Lack of twin engine E/ABs

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aeromomentum

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Stuart, FL USA
As an automotive based aircraft engine builder that has delivered hundreds of aircraft engines and with over a hundred flying I would like to take this opportunity to defend using an automotive engine as the basis for an aircraft engine. And of course pitch our engines.
First I would like to point out the certified Thielert/Continental CD-155 and the certified Austro engines are based on the MB OM640 automotive engines. These engines now have an 1800 TBO and claim a 100,000 hour MTBF. I am skeptical of the 100,000 hour MTBF but in any case they currently have an excellent reputation and can be operated at over 90% power continuous. While these engines do not have ignition they are FADEC and are absolutely dependent on electricity to run. Even with this electrical dependency they are the same or better reliability as other certified engines.

I am not sure about the electric power requirements of the Austro but our engines need about 2 amps and another 4 amps for the fuel pump so 6 amps total. If your alternator fails, your engine will keep running on the battery for a few hours. Plenty of time to find an airport to land.

It is simple to change the RPM of the alternator by changing the pulley diameters. We do this as does Austro. Most legacy engine alternators have a hard time making it to the 2000hr TBO of the engine. On cars today, alternators can last over 200,000 miles and this is over 5,000 hours. Most of the legacy alternators were just car alternators from back in the time the engines were certified.

PSRU engines have been used since the very first powered aircraft to fly. Most WWII aircraft had PSRUs. The real reason for direct drive on GA legacy engines was to reduce cost. Using the technology of the 1940's and at the power range needed for GA aircraft is was cheaper to make them direct drive. There were even attempts to make direct drive cars at that time. But technologies, cost effectiveness and the need for efficiency have changed.

Cooling is a hassle with every engine especially air cooled. With air cooling it is hard to get higher power without detonation. It is so hard that they resort to super rich mixtures even if they contribute to high fuel usage and plug fowling. With liquid cooling you also need to do it correctly but do not need to resort to super rich mixtures.

With any engine, legacy or automotive based, you do need to have an exhaust systems and the issues are about the same. Good design and materials are critical.

Yes, GM and most automotive engines do not come with aircraft standard mounting ears. Nor do Rotax engines. But you can buy them from a few suppliers.

There are many suppliers of CS props that do not require oil and a mechanical prop governor. For example Sterna, DUC, Airmaster, FP, MT and a bunch of others. Some of these are much lower cost than certified hydraulic props.

A new certified 118hp Lycoming O-235 has a list price of over $80,000. Really. They do provide some deep discounts depending on how you buy but still is over $50,000. A non-certified O-235 is about $35,000 today. Our 117hp EFI AM15u is $12,000. So less than 25% of the certified Lycoming and about 1/3 that of non-certified Lycoming. Of course this is a sales pitch but it is also to defend the idea that especially with a twin there is the option of engines that cost 25% of a certified Lycoming of the same power.

So for an EAB twin you could start with a single engine design like an RV6 and put two smaller automotive based engines on it and end up with a twin that meets or beats the performance of the single engine version but at a lower cost and with much better one engine out performance. Of course your build time will be much higher since you are doing more design and fabrication.

If there are any designers working on an EAB twin please contact me and I will try to help as much as possible.
 

rpellicciotti

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Memphis, TN
Someone may have already mentioned this and I missed it. The FAA is about to declare the Wind Derringer design to be "abandoned". That opens up the opportunity for anyone to gain access to the engineering, drawings, etc. This airplane was designed by John Thorp and is very simple to build.
 

PMD

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Martensville SK
Someone may have already mentioned this and I missed it. The FAA is about to declare the Wind Derringer design to be "abandoned". That opens up the opportunity for anyone to gain access to the engineering, drawings, etc. This airplane was designed by John Thorp and is very simple to build.
Stretch formed and chem milled wing skins are not what I would call a very simple build!

That said, I would LOVE to see this airplane return to production.
 

pfarber

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Me-262 with small turbines, would be a twin engine E-AB worth doing.
There is a replica 262. Full size. A total of 5 units. Not sure if still in business

Its completely impractical and not something 99.99999% of what people want or need or can afford.
 

Victor Bravo

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There is a replica 262. Full size. A total of 5 units. Not sure if still in business

Its completely impractical and not something 99.99999% of what people want or need or can afford.

I am well aware of the full-size museum quality replicas.

My comment purposely mentioned small turbines, and was based on a 2/3 or 70% size light weight replica.
 

cluttonfred

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In the category of "totally impractical but wouldn't it be fantastic" how about a 3/4 scale Grumman XF5F Skyrocket? Blackhawk comic book color schemes would, of course, be an option! There is even a fictional precedent for an inline variant with a pair of AM engines, or you could go with round cowls anyway. 75% scale gets you a 31' 6" span and wing area of 170 sq ft and the unusually large canopy of the original short-nose version would give you plenty of room for the unscaled pilot.

The_latest_type_of_a_Grumman_Navy_fighter_-_NARA_-_195921.jpg XF5F-skyrocket.jpg

Grumman-XF5F-Skyrocket-Title.jpg grumman_f5f.gif

FUN_48023-2.jpg f5f-inln.jpg
 

Scott Black

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The lack of twin E/AB aircraft is related to the lack of demand for same.
And the lack of demand is because people realized a long time ago that simple is the way to go. Look at the ratio of single to twin certified aircraft at any airport. Now take away the twins operated by flight schools. There’s your answer right there.
 

arj1

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UK
And the lack of demand is because people realized a long time ago that simple is the way to go.
Over here in Europe the only reason not many fly twins is variable cost per hour. I know of quite a few people that actually DO fly certified twins (over North sea, mountains, Atlantic, night etc).
Many understand the benefits, but don't fly twins unless they are with their family.
And in Europe another challenge is that if you want to fly twin, it is cheaper to buy older SENECA than to build a new aircraft. Plus (unlike in the US), homebuilts are not getting IFR privileges that often, mostly they are Day/VFR.
 

TFF

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The people who fly twins in the US are not worried about cost. Once it becomes an issue, it’s time for a single.

Twins can be cheap on the market. What single engine pilots have to learn is those are core aircraft waiting for money. They learn and it’s back on the market. A Beach Duke that needs engines and props is just about worthless. Some as low as $30,000 probably $60,000 if it can be flown ok. Engines are unable so it’s not getting pistons unless you have hoarded parts. There is a company that converts them to turboprop. It’s a cool $2,000,000 to do so. They have a ten year waiting list. A friend’s Aerostar constantly was breaking. One of the nicest ones too, what a pos. Traded in on a turbine Piper.

If they are not making YouTube videos, they don’t care about cost. Even the students who buy a twin and after flight time sell it can afford it. Europe has a problem of showing wealth off. A twin is a calling card. It might not be 20 Ferraris rich, but it’s everyone’s wearing a Rolex target.
 

arj1

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@TFF, agree on some times - yes, twins are cheap because they need parts and work. And it depends on how much it needs. :)
Disagree on twins in Europe - here it is mostly for those who does not like flying at night or over water on a single point of failure. Easier in the US - in most places Cirrus is OK as you could just pull a chute, in Europe it is not the case, you need to land somewhere. And in Europe calling card for wealth is turbine. When someone wants to show off they buy a TBM or PC-12. :)
 

Pops

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@TFF, agree on some times - yes, twins are cheap because they need parts and work. And it depends on how much it needs. :)
Disagree on twins in Europe - here it is mostly for those who does not like flying at night or over water on a single point of failure. Easier in the US - in most places Cirrus is OK as you could just pull a chute, in Europe it is not the case, you need to land somewhere. And in Europe calling card for wealth is turbine. When someone wants to show off they buy a TBM or PC-12. :)
And if you really have money, you buy a Gulfstream.
 

TFF

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It’s always the balance of doubling the points of failure to halving the chance of safety.

Plenty of the excuses are night and water in the US too, but it’s trying to buy yourself out of a jam that probably doesn’t exist. Back to people with money. The problem with most small twins is they are not better than the singles.

I use to have some data that shows you are worse off in a Barron than a Bonanza. Most of it is pilot. Most are not really up on skill when the engine does quit. Not day in and out unless you are a professional. You can’t deny if one is still running, you should be good. Unless really on your game, the yaw will freak the pilot out. Especially now while they are playing candy crush as the GPS takes them where they want.

One friend of mine has had a double engine failure in a Dash8 and a Navaho. He got one engine back partial on each. Lucky than good in that respect. He is good, but both times the plane just went quiet. The Navaho was just after takeoff with the gear stuck in transition. Leveled off to cycle the gear and the engines quit. Got one running enough to cycle the gear and get back to the airport.
 

arj1

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@TFF, I read a few pieces on analysis as well, and it was also the pilot(s) - in a twin pilot's behaviour is much riskier, i.e. pilot would take-off with such problems present that on a SEP you wouldn't even dare to taxi! :)
And of course phases of flight - while take-off/landing are always more dangerous (and nothing you can do here unless you fly MET/Turbofan on a long runway), my biggest concern is engine failure enroute. And for that ME aircraft is great - most planes ARE controllable.
 

D Hillberg

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very low low low earth orbit
As an automotive based aircraft engine builder that has delivered hundreds of aircraft engines and with over a hundred flying I would like to take this opportunity to defend using an automotive engine as the basis for an aircraft engine. And of course pitch our engines.
First I would like to point out the certified Thielert/Continental CD-155 and the certified Austro engines are based on the MB OM640 automotive engines. These engines now have an 1800 TBO and claim a 100,000 hour MTBF. I am skeptical of the 100,000 hour MTBF but in any case they currently have an excellent reputation and can be operated at over 90% power continuous. While these engines do not have ignition they are FADEC and are absolutely dependent on electricity to run. Even with this electrical dependency they are the same or better reliability as other certified engines.

I am not sure about the electric power requirements of the Austro but our engines need about 2 amps and another 4 amps for the fuel pump so 6 amps total. If your alternator fails, your engine will keep running on the battery for a few hours. Plenty of time to find an airport to land.

It is simple to change the RPM of the alternator by changing the pulley diameters. We do this as does Austro. Most legacy engine alternators have a hard time making it to the 2000hr TBO of the engine. On cars today, alternators can last over 200,000 miles and this is over 5,000 hours. Most of the legacy alternators were just car alternators from back in the time the engines were certified.

PSRU engines have been used since the very first powered aircraft to fly. Most WWII aircraft had PSRUs. The real reason for direct drive on GA legacy engines was to reduce cost. Using the technology of the 1940's and at the power range needed for GA aircraft is was cheaper to make them direct drive. There were even attempts to make direct drive cars at that time. But technologies, cost effectiveness and the need for efficiency have changed.

Cooling is a hassle with every engine especially air cooled. With air cooling it is hard to get higher power without detonation. It is so hard that they resort to super rich mixtures even if they contribute to high fuel usage and plug fowling. With liquid cooling you also need to do it correctly but do not need to resort to super rich mixtures.

With any engine, legacy or automotive based, you do need to have an exhaust systems and the issues are about the same. Good design and materials are critical.

Yes, GM and most automotive engines do not come with aircraft standard mounting ears. Nor do Rotax engines. But you can buy them from a few suppliers.

There are many suppliers of CS props that do not require oil and a mechanical prop governor. For example Sterna, DUC, Airmaster, FP, MT and a bunch of others. Some of these are much lower cost than certified hydraulic props.

A new certified 118hp Lycoming O-235 has a list price of over $80,000. Really. They do provide some deep discounts depending on how you buy but still is over $50,000. A non-certified O-235 is about $35,000 today. Our 117hp EFI AM15u is $12,000. So less than 25% of the certified Lycoming and about 1/3 that of non-certified Lycoming. Of course this is a sales pitch but it is also to defend the idea that especially with a twin there is the option of engines that cost 25% of a certified Lycoming of the same power.

So for an EAB twin you could start with a single engine design like an RV6 and put two smaller automotive based engines on it and end up with a twin that meets or beats the performance of the single engine version but at a lower cost and with much better one engine out performance. Of course your build time will be much higher since you are doing more design and fabrication.

If there are any designers working on an EAB twin please contact me and I will try to help as much as possible.
Your engine may require 6 amps but the rest of the flying machine might have a higher draw.
radio stacks, trim, gear, intercom, flaps. and a battery that tops out at 3 amps when loaded for a few minutes etc.
 

mm4440

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326
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LA area, CA
It is possible to build a turboed V-8' to well over 1000 hp. If that is not enough to win Sport Class Gold, you have a crap airframe or you can use 2. A DO 335 like aircraft would be the best configuration for a twin with the DH 103 a close second. I believe a race is about 8 min. E 85 might be the best fuel for racing. A high performance piston twin might be a viable kit plane if designed to be powered by the big 6 cylinder AC engines or V-8s. 6 place for the general public and a special 1+1 version for racing.
 

pfarber

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Feb 21, 2019
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Location
Dollywood
And the lack of demand is because people realized a long time ago that simple is the way to go. Look at the ratio of single to twin certified aircraft at any airport. Now take away the twins operated by flight schools. There’s your answer right there.
E/AB breaks that paradigm.

With auto engines your only real cost is fuel. Rebuilding an auto engine is hundreds, not tens of thousands of dollars.

And I am sure that a twin auto engine powered AC could fly single engine.

Remember, a new design means you can design out all the faults that people complain about.

Id prefer a twin over a single. Especially if single engle flight is possible.

Why spend $$ on a BRS when you have a second motor that is cheaper to operate
 
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