you have any idea how big and heavy the DC motor would have to be? How about the weight of batteries and high amperage cables? Whatever power source is selected in the future, it will have to be light-weight and probably environmentally clean.

Commercial fuel cells are probably at least 5-10 years into the future, and they still require a carbon source to fuel them, probably natural gas, which in turn, requires a strong (heavy?), high-pressure tank. A fuel cell powerful enough to power an aircraft would have to be huge and expensive to generate the amperage needed.

As long as we are talking future hopes, why not a helium or hot air filled vessel with nuclear-heated steam jet propulsion?

Do you have any idea how big and heavy the DC motor would have to be? How about the weight of batteries and high amperage cables? Whatever power source is selected in the future, it will have to be light-weight and probably environmentally clean.

Commercial fuel cells are probably at least 5-10 years into the future, and they still require a carbon source to fuel them, probably natural gas, which in turn, requires a strong (heavy?), high-pressure tank. A fuel cell powerful enough to power an aircraft would have to be huge and expensive to generate the amperage needed.

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Ok, first things first. I couldn't tell you specific numbers on the weight of a DC or an AC electric motor but I do know that a 20 hp electric motor generates more torque than a 150 hp internal combustion engine could ever dream of. Plus it is instantaneous tourque. The second the electricity is put to the motor it is generating 100% of its capable torque. That 20 hp electric motor is going to weigh somewhere in the neighborhood of 50 to 100 lbs. What does that 150 hp internal combustion engine with all of its necessary secondary components weigh?

Second, the hydrogen fuel cell does not require batteries. The fuel cell converts electron flow to usable electricity as the chemical reaction of the fuel cell strips hydroden atoms off of the "carbon source" fuel and those hydrogen electrons flow through a membrane. In fact, if science can overcome some obstacles, the ultimate fuel would be H20. Good 'ol water has the necessary energy stored in it to generate the electricity. And the last time I looked water weighs less than gasoline whether MOGAS or 100LL.

Now, third, you tell me. What is cleaner? Burning fossil fuels in an internal combustion engine or a chemical reaction with H2O that generates electricity as electrons flow from one side of a membrane to another and leaves left over hydrogen and oxygen atoms as waste?

Lastly, the hydrogen fuel cell definetly does not have to be huge and expensive. It is huge and expensive now for the same reason Lycoming engines are huge and expensive now. Both scientist(s) and aircraft companies (Lycoming, Continental, etc.) currently are attempting to recover any R&D and/or liability costs as quickly and as easily as possible.

RVBYSDI
Steve

Sun 'N Fun race results and alternative engines

Quote: Cobra "Id probably pick a Subaru over a Lyc as well, because they run so much smoother and cost less over their lifetime too. I feel the Rotary is the best option of the three, but a small cheap turbine engine would force me to reconsider."

Tracy Crook competed in the 2004 Sun ?N Fun 100. He ran in the 160hp category and came in 3rd.

The 2004 Sun 'N Fun 100 Race, had (4) categories: Generic +300hp, 180hp and 160hp classes and one 180hp RV category. Tracy flying in the 160 HP category came in third, at a very respectful 189.172 knots. He claims his engine puts out 185hp? Why race in the 160hp class? Is that all the rotary can do, 160hp? Why not run in the generic-180hp or 180hp-RV classes?

In the 180 HP RV class the winner (Lyc) came in at 204.254 knots. The top 5 finishers all came in above Tracy's 189.172 knots. In the generic 180hp class the top 6 finishers came in between 228 to 193 knots. Note: SNF 100 absolute times are known to be a little inflated due to the fact the race is not a true 100 miles as I have been told, ref. Van's RVator article a few years ago. http://www.aircraftspruce.com/sunfunraceresults1.php

Yes I agree the Lycoming is easier to install, and the installation time Tracy has spent "experimenting" on his RV-4 rotary engine, is probably approaching the time to build a whole RV. Nothing wrong with that but lets get real.

Tracy has tweaked the hell out of his plane and he is still off the pace, and my hat is off to him. I admire his work. Granted the other RV's airframe may be a little more elegant and have less drag, but that is the point. Most alternative engine installations have high cooling drag, despite the superior water-cooling. Certainly this is an area that needs more work in the alternative engine world. I am watching with interest.

Lycoming is a specific built, low rpm, high torque air-cooled purpose built aircraft engine, designed to be light and directly drive a propeller, fixed or hydraulic constant speed. I will be the next to install an alternative engine when Van's aircraft has a flight test of an alternative engine RV that cost the same or less than 180hp Lyc RV while giving better performance and economy or when the RV's with alternative engines start winning races. They are just not quite there yet. Also a hydraulic prop control would be nice in the reduction drive for these alternative engines.

