T

T.S.

Active Member
So I had a tech visit for the HS and am confident to proceed and order QB now.
Researching carb vs FI, I got the impression it was much more expensive than the approx. $700 difference for O vs IO 360 stated today from Mattituck (plus elec pump from Van's). I got the impression it is now under 2K difference. Add $1700 for horiz. intake for a couple of more ponies.

A. Am I missing something here? I am a newbee.
B. Is it wise to order the finishing kit at the same time as wings and fuse? It would save shipping costs, but decisions would have to made at this time.
C. Is FI worth it? Opinions anyone...

Building a 7 series, 180hp, tip up in southeast Wisconsin
Have a lead for a tailwheel ride for final front / back wheel decision.

Misery loves a lot of options.

Thanks in advance for input.
T.S.
 
You're going to get a lot of opinions here, so I might as well start.
Carburators are cheap, simple, work great with little or no maintenance and use low pressure fuel. FI is expensive, uses high pressure fuel, usually harder to start when hot, has slightly better fuel distribution, is mostly imune to induction icing (normally not a problem in Lycoming powered RVs). Contrary to popular belief, FI does NOT increase hp. I like carbs! My $.02. (I'll be ducking now!)
 
Ok, Mel lobbed the ball over here, so lemme doink it back to the other side of the court.

Nothing wrong with carbs...but...FI = the ability to run LOP = $$$ saved.

LOP = saving 1-2 gph, reliably. Saving say $6 per hour, the system will "pay for itself" (I'm talking about the up front cost plus the add'l items like the high pressure boost pump that Mel mentioned) within 2-3 years.

Not to mention added RANGE for your airplane! Or RESERVE!

Will you fly a lot (i.e. 150+ hours per year?) if so, get the FI and thank me later when avgas costs $10/gal (I would say "when avgas costs $5/gal" but it already does in several places).

More and more people are realizing how effective LOP operation is. With a carb, you're basically giving up that option. Yes, I know a handful of carb drivers do run LOP, but they're extremely lucky if their engine is running balanced like that.

The other day, a formation buddy of mine with an RV-8 + O-360 couldn't get his plane started. He had flooded it. He stayed home. We went and had fun while he sat on the ground waiting for his airbox to dry out. With a carb, you really can't control where the fuel is going and where the air is going and how much (ok, ok, operator error, yeah, yeah). But with injection, you control precisely what's going where and how much. It's true control (yes, I'm a control freak like everybody else on this list).
 
I agree with both Dan an Mel.

I am running a carb on my O-320 for the past 9 years and 1,956 hours.

For a quick comparions on FI vs Carb horsepower differences, reference ECI engine comparion.

If my math is correct, the cold air induction with Fuel Injection is about 3.5 % more horsepower on the ECI 340 and about 2.5% more HP on the 360.

Cold air induction vs updraft carb could be a long post. Lycoming publishes in the carb engine manuals that for every 10 degree F drop in temp below standard, you will see a 1% increase in power. Now the increase that is seen in the ECI table would be for temp drop, reduced air resistance in the intake, and less resistance through the fuel injection butterfly than what you would have through the VENTURI and butterfly in the carb.

Maybe someone has the equipment to measure the flow delta between a carb and FI servo and can post the results.

I am nearing a overhaul / top rebuild. I am debating if I want to add FI to my 320. I really want a 360. Do I spend some of the money I have for FI now or save it toward the purchase of a 360. The 360 will have FI. For around $5,500, I could add ECI FI to my 320. The only unknow is will my existing exhaust work or will I need to spend more money on that.

I am going to follow this thread to help me make up my mind on switching to FI in my 320. I do know that Danny Kight's RV-6 with 320 FI is faster than my RV-6 320 without fuel injection.

An additional $5,500 at overhaul is a large percentage of my expense. The percentage cost increase of FI instead of carb on the price of a new being build RV is small.

Get what you want. There are pros and cons to both. I will eventually have FI becasuse I want it.

BTW. I run as lean as I can that will allow the engine to run smooth. On the way home from Homecoming, I ran a test. Was at cruse altitute and power. Increased my mixture. Everything else left the same. Fuel flow went up 1.6 GPH, air speed went up 10 knots (TAS and GS), map rose 0.1 inch. Yes you can run a carb lean. I may be running LOP but my RMI engine monitor does not show that indication. My EGTs keep getting hotter.

You will have a lot of fun with the airplane regardless of carb or FI. I believe that everyone flying an RV will agree with that.
 
Like Gary says, Both Mel and Dan bring up good and accurate points. If everyone had the same opinion, every RV would be the same model, be painted the same, with the same instruments and the same engines. Obviously, they all aren't the same and obviously some options better suit some operators over others.
I think that carbs are simple, easier to possible self fix and certainly less expensive at overhaul. But they are not as fuel efficient, as a fuel injected engine, and they can't sustain inverted flight for any period of time. In addition, you have two different cowling choices, on an RV, if the fuel injected engine is considered. Snorkeled, if going with a carb or vertical fuel injection and snorkel-less if going for horizontal induction. So, the cleanest aircraft with the most power at altitude, in theory going the fastest, will be the horizontally fuel injected engine on an aircraft with the smokeless cowl. If going with the vertical sump, I think the fuel injected engine will develop similar power as compared to the carb'd engine and the aircraft similar speed. But, I think that the Fuel injected engine will provide better fuel economy by maybe .5 to 1 gph when running ROP at the same egt level on the leanest cylinder, then the exact same aircraft and engine combination with a carb. The fuel injected vertical engine might make a little bit more power at the same leaned power setting as compared to the carb'd engine, by getting a bit more out of the cylinders that aren't running richer then the leanest one. But at the same token, induction air, at the cylinder, is considerably cooler on a carb'd engine vs. a fuel injected one, so maybe the small lean advantage in power, on the fuel injected engine, is overcome by the cooler air in the carb'd engine. I don't know for sure, but I am pretty confident that the difference between those two, is relatively small. The power increase of the forward facing sump, fuel injected engine over the vertical carb'd or fuel injected engine is real and a consideration if power is an objective. Are those considerations important or a life shattering conclusions...not to me, but to some it is very important because their use profile is different then mine would be. To some, speed at altitude is the major concern, to others inverted flight is a major concern and to others fuel economy is the big thing and others ease of maintenance is the biggy.
I think you have to look at how you plan to use the aircraft and find the best fit for yourself.
I don't think that, once you consider that, that you will have a hard time choosing.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at you own risk."
 
I vote for Mel. Life cycle cost of carbs is downright cheap compared to FI, kitchen counter overhaulable, and initial installation is easier. FI's advantages are most available to user extremes, e.g., aerobatics, but I'd bet they aren't used more than .1% of operating time for most pilots. As to economy, my flying -7 yields 7.3 gph, LOP (on two cylinders) @ 193 true. Want 201 mph? Can do, but 2.7 gph more for 8 mph? It's a stock-clone 360, CS, with a carb and dual Lightspeeds. FI might get such economy or better and maybe a tad smoother. Maybe. YMMV, but costs and complexity will for sure be greater. I prefer stone simple. You?

The month-from-flying -7 has a parallel carbed 360 with flow balanced Lycoming cylinders, the old style cam profile, and a Superior aluminum sump, all clamped onto an otherwise stock ECI engine. It dyno'd 205 hp after only 1 1/2 hours, that using slave mags in the test cell, not dual EI. That 25 hp bump over spec cost a non-recurring $1,400. Spending more than that on FI but still around 180 hp without those mods doesn't attract me.

Choosing a wife is easier.

John Siebold
 
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FI if new, Carb is good enough

Opinion with no facts, if you are buying brand new engine, you are right the price between carb/FI is small. However there is another say $600 for the FI extra high pressure boost/Aux pumps.

With that said if you come by a new or used engine w/ a Carb, you can buy at a super price, don't pass it up just because its Carb.

Switching from carb to FI as a retro-fit cost +$3,000, so that is real expensive. You can sell the old carb and mechanical pump to recoup some cost. The mechanical pump is also high pressure and needs to be changed by the way. However if buying a new engine where the price premium is so small, I would consider the approx extra $1,300 worth while. However if every nickle counts, Carb's work and are fine.

Yes you will hear about LOP and better fuel economy. That's true to a point if you lean. The real advantage of FI over the carb is in cruise. If you spend a lot of time in cruise (below 75% power leaned real well) as part of your normal flying, you will gain the most from FI.

With fuel prices up to +$4.00/gal saving fuel is a worth while thing. You can expect to pay your self back for the extra cost of the FI before you first engine TBO. Flying 100 hours a year might take lots of years, but you will save some fuel, but only IF you lean optimally. If you don't lean you don't save. If you have a guy with a carb and is real careful about power settings and leaning, verses a less attentative pilot with FI, than it does not matter. People like Dan are very very attentative and get the max out of their equip, you milage may vary as they say.


My point is the PILOT is a big factor. That is where FADEC comes in, taking the pilot out of the loop, but at +$8,000 for that option it's a bigger gulp. I not anti-FADEC but kind of laugh at it. I'm perfectly happy to have that red knob on my panel. You may only move the mixture knob 4 times from engine start to shut down in one flight, so its not like it's a big burden.

On the other hand Carbs are real simple. If you plan on flying IFR get the FI to avoid any issue of carb ice, even though carb ice can be countered, FI is better in this respect. You need all the help you can get in single pilot, single engine operations.

To summarize:
Buying a new engine with a $600 FI premium (plus $600 install), get FI
Used or super deal on a Carb engine, stick with the carb, good enough.


PS: As a new be may I suggest you check your questions first on google or search the archives of this forum (search on pull down menu). Vans site also has FAQ. All the best
 
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FI easier to install

I would disagree that installation is easier with a carb if we are talking about both engines having vertical induction. If you go with a Bendix style injection system on a vertical induction engine, then there is no messing with the airbox to make provisions for carb heat (no cutting extra holes in airbox, routing air around the exhaust, etc). You just have to worry about throttle and mixture controls.

Some make it even easier by not adding the alternate air intake. Just slap the airbox on the FI engine and go. I, however, added the alternate air option.

I would post pics but I'm in the process of moving the website.
 
Just the facts

Here are facts about pressure drop.

The pressure drops across the throttle bodies are as follows. All units were tested with the throttles wide open and the standard air box approach on the throttle body. Also note that the throttle bodies were flowed dry. In the case of a carburetor there is a slight increase when there is fuel flowing through it due to th fuel taking up volume at the choke.

This is tested at 1400 PPH airflow which is a little over 200 HP.

MA-4-5 Carburetor 15?H2O @ 1400 PPH airflow.

RSA-5 Fuel Control 8.6?H2O @ 1400 PPH airflow.

FM-200 Fuel Control 4.9?H2O @ 1400 PPH airflow.

What does this all mean? Well probably not much at sea level, but as you increase in altitude the velocity of the air passing through the throttle body goes up, there fore increasing the pressure drop. So the unit with less pressure drop will give better performance at higher altitude. Also in the instance of a Lycoming 540 there?s a definite power advantage going with less pressure drop unit as the maximum airflow is in the 1600-1800 PPH range. Pressure drop is a square function. Double the airflow equals four times the pressure drop. What?s an inch of MAP worth?
 
Don at Airflow lots of questions for you

Don at Airflow said:
What?s an inch of MAP worth?
Click to expand...

Interesting, "Don at Airflow"

First you make the carb seem like its a brick wall? :( Gee, I have been told by engine "experts" who have excellent reputations that you can make as much HP on a carb. Clearly there are NHRA drag race cars with carbs that are blowing doors off of FI cars.

Fortunately, from your numbers 15 - 4.9 = 10.1" is equal to 0.74 in-Hg, but is that really what happens on an engine mounted in a plane?

If you can boost MAP by 0.74 in-hg, I calculate about 5 to 7 HP. This is the best possible case between carb and FI. Doing between the RSA-5 and the AFP is 0.27 in-hg, or about 2.3 HP. Every little bit helps, but I have doubt that the ideal on the bench test works the same on the actual engine.

I have to be honest, I'm always skeptical of bench tests vs real world, meaning, what does it really do in a plane, especially when there is a large difference in the numbers. Murphy gets in the way usually, and building car engines a change has to work with the other parts to achieve its full potential.

"You can't put 10 lbs of stuff in a 2 lb bag", if you know what I mean. It does not help to have a bigger better fuel injection throttle body if there are other bottle necks. That is my simple way of looking at it. However it does not hurt obviously to have a better flowing part, usually.


Also as you climb, correct me if I am wrong, the engine flows less mass air? :confused: , There is less PPH mass air flow as you climb because there is less air (atmo lower pressure or density). May be I am confused with velocity increases, not sure. Can you explain? I assume pressure drop is linear with flow?


An engine is only going to such or use so much air. With out a super charger or turbo you can stuff more air in. However not doing harm (to the air flow) is a good thing. Ram air is fine, from screaming thru the sky with your hair on fire, but we are talking about, best case a few 1/10ths (in-hg) of MAP. Its possible that you can take more advantage of ram air with the AFP injection? That brings me to my first question, has a comparison test been done on planes.



There's no doubt your product is excellent and flows better, but why? Is it just a bigger area or is there more to it.


Do you have any before and after data on the same plane, flying with one system than switching over to AFP's system?

Question about your comment, "What?s an inch of MAP worth?" An inch of H2O? Or are we talking about an inch of H20, which is 0.07 in-Hg. I am not sure you are going to get an inch difference ever, but I could be wrong.

You test a Bendix RSA-5, but what about the later design, the Silver Hawk (tm), Precision Airomotive's version of an experimental FI system. Is the Silver Hawk better than the original Bendix RSA-5 design (flow wise)? I don't know just asking.

What about flow on ECI's new FI system. Any plans on testing that?

Again AFP's fuel injection has a great reputation and word on the street is its considered to flow better, as you back up. Can you explain why and what you think you see in the airplane?

Is there other cool features you can share that separates your product? :D

Thanks for your time. Since you are Don at Airflow, I concede you know way more than I do. I am ready to be schooled. :D
 
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at 150 HP

Don at Airflow said:
Here are facts about pressure drop.

The pressure drops across the throttle bodies are as follows. All units were tested with the throttles wide open and the standard air box approach on the throttle body. Also note that the throttle bodies were flowed dry. In the case of a carburetor there is a slight increase when there is fuel flowing through it due to th fuel taking up volume at the choke.

This is tested at 1400 PPH airflow which is a little over 200 HP.

MA-4-5 Carburetor 15?H2O @ 1400 PPH airflow.

RSA-5 Fuel Control 8.6?H2O @ 1400 PPH airflow.

FM-200 Fuel Control 4.9?H2O @ 1400 PPH airflow.

What does this all mean? Well probably not much at sea level, but as you increase in altitude the velocity of the air passing through the throttle body goes up, there fore increasing the pressure drop. So the unit with less pressure drop will give better performance at higher altitude. Also in the instance of a Lycoming 540 there?s a definite power advantage going with less pressure drop unit as the maximum airflow is in the 1600-1800 PPH range. Pressure drop is a square function. Double the airflow equals four times the pressure drop. What?s an inch of MAP worth?
Click to expand...

Don ... thanks for the interesting figures....

If I take your numbers and scale them for 150 HP in cruise (0.75 of the flow rate), and use the square function you mentioned, I get these numbers

Extropolated at 1050 PPH airflow which is a little over 150 HP.

MA-4-5 Carburetor 8.45? H2O @ 1050 PPH airflow.

RSA-5 Fuel Control 4.84? H2O @ 1050 PPH airflow.

FM-200 Fuel Control 2.76? H2O @ 1050 PPH airflow.

And dividing by 13.6 to get into inches of Hg which our gauges read...

MA-4-5 Carburetor 0.62? Hg @ 1050 PPH airflow.

RSA-5 Fuel Control 0.36? Hg @ 1050 PPH airflow.

FM-200 Fuel Control 0.20? Hg @ 1050 PPH airflow.

It now seems to me that this pressure drop advantage reduces for cruise or lower power engines. The $$ give a 0.42 inch MAP advantage... and only 0.26 inch MAP with the RSA Bendix system.

Are my assumptions and calculations correct?

gil in Tucson - nice to have real numbers.... :)
 
Back down here in the shop;

A. Looks like I did not miss anything. Current prices have brought carb and FI closer $ than stated on previous threads and quotes.
B. Keeping options open if a "can't pass up" carb motor comes along, FI vert is on the order form for finish kit.
C. Lots of great opinions and facts! Thanks, I'm learning.

T.S.
Your only security is your own ability.
 
Lots of answers

Hey, I was just stating some facts as some one wanted to know the pressure drops across different throttle bodies. I wasn?t slamming one design over another and certainly not slamming carbs. They have their place too.

But gmcjetpilot, have you seen any top fuel dragsters or funny cars running carbs lately? Let?s not get into that debate.

You missed the point of my statement ?What does this all mean? Well probably not much at sea level?. The installation in the plane or car for that matter, makes all this dyno, airbox testing go out the door if control parameters are not kept the same, and their not.

We have gotten dyno numbers back from a few shops that can actually measure HP (not just a prop stand) and results are typically as follows comparing a updraft sump 360 to carb to FM-200 no change, RSA-5 to FM-200 2-3 hp. IO-390 RSA-5 to FM-200 5 hp. IO-540 up draft sump RSA-5 to FM-200 7-15 hp. Your results may vary. And yes, you don?t fly the dyno. And your correct to some extent that just because the throttle body is bigger it doesn?t mean you?ll make more hp. An engine is just an air pump and can only consume so much air. But it is a known fact that on a four-stroke cycle engine in a mild state of tune (not some full blow crotch rocket engine, boy they sound good) approaches 10? H2O carb loss (pressure drop across the throttle body) you start to loose hp.

All of these devices (carbs, Bendix, Airflow) are not really truly mass airflow metering devices. The ventures operate off velocity, so think of a bunch of cars going through a necked down area in a road (each car being a unit of mass) the cars have to speed up as they go through the necked down portion of road to keep a certain flow rate. If you take some of the cars away less total cars go through the restricted area but they can go through there faster because there?s less cars. Bernoulli?s principle. Simply stated double the airflow equals four times the pressure drop. Pressure drop is not linear with flow it?s the square of flow. There are certain models of Bendix RS and RSA injection systems that are mass air flow devices as they employ an AMC (automatic mixture control) that compensates for the change in velocity through the venturi due to changes in density. But even these systems require leaning at altitude under cruise power conditions to optimize the mixture, since the AMC curves are set to control a full throttle climb mixture.

At Airflow Performance we are all for getting facts. And I have offered before that anyone that has the like aircraft, like engine and one with a carb, Bendix/Precision, FADEC and Airflow, fuel metering systems come to our facility and we?ll have a controlled fly off. That?s what really counts. So far no takers.

There seems to be lots of people seeking more knowledge on fuel injection systems and their operation. I will offer to all out there that we are having our last Fuel Injection 101 Class for 2006 November 3-5. There?s still time to sign up. The cost of the class is $275 per person but we have a great time with a couple of home cooked lunches and dinners we provide and lots of good fellowship and hanger flying plus everybody that has attended has gotten a lot out of the class. Shoot, we even do some nozzle tuning if people bring their planes in.

I need to get back to work.

Oh yea, The Silver Hawk is identical to a RSA-5 except the throttle body is machined from billet. They both flow and operate the same.
 
Don at Airflow said:
Hey, I was just stating some facts as some one wanted to know the pressure drops across different throttle bodies. I wasn?t slamming one design over another and certainly not slamming carbs. They have their place too.

But gmcjetpilot, have you seen any top fuel dragsters or funny cars running carbs lately? Let?s not get into that debate.

You missed the point of my statement ?What does this all mean?
Click to expand...
No I did not miss the point, I was confused and wanted to pick your brain. I am quite sincere when I say you know way more about it than I. You answered all my questions very well and I thank you for your time and expertise. Much appreciated.

As far as **6000 and 8000 hp dragsters, I was thinking more in-line with Street, Gas, Comp, Super Stock, Stock Eliminator classes. Bad boy bringing up top fuel, which uses 10-12 gals in 4.5 seconds!!!! What is that (12 gal/.25 mile) or 48 gal/mile!!!! :eek: GALLONS PER MILE! That's gas milage of 0.021 mpg! Working it out, it's about 1,400 to 9,600 times the fuel flow of my Lyc. Please...... that's not fuel injection, that's a gardens hose, no, a fire hose. Fun fact: There are 42 fuel nozzles, 10 injectors above the supercharger, 16 in the intake manifold and two per cylinder on a top fuel engine. The pump flows 92 gallons/minute at 500 PSI fuel pressure. ha ha :D Just like my Lycoming. :rolleyes:

** can't be practically dyno'ed so its estimated.
 
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Airflow Performance

:) I went with Airflow Performance. Don is easy to work with and has a great product with excellent support. I live close to Don?s facility and the people and facility are outstanding. I have the updraft and it was easer to install than carbonator.
 
Vertical vs horizontal induction

I keep hearing how "cold air" horizontal induction FI systems produce a couple more HP than vertical induction FI systems. Yes, well maybe in a test stand where both engines are free to suck air without restriction.

However in an RV I see that virtually all of the horizontal induction engines have no scoop under the cowl (Dan C is one of the exceptions). So they suck their air from the left engine inlet scoop....at 90 degrees to the flow....down and around in a convoluted pathway to the throttle body.

The vertical induction system however has virtually ram air with the scoop inlet directly in front of the throttle body.

Therefore I'm betting that in the real world there will be no measurable increase in HP for the horizontal induction if the cowl scoop is discarded. Anyone got any figures to prove otherwise.
 
az_gila said:
Don ... thanks for the interesting figures....

If I take your numbers and scale them for 150 HP in cruise (0.75 of the flow rate), and use the square function you mentioned, I get these numbers

Extropolated at 1050 PPH airflow which is a little over 150 HP.

MA-4-5 Carburetor 8.45? H2O @ 1050 PPH airflow.

RSA-5 Fuel Control 4.84? H2O @ 1050 PPH airflow.

FM-200 Fuel Control 2.76? H2O @ 1050 PPH airflow.

And dividing by 13.6 to get into inches of Hg which our gauges read...

MA-4-5 Carburetor 0.62? Hg @ 1050 PPH airflow.

RSA-5 Fuel Control 0.36? Hg @ 1050 PPH airflow.

FM-200 Fuel Control 0.20? Hg @ 1050 PPH airflow.

It now seems to me that this pressure drop advantage reduces for cruise or lower power engines. The $$ give a 0.42 inch MAP advantage... and only 0.26 inch MAP with the RSA Bendix system.

Are my assumptions and calculations correct?

gil in Tucson - nice to have real numbers.... :)
Click to expand...


Gill, your math is correct but on a 320 a MA-4 is used (smaller choke than an MA4-5). The RSA-5 used on a 320 has a smaller venturi, and we install a FM-100 on a 320 so the pressure drop numbers are not correct. And all these pressure drop numbers are meaningless if your running part throttle cruise power. It only applys to WOT operation.

Don
 
True for a standard cowl

Captain Avgas said:
I keep hearing how "cold air" horizontal induction FI systems produce a couple more HP than vertical induction FI systems. Yes, well maybe in a test stand where both engines are free to suck air without restriction.

However in an RV I see that virtually all of the horizontal induction engines have no scoop under the cowl (Dan C is one of the exceptions). So they suck their air from the left engine inlet scoop....at 90 degrees to the flow....down and around in a convoluted pathway to the throttle body.

The vertical induction system however has virtually ram air with the scoop inlet directly in front of the throttle body.

.
Click to expand...

My Sam James aftermarket cowl (and Dan's, Walter's) has two things going on.
1) the Ram air inlet
2) The ram air is at 90deg to the cooling air intakes. What that means is, if you look at the indexing of the prop, it has the back edge of the blade going past the air intake just as the inlet valve is closing on each cylinder.

In theory (lovely terminology that) it should give a little more cylinder compression.

How much if any difference does this make?...I have no idea but Ken Paser did apprently see some benefit.

When building the cowl inlet I did set the inlet ring at a few degree to catch the rotational wind off the prop and the inlet ring is 0.5 inch behind the prop at coarse pitch.

Frank
 
Well its more complicated than that

frankh said:
My Sam James aftermarket cowl (and Dan's, Walter's) has two things going on.
1) the Ram air inlet
Click to expand...

Well Van's cowl has RAM air effect. Mr. James overestimates the advantage of his cowl and airbox. The main difference in SJ's cowl is the cone shaped K&N air filter. Vans uses round filters. Sam thinks that his air filter with twice the filter area will flow twice as much. IT will not.

First, the pressure drop across a K&N filter, either in vans air box or SJ's is very small already at the rated CFM or flow. So 1/2 of nothing is not much. We are talking about 0.05 in-hg. OK.

Second, and again the engine flows only so much area. The filter in SJ's cowl will not flow more than vans filter. However there is an advantage that you will not have to clean the SJ cowl filter as much. The greater area does help.

If you don't believe me call K&N. Yes there is dynamic air pressure to recover but there is no major difference between vans cowl and SJ in regard to induction. In fact for vertical induction engines the SJ cowl uses vans air box I believe. If you are talking about SJ's longer cowl for the fwd facing induction, there may be slightly less external drag, simply less frontal area. How much difference? 0.09 mph? I don't know but not much. Now SJ, cooling drag for the engine is much less. All the gain or 99.99% is from the cooling drag reduction not induction.


frankh said:
2) The ram air is at 90deg to the cooling air intakes. What that means is, if you look at the indexing of the prop, it has the back edge of the blade going past the air intake just as the inlet valve is closing on each cylinder.
Click to expand...

Good luck getting that. If you read Speed with Economy he need to put the scoop for the induction with in like 1/4" of the prop and angled it into the prop, 10 degrees. Also key is being away from the hub (spinner). The prop thrust gets greater as you go towards the tip. You want to be further out. The result is what you saw in the book. A very weird snorkel tube extending for a few feet. It looks weird.


frankh said:
In theory (lovely terminology that) it should give a little more cylinder compression.
Click to expand...

The problem with THEORY is the engine does NOT breath continuously. It flows and stops, flows and stops, in pulses. If you try to stuff air into the induction and it has not place to go, like a large volumn or plenum its just going to spill out around the scoop. The added weight and external drag may delete any gain you get. If you want to increase compression or add a turbo you can gain HP. Passive intake tricks or theory are great but the stock Van's intake is pretty darn good, believe it or not. Van is no dummy and he has tested it.

As Captain Avgas mentioned about the horizontal induction engines have no scoop under the cowl, and "suck their air from the left engine inlet scoop....at 90 degrees to the flow....down and around in a convoluted pathway to the throttle body." Vans cowl and fwd face induction (intake from left cowl inlet) is an excellent design and has advantages. The external drag is less, and Van wrote an extensive article about this design in the RVator many years ago (10?). It may be convoluted but it has other advantages. It would seem not to work as well, but it DOES! Why? For one there is more room for a large plenum with volumn. That LONG trumpet is ideal diffuser. As I mention engines suck, stop, suck, stop and pulse. That long area and volumn of air is ideal for feeding the engine.

Captain Avgas also wrote; "Therefore I'm betting that in the real world there will be no measurable increase in HP for the horizontal induction if the cowl scoop is discarded. Anyone got any figures to prove otherwise." Correct, there is little difference in vertical and horizontal induction. They all have to turn a corner at some point, branch out, and go vertical into the cylinders. The problem with the Horz induction is there is not much room to develop a good diffuser, taking high speed air, slowing it and having a nice reservoir for the engine to draw from. With Vertical induction there is more room to develop a decent airbox. Cold induction is better and VERY VERY expensive. I think for a daily flyer its too much effort. Standard airbox'es, exhaust and cowls may not work. Plus I believe it's an expensive option. Yes it adds more HP because you have cooler air (higher density).

frankh said:
How much if any difference does this make?...I have no idea but Ken Paser did apparently see some benefit.
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Not much as I said. If you add a 3 foot long induction you will see more people look at your plane on the ramp at the air show. I think it looked terriable but beauty is in the eyes of the builder. I think external drag will kill most of the gain. There are flight test numbers and info, see RVators for the last 15 years? May be someone has some back issues.


frankh said:
When building the cowl inlet I did set the inlet ring at a few degree to catch the rotational wind off the prop and the inlet ring is 0.5 inch behind the prop at coarse pitch.
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10 degrees for the realtive air flow is what Kent used. That varies with angle of attack, speed and RPM. You got it 0.50 inch behind the prop? Are you real close to the hub or further out on towards the tip of the prop. The first 1/3 of a prop blade span is beating the air into submission. Most of the thrust (on GA planes) on the prop does not really get going until 1/2 blade length.


frankh said:
Frank
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Good stuff Frank. My rule for mod is do no harm. Don't make it worse. The question I ask myself, is all the effort: time, money, weight, complexity worthy of the perceived or hoped gain (in theory). Usually the KISS or stick to the plans method rules. There are very few free lunches laying around on the aviation table. There are always trade offs. You may pick up 0.10 inches-Hg or 1/2 HP, but you may add 2 lbs of weight and minus 1/2 mph in drag. Of course your 1/2 HP got you 1/4 mph, but with the 1/2 mph drag you are in the hole a 1/4 mph. You really don't know until you try, but its hard to measure small changes like +/- 1/4 mph. Bottom line it all has to work together as a complete design or system.
 
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doug?

doug
you should start a new section called the hairsplitters club. :rolleyes:
maybe already pointed out but the benefits of fi are mostly being performance...the carb is simply simple. :) MY.02
 
Hairs on the backside of a nat

cytoxin said:
doug
you should start a new section called the hairsplitters club. :rolleyes:
maybe already pointed out but the benefits of fi are mostly being performance...the carb is simply simple. :) MY.02
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I agree. Despite all my research, I have a Carb and Vans FAB360 air box on a stock cowl. I am modifying my stock (epoxy) cowl inlets to round rings coupled to a solid plenum, but the induction is pretty much pure Vans. I did make a solid couple between the air box and cowl to eliminate leakage. To do that requires a slight extension of the scoop and an access door. I also went from vans oblong entrance to a round intake scoop to match the cowl inlets. Basically its a stock Vans vert intake to a Carb.

If you have FI than both Vet or Horz air-boxes work well. The Horz box is very good. Like I said, find the original article on the design of the induction. It may seem convoluted but it works well in service. There are only hairs left after that, and that comes at great expense and extra work. Sticking with off the shelf stuff saves lots of time, effort and headaches.
 
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For my money, FI, just like I'd get a CS prop. I feel these airplanes are hobbled by FP props and to some degree, Carbs.

Remember, negative G's. :)
 
Ooops

Don at Airflow said:
Gil, your math is correct but on a 320 a MA-4 is used (smaller choke than an MA4-5). The RSA-5 used on a 320 has a smaller venturi, and we install a FM-100 on a 320 so the pressure drop numbers are not correct. And all these pressure drop numbers are meaningless if your running part throttle cruise power. It only applys to WOT operation.

Don
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Don ... thanks for the correction.... I was not allowing for the WOT operation.... :eek:

gil in Tucson
 
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