Van's Air Force
Don't miss anything! Register now for full access to the definitive RV support community.
Continental Turbo Diesel
- Thread starter Tandem46
- Start date
John Clark
Well Known Member
Diesel power
Tobin, almost everyone in the aircraft piston engine industry has "been working" on the diesel alternative. Here is a very encouraging article, sadly it is from the 1998 NBAA Convention. I am seriously interested in a diesel, but not holding my breath.
http://www.aviationweek.com/shownews/nbaaday1/hardwr18.htm
John Clark ATP, CFI
FAAST Team Representative
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA
Tobin, almost everyone in the aircraft piston engine industry has "been working" on the diesel alternative. Here is a very encouraging article, sadly it is from the 1998 NBAA Convention. I am seriously interested in a diesel, but not holding my breath.
http://www.aviationweek.com/shownews/nbaaday1/hardwr18.htm
John Clark ATP, CFI
FAAST Team Representative
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA
Tandem46
Well Known Member
John,
Thanks. Yes, I've been following the diesel thing for about ten years. The GAP program was a disappointment and DeltaHawk......well, you know. The Continental ad "photo" looked like a finished product. Btw, found this from May of this year: https://docs.google.com/document/d/...w/mobilebasic?authkey=CLWTs7wO&pli=1&hl=en_US
Maybe I'll giveContinental a call.
Continental diesel
Last year, before being purchased by the Chinese, TCM purchased the technology from SMA to further refine and produce the 4 cyl, 4 stroke turbo diesel engine at 250 hp. From what I've read, the diesel technology was the main reason that the Chinese purchased the company. They're dead serious about developing diesel technology for the growing Chinese GA market. They also see the writing on the wall for the US market, with the inevitable elimination of 100LL.
A good website for updates on diesel aircraft engines is www.dieselair.com
I've got a Wilksch 120 hp diesel in my RV9. I've been flying it for 250 hours now, with excellent economy and reliability. I think diesel / jet A has a bright future in GA.
Kurt
RV9 / WAM120 diesel, 257 hours flying.
Last year, before being purchased by the Chinese, TCM purchased the technology from SMA to further refine and produce the 4 cyl, 4 stroke turbo diesel engine at 250 hp. From what I've read, the diesel technology was the main reason that the Chinese purchased the company. They're dead serious about developing diesel technology for the growing Chinese GA market. They also see the writing on the wall for the US market, with the inevitable elimination of 100LL.
A good website for updates on diesel aircraft engines is www.dieselair.com
I've got a Wilksch 120 hp diesel in my RV9. I've been flying it for 250 hours now, with excellent economy and reliability. I think diesel / jet A has a bright future in GA.
Kurt
RV9 / WAM120 diesel, 257 hours flying.
Tq vs HP: higher level discussion
I too have been interested in an experimental diesel option considering the efficiency, high torque, and availability of diesel with the largest downfall being weight.
While on this subject, I cannot reconcile why manufacturers rate engines in hp instead of publishing torque. If I remember correctly, power loading is measure in lbs of force of thrust produced versus aircraft weight. Additionally, the ability of an aircraft to accelerate is the difference of thrust required (drag) from the thrust available. Especially in the case of a constant speed prop, I think that engine torque is a more meaningful statement of thrust. Assuming steady state, an angular velocity at a specified resistance (blade drag) is the amount of work required or torque to create thrust. Please correct me if I'm wrong.
I just think to be comparing apples to apples, we need published torque values of lycoming/continental engines to be compared against torque values of diesel engines of interest. With that information, thrust specific fuel consumption can be compared, and relative efficiency of each engine as well as peak engine efficiency settings can be determined.
However, it is possible that I'm missing something since reciprocating engines in aviation have been rated in terms of horsepower for as long as I can remember.
Feedback appreciated.
I too have been interested in an experimental diesel option considering the efficiency, high torque, and availability of diesel with the largest downfall being weight.
While on this subject, I cannot reconcile why manufacturers rate engines in hp instead of publishing torque. If I remember correctly, power loading is measure in lbs of force of thrust produced versus aircraft weight. Additionally, the ability of an aircraft to accelerate is the difference of thrust required (drag) from the thrust available. Especially in the case of a constant speed prop, I think that engine torque is a more meaningful statement of thrust. Assuming steady state, an angular velocity at a specified resistance (blade drag) is the amount of work required or torque to create thrust. Please correct me if I'm wrong.
I just think to be comparing apples to apples, we need published torque values of lycoming/continental engines to be compared against torque values of diesel engines of interest. With that information, thrust specific fuel consumption can be compared, and relative efficiency of each engine as well as peak engine efficiency settings can be determined.
However, it is possible that I'm missing something since reciprocating engines in aviation have been rated in terms of horsepower for as long as I can remember.
Feedback appreciated.
I haven't looked at the math behind it in a long time so I may be off, but HP is (torque*rpm)/5252. If you look at dyno graphs from engine builders you'll always see the HP and torque curves intersect right at 5200 RPM for this reason. With diesels usually producing all their torque down low due to much higher compression, this is why the HP numbers always seems so much lower, so Zoomie I think you've got a good arguement. However there is much more to the argument when you start talking about airfoil effeciency, RPM, HP/thrust required, etc.
Agreed, hp equals work over time or can be equated by torque * rpm/5252. The 5252 is essentially a scaling factor for unit of measurement and distance translated to 2 pi radians travelled. Because of this, tq and hp curves should always intersect at this point.
Because of this relationship, F1 engines can spin 15k rpm and make gobs of power out of little torque. On the other side, diesels have a long stroke and high cylinder pressure to make lots of torque at low rpm yet never achieve high hp due to the low engine speeds.
Most dyno's measure torque and then back out hp using rpm; roller dyno's measure how quickly an inertial mass can be accelerated to back out torque and then use engine rpm find a horsepower rating.
In reguards to diesel you are correct- the diesel cycle is more thermodynamically efficient due to compression ratio.
So back to airplanes...All other aircraft characteristics aside, an aircraft can be modeled as a point mass by comparing wing loading and power loading. It makes sense to me, propellor efficiency aside, to measure thrust on a reciprocating engine with torque. I just think we can get a more accurate comparison of engines by comparing torque values vs hp. If so, it seems strange that the industry has rated engines in hp for so long. Maybe the consumer is more comfortable/familiar and its a carryover from the auto industry or somewhere my recollection of physics is twisted (quite possible). Can anyone help with this?
Because of this relationship, F1 engines can spin 15k rpm and make gobs of power out of little torque. On the other side, diesels have a long stroke and high cylinder pressure to make lots of torque at low rpm yet never achieve high hp due to the low engine speeds.
Most dyno's measure torque and then back out hp using rpm; roller dyno's measure how quickly an inertial mass can be accelerated to back out torque and then use engine rpm find a horsepower rating.
In reguards to diesel you are correct- the diesel cycle is more thermodynamically efficient due to compression ratio.
So back to airplanes...All other aircraft characteristics aside, an aircraft can be modeled as a point mass by comparing wing loading and power loading. It makes sense to me, propellor efficiency aside, to measure thrust on a reciprocating engine with torque. I just think we can get a more accurate comparison of engines by comparing torque values vs hp. If so, it seems strange that the industry has rated engines in hp for so long. Maybe the consumer is more comfortable/familiar and its a carryover from the auto industry or somewhere my recollection of physics is twisted (quite possible). Can anyone help with this?
This one has to crop up every 6 months or so it seems. Hp is a measure of work or the rate of energy release, torque is simply force which by definition is not work- you have not moved any mass over any distance over any time period.
Diesels don't have higher torque than than similarly sized SI engines running similar manifold pressures with the same number of power strokes. If you can provide any example that counters this statement, please produce the evidence. Most modern diesels "appear" to have high torque only because they are turbocharged and running considerable manifold pressure and people compare them to atmo (normally aspirated) SI engines.
So the reason why all engine manufacturers rate their engines by hp rather than torque is because hp is the meaningful way to compare the ability to do work.
Mike S
Senior Curmudgeon
What Ross said.
Consider the tightening of a big nut------VW flywheel nut for instance.
You put all your weight on a long extension, and get the nut tight ----couple hundred pounds/foot at least.
But, the engine is locked with a flywheel lock, and can not turn.
There is no work being done, and by the formula for HP, there is no HP also, due to the zero RPM.
Consider the tightening of a big nut------VW flywheel nut for instance.
You put all your weight on a long extension, and get the nut tight ----couple hundred pounds/foot at least.
But, the engine is locked with a flywheel lock, and can not turn.
There is no work being done, and by the formula for HP, there is no HP also, due to the zero RPM.
Might have answered my own question: if you always rate the hp at a certain rpm say 2500 or 2700, you are essentially giving the torque rating of the engine too. If certain engines are always compared at the same rpm, you are actually comparing the torque of the two motors. Because most props are limited to 3k rpm or so this is relatively easy to keep consistent vs autos that have no outside factor limiting powerplant rpm.
flyvans.com
Well Known Member
definitely an issue from the psychology department and not engineer thinking...
same issue with mph vs kts or kW vs hp.
the bigger, the better, right ;-) ?!
turbines/turboprops measure/indicate torque by the way.
with our engines, i suppose it could have something to do with the way thrust has been measured / engines have been dyno'd / instrumented historically.
rgds bernie
same issue with mph vs kts or kW vs hp.
the bigger, the better, right ;-) ?!
turbines/turboprops measure/indicate torque by the way.
with our engines, i suppose it could have something to do with the way thrust has been measured / engines have been dyno'd / instrumented historically.
rgds bernie
John Clark
Well Known Member
Semantics
Much of the rest of the world expresses automotive power in kW. All sorts of things work, but telling someone that you have a 128,327,295.160295 calorie Lycoming is a little awkward.
John Clark ATP, CFI
FAAST Team Representative
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA
Much of the rest of the world expresses automotive power in kW. All sorts of things work, but telling someone that you have a 128,327,295.160295 calorie Lycoming is a little awkward.
John Clark ATP, CFI
FAAST Team Representative
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA
rich
Well Known Member
Hay Tobin,
Have you seen these articles in AvWeb from May,2010 issue.?
http://www.avweb.com/cgi-bin/texis/...qA5BdGOe6DwwBnmFqnmn5qnzmwwxeamww/search.html
Best,
Have you seen these articles in AvWeb from May,2010 issue.?
http://www.avweb.com/cgi-bin/texis/...qA5BdGOe6DwwBnmFqnmn5qnzmwwxeamww/search.html
Best,
Thanks for the response
Not sure if I buy this one completely.... work is the integral of force over a distance. Torque is more than a force, it is a force at a moment. In this case, its the integral of one revolution of the engine (2 pi radii). If the engine isn't turning, or we are using tq to tighten a static nut, I buy your argument. Moving on...
I understand your concern to keep certain factors constant, however consider ambient pressure and temperature rather than manifold pressure constant.
All things equal (piston area, stroke, engine speed), cylinder pressure is the biggest factor for tq. Granted gasoline is more energy dense than diesel, a higher compression motor will have higher cylinder pressure. Where the trade occurs between gas and diesel, I'm not sure.
The real advantage of diesel is in the form of forced induction/turbocharging- you cannot have 'artificially' high torque. Why limit ourselves to natural aspiration? The limitation of gasoline is in the form of knocking or preignition/detonation. Diesel allows us to cram more fuel/oxygen into the cylinder and ignite it in a more isentropic manner with the addition of reclaiming spent exhaust energy. IF it can be done light enough, I think it can outperform gas reciprocating engines in the category of power loading due to the fact thrust is based off engine tq.
My 2 cents.
This has been discussed to death previously here: http://www.vansairforce.com/community/showthread.php?t=46423&highlight=love+torque
And here: http://www.vansairforce.com/community/showthread.php?t=57932&highlight=atmo
Yes torque is force with a moment but no time constant is involved, therefore no work has been done. Lb/ ft.
All things are not equal between SI and CI engines unfortunately so we must use dynos to quantify actual hp (work) that a given engine can perform. SI engines have a huge advantage in the rpm department which is one reason they will always have substantially higher hp output than the same configuration CI engine. The argument about detonation limits as related to aviation use is a moot point as we can easily produce enough power with turbocharged SI engines to satisfy requirements long before detonation becomes an issue and it takes far less manifold pressure to do it on an SI engine so we don't have the same turbomachinery issues at altitude as many aero diesels do (the SMA is limited to 12,000 feet due to N1 limits being reached on the turbo).
You are using the same argument always used by diesel advocates- comparing atmo SI engines to turbocharged CI engines. We should be fair and compare engines with the same displacement, same number of strokes and same manifold pressure. In this light, CI engines do not compare to SI engines favorably either in peak torque or hp. In fact, to use a comparison I've used before, the turbocharged Audi Le Mans Diesel does not even match the specific output of an atmo street production Honda S2000 engine.
As related to powering aircraft, 4 stroke diesels exist which do the job with a fair weight penalty, high cost penalty and to date, inferior lifespans in the real world. The 2 stroke diesel is much more promising from a weight and power standpoint however the SFCs are similar to existing SI aircraft engines so the only real advantage is using cheaper fuel. In certain parts of the world where avgas is scarce, the diesel and turbine make a lot of sense.
I agree, when an affordable, equally reliable diesel with similar power to weight ratio becomes available, they would make a viable choice to power aircraft. So far, nothing has come along to satisfy all those requirements- at least nothing with a proven flight record of 10,000+ hours.
I agree.
As long as I can land at most any GA airport and purchase it from a self serve island 24 hours a day.
It should only get better....
In the three years I've been flying my Diesel RV9, I've landed at a LOT of GA airports in the western US and Mexico, and have only had one occasion where I've had to plan ahead because Jet A wasn't available. Remember, too, that the diesel, even the 2-stroke, is quite a bit more efficient over the whole flight profile than its gasoline counterpart, so I can make round trips on diesel fuel (cheaper and more BTU's than JetA), where my Lycoming friends have to fuel up along the way.
As the "green" movement gains traction and 100LL is eliminated, it will surely be replaced by a higher tech, environmentally friendly fuel with a much higher price tag. Will it be as available as 100LL is now? Who knows? But we all know that avgas as we know it will soon be history. The military has the goal of using heavy fuel exclusively where possible, so to me the it seems inevitable that GA will eventually change over as well.