Whether it is a Rotary, Subie or an engine yet invented, I am waiting with interest. For now a new Lycoming will provide the average RV pilot with more than 13 years of reliable service (from 60 years of statistics) without an overhaul. My old Apache had 160hp 2200 hour O-320's and good compression and low oil use, but than it was flown almost daily. It was still going strong when I sold it.

All the claims of better service and economy with an alternative engine is conjecture at this time. I'll get back you when I can point to a RV that has flown with a rotary for +2000 hours, +13 years, with no modification and only routine service. All tinker time must be recorded. Most of these planes are worked on more than flown, my be just for fun. Alternative engines are tinker heaven. Not that there is anything wrong with that. You want to fly, Lycoming. A new O-360 cost $18,000 and can be installed with "off the shelf" stuff with no modification. You want to tinker, put something else in. Oh yea, did I say LYCOMING RULES. (Nuff said it has been fun)

Cheers George

PS: "Small cheap turbine" is an oxymoron. For general (private) aviation in small aircraft, they are too expensive and likely always will be, when weighted against the number of hours of utilization, the flight "mission" and the mis-match of airframe and engine performance. If you need 500-6500hp engine, fly +800 hours a year, turbine yes, if you have $$$$$$.

And the last time I looked water weighs less than gasoline whether MOGAS or 100LL.

RVBYSDI
Steve

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Steve,
Not true. H2O is 8 lbs./gal.; Gasoline is 6 lbs./gal. This is why the sump drain in your airplane is at the lowest point when the airplane is at rest.

Interesting facts about fuel cells, though. I hope they get them R&D'ed soon. Would be an interesting way to power an aircraft.

Best,

since this thread is already in the weeds, let's have some fun with fuel cells:

there are already fuel-cell aircraft in the air...low-power, high-altitude solar/fuel-cell platforms that can loiter for months.

H20 doesn't contain "energy" in the conventional sense (we'll skip the quantum physics), i.e. water is not a fuel (unfortunately!).

Fuel cells require hydrogen and oxygen, which requires a LOT of electricity to "crack" H20 into 'H' and '0'.

Since H20 is among the most inert substances known, it requires (absorbs) large amounts of energy to break it apart.

the reverse is also true, i.e. H and O are among the most reactive of all elements (which is why both are not found in pure form in nature). allowing H and O to combine releases a large amount of energy in the form of heat.

the world's biggest fuel-cell vehicle is the space shuttle. that big tank is nothing but liquid H and O stored in separate tanks. the fire lights when the valves are opened. no spark necessary.

trivia: the fuel pumps on EACH shuttle engine could fit under the cowl of an RV yet they generate 70,000 hp. (it's no typo: seventy thousand) pumping 30,000 gallons per MINUTE ...or slightly higher than a rotary

most of our electricity comes from fossil fuels, so when you take into account the whole energy loop, fuel cells in cars are roughly the same total pollution as normal cars.

in the ULTIMATE 'hollywood' irony, the only "clean" fuel cells are those made from water "cracked" by electricity from nuclear power plants.

H2 and O2

I enjoy these conversation as I am always learning. My point for bringing up the discussion on Hydrogen fuel cells is that there are other alternative engines out there that may ultimately prove to be the best choice for producing thrust in our toys. The real change comes when someone thinks outside the box. The auto conversion people are attempting to do just that. Lycoming engines are definetly a proven commodity in the engine realm that is hard to beat when you look at overall cost and long term use. On the other hand as many in this thread have stated, if your goal is to experiment with your "experimental aircraft" and enjoy the tinkering process then the auto conversions may be a good alternative choice.

If anyone here is willing to admit the facts of the matter, the truth is that when we make a decision about the particulars of one engine type over another we are really looking at it in terms of the perspective that we choose to see it in. Lycomings rule! Subies rule! Wankels rule! Hydrogen rules! Well it all depends on the particular perspective one is looking at things. That is the way all our choices in life are decided upon. After all why did you choose an RV over a Glassair? Are RV's "better" than a Glassair? An argument that could go on for ever as I am sure Glassair pilots are just as loyal to their aircraft as anyone. "Better" is a point of perspective that can never have a definitive answer.

Thanks for the teachings. I will continue to be a willing student to all who are in the know. I will read and absorb as much as I can from everyone out there whenever I can.

RVBYSDI
Steve

Steve-
I have no idea how much DC power will be needed to fly- I do know that powerful dc motors tend to be very heavy and that they generate a lot of heat (and ozone, btw).

Re batteries- it is true that fuel cells do not require batteries to operate, but you do have to store the power when the current is not being used and more importantly, to meet peak loads. A large (heavy) capacitor might work, who knows?

As mentioned, water is heavier than gasoline and diesel (they float on water). Unless you can find a metallic catylist to split apart H-O bonds to free up the hydrogen fuel, it will take too much gross power to be efficient.

A fuel cell is environmentally friendly, but it needs hydrogen atoms to operate. What source do you propose as a hydrogen source? Because hydrogen is difficult to store (requires pressure tanks and is extremely corrosive/reactive), the easiest way to obtain it by oxidizing (burning) a hydrocarbon close to the fuel cell. Natural gas is a clean burning fuel- only water vapor and carbon dioxide are liberated; CO2 is a greenhouse gas however...

"The hydrogen fuel cell definetly does not have to be huge and expensive." My best guess is that it will have to be extremely large to generate sufficient amperage to power an aircraft- that requres a lot of membrane plate area. Most fuel cells now provide only low amperage.

George-
Didn't Tracy win the 2003 contest at 209 mph? His brochure mentioned a 3rd place finish at 217.5 mph in the 2004 race.

In any case, top speeds are not a particularly good way to compare power output between different aircraft, because so many other variables are involved (aerodynamic efficiency, pilot skill, weight differences, propeller efficiency, etc).

The only way I know of to actually measure HP is on a dynometer, and even there, they generally measure acceleration of a known mass moment to approximate torque, note the rpm, then calculate HP. IMHO, the actual peak ratings used for purposes of race classifications are probably estimated more often than not.

One additional thought: The "tinkering" that Tracy and others have done benefits everyone else thereafter- there is no need to reinvent things already accomplished. To assume that everyone has to go through the same development processes is incorrect, because rotaryaviation and other manufacturers offer the developed products at a reasonable price. The motor is the easy part, the difficulties involved development of the redrive, ECU electronics, and finding lightweight substitute parts where needed. To most of us, the work now only involves assembly.

More of my .02

Cobra,
I don't know if Hydrogen fuel cells will be a solution in the immediate future or not. What I do think about it is that the potential exist to make it work. Perhaps it will be an alternative. It will take some effort and inginuity by people willing to look at the alternatives to existing technology to do so. The way I look at things is this. I do not want to put aside an idea just because it hasn't been done before. This whole debate over traditional vs alternative powerplants is motivated by those who are always looking to change things for the better and those who are always living by the statement that "If it aint broke don't fix it".

The argument that I see against auto conversion engines stems from the philosophy that: "we have this proven technology (Lycon engines) that is designed specifically for aircraft use that works relatively well. Why would anyone want to do anything differently?" There are a miriad of reasons why I would choose to go with an auto conversion over a Lycoming. There are also a miriad of reasons why I would choose a Lycoming engine over the auto conversion. I need to examine for myself what I feel are the most legitimate reasons for one or the other and go with that decision.

Many people I see building and flying RV's are looking for one thing. Speed! Others, and I would lump myself into this group, are looking at RV's as a relatively inexpensive way to get into a very fast well designed cruiser that is enjoyable to fly. I am not exactly looking to build the fastest drag racer, hotrod Reno winning flyer. Others are building RV's because they enjoy the building process and enjoy tinkering with well proven designs. They are out there wanting to experiment with things to make the plane better, cheaper, faster ("We can rebuild him, we have the technology. . .na. . .na. . .na. . .").

I think the first group of speed merchants would be looking for the high HP output lightweight screaming engines (is that why the Rockets were designed?). The second group is looking for dependable long lasting performance from well proven engines that will not cause them too much headaches or hassles over long years of flying. The last group are the true pioneers who always feel there is a better mouse trap out there. They are going to always be pushing the envelope to find that better design that is going to allow for more. . .(more HP, more speed, more economy, more ???).

Just tell me to "shut up ah-ready" if you are tired of my comments and I will. Whether I continue to contribute or not, I will continue to enjoy the debate.

RVBYSDI
Steve

ship said:

the world's biggest fuel-cell vehicle is the space shuttle. that big tank is nothing but liquid H and O stored in separate tanks. the fire lights when the valves are opened. no spark necessary.

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I really like your contribution to this thread, and I am enjoying reading it. Apparently a lot of others are too, as indicated by the number of viewers. I dislike being an email cop, but for the sake of accuracy, I feel compelled to correct one little bit of your reply.

Hydrogen and oxygen are not hypergolic ( no ignition required for combustion). The Main Engines (3 SSME's on the back end of the Orbiter) do consume "vast quantities" of hydrogen and oxygen as you mention, but they do have spark igniters to initiate combustion. There are hypergolic propellants used on the space shuttle for the reaction control systems (RCS) and the APU's providing hydraulic pressure for the Thrust Vector Control systems for both the SRB's and the SSME's. You may have gotten these propellants confused with the SSME propellants.
For the historical record I hope this helps.
Don Hull

rv7boy said:

Hydrogen and oxygen are not hypergolic ( no ignition required for combustion). The Main Engines (3 SSME's on the back end of the Orbiter) do consume "vast quantities" of hydrogen and oxygen as you mention, but they do have spark igniters to initiate combustion. There are hypergolic propellants used on the space shuttle for the reaction control systems (RCS) and the APU's providing hydraulic pressure for the Thrust Vector Control systems for both the SRB's and the SSME's. You may have gotten these propellants confused with the SSME propellants.
For the historical record I hope this helps.
Don Hull

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Thanks for the kind words. You are absolutely correct. I was cross-feeding while editing to keep the post mercifully short. I was thinking about the peroxide in the RCS units. NAStee stuff! The LOX in the mains needs a Champion spark plug to get 'er lit

"Ok, first things first. I couldn't tell you specific numbers on the weight of a DC or an AC electric motor but I do know that a 20 hp electric motor generates more torque than a 150 hp internal combustion engine could ever dream of. Plus it is instantaneous tourque. The second the electricity is put to the motor it is generating 100% of its capable torque. That 20 hp electric motor is going to weigh somewhere in the neighborhood of 50 to 100 lbs. What does that 150 hp internal combustion engine with all of its necessary secondary components weigh?"





Since others have already commented that on the weight of water and that water cannont be used as a fuel, I won't get into that. I can't help but comment on the electric motor torque thing. Electric motors generate the most torque at zero speed, which means zero horsepower and can generate large amounts of torque at low speeds, but I think that we need a small physics lesson.

Horsepower, not torque is the number that matters. It's just basic physics. Power is the rate of energy conversion. ANY engine or motor producing 150HP at 2700RPM produces 291.8 ft-lbs. The equation to do this is Power = Torque * Rotational Speed where Power is in Watts, Torque is in N-m and rotational speed is in radians/sec. Since we generally use HP, ft-lbs., & RPM, the equation to use is:
HP = ft-lbs*RPM/5252

A 20HP electric motor will produce 10,504 ft-lbs. of torque at 10RPM (assuming that it produces 20HP at that speed), but it is still only 20HP.

In other words, assuming the same prop efficiencies, you will need a 150HP electric motor to keep up with a 150HP Lycoming.

This board is a lot of fun... thanks guys

just another .02 cent post, then I'm going to shut up and read more

Just to clarify:
Fuel Cell != Hydrogen engine... The two terms are improperly used as synonyms in the media.

Hydrogen combustion engines (both the shuttle: a rocket, or a conventional IC) operate on the same principle as any other combustion engine, the Main advantage to them is that they emit mainly H20 (although, they can also emit small amounts of HO (Hydrogen monoxide), so they're not completely clean. They also tend to react (combust) extraordinarily quickly, so they're better suited for rocket motors. In all other respects, Hydrodgen is an inferior fuel to Hydrocarbons. It packs a significantly lower energy density (almost 2:1 lower) meaning you need _Far_ more of it (in both volume and weight) for the same punch, is far more difficult to store and it is gaseous at atmospheric preassure (harder to work with).

You'll notice, the only hydrogen-powered rockets are _ENORMOUS_ vehicles... most smaller rockets actually are powered by methanol (a hydrocarbon) or its variants... on a small scale, the higher energy density far outweights the less efficiant (for _rockets_) burn.

But as it happens, slower burn tends to be better for IC's anyways.

So... Hydrogen itself is a pretty suboptimal fuel (especially when you consider it's very difficult to create in quantity).

Now-

fuel-cells are a (relatively) new technology. Both combustion engines and fuel cells capture the exothermal energy from a fast oxidizing chemical reaction. Combustion engines, however, are by definition extraordinarily thermodynamically innefficiant. Remember what I said about energy density? Well, a good combustion engine is capturing maybe, at _BEST_, 15% (haven't read the number in a few years, I think I'm being optimistic) of the available energy from reaction. The remaining 80-85 is lost to heat, noise and other undesirables.

Fuel cells, on the other hand, catalyze the exact same chemical reaction as combustion, but they do it in a very controlled environment where they can actually extract the exothermic electrons from the reaction and convert them straight into electric current. The advantage? a Thermodynamic efficiancy in the 50-80%... some of the most efficiant chemical processes known to man... Theoretically, fuel-cells converting fuel into energy at the same rate as a combusion engine will produce 4-8 TIMES the usable energy from the same amount of fuel consumed. Now, this energy is electric, not kinetic... so figure another 50% hit from the electric system and motor innefficiancies, but you're still looking at 2-4 times better efficiancy (more usable energy per fuel) than even the best combusion engines. Now go back to what I said about Hydrogen - it has half the energy density of Hydrocarbons... therefore the 'green' reason for a 'hydrogen fuel cell', is theoretically, you could get the same usable energy out of the same quanity of fuel as we're used to dealing with today... What the media doesn't tell you, is that if you ran a hydrocarbon through those same fuel cells (well, the catalysts have to be different for the different fuels), you would get twice the energy from _that_, ie, 2-4 times the range on the same time, and you wouldn't have to deal with the hugely inefficiant process of creating the hydrogen in the first place (a hydrogen based economy will only exist if we somehow find a vast, limitless supply of electrical energy such as space-based solar or fusion... barring that, creating the hydrogen with modern generating technology creates _FAR_ more pollution than burning the equivolent hydrocarbons... I hate to say it, but its true).

But, I digress.

The other rub the Fuel cells (and why they're taking so long) - note in my above caveat, I say that "If you're reacting fuel at the same rate as a combustion engine...", well, we're not yet. In fact, so far we're _far_ from it. Now - the added thermodynamic efficiancy means you don't nead to react as much fuel to get the same energy of course, but current fuel cell car's require multiple large and heavy fuel cells in produce enough current to provide for fairly mediocre automotive performance. Now, there's no reason why this won't change, and god knows, a bunch of people a hell of a lot smarter than me are spending a lot of time working on it... But until fuel cell weights and rates get a _LOT_ better than they are now, you won't be seeing them in a plane any time soon. (we're probably 10-15 years before they're suitable for cars, give or take... give it another 10 or so before they are light enough for planes? I dunno... I pulled those numbers straight out of my rear... but don't hold your breath)

I am glad I have all of this info to decipher

Let me preface anything I say from here on out with this statement. I am not an engineer, heck, I am not even a mechanic, I am just your average airplane manufacturer (after all that is how the FAA sees me when I register my homebuilt RV) out there trying to build the best airplane that I can so I can enjoy the pleasures in life I have chosen for myself to enjoy

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Thanks to everyone who has set this po' boy straight concerning the skinny on all of this high tech mechanical/scientific stuff. I definetly will be the first to say that I am not the smartest kid on the block. . . wait I did say something like that in my first posting (yeah that was my quote above). I am on this website to learn as much as I can so I am glad you guys are here. My comments about hydrogen fuel cells and electric motors were to open the debate to include true alternative powerplants. I for one am unwilling to accept the fact that internal combustion engines that were created over a century ago are the ultimate answer to powerplant capabilities.

This thread seems to have started with the discussion of traditional aircraft powerplants vs alternative (auto conversion) powerplants and everyone seemed to be sticking with their own perception of what they thought were the "best" for our RV's. I hope my posting on fuel cells has not detered others from continueing with that original intent of this thread.

RVBYSDI
Steve

RVbySDI said:

I hope my posting on fuel cells has not detered others from continueing with that original intent of this thread.

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Actually, I think we have a classic in the making. I don't know about anyone else, but IMHO this thread is just STARTING to get interesting. THIS is what 'experimental' is all about , i.e. educational as per FAA Part 'whatever' that oulines the nebulous 51% rule.

Just look at the "views" on this thread.....higher ratings than American Idol

The ultimate beauty of it is there's no "right" answer....never will be.

I actually make a point to check this thread religiously. As far as I'm concerned, we've got a TERRIFIC virtual hanger with a bunch of liars sitting around telling tall tales willing to learn a thing or two from each other. Now all we need are some virtual beers...

PS: fuel cells (and hydrogen engines) ...and electric cars...have been around as long as the IC engine.

PSS: there's a nuke powered airplane ...flew long ago. There truly is nothing new....so far. Practical? that's another story.

KEEP THOSE LETTERS COMING !!!

uh, wasn't this thread about engines?

SCENIC DETOUR

hypergolic
exothermic
thermodynamic efficiency
energy density
catalyze

uh oh..I can hear some eyes glazing over. we're getting into deeper waters with some of these technical terms.

in the spirit of keeping this thread educational and fun, let's define them in laymen's terms so we don't leave anyone feeling left out when they crop up in the engine discussions (remember them??):

**disclaimer** chem was my WORST subject in engineering school but I somehow aced physics and thermodynamics. don't ask me how.

HYPERGOLIC = combustion without external ignition source
-- certain chemicals, when mixed, will ignite explosively without provocation
-- my first marriage

EXOTHERMIC = any chemical reaction that gives off heat
-- your 5-year-old lights the living room carpet on fire
-- the average mother-in-law
-- tabasco sauce (not really exothermic but you get the idea)
-- all internal combustion engines utilize exothermic reactions

freebie:
the opposite of exo- is ENDOthermic = any reaction that removes heat or needs heat
-- welding
-- the average marriage
-- evaporation
-- baking cookies

THERMODYNAMIC EFFICIENCY = warning: don't spring this one at the cocktail party unless you KNOW there's nobody in the room who knows what you're talking about!!!
-- here's the "money" line for impressing your date = "the percentage of "E=MC squared" that ACTUALLY gets converted into work (kinetic, mechanical, moving) energy via heat transfer"....hooyah!!
-- when the schlub next to you asks what that means, you rattle off: "how much of the fuel's mass gets converted into heat gets converted into pressure which gets converted into moving that piston down or turning the turbine wheel which is measured as horsepower"
-- when they melt and ask for your autograph, you say in a suave, cool voice of confidence: "the percentage of the heat that is converted into horsepower. a 100% therm. efficient IC engine would be silent, cold with no exhaust"
-- leave the party NOW!! while you're still in the smoke screen.

freebie:
this is not to be confused (as it usually is) with mechanical efficiency, i.e. friction losses, etc. which actually GENERATE heat ....

"but you just said that heat= power? so an engine can create it's own power?" NOPE!!

clear as mud, right??

ENERGY DENSITY = horsepower per unit of weight or volume of fuel
-- how many hot dogs per gallon of propane in the grill as compared to burning a gallon of 100LL OR a gallon of hydrogen in the 'ole Weber

-- (yes yes I know it's BTU not horsepower per unit but it's easier to take the short cut for the sake of explanation )

CATALYZE/CATALYST = a substance that initiates or accelerates a chemical reaction without itself being affected
-- the chemical version of your basic spark plug
-- the average mother-in-law


WHEW!....i'm tired of reading this myself....back to our regularly scheduled program

Hydrogen is Not the 'Holy Grail'

Hello everyone,

I too have been following this thread with great interest. It is interesting to hear the many ways that people have tried to raise the efficiency of the Otto cycle piston engine over the years. We all seem to tackle the problems of inefficiency by looking to different fuels and by porting the heads.

Hydrogen has been hearalded as the panacea for years and we have spent billions in research trying to make a square peg fit into a round hole. I have heard the truth about hydrogen only once in all of my research into alternative fuels and engines. It is that there are only two ways to make enough of it to make a difference. Large scale nuclear and even larger scale wind. Both will take a catastrophe before being implemented.

Engineers use ?well-to-wheel? analysis to determine which engine option has the most promise. This accounting approach considers the energy consumed in the following processes: extracting the raw energy source (e.g., crude oil, natural gas), transporting the raw energy source to a refinery, refining the raw energy source, transporting the refined energy source to the consumer, transforming the refined energy source into vehicle motion.

The well-to-wheel analysis uses three energy sources: petroleum, natural gas, and renewables/electricity. The most desirable systems require the least amount of energy to move a vehicle 1 mile. The following key describes each approach:

Gasoline ICE: Gasoline-powered internal combustion engine (Otto cycle)
Diesel ICE: Diesel-powered internal combustion engine (Diesel cycle)
Gasoline Fuel Cell HEV: Fuel cell hybrid electric vehicle with gasoline reformer
Diesel ICE HEV: Diesel-powered internal combustion engine, hybrid-electric vehicle
Naphtha Fuel Cell HEV: Fuel cell hybrid electric vehicle with naphtha reformer
FT Diesel ICE: Fisher Tropsch diesel-powered internal combustion engine
CNG ICE: Compressed natural gas, internal combustion engine
FT Naphtha FC HEV: Fisher Tropsch naphtha, fuel cell hybrid electric vehicle
Liquid H2 FC HEV: Liquid hydrogen fuel cell hybrid electric vehicle
Methanol Fuel Cell HEV: Methanol fuel cell hybrid electric vehicle
Gaseous H2 FC HEV: Gaseous hydrogen fuel cell hybrid electric vehicle
E-85 ICE: 85% ethanol/15% gasoline internal combustion engine
Electrolysis GH2 HEV: Electrolysis-produced gaseous hydrogen hybrid electric vehicle
Ethanol Fuel Cell HEV: Ethanol fuel cell hybrid electric vehicle

The results of this study showed that the most efficient systems they examined are the fuel cell hybrid electric vehicles, followed closely by diesel hybrid electric systems.

The most efficient system considered (fuel cell hybrid electric vehicle) is only about 20% more efficient than a conventional diesel engine and about 35% more efficient than a conventional gasoline engine. Considering their great cost and complexity, these conventional approaches hardly seem worth the trouble.

So we need to stop deluding ourselves in thinking that we are going to get anywhere with these collective efforts in raising efficiency. We need to come up with a different type of engine that will deliver:

High efficiency (44%-64%)
Low Pollution
Low Cost
Low Maintenance
Long Life
High Power Density
Negligible Vibration
and Multi-fuel Capability

This seems like a lofty list dreamt up by some pilot who lost touch with reality! To obtain an efficiency of 60% one would have to design an engine that would HALF the fuel consumption of established engines.

There are 2 patented engines out there that can put a check mark beside every one of the deliverables listed above. They are truly revolutionary. (please excuse the pun) The problem with the current engine manufacturing establishment be it automotive or aerospace is that of inertia. The established engine manufacturers have millions, if not billions invested in producing the Otto cycle engine. This type of engine has become the standard and they will fight to protect their investment. You have all heard the story of the little guy who invents a carb that returns 80mpg. He takes it to the establishment and they promptly buy him out. At all costs!!

I put out a feeler the other day to a forum that I belong to. One that listed the hypothetical engine characteristics of these two engines. I then asked a simple question. "What would a company have to demonstrate to you with regard to the hypothetical engine before you would be comfortable buying one?" The responces were varied and I think that a few people thought I was off my nut!!

I was pleased to receive a number of responces from people who truly believe that we are still innovators and inventors. We are going to be flying 100 years from now burning fuel that we grow in a sustainable way using engine technology developed today wondering why there were so many of the flying establishment resistant to change.

Let's all open our minds to the possibility that we can convert more than 30% of the btus in gasoline to work done. Let's shoot for an engine that will approach 70% efficiency and put one in an airplane and as one respondent suggested "...fly it across the Atlantic..." just to thumb our nose at the establishment!!

Dave Hertner
Effectus AeroProducts Inc.

Skepticism

Let's all open our minds to the possibility that we can convert more than 30% of the btus in gasoline to work done. Let's shoot for an engine that will approach 70% efficiency and put one in an airplane and as one respondent suggested "...fly it across the Atlantic..." just to thumb our nose at the establishment!!

Click to expand...

Dave, It sounds like you have information on this engine, and you want to get it developed. If the designs are patented, then there should not be a problem telling us the details. Most of the responses to your earlier post were what I would call healthy skepticism.

When electronic ignitions came out for aircraft engines, 99% of the people spent a lot of time telling us how horrible and dangerous they were. Today, they are accepted as "good things". The same will happen with your proposed engine once people see it working. It's as simple as that.

I stand by my earlier comments to your original post. If you can develop such an engine, I would not waste time on the aviation business - the market is too small. I, for one, would love to hear more details.

Dave Hertner said:

To obtain an efficiency of 60% one would have to design an engine that would HALF the fuel consumption of established engines.

Click to expand...

...or double the amount of work extracted for same fuel.

There are 2 patented engines out there that can put a check mark beside every one of the deliverables listed above. They are truly revolutionary.

Click to expand...

since they're patented: what are they? Fisher Tropsch? what fuel types?

What are they?

Ship and Mickey,

Have a look at www.starrotor.com and www.quasiturbine.com and let me know what you think.

Dave

Maximum thermo Efficiency

Just so we are truly all on the same page when talking about increasing the efficiency of a heat engine.
Some french guy named Carnot, showed the maximum thermodynamic efficiency possible in a heat engine operating between two heat reservoirs could be described as the (Tmax-Tmin)/Tmax.

If we look at the peak combustion temp in the engine as being around 5000 R and the exhaust at around 2000 R, then the max possible thermo efficiency is 60%. This accounts for no frictional losses and other heat losses. The actual
carnot cycle is purely theoretical and an internal combustion engine is pretty far removed from that.
While the actual thermo efficiency of a well tuned otto cycle engine is probably 30% or less, the ability to double that in the real world is unlikely. The Carnot efficiency is like the speed of light; you can't exceed it for a HEAT engine.

Dave Hertner said:

Ship and Mickey,

Have a look at www.starrotor.com and www.quasiturbine.com and let me know what you think.

Dave

Click to expand...

Interesting stuff, but the plot in Quasi website says it all: gasoline and diesel piston engines are STILL the most efficient converters of BTU to work after 100 years (nuke doesn't count for this exercise).

I had a long-winded response outlining the shortcomings of both, but I decided it was better to spare the forum from any more torture.

It is probably possible to improve the efficiency of any internal combustion engine simply by letting it run hotter- it just will not last very long without lubrication and will blow itself up from detonation. Cooling is not compatible with high-efficiency because it compromises btu's generated from fuel oxidation. Everything is a compromise; most of us prefer an engine that runs reliably with as much durabiltiy as we can get.

Id guess the most efficient motor is probably electric and/or ion drive, but only under cryogenic conditions with superconducting magnets and windings- hardly practical in a small aircraft.

btw- I found the quasi-rotary engine quite interesting. partiucularly that it was designed to run in the detonation mode. Compared to the Mazda, it looks (to me) like it would have big problems with hot spots, durability, and carbonizing with its rollers completely exposed to combustion heat and fuel mixture. Eventually, it would lose compression and fail as the "parallegramed levers" freeze- it therefore looses the real advantages of the rotary design (simplicity, reliability, durability).

If I understand the first example, it looks like a normal jet engine with an external combustion chamber between the compresser and turbine (I dont see any advantage there).

Starrotor's main design feature violates the intake heat paradox of heat engines, i.e. adding more heat to the intake charge will lower the power density.

Quasiturbine is more realistic in theory, but it appears to be a modified Wankel despite the rhetoric to the contrary. I would expect similar "negatives" as Wankel: Low compression, poor low-end torque; poor fuel efficiency & emissions problems. The "flexing" rotor is worrisome. And there's no clear way to transmit power out of the engine.

The "detonation" theory is poorly articulated on the Quasi site. The discussion fails to account for the VERY scary dynamics of shock waves, i.e. reflection, interference, wavefront compression, etc. etc.

Detonation engines have historically done just that: detonate.

In pure 'work' terms, the most efficient engine system is still -- drum roll please -- the closed-loop steam turbine. Stick a nuke in the burner, add secondary recovery and you've got the holy grail (so far). Staggering power out of mere kilograms of fuel with no combustion byproduct, almost zero friction loss and low heat loss with regenerative recovery systems. See "Navy".

Not exactly practical for everyday use in planes ...but it HAS been done

I agree Ship,

Detonation has a nasty habit of reforming metal (into missiles?). I should add that pressure and heat cause detonation.

The downsides you mentioned with Wankels are partly overcome by turbocharging (lower noise output, increases the "implied" compression ratio, better low end torque, better effiiciency, better forced airflow) but it still has some issues with leakage between the exhaust and intake cycles that hurts emissions.

Good call on the efficiency of the nuc steam engine. Doesn't the Navy still use generators and electric motors between the engine and propeller?

Ship, you're correct to dismiss the starroter and quasiturbine as revolutionary new engine technologies. Their claims are typical pie-in-the-sky bulls**t one hears reads about untested "new" ideas. All upside and no discussion of the disadvantages. As cobra pointed out, they are similar in many respects to existing technologies and suffer from additional drawbacks.

However, on one point, I must disagree with your assessment. The starroter's heat recovery mechanism is a reasonably good idea. Note that the exhaust heat exchanger is inserted downstream of the compressor and upstream of the combustor. In this position, it heats up the compressed inlet air in the same manner as the combustor. A well-designed exchanger in this position could make a significant improvement to the overall efficiency. It wouldn't make up for the design's mechanical problems or the low pressure ratio (6:1). The same idea could be applied to a gas turbine engine. In fact, I bet it's been tried but the high air flow rates of a turbine probably make it impractical.

My 2 cents.

Kev

kcameron said:

the exhaust heat exchanger is inserted ... upstream of the combustor.
Kev

Click to expand...

you're right...I didn't look closely enough and assumed fuel was being introduced earlier. The low p.r. would make preheat more effective vs. high p.r. engines.

either way, the concept is d.o.a.

E-plane

cobra said:

Steve-
I have no idea how much DC power will be needed to fly- I do know that powerful dc motors tend to be very heavy and that they generate a lot of heat (and ozone, btw)....

A fuel cell is environmentally friendly, but it needs hydrogen atoms to operate. What source do you propose as a hydrogen source? Because hydrogen is difficult to store (requires pressure tanks and is extremely corrosive/reactive), the easiest way to obtain it by oxidizing (burning) a hydrocarbon close to the fuel cell....

My best guess is that it will have to be extremely large to generate sufficient amperage to power an aircraft- that requres a lot of membrane plate area. Most fuel cells now provide only low amperage.

Click to expand...

This discussion prodded my memory. I was at Oshkosh 2003, and saw an electric plane (trucked in from Worcester, MA). I haven't heard much from them since.

A non-profit associated with Worcester Polytechnic (FASTec) was trying to adapt a fuel cell to a Dynaero Lafayette III modified glider. They were supposed to be starting with a 25kW cell and moving up to 75kW for a 2004 race sponsored by Boeing. No word on if the project got off the ground. Pun intended.

Aviation Today article
WPI article
Aviation Now article

Regards, Paul

Now, this I know

cobra said:

Good call on the efficiency of the nuc steam engine. Doesn't the Navy still use generators and electric motors between the engine and propeller?

Click to expand...

Steam plant efficiencies (thermal) are on the order of ~30-33%. Lot's of heat rejected to seawater. The Navy currently uses steam turbines attached to to propeller via a reduction gear system. It also uses steam driven generators for electrical loads on the ship. By the way, the Navy is researching a way to use an electric propulsion system on all its future vessels. CHINFO website

As far as nuclear powered aircraft, it has been tried, believe it or not. I spent 6 months up at Idaho Nuclear Engineering Lab during navy nuc training and saw the carcass of the project failure on site.

AirAttack.com article INEL site info radiationworks.com site

cobra said:

Doesn't the Navy still use generators and electric motors between the engine and propeller?

Click to expand...

in newest subs, yes. steam turbines drive gens. near-total heat capture & regen. cryogenics. exotic alloys for corrosion control. very compact. ultra slick. obviously money is no object.

nuke surface ships use direct-turbine shaft propellers (geared). electric pods have proven troublesome so far on massive cruise&cargo ships. might see them on next-gen stealth ships.