# Lack of twin engine E/ABs

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#### aeromomentum

##### Well-Known Member
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

##### Well-Known Member
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

##### Well-Known Member
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

##### Well-Known Member
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.

#### challenger_II

##### Well-Known Member
The lack of twin E/AB aircraft is related to the lack of demand for same.

#### Victor Bravo

##### Well-Known Member
Supporting Member
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

##### Well-Known Member
Supporting Member
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.

#### Scott Black

##### Member
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.

#### dog

##### Well-Known Member
mini defiant on barnstormers

#### arj1

##### Well-Known Member
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

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