Ross, you say that when a reliable, equally affordable, similar power-to-weight ratio diesel is available, it would be a viable replacement. Well, I'm flying one every week. My WAM 120 cost no more, and weighs less than an O-235 Lyc of the same power. There are 20 or so of us flying with this engine and so far it has proven reliable. Obviously, the fleet has to build time to prove reliability, but we're off to a good start. WAM has done an excellent job of supporting these engines, along with developing higher HP versions. In today's economic climate, this has not been an easy task, but their owner, along with so many others (TCM, SMA, DH, Austro/Diamond, Centurion, etc), knows that it will be worth the investment. I'm grateful for these forward-thinking pioneers.
Kurt
In the three years I've been flying my Diesel RV9, I've landed at a LOT of GA airports in the western US and Mexico, and have only had one occasion where I've had to plan ahead because Jet A wasn't available. Remember, too, that the diesel, even the 2-stroke, is quite a bit more efficient over the whole flight profile than its gasoline counterpart, so I can make round trips on diesel fuel (cheaper and more BTU's than JetA), where my Lycoming friends have to fuel up along the way.
As the "green" movement gains traction and 100LL is eliminated, it will surely be replaced by a higher tech, environmentally friendly fuel with a much higher price tag. Will it be as available as 100LL is now? Who knows? But we all know that avgas as we know it will soon be history. The military has the goal of using heavy fuel exclusively where possible, so to me the it seems inevitable that GA will eventually change over as well.
Ross, you say that when a reliable, equally affordable, similar power-to-weight ratio diesel is available, it would be a viable replacement. Well, I'm flying one every week. My WAM 120 cost no more, and weighs less than an O-235 Lyc of the same power. There are 20 or so of us flying with this engine and so far it has proven reliable. Obviously, the fleet has to build time to prove reliability, but we're off to a good start. WAM has done an excellent job of supporting these engines, along with developing higher HP versions. In today's economic climate, this has not been an easy task, but their owner, along with so many others (TCM, SMA, DH, Austro/Diamond, Centurion, etc), knows that it will be worth the investment. I'm grateful for these forward-thinking pioneers.
Kurt
My point was mainly that none of the 4 stroke aero diesels have delivered on the promise of lower overall costs-acquisition, maintenance and operating and superior reliability/ longevity to date. WAM has done better than the big manufacturers but with a much smaller fleet flying and no substantial flight hours on any of them, long term reliability is unknown. A few hundred hours on a handful does not really tell us much but is at least encouraging and I salute WAM especially for what they have done and all those who are trying new and different engines in GA. We will never have a new bar if everyone flies the same old stuff and we can learn as much from failures as successes.
I'd still be interested in comparing fuel burn/ TAS on an O-235 RV9 vs. the WAM. From what others are reporting here and Van's numbers, they seem pretty close to your's. Have you had the opportunity to fly a trip side by side with one? I see some people getting 135-140 knots on about 5-5.5 GPH. The new IO-233 LSA is down to about 4.5 GPH at 65% power and is quite a bit lighter than the O-235.
Certainly Jet fuel will be with us longer than leaded avgas and diesels will be well positioned to continue to fly no matter what happens with the "new" avgas supply.
I agree with you; we've got to start somewhere.
I've tried to find someone with an RV9/O235 plane to fly side-by-side to compare notes with, but there aren't too many around. Most folks like the "big" power! When Ken K and I did the side by side testing with the factory '9A/O320, a one-hour flight under the same conditions (well at least close; I had Marc Cook with me and we were about 50 lb heavier - pure lard), we burned substantially less fuel. Seems like Ken burned 7 gal, and we burned 5.2. That's at the same speed, altitude, flight profile, etc. We both were doing all we could to get the best fuel burn.
I often hear people say that it's better to install the o-320 or O-360, and just run at lower speeds and power settings to achieve the same fuel burn as the O-235, and I believe that's mostly true. If so, the WAM is more efficient. But in all honesty, if the o-235 numbers you quote are true, it's not far off from what I can do with the diesel. I suppose that these low numbers are based on LOP cruise at 8K' or so, running 65% power. I think where the diesel shines is that I'm AVERAGING 5 gph, including the takeoff and climb. So the shorter the flight, the better the diesel looks.
The WAM has indirect injection, which is the reason for the "poorer" economy. Direct injection versions have been proposed, which would increase fuel economy by 10-15%. I'm told that DI 2 stroke diesels can achieve the same fuel efficiency as the 4-strokes. Also, the WAM's injection system is completely mechanical, which, I'm sure, is not as efficient as the newer common rail electronic systems. I'm willing to sacrifice a bit of efficiency for the reliability of the mechanical system.
Kurt
