# Lack of twin engine E/ABs

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#### Riggerrob

##### Well-Known Member
Oops, I missed that post. Have not read the actual rules, but from speaking with a number of pilots there is a wide belief that you can stick a bit more airplane than that into OM and use any engine you please.

Thanks for setting that record straight (for me as well). My confusion over this issue comes from the LSx powered RC3s operating under OM: Canadian Aircraft Regulations
At one point we had Republic RC-3 Seabees - with 4 different engines at Pitt Meadows.
One had the original stock Franklin 6AS-215-BAS 6-cylinder that produced a mere 225 horsepower on a good day. combine that with a large cabin, 4 fat passengers, fish-wells and a mountain lake at a high density altitude and climb-rates were "leisurely." As Franklin spare parts ran out, more and more Seabees were grounded.
The second had a 6-cylinder Lycoming installed under an STC. Since the Lycoming lacked a propeller extension shaft, it had to be mounted so far aft that it needed a truck battery installed in the nose for balance. The extra weight of the truck battery reduced it to a 2-seater.
The third Seabee had a Pratt & Whitney, PT6A turboprop installed during the development program for the proposed Avalon light amphibian. While the turboprop was far more powerful, it was also more thirsty, needing extra fuel tanks installed in the wing roots. The extra weight of the fuel reduced it to a 2-seater.
The fourth Seabee had the Canadian LS Corvette engine installed. The Corvette engine got a propeller extension for balance. It produced 300 horsepower on half the fuel burn of the original Franklin. The Corvette engine also allowed hot water to be pumped into the cabin for heat. The Corvette conversion proved the best for Seabees.

Back to my personal tastes. Since a Spencer Air Car is the biggest homebuilt that I would need, a Corvette engine would be ideal. Spencer Air Car is basically a Seabee updated made of wood, fiberglass and steel tubing.

#### robertl

##### Well-Known Member
Anyone have a good reason why there are almost no multi engine E/ABs?

Iirc FARs don't forbid it and they are not overly complicated.

Someone did slap a second motor on an RV and it seems to be going well.
I would think $#### Riggerrob ##### Well-Known Member " ... I guess if you made good engine-out handling and performance a requirement the engines would be even bigger, heavier, and more expensive (and the airplane "overpowered", if there is ever such a thing?) ... " Yes, it is possible to "over-power" a twin-engined airplane. Consider the Polish-built PZL M28 Air Truck Sky Truck that was developed from the piston-pounding Antonov AN-14 which only had 300 horsepower per side. The latest version of Sky Truck is powered by a pair of 1,100 horsepower PT6A-65B turboprop engines. The new engines are so much more powerful that one can quickly over-power the rudders. So if one engine fails, the immediate action drill is to pull back power on the "good" engine before it over-powers rudders and flips you inverted. The USAF operated 16 MC-145B Wiley Coyote variants for a few years, but most have been retired by now. The USAF flew their C-145s in support of Special Forces bases in Afghanistan and other sneaky-peaky missions that are not discussed in polite company. The long-term plan had been to gift the C-145s to the Afghan Air Force, but apparently the USAF did not hate the AAF enough. Hah! Hah! #### tspear ##### Well-Known Member Supporting Member When I was looking into insurance for the Lightning, only 1 company even quoted and it was$2800 for liability only. If you think there was a less expensive liability only solution I would be very interested to hear about it.

When I talked to Avemco, there were more than one liability policy available; there are three basic policy types.
1. Hull, this covers your property.
2. General liability, this covers you from damage caused to other by your plane/actions. This includes people on your plane...
3. Movement liability (I think this was the name). It only covers damage to property on an airport; and was designed around meeting DOT funding requirements which are enforced by state laws in many states.

The third one was specifically designed around meeting requirements to move/operate on airports; and was a single pool of all high risk aircraft.

Tim

#### ToddK

##### Well-Known Member
Supporting Member
Having lived with my Air Cam for 12 years now, I would disagree that the handling is horrible. It flies just fine and the single engine characteristics are not out of the ordinary. It is capable of a single engine takeoff, although I can't think of a situation where you would need to do that.
The airplane is high drag and low inertia so it's possible to get in trouble if you haven't gotten a decent checkout. There are lots of experimentals in that category ..
I think the main reason that you see Air Cams for sale is that it is just plain slow. I flight plan 70 knots and 6.5 gallons an hour. Going anywhere is like driving your car.
Where the Air Cam excels is in short field performance and flying in relative safety over hostile terrain for the purposes of sightseeing and aerial photography. If that's not your mission then it's not the right aircraft for you.

Great to hear. Thanks for sharing.

#### ScaleBirdsScott

##### Well-Known Member
Well then, if loosing an engine is the main issue with a twin, then "mo is mo bettah" is clearly the solution!
The more I see it, the more that 10-motor hybrid power B-29-cockpit lawn-dart of a concept aircraft they keep bringing to Air Venture could make some sense here.

A twin-engine STOL might be cool to see. I'm surprised that hasn't been messed around with more by those guys. Maybe a way to compete with Scrappy.

#### REVAN

##### Well-Known Member
I would say that even two LS motors are cheaper per hour than a single IO-360. Even now mogas is still cheaper than 100LL in mist places.... So 2x the fuel still costs less than AVGAS.

I would think a new design twin based off car motors could be done cheaper and you can correct many of the flaws in the ancient designs out there now.
The PSRU is the weak link to using an LS engine in aircraft. However, I've long believed that there was good potential to be had for someone so inclined to design a good propfan (small diameter, probably 6 deep-chord swept blades) and interface it to the LS through a direct drive bearing support to absorb the thrust and gyroscopic loads. Keep the max RPMs of the engine down in the mid-to-low 3000s to de-rate the engine for longevity. Then develop an airframe that would mount the engines with minimal offset for controllability with an engine out. Most likely, this would be pod mounted on the empennage, biz-jet style, with the props squeezed in behind the tail cone.

The BIG obstacle: Designing and building an effective propfan is well beyond the skillset of most homebuilders. Truth is, building a good PSRU also falls into this category, but some people get in the mindset that they can build a PSRU; some succeed, most do not.

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##### Well-Known Member
Supporting Member
Mid-to-low 3000s is low enough to direct drive a 170 cm prop, which will have reasonable efficiency at the speeds most folks would be looking at for an LS. Would need to go to wide chord, or maybe five blade, but that’s pretty close to off the shelf.

#### PMD

##### Well-Known Member
Interesting thing to do with an unloved AA-1...
Wow, not only have never seen this, but could never IMAGINE it! In one fell swoop would pee off John Thorp, George Wing and Ferdinand Porsche.

John Thorp?

#### PMD

##### Well-Known Member
First of all: there ARE a few proven PSRUs for LSx engines. No need to re-invent that wheel.

Second: hate to rain on the centerline thrust parade, but IIRC the 336 and 337 (yes, there was a fixed gear version) did not have any better crash rates and survival than fan-on-the-wings twins. Sadly: I have some familiarity from a 336 crash on takeoff at CYYL some time ago. Young pilot flying nurse off in heavy snowfall to a medical call at night. Official investigation claimed pilot responsible (fatal) but when we looked at prop it had straight back scratches (don't ask how we gained access) and no leading edge damage. Long story I will leave aside (the reason why I take accident reports with a HUGE grain of salt) but rear engine failure at the worst time, not detected before the lack of expected thrust caused departure stall.

#### Tiger Tim

##### Well-Known Member
I take accident reports with a HUGE grain of salt
Same. I got a call one day from the investigators for information about the “dangerous low speed handling characteristics” of a type and I tried explaining that they were misinformed. There was no changing their minds, I even offered to take them up for a demo.

#### dog

##### Well-Known Member
There is a riems f337 that has been converted into an engine test bed for electric propulsion
with one ICE and a big electric and two small
electrics mounted where the booms come to the front of the main wing,the idea was to optimise
for a loiter configuration useing the two small
electrics
cant take a 337 to OM,so then it would need a total rebuild as a 51% and use it as a test mule

##### Well-Known Member
Supporting Member
51% is for experimental homebuilt; most aircraft like that are in a different experimental category (R&D, marketing research, etc).

#### edwisch

##### Well-Known Member
A problem not yet mentioned is that many very small twins have the engines close to the centerline for better single engine controllability, but this gives interference drag between the nacelles and the fuselage.

#### dog

##### Well-Known Member
51% is for experimental homebuilt; most aircraft like that are in a different experimental category (R&D, marketing research, etc).
I have heard of certified aircraft bieng rebuilt as experimental,and certified aircraft "cloned" and
registered as experimental.
I imagine that taking a certified project that was
stripped back,no rigging ,no systems or fire wall forward,wings opened up,control surfaces off,doors off,no glass,its going to look a lot like any old quick build kit plane before a pre cover inspection,and qualify as an experimental homebuilt,or I would like to think.

#### tspear

##### Well-Known Member
Supporting Member
I have heard of certified aircraft bieng rebuilt as experimental,and certified aircraft "cloned" and
registered as experimental.
I imagine that taking a certified project that was
stripped back,no rigging ,no systems or fire wall forward,wings opened up,control surfaces off,doors off,no glass,its going to look a lot like any old quick build kit plane before a pre cover inspection,and qualify as an experimental homebuilt,or I would like to think.
Probably not. That is a lot of systems work. The 51% applies to tasks. A good example is wing ribs, they count as a task. But consume massive number of hours on a tapered wing....

Tim