H6 Sube Fuel Flows

Eggenfellner has just finished testing fuel flows with modified fuel pressure on his H6 engine and showed some tangible performance gains:

Old:

4830 engine rpm
FF 10.1
TAS 148 knots

New:

4830 engine rpm
FF 8.4
TAS 160 knots

Leaning the overly rich OE ECU settings has reduced fuel flow and increased power. Good news for Egg owners and kudos to Jan for testing and improving his products.

Full power or cruise?

H6 fuel flow

That is full power (2650 prop rpm -> 1.82 PSRU).

Great economy for full power!

8.4 gph at 160kts is approximately one gallon per hour more than an O-320 with a Hartzel, on an RV7a.

I know one builder who can fly at 7.5 gph all day long at 161kts, in an rv7-a that is a little heavy (full interior, paint, IFR panel). It is a carbureted engine and he runs at 50-100 degrees rich of peak.

Of course an O-320/ Hartzell FWF could easily be completed for less than 25K and with half the parts count.

Do people intend to fly these things in cruise at 4800 rpm?

Merely relaying the progress being made on this front with the Sube, 1.7 gal./hr. less and 12 knots more is significant. Yes, standard cruise rpm on most Sube conversions is between 4200 and 4800 rpm. About the same piston speed as an O-360 at 2600 rpm. Many thousands of hours at these rpms have successfully been flown now. Nothing much to be concerned about.

rv6ejguy said:

Eggenfellner has just finished testing fuel flows with modified fuel pressure on his H6 engine and showed some tangible performance gains:

Old:

4830 engine rpm
FF 10.1
TAS 148 knots

New:

4830 engine rpm
FF 8.4
TAS 160 knots

Leaning the overly rich OE ECU settings has reduced fuel flow and increased power. Good news for Egg owners and kudos to Jan for testing and improving his products.

Click to expand...

Increasing speed from 148 to 160 kts, all else being equal, is a ~25% increase in power. Reducing fuel flow from 10.1 to 8.4 gph is a ~20% reduction in fuel flow. Combined, that means the SFC went down by a third...pretty good improvement! (It must've been pretty bad before, though)

So I guess he's using fuel pressure to adjust mixture, since he can't fiddle with the Subaru ECU's settings? I wonder why the ECU runs rich? Must be the software designers assuming that "If the driver has hit foot down and the RPMs up, he must care about power more than fuel economy...fatten up the mixture!"

Subaru ECU mapping

So I guess he's using fuel pressure to adjust mixture, since he can't fiddle with the Subaru ECU's settings? I wonder why the ECU runs rich?

Click to expand...

I believe this is the case. I think Ross (rv6ejguy) needs to get his sales guys to get on the phone to Eggenfellner to sell his unit. I personally would be much happier with a simple system to control the fuel and the fire.

I know that alot of people focus on piston speed. However, the problem with High RPM is not piston speed, it is acceleration and inertia loads on the rod, crank, pin, etc...

A piston must stop and accelerate twice per stroke, from a dead stop to full speed. Thats four times per revolution. The load is greatest, on the reciprocating assembly, at these times.

4800 X 4 = 19,200 acceleration cycles per minute

2600 x 4 = 10,400 acceleration cycles per minute.

In addition, even if the stroke were as short as half the lyc stroke, and it is longer, piston speed is still higher in order to travel the route twice as many times in a given time frame.

3.875, lycoming O-320 stroke.
x 4 = 15.5 inches travelled per revolution.
x 2600rpm = 40,300 inches travelled per minute
672 inches per second

3.15, Subaru H6 stroke in the Outback.
x 4 = 12.6 inches per revolution.
x 4800rpm = 60,400 inches travelled per minute
1008 inches per second.

O-360 stroke 4.375 inches.
piston speed 759 inches per second at 2600 rpm.

Just some math to illustrate my point, but an H6 at 4800 rpm must start and stop a piston alot more times every minute and it must accelerate to a higher speed each time than does either an O-320 or O-360.


But, as demostrated, the piston speed is NOT "about the same" as the lyc at 2600 rpm.

Yes, high fuel flows on the Egg conversions was a problem due to the very rich near WOT default open loop programming of the OE ECUs. These were setting AFRs richer than 11.5 in some cases causing a loss of power and high fuel flows.

The lower fuel pressures have been easier to implement than reprogramming the ECUs at this stage. Eggenfellner is working on other ECU solutions and new redrive ratios in a further effort to reduce fuel flows.

Piston speeds in the engine design/development area are usually denoted in ft./min. 1750-2000 is commonly thought to be a very safe limit with modern forged, ferrous connecting rod materials and construction as used in the Subaru engines for instance. My EJ22 in cruise at 4600 rpm would have a piston speed of 1130, a Lyc. O-360 would be 948 at 2600. So yes, my Sube has a higher piston speed but it is far, far below any critical fatigue range.

The short stroke design of the Sube permits much greater crankpin overlap than on a long stroke design. The EJ22 has .750 overlap.This coupled with 5 main bearings instead of 3 as on a Lycoming makes for a far stiffer and well supported crank assembly. In addition, the parts are far lighter, reducing tensile and compressive loads. The pistons are under 600 grams, the crank is only 13.5 inches long and weighs 20 lbs.

I'll reiterate this for about the 3rd time. I can find no documented cases of crankshaft or rod failures on EJ, EJ or EZ engines used in aircraft. They have accumulated well over 100,000 flight hours to date. The STI EJ engines have demonstrated power outputs in excess of 950hp using the stock block and crankshaft for short periods. This would equate to an O-360 producing 2242+hp. IMHO the Lyc would be shrapnel before it got to half that output in less than 1 second. You decide which is the stronger engine.

Fact, piston speed on a Sube IS higher than a Lyc at typical cruise power settings.

Fact, this is a non-issue as the stress levels are far below the point of critical fatigue life. This is born out both by analytical and real world flight experience.

Nuff said.

Jconard,
I agree with your comment regarding inertia and stress, but I believe you left out an important component- the mass difference of the piston and con rods. A short stroke with light pistons will have much less stress, even at higher engine speeds, than a long throw, heavy piston engine. Heavy (large diameter} pistons have to be designed with heavy industrial strength rods to withstand the constant pounding, stretching, and vibration they receive and pass on to the soft rod and main bearings. FWIW, there is also an issue with excessive side loading (wear) of piston skirts and cylinder walls with long-throw engines caused by the larger crank-to-rod angles at 90/270 crankshaft throw angles (evntually wears an oval shaped bore, creates ring seal and cooling problems).

Most racing engines are built with lighweight components and a short stroke to enable sustained high rpm operation. Course, they seldom go for more than a single race before overhaul...

If you are concerned with reciprocating stresses at high rpm, go rotary. That and related reliabiity issues are the reason I am, even though I really like the Subaru engine.

Cobra,

The side loads in long stroke engines are a result of rods which are too short. The best example, and where this theory was widely started, is the chevy 400 small block. The deck height of the small block necessitated short rods in the bored and stroked 400 cubic inch version.

I do not believe that the lycoming suffers this geometry issue. I do have a set of barrels with 2200 hours on them that could be honed and re-used. The pistons in this engine have no pin offset...so it would seem that the geometry issue is resolved.

Inertia is a function of acceleration, which is much higher at high rpm, both as a function of piston speed, and acceleration cycles (A=v2-v1/time).

In addition, parasitic loss increases with RPM.

You are correct that racing engines use high rpm, but that is a function of the rules. Racing classes are typically based on engine displacement. Within a limited displacement, high rpm is the way to make power. This is not the case with aircraft engines, and for reliability purposes, best practice for decades has been large displacement, slow turning engines.

The lower stress not only mitigates the chance of failure, but it also makes failures less spectacular when they do happen.

I witnessed a Mazda factory car loose a rotor at Mosport (high speed tack in Bowmanville, Ontario). I was there as a driver in the F2000 series. For all those considering aluminum rotor housings, all I can say is that when they let go it is SPECTACULAR. Literally blew the side off the car.

To be clear, I understand all the benefits of the systems that are used to race these car engines. As a driver, I can appreciate the benefits of throttle response, and tracktability that EFI brought us. Though, to be fair the Atlantic engines always had more power in a carbureted version.

It is just that those needs do not exist in airplanes. Before I get flamed...throttle response in an airplane is not the same as in a car, and frankly in an airplane a little softness of response for half a second is fine in an airplane, but would make a formula car very difficult to drive.

I am not picking on those who want to do the car engine thing. I just worry that the options are not accurately described to beginers. But even with these recent improvements the conversions are still heavier, slower, and use more fuel. They also have double and triple the system complexity. Anyone considering this route, in order to fly, should consider that. Of course, to those who simply want the challenge and experience, those points will not matter.

jconrad,

a little off the subject here, but i was wondering what sort of rpm and hp the rotary was producing when it blew? i've been planning a rotary installation for quite a while now, and have been following the soob's as an option as well. of course, nothing is ruled out at this point since i'm years from an engine.

curious.

not sure, it was an old GTP car that a rich guy was running, but it had all the Mazda factory goodies.

The guys running the formula mazda cars said that it was a result of the eccentric shaft breaking and the rotor housing being aluminum or magnesium. In essence they told me that those failures never get that crazy on the engines with iron rotor housings.

Apparently as RPM, Horsepower, and Boost go up the eccentric shaft that the rotor drives is the week part.

The formula Mazda cars use a relatively stock engine, and it seems pretty bullet proof, so maybe the answer is iron housings, and low levels of modification. I also know that the FM teams will spend alot of time informing the rookie drivers not to rev the engine...apparently free reving them damages the tip seals. The stock engine is pretty fun to drive in a 1000 pound car. For the record they are fed by a double throat downdraft weber carb.

Over the years I have built a number of race engines for personal consumption, including a 911, and several Super Vee and rebuilds on Atlantic engines...I just completed the assembly on my O-320. Mine will be carbed, with mild compression. I did spend money on custom balanced pistons, rotating mass, and Lycon Cylinder work. His port work is some of the nicest I have seen. Even with the new jugs and machine work, I will have the engine done from a single run core for about 13K with new mags and carb. The pistoms came matched and ready to go...Lycon estimates about 170HP, but it should be pretty durable. Best of all, 2 wires, three cables, and a fuel line is all it needs to run.

If it ain't broke...giter'done

Jconard said:

The pistons came matched and ready to go...Lycon estimates about 170HP, but it should be pretty durable. Best of all, 2 wires, three cables, and a fuel line is all it needs to run.

Click to expand...

LOL Ha Ha Ha Ha, I pass the Lycoming defending crown to you my friend.

George RV-4/RV-7 Lyc O-360A1A/Hartzell

Well at least many people find this topic interesting, 375 views to date.


The original post was to inform those interested that progress was being made to address the high fuel flows at high power settings on these conversions. Still inferior to a well set up Lyc? Yep, but getting better.

Jconard said:

The guys running the formula mazda cars said that it was a result of the eccentric shaft breaking and the rotor housing being aluminum or magnesium. In essence they told me that those failures never get that crazy on the engines with iron rotor housings.

Apparently as RPM, Horsepower, and Boost go up the eccentric shaft that the rotor drives is the week part.

The formula Mazda cars use a relatively stock engine, and it seems pretty bullet proof, so maybe the answer is iron housings, and low levels of modification.

Click to expand...

Funny, I've never seen or heard of iron rotor housings. Maybe you are thinking about the side housings, which are normally cast iron, but can be replaced with aluminum. I haven't heard much on the reliability of the aluminum side housings, but I will say that they are running 10K RPM in the racing engines, whereas most airplane owners would not think of going over 6500.

Also, from what I have seen, the eccentric shaft on the rotary engines is pretty stout. I doubt that it is a weak link, but I could be wrong.

Of course, I did see a few pictures a few months ago from a guy who was flying a Lyco (I think it was a Cherokee or a Traveler with an O-360 of some sort) where half of the engine was blown away by what looked like a rod coming through the side of the engine.

I think we can find plenty of examples where racing engines pushed to their limits fly apart, but we should be concerned about engines used in aircraft. It does no good to try and scare people about a particular engine coming apart, if it is being used to race. Show me the rotary engines flying apart inside of a cowl. Actually, you will not find any. All you will find are examples of rotary engines continuing to fly to an airport after what would normally be a catastropic failure on a Lycoming.

Cheers,
Tracy.

You guys have awakened the giant.

Tracy,

you are correct...the race versions get pushed pretty hard. I was relaying seond hand guesses about the root cause as explained to me. I will say that I know several folks who raced rotary engines in road race and autocross settings, and they have all relayed the information about the eccentric shaft.

Based on your obvious experience and mastery of the rotary installation in your own plane, I must defer on the issues of reliability in Aircraft. By the way, I have spent hours on your (very good) website, and found it enjoyable and informative.

Actually, I was only passing information on as to what I had witnessed when one failed, and I clarified as a result of cjensen's inquiry. But I will again say I have never seen an engine failure so thoroughly destroy a car in road racing...just like a nitro dragster letting loose.

For what it is worth, I did see a crank at the local machine shop from an O-360 that broke irregularly at the front bearing to fillet juncture. It caused vibration but 30 minutes later the plane landed under power. Aparently there was a previous un resolved prop strike...but it goes to show with the proper failure mode and luck any engine might make it home damaged.

As earlier, I do not oppose the notion of car conversions, just the comparisons that get made innacurately. When I was shopping I remember being told by one famous sube seler that I could spend less, go faster, and on less fuel. I did not know enough to ask about weight, but the website indicates a wash. Fact is that choice would have cost more, weighed more, gone slower, and used more fuel.

All for experimentation, based on informed choice. For the record my guess is that the rotary will end up a better choice whith development, simply because it will have fewer probles with weight and re-drive harmonics. But that is just a guess.

thallock said:

Funny, I've never seen or heard of iron rotor housings. Maybe you are thinking about the side housings, which are normally cast iron, but can be replaced with aluminum. I haven't heard much on the reliability of the aluminum side housings, but I will say that they are running 10K RPM in the racing engines, whereas most airplane owners would not think of going over 6500.

Also, from what I have seen, the eccentric shaft on the rotary engines is pretty stout. I doubt that it is a weak link, but I could be wrong.

Of course, I did see a few pictures a few months ago from a guy who was flying a Lyco (I think it was a Cherokee or a Traveler with an O-360 of some sort) where half of the engine was blown away by what looked like a rod coming through the side of the engine.

I think we can find plenty of examples where racing engines pushed to their limits fly apart, but we should be concerned about engines used in aircraft. It does no good to try and scare people about a particular engine coming apart, if it is being used to race. Show me the rotary engines flying apart inside of a cowl. Actually, you will not find any. All you will find are examples of rotary engines continuing to fly to an airport after what would normally be a catastropic failure on a Lycoming.

Cheers,
Tracy.

Click to expand...

Just had a 172 blow a barrel right off the engine here last week in the circuit. Looked like a rod let go. The guy managed to slam it back on the runway luckily and nobody was hurt.

Tracy, what fuel flows and speeds are you seeing with your present setup? This has been the subject of much discussion.

Power to weight ratio and RPM

Jconard said:

You are correct that racing engines use high rpm, but that is a function of the rules. Racing classes are typically based on engine displacement. Within a limited displacement, high rpm is the way to make power. This is not the case with aircraft engines, and for reliability purposes, best practice for decades has been large displacement, slow turning engines.

Click to expand...

High RPM is also used to get a better power to weight ratio out of an engine. Hence the high rpm design of such weight-dependent applications as model aircraft, weed-trimmers, dirt bikes, etc. All other things being equal, a high-rpm low displacement engine will have a better power to weight ratio. Of course all things are not equal in these comparisons, since we're comparing liquid cooled to air cooled and direct drive to geared.

Oops, I don't want to represent myself as a rotary expert--I am not. I am just an observer at this point. It is true that I am going to install an RX-7 13B rotary engine in my RV-7A, but I have not yet ran the engine at this point. So, anything that I say should be taken with a grain of salt--the ole 2-cents. These are just my observations.

Obviously, without having a running engine, I don't have any first-hand information about fuel consumption. I only know that the rotary has a bad reputation for fuel economy, and there are few people who can refute that. However, based upon the feedback from Tracy Crook, it appears that the numbers are not as bad as people would suggest. Tracy has determined that the rotary can be leaned way beyond what would be acceptable for a Lycoming, and I think he cruises at around 5-6GPH. But let's be honest here, Tracy is cheap, and doesn't mind crusing around 140Kts. If you pull the power back enough, your fuel consumption will go down, and you will get reasonable numbers. These numbers hove no meaning unless you fly side-by-side. Of course, this was done a few months ago, and in the fuel consumption and noise categories, the rotary lost (RVATOR two issues back). The good news is that while the fuel consumption was higher, it was just marginally higher (something like 10%, I think).

Also, I didn't want to blast Jconard, either. I just wanted to make sure that when we point out failures, they are relevant to aviation installations. Of course, there's the old saying "win on Sunday, sell on Monday", so there probably is some relevance here.

Also, it is not my intent to blast the Lycos by pointing out an engine failure that just happened to be catastropic. Again, we should focus on the trends, not the exceptions. Personally, I like Lyco engines. I think the trends are that the Lyco engines have proven to be very reliable with reasonable power-to-weight, I just wish that I could afford one.

BTW, Jconard, thanks for the compliment, I appreciate it. But, alas, I suspect that you are probably referring to Tracy Crook's website (http://www.rotaryaviation.com/), which I agree, has exceptional information and which I enjoy re-reading on occassion. I would highly reccommend his website to anyone who is interested in alternate engine installations.

Now, back to the original intent of this thread, which is that the new fuel flow numbers for the H6 are now 8.4 GPH at 160kts, .vs. the original 10.1 GPH at 148kts. I think this is great news. Those of us who have followed the Eggenfellner installation for the last few years have been a little disappointed in the numbers. The speeds have been too low, and the weight and fuel flow has been too high, not to mention the price. With the new numbers, the Subie is starting to match the Lyco. Just have to work on that weight issue.

This is what alternate engine developement is all about. If we all gave up after the first installation had a problem or failed to live up to the expectations, we would never have these new choices. I salute Jan's efforts, and thank him for giving the alternate engine movement a little more credibility.

Cheers,
Tracy.

well said tracy, and i think you have a fine website! i like lyc's as well, but the rotary has just had me fascinated since the first RX-7 i owned (i've had three!).

good to see that the h6 is getting better fuel flow and speed. they'll keep getting better. 'course, so will the lyc's and clones.

I made an ass- umption that Tracy Crook had joined the forum. Sorry.

Thanks for your input and realistic responses.



As we learn more, things should improve. We're going with 10 to 1 CR and different gearing to slow the engine down in cruise on our latest project. Looks like we may see a 6-8% drop in fuel flow if all works as planned.

This is really the first constructive thread I've seen on this subject in awhile. While I drive behind a Lyco, I'm still supportive, curious, and reasonably positive about alternative engines.

I really like to see hard and factual numbers, in a real world application. This non-sense of comparing "he said / she said" things is ridiculous. It's all too common in the homebuilt world....everyones "improvements" always claim something crazy like being 20kts faster, 150lbs lighter, thousands of $$'s cheaper, and burn 5gph less It's refreshing and positive when you see someone actually state real numbers.

That being said, stating anedoctal evidence about Lyc's vs. Subes in aircraft reliability is also a bit dubious at best without doing the math right. It shows absolutely nothing unless you've done the math correctly. Yep, there have been a LOT of Lyc's fail for various reasons, but they also have delivered over a million engines with countless millions of flight hours on the lot of them. Simply stating that a 320 had a jug blow off in the pattern is a bit preposterous and only stands to muddy the waters for the greenhorn, newbie, or beginner looking for good information. One could just as easily point out that some time ago an RV7 with a Subie flipped over in a bean field because his timing belt came off, or another RV with a Subie had an emergency because his engine died after an electrical failure. Now, those in the "know", know there is a lot more to both stories (like an improperly aligned supercharger belt & missing shield causing the timing belt problem, or lack of any backup electrical system and warning on the dead ignition). My point is that without knowing or sharing the WHOLE story (both sides of it), comparing accidents without facts, history, and accurate statistics just causes corruption of truth and opinion and serves no compelling purpose in advancing either parties principles or cause.

I don't mean to rant or sound defensive because I'm not at all, but I really like to see people keep things in perspective. When it comes to alternative engines and any hope of success over the long term, honesty will win hands down. If it burns more fuel, so be it! Sell the thing on it's other benefits - and make sure they're not just perceived beneifits, but real benefits with real figures and real numbers. Some are willing to do that and have gained a great deal of respect (such as Tracy Cook, etc..), but others have and are quickly losing respect because of being a bit overly optomistic about their offerings.

Keep the objective posts and numbers coming...they create the opportunity for an accurate and factual development of opinions and options.

OK, I'm done!

Cheers,
Stein.

I started this thread to inform and unfortunately it quickly got off topic and the Lyc. boys start slaming the the auto engines so, being the child that I am, I had to relate the latest Lyc. failure at my airport to get even. Stein is absolutely right here. Let's keep it on topic and as factual as possible.

The two Egg failures have been addressed with fixes long ago and lately have racked up several thousand hours of reliable flight. He continues to improve the installations and performance which is good for all who are interested in his conversions.

My first response was based on the comment one person made that 8.4 gph @ 160kts was "great fuel flow for full power"

My post was not a "Slam". It was factual.

I simply wanted to point out that such flow/speed is fatter on the fuel and lighter on the speed than could be achieved with a carbed 320 on the same model of airframe.

My only point in doing so was that I hear all the time about crazy claims, and unsubstantiated references to the benefits of "newer technology"

As pointed out earlier, the technology being used is newer and better in its designed for application, but that in the airplane application it is missapplied.

As evidenced by actual performance.

I run into so many people who are snowed, the same way I was when I first talked to the purveyors of this stuff, that I wanted to point out where that fit in the airplane world.

To repeat, I think that for people who want to be different and experiment, this is a neat area. For people who want to fly reliable, light airplanes that are fast and use minimal fuel I wish the conversion sellers would be a bit more honest.

Car engine= More interesting to some + More Weight, More fuel, Less Speed.

Lyco= Less innovation and experimentation + Less Weight, More Speed, Less fuel burn, Less Money.

As an aside, if the result of an approach is lower performance, is it really innovative, or is it simply different?

Jconard said:

Car engine= More interesting to some + More Weight, More fuel, Less Speed.

Lyco= Less innovation and experimentation + Less Weight, More Speed, Less fuel burn, Less Money.

As an aside, if the result of an approach is lower performance, is it really innovative, or is it simply different?

Click to expand...

Three comments:
FIRST: I can't wait to see two RV-10's one w/ a 540 Lyc and one w/ a 20b weigh to see what the weight difference is. I'm wondering which will be lighter. I sure wish someone would hurry up w/ their Mazda 20B RV-10!

SECOND: Not sure I'd say the Lyc is less money. It is of course unfair to compare a used and rebuilt Mazda 20b to a new lyc, but comparing a used to used I'm still not sure the 'less money' falls to the lyc. I recently saw a rebuilt 540 on e-bay for $5000 - about the same as the 20b from the same site. However, both need ignition, fuel delivery, exhause, cooling, mounts, among a pletora of additional parts. I expect all said and done, they come out about the same.

THIRD: As for the innovation vs different - definitely different, but an approach doesn't have to result in better performance to be innovative. It could be innovative merely because it is using a technology for an application different than what it was originally designed for - IMHO.

Jconard said:

...As an aside, if the result of an approach is lower performance, is it really innovative, or is it simply different?

Click to expand...

Since overall performance is many faceted and certainly factors in more than just speed and fuel burn, there is enough of a jury out on this subject to drive choices in either direction.
I am not sure you can defend a blanket statement of the auto conversions as being a misapplication of the power unit. They certainly have not had the benefit of time for fine tuning the airplane application as has lycoming and, as such, are lagging behind in some of the performance measures.
In areas such as shock cooling, detonation control, all weather starting and general fuel mixture management, the conversions have had most of those bugs well sorted out and need no special operator intervention to benefit from them.
I believe that given enough time and effort by the experimenters out there they will attain fuel use and speed similar to the lycoming.
This is obviously a defense of auto conversions but not at the expense of slapping lycoming. Their engine is certainly optimised for its application but it has a certain fragility that requires somewhat closer attention by the operator (not necessarily difficult but required nonetheless) to attain its potential.

All that having been said, I am still going to go with an O-320 for my 9A.

My reasons are this: It is obviously the shortest time to flight (and maybe cheaper when compared to some of the auto conversions) since the installation is per plans and time is an issue for me. If I were twenty years younger I would definitely go rotary.

Once this one is built and I get my flying fix satisfied regularly, I will build another using an auto conversion for sure!

As to shock cooling...

If you read Deakin's columns on engine management, you will find that the myth of shock cooling the flat four engine, or damaging it by driving it with the prop, are old wive's tales and were applicable if at all, to raidals.

And, if mixture distribution and optimisation were an issue resolved in an airplane but the use of EFI, you would expect better fuel economy....just ain't so.

The benefit of electronic fuel injection, as used in cars was marginal economy (compared to a well tuned carb) and easier drivability, flexibility....all things which do not apply in an environment where power only needs to be delivered of a 500-1000 rpm band. For this application a simple carb or mechanical injection is easily optimised.

I suspect that unless the EFI systems go to multiple, selectable maps, as the fadec systems use, they will never be able to achieve the economy that a somewhat skilled pilot can with a mixture knob. This is because the operating regimes are too different between power and cruise.

I know I will hear alot of disagreement with that last statement but the proof is in the pudding. These systems have been around for three decades. People have been working on conversions since the first Model A powered Jenny, and the numbers just aren't there.

http://www.avweb.com/news/columns/186778-1.html

see other deakin columns...

Yes, these engines are different. Missapplied, hardly. They are giving their owners the benefits they desire for the most part and getting them into the air, enjoying their aircraft. As discussed at length here, many people value other attributes in making this decision.

Newer technology is relative. 4 valve heads, overhead cams and EFI have been around for 30+ years so this is not new. The design of the Sube engines is newer than cert engines. Better? In some ways yes, other ways no.

Absolutely, the auto engine conversion segment has been tainted by snake oil salesmen and dubious or outright false specs. The worst offenders are now gone, being "reorganized" or have damaged their reputations so much from this BS that they'll never hold any significant part of this market. Eggenfellner has moved to the front of the line in this market by ignoring the critics, improving problem areas, issuing fixes and warnings rather than coverups and supporting his clients. The biggest thing he has done to make this viable for many is the complete package, always done the same way with good manuals and support.

There is a dearth of real data with either side by side comparisons such as done by Van's with the Powersport Wankels or reliable sources such as CAFE. I'm sure in the future, some vendors will show up at Van's and let us see what is really up. In the near future, I don't see any auto conversions besting a Lyc. in the weight or fuel burn vs. speed contests at high power settings but progress is narrowing the gap.

While at Reno this year, it was very interesting to study the Thunder Mustang with its atmo V12, liquid cooled, EFI engine compared to the Lancairs with turboed, mechanically injected flat 6 Contis. Both sounded wonderful and looked beautiful. I'm glad both types were there flying. I was impressed that the TM is now the fastest atmo engined aircraft and that Greenameyer's Conti was able to go that fast without disintegrating. Wonderful stuff!

I knew we could find something to agree on.....

The falconer V-12 is one of the coolest engines, independently produced, since perhaps the HART engines that brought Senna to the tolman team.

I guess it went well in the thunder mustang? I had heard that falconer was no longer going to support that installation, but that must have been rumor...it is a cool, sweet sounding twelve.

By multiple selectable maps, I assume you refer to speed-density systems?

I believe most modern automotive sytems use mass air FI systems that continually provide sensor feedback that modifies mixture/spark timing until they reach the optimum tune. I have a Mustang that has an aftermarket programmable chip installed that can alter the target tables to increase performance as well. It still takes the computer a week or so to relearn any new changes.

Unless you (old school) pilots have an expensive wide band O2 meter installed (which will be ruined by the lead content of avgas), I seriously question whether you can set OPTIMAL fuel/air mixture by sound, feel, and egt in a noisy, vibrating airplane under most conditions. Maybe close is good enough, but my intuition suiggests an optimum tune should be safer and a bit more economical.

I suspect the small differences seen in speed and fuel economy between Lycs and the conversions have more to do with small weight, balance (drag/trim) and prop efficiency differences than anything inherent to the motors. Could be wrong of course. Some conversions are just now comming out with hydraulic c/s prop capability- it will be interesting to compare the results with the same props.

No,

I mean completely different maps/programming for the different regimes.

Wide band oxegyn sensors are not necessary. Pilots achieve fuel flows, in economy cruise that are excellent.

The maps for your mustang are not targets, they are hard fixed relationships between airflow, rpm, tps, etc...and the resulting fuel and spark. In addition, in your mustang to get out of corners weel and have good response you are probably quite a bit further rich than in airplane operation. I know that you want to believe that using the same system is safer and results in more economy, but it just has not yet been the case. In fact, in speaking with Aerosance, they are seeing most of the economy coming from the spark timing, and not from the fuel mixture. The have, in that system, what would equate to two seperate "chips" in your mustang. That's what I mean by seperate and discreet maps.

By the way, cars have been tuned for years with just egt...at least in racing. The oxegyn sensor is generally only used in closed loop mode, because it is simply not a great way to set mixture. The maps and relationship between spark, fuel, and other sensors is typically set on a dyno and through track testing.

Closed loop oxegyn sensor operation is typically very rich because the system cannot respond quickly enough to run even moderately lean.

In cruise you have a, by car standards, very very very steady load/output/rpm. This makes it very easy to set mixture manually. Trends are slow and it is easy to follow them. By the way the fuel/speed numbers I posted were a 320 running 50-75 degrees rich of peak, and achieving better economy/speed than the modern equivalent.

This seems to suggest that even a moderately unskilled pilot could get pretty darn good numbers....its not that hard to set power and mixture at 50 degrees rich. I regularly got similar fuel flows from my Citabria, which had no EGT, simply by sound and feel. My engine ran great, clean and when I sold it at 1800 hrs since overhaul still had compression, and oil pressure numbers that suggested at least 400 more hours. It only used 1 quart every eleven hours with acro or every 18-19 hours in relatively sedate flying.

not hard to do, easy to learn.

Jconard said:

No,

I mean completely different maps/programming for the different regimes.

Wide band oxegyn sensors are not necessary. Pilots achieve fuel flows, in economy cruise that are excellent.

The maps for your mustang are not targets, they are hard fixed relationships between airflow, rpm, tps, etc...and the resulting fuel and spark. In addition, in your mustang to get out of corners weel and have good response you are probably quite a bit further rich than in airplane operation. I know that you want to believe that using the same system is safer and results in more economy, but it just has not yet been the case. In fact, in speaking with Aerosance, they are seeing most of the economy coming from the spark timing, and not from the fuel mixture. The have, in that system, what would equate to two seperate "chips" in your mustang. That's what I mean by seperate and discreet maps.

By the way, cars have been tuned for years with just egt...at least in racing. The oxegyn sensor is generally only used in closed loop mode, because it is simply not a great way to set mixture. The maps and relationship between spark, fuel, and other sensors is typically set on a dyno and through track testing.

Closed loop oxegyn sensor operation is typically very rich because the system cannot respond quickly enough to run even moderately lean.

In cruise you have a, by car standards, very very very steady load/output/rpm. This makes it very easy to set mixture manually. Trends are slow and it is easy to follow them. By the way the fuel/speed numbers I posted were a 320 running 50-75 degrees rich of peak, and achieving better economy/speed than the modern equivalent.

This seems to suggest that even a moderately unskilled pilot could get pretty darn good numbers....its not that hard to set power and mixture at 50 degrees rich. I regularly got similar fuel flows from my Citabria, which had no EGT, simply by sound and feel. My engine ran great, clean and when I sold it at 1800 hrs since overhaul still had compression, and oil pressure numbers that suggested at least 400 more hours. It only used 1 quart every eleven hours with acro or every 18-19 hours in relatively sedate flying.

not hard to do, easy to learn.

Click to expand...

Auto engines are quite different with spark advance requirements while operating at lean mixtures and high power. We have done in flight testing with our EMS and found that there was no gain to advancing spark on the turbo Sube with regards to reducing fuel flows in cruise, but big gains by leaning the mixture in cruise.

With our EMS, it is possible to have it do totally automatic mixture and spark timing and achieve very good results under all conditions. However for safest and best economy operation, we prefer to and recommend manaul leaning once cruise power is set via EGT. The biggest gains we find with EMSs are in the warmup, taxi and climb areas where an estimated 5-7% lower fuel use for a short or high altitude mission is possible. Workload in flight is far lighter than with a carb. Lean it once at the end of the climb, richen it back in the pattern. All else is automatic and no carb heat to fuss with.

EGTs in race cars are a poor choice for tuning an engine for best power as they react too slowly to the rapid, non- steady state conditions present here. There are a good monitor however once the best power EGT has been established on a dyno for highest torque/ power. Certainly the modern wideband O2 sensors have revolutionized tuning modern performance engines. These are instant and generally very accurate within certain techical limitations such as intolerance to leaded fuels.

Closed loop operation in cars is certainly NOT rich. Closed loop tried to target stoichiometry at an AFR of around 14.7 for gasoline as is generally in operation only at part throttle and low to medium revs for emissions and fuel economy. Some engines fitted with 3 way cats and wideband sensors target AFRs as lean as 19 to 1 at light load.

Open loop mode is generally set up rather rich for safety and best power- typically 11.8 to 13 to 1. Some modern cars use wideband O2s to run in closed loop at all times. The different signal makes this possible and allows best power/ best economy at all times. Self learning features coupled with active closed loop knock sensing and DSP for individual cylinder control of fuel and spark makes these systems quite a bit more sophisticated than present piston aircraft FADECs.

I talked extensively to the one Thunder Mustang owner and he reported then the supercharged race engine development was on hold pending a $ponsor but that engines for standard TM projects would continue to be supplied by Falconer. Unfortunately atmo engines will not be competitive against the turboed ones so I hope they do find that sponsor. Greenameyer obliterated everyone this year. You should see the ADI and water injection tanks on his aircraft. They take up the right side of the cockpit.

Getting Better

An RV7A owner just posted some new data on Eggenfellners site. He has the H6 fitted with most of the latest refinements except the new 2.56 to 1 redrive. He was seeing 165 knots TAS on 8.5 gals/ hr.