Small single seat 3 surface concept

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Wild Bill

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About 15 years ago I had this idea for a small twin engine single seater. I sketched it out on a piece of paper and made a very small hand toss glider. Afterward, I bought a flying airplane and was busy with work and flying XC’s on the weekends.
Some years later I started building the RC test model at around 28% scale. Uncertainty about the design and various other things going on at the time caused it to go on the back burner again.
During this covid thing I started back on it and made a flying test model.
I anticipated a bunch of issues with it, but it actually turned out to fly well.

I know 3 surface designs don’t get a lot of love here on the forums. But to me the benefit of this configuration is that the pilot is in a ideal position. Not directly over the wing. If you build something around the size of the cri cri for example you pretty much have to sit directly over the wing.
This configuration lets you place the pilots center of mass on the CG of the plane, and between the main wing and canard. Heavily reclined seating keeps the canopy small.
The general proportions are similar to the piaggio avanti.
I went back and forth on what sort of controls it should have. And then I thought about Bruce Bohannons modified Miller JM 2 design. In its final configuration it had a small lifting canard with no control. (I’m assuming this was added because of pilot weight gain or making it go around pylons better.)
So for the model I kept it simple and the only control it has is a conventional elevator on the T tail and ailerons.
This really worked much better than I expected. Control was very good at all speeds.
I don’t know how it would scale up. I guess surfaces could be added to the canard. They could possibly work separate from the elevator... Flaps if you will... Not sure
Would make things much more complicated.
My thinking for the full scale would be electric power or a couple of 200-300 cc two strokes.
Retractable nose gear and a sailplane style main gear. Maybe with small retractable gears in the engine pods to keep it from tipping side to side.

At this point it’s a pipe dream for me.
After how well the model flew I just had to share.
 

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Victor Bravo

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WB, that is PFC !!! A sailplane style canopy, or a Q-1 Quickie style canopy, and scaling it up to the size of a Q-1 or Cri-Cri... is really interesting. The 3-surface layout seems like it would allow a much smaller overall aircraft size. The pilot could take up the entire space between the main spar and the canard spar.

The primary reason for 3-surface airplanes, as I understand it, is to have a flap on the canard that comes down when the main wing flap comes down, so they balance out each other. (On most 2-surface airplanes, when you put the flaps down it requires a huge control deflection and "trim force" at the tail).

Having the canard flap come down means that the tail control surface (elevator, stabilator) does NOT get highly loaded when the wing flaps come down. So this could allow the aircraft to have much smaller flying surfaces with larger flaps or flap deflections.... resulting in a faster cruise and a slower takeoff/landing speed.
 

Wild Bill

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Is the vertical tail big enough for single engine?
I haven’t got that far with testing. The model was built with materials and components that I had on hand.
I left it in an unfinished state so I could experiment with various things.
As it is, it’s underweight at 11 lbs and is also underpowered.
It has no rudder at this point. Only differential throttle control.
The next step is to add a rudder and larger motors.
 

Wild Bill

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The primary reason for 3-surface airplanes, as I understand it, is to have a flap on the canard that comes down when the main wing flap comes down, so they balance out each other.
Having the canard flap come down means that the tail control surface (elevator, stabilator) does NOT get highly loaded when the wing flaps come down. So this could allow the aircraft to have much smaller flying surfaces with larger flaps or flap deflections.... resulting in a faster cruise and a slower takeoff/landing speed.
I believe the control system in the piaggio works in this manner and has an automated flight control system.
I would think you could build a flap system where flaps on the main wing are connected to control surfaces on the canard.
For a small plane that would rarely if ever make cross country flights, I don’t know if it would be worth the added complexity.
My interest in the 3 surface configuration over a canard, was driven by fact that a canard design requires a lot of sweep in the wings or booms to place the verticals far enough aft to be effective.
 

Vigilant1

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Is safe single engine flight part of the design goal?
- If not (i.e. if you'll need two engines to get safe climb), then my personal choice would be to eliminate 2stroke engines from consideration unless I'll always be over safely landable terrain. Others will disagree.
- if safe single engine ops are desirable, I'd strongly consider putting both engines on the centerline.
- Unless this is going to be a Part 103 vehicle, if you don't already have a MEL rating, maybe investigate the FAA's rules/implementation of those rules for multiengine EAB solo aircraft. There's some discