multiple engines on single engine designs

[blane.c]

I am looking for some thoughts on the idea of using a Cri-Cri type motor mount on some ultralights originally intended for single engine. Both pusher and tractor, the mount should work similarly on either adaptation, weight and balance concerns can be assumed.

 

[Topaz]

Interesting question. I think the answers are largely dependent upon the individual airframes involved. One way to minimize the potential problems is to have the engines driving concentric propellers.

Curious - what do you perceive as the advantage of such an arrangement? I've always found two smaller motors to be about the same cost or even more expensive than a single motor of the same total power, and twin-engine safety statistics are actually slightly worse than single-engine. What brings your interest to this idea?

 

[saini flyer]

I have pondered on this one too...

1. Low power electric motor can only be liquid cooled
2. Low voltage controllers are cheaper
3. The Jabiru twin engine does not have W&B issues as the twin 2200 are pushed back towards the FW
4. 
   
5. The close to centerline thrust twins should give better engine out performance.

 

[TFF]

Two engine mounts are going to be heavier than on for a larger engine. You have to have two structures to hold engines to the airframe when you needed one, you have to have two fuel tanks that will weigh more than one of equal capacity. Two 20 hp engines probably pull a little better than one 40, but you will not beat the weight added for the same amount of HP. Efficiency of two running will be less than one of equal power.

 

[blane.c]

I flew what are now unusual airplanes DC-4 and DC-6, among other things I have pushed the feather button over 100 times for cause (not for training or checkrides) an example of a cause is when the cylinder is going up and down and oil is spewing all over the hot exhaust, there were many other causes. Therefor my view of the reliability of engines may be slightly jaded compared to yours. Also I am very competent at handling a engine out on multi-engine coupled with the fact that the arrangement I am proposing would be fairly easy to handle, and as an ultralight would be in daylight vfr. Some other things I would point out is that you could test out different engines (without going nuts) you could put a different engine on one side to see if it was going to perform the way you anticipated and still have a backup to get home if it did not. A twin engine aircraft with one engine out will have at worst a better glide ratio than a single engine airplane with one engine out. As far as safety records go the twin engine ultralight "Lazair" has a very good safety record, one reason is probably because the two engines are so close to centerline that an engine out is fairly benign. I am seriously looking at the Lazair's for my little plane they are an excellent ultralight but I would actually prefer something that goes a little faster ie less draggy more fuel efficient. It is unfortunate that at this time the FAA does not allow multi-engines in LSA that would be my preference. I would be happy to answer any other questions you may have if I have missed or glazed over something. Thank you, Blane.

 

[blane.c]

I have pondered on this one too...

1. Low power electric motor can only be liquid cooled
2. Low voltage controllers are cheaper
3. The Jabiru twin engine does not have W&B issues as the twin 2200 are pushed back towards the FW
4. 
   
5. The close to centerline thrust twins should give better engine out performance.

Very very cool, do you have any engined up and running?

 

[saini flyer]

Very very cool, do you have any engined up and running?

Here is the video of the first flight: https://www.youtube.com/watch?v=keBcWXPUPaw

I am very interested in the outcome of replacing the single ICE with twin electric motors like in Cri-Cri. Maybe I should start another thread on this specific configuration to discuss the plus and minus of using electric motors. One problem with this Jabiru twin is access & visibility.......

 

[blane.c]

Two engine mounts are going to be heavier than on for a larger engine. You have to have two structures to hold engines to the airframe when you needed one, you have to have two fuel tanks that will weigh more than one of equal capacity. Two 20 hp engines probably pull a little better than one 40, but you will not beat the weight added for the same amount of HP. Efficiency of two running will be less than one of equal power.

While undoubtedly heavier than some, I do not think the Cri-Cri style motor mount would be to heavy for consideration and may be lighter than a few because it would not have to protrude as far forward for weight and balance reasons. You do not need 2 fuel tanks both engines can feed from 1 tank just fine, again the Lazair for an example. Some examples of close centerline twins are very efficient, certainly for me a small difference of efficiency with the right airframe would be negligible in comparison to the added redundancy of another engine. about the engine weight thing with 2 DLE200 twenty three horse engines 55 lbs, this less than 1 forty horse Hirth engine at 70 lbs and the 15 lb difference should offset any motor mount weight difference.

 

[blane.c]

Here is the video of the first flight: https://www.youtube.com/watch?v=keBcWXPUPaw

I am very interested in the outcome of replacing the single ICE with twin electric motors like in Cri-Cri. Maybe I should start another thread on this specific configuration to discuss the plus and minus of using electric motors. One problem with this Jabiru twin is access & visibility.......

I watched a bit of the video very impressive little scoot I will watch all of the video soon. The problem with electric here in US is the FAA goes by battery volume for ultralights and it cannot exceed 5 gallons this is very limiting and we need another revelation in battery's or a modification of the rules for electric powered ultralights to proceed very far with them. For airplanes of your size however things look pretty rosey a close centerline twin electric would be very nice and on that plane should reduce the side bulges quite a bit. The flight visibility from the camera is really quite good I think looks like a lot of fun to fly.

 

[saini flyer]

The ultralight is severely limited as compared to the new deregulated class across the pond.

The only way to have multiple engines is to call it a motorized sailplane. Rutan is doing this with his skigull.

 

[Dana]

Google "Kolb Flyer" and "Kolb Ultrastar". Two very similar airplanes; the earlier Flyer had two 15HP Solo engines and the later Ultrastar had one 35HP Cuyuna engine. The Flyer wouldn't quite maintain altitude on one engine but it would manage a very long shallow descent. I toyed with the idea of retrofitting my Ultrastar with two 25HP paramotor engines, which would weigh a bit less than the Cuyuna and give it spectacular performance, but I never pursued it.

The ultralight is severely limited as compared to the new deregulated class across the pond.

The only way to have multiple engines is to call it a motorized sailplane. Rutan is doing this with his skigull.

Not at all, you can have as many engines as you want on an ultralight, the Lazair is the classic example, or the Kolb Flyer I mentioned above. It's Light-Sport aircraft that are limited to only one engine.

Dana

 

[blane.c]

Thank you that is very interesting I will gather more information on motorized sailplane that is for sure.

 

[blane.c]

Google "Kolb Flyer" and "Kolb Ultrastar". Two very similar airplanes; the earlier Flyer had two 15HP Solo engines and the later Ultrastar had one 35HP Cuyuna engine. The Flyer wouldn't quite maintain altitude on one engine but it would manage a very long shallow descent. I toyed with the idea of retrofitting my Ultrastar with two 25HP paramotor engines, which would weigh a bit less than the Cuyuna and give it spectacular performance, but I never pursued it.



Not at all, you can have as many engines as you want on an ultralight, the Lazair is the classic example, or the Kolb Flyer I mentioned above. It's Light-Sport aircraft that are limited to only one engine.

Dana

I will look up the flyer kolb has good products. Thank you.

 

[saini flyer]

Google "Kolb Flyer" and "Kolb Ultrastar". Two very similar airplanes; the earlier Flyer had two 15HP Solo engines and the later Ultrastar had one 35HP Cuyuna engine. The Flyer wouldn't quite maintain altitude on one engine but it would manage a very long shallow descent. I toyed with the idea of retrofitting my Ultrastar with two 25HP paramotor engines, which would weigh a bit less than the Cuyuna and give it spectacular performance, but I never pursued it.



Not at all, you can have as many engines as you want on an ultralight, the Lazair is the classic example, or the Kolb Flyer I mentioned above. It's Light-Sport aircraft that are limited to only one engine.

Dana

Dana between the twin engine Vs single engine kolb what changed in terms of flying surfaces. The only way to get multi engine configuration without the twin/multi engine rating is to go the sailplane route outside of the UL regime. As I suggested earlier, I am more interested in what was done in the twin J430 as none of the flying surfaces changed. I will start a new thread after I do some W&B calculations on how two electric motors with their battery, controller, charger, BMS work out in this configuration. My good old friend flies a twin engine Aerostar for the twin engine's potential safety but the statistics say otherwise and I think that the twin Jabiru configuration has good merits to it.

 

[Topaz]

Dana between the twin engine Vs single engine kolb what changed in terms of flying surfaces. The only way to get multi engine configuration without the twin/multi engine rating is to go the sailplane route outside of the UL regime. ...

Powered sailplanes (certificated) are limited to a single engine by the FARs. E-AB is more "fuzzy", of course, but since powered sailplanes are flown with a conventional pilot's certificate and a Glider rating, I can't see how the need for a multi-engine rating wouldn't still apply. Where are you getting that you can have a multi-engine powered sailplane and not need the appropriate multi-engine sign-off?

 

[Dana]

Dana between the twin engine Vs single engine kolb what changed in terms of flying surfaces.

They're pretty close. The big difference between the Flyer and the Ultrastar (other than the engines) is structural; the Flyer has non folding wings, two spars, and two struts, whereas the Ultrastar has folding wings with a single large tube spar, and one wing strut.

Powered sailplanes (certificated) are limited to a single engine by the FARs. E-AB is more "fuzzy", of course, but since powered sailplanes are flown with a conventional pilot's certificate and a Glider rating, I can't see how the need for a multi-engine rating wouldn't still apply. Where are you getting that you can have a multi-engine powered sailplane and not need the appropriate multi-engine sign-off?

For airplanes you have ratings for "airplane single engine land" and "airplane multi engine land", but for gliders it's just a "glider" rating, which obviously doesn't come in "single engine" or "multi engine" flavors. Motorgliders require a "self launch" endorsement; it's not a rating.

For that matter, you don't even (I think) need a glider rating to fly (solo only) an experimental glider, just as a PP-ASEL can legally solo (but not carry passengers in) an experimental seaplane, or a multi engined plane, unless the aircraft's operating limitations specify otherwise.

Dana

 

[Topaz]

... For airplanes you have ratings for "airplane single engine land" and "airplane multi engine land", but for gliders it's just a "glider" rating, which obviously doesn't come in "single engine" or "multi engine" flavors. Motorgliders require a "self launch" endorsement; it's not a rating.

Well I'll be danged. I just looked up the FAR (it's actually AC21.17-2a), and there's no restriction on the number of engines. Thought certain that there was, but seems I was mistaken.

For that matter, you don't even (I think) need a glider rating to fly (solo only) an experimental glider, just as a PP-ASEL can legally solo (but not carry passengers in) an experimental seaplane, or a multi engined plane, unless the aircraft's operating limitations specify otherwise.

True, but you'd still need the proper logbook endorsement for whatever launch method you're using: Ground tow, aero tow, or self-launch. That's covered in FAR 61.31(j)(iii). Similar to a tailwheel endorsement, it's not subject to the exceptions for solo pilots of experimentals.

 

[blane.c]

Ok so we can build a multi-engine glider and fly it under glider self launch, and we can fly it under experimental category without a glider license if we are solo, but we would need a self launch endorsement to stay legal. Wow! Do I have that understood correctly?

 

[blane.c]

So how much can a multi-engine glider weigh, is it fuel restricted, and how many seats could it have (for someone with a glider rating)? (This is getting interesting).

 

[blane.c]

Maybe there is a way to build a 100 mpg glider, instead of a 100 mpg airplane. Works for me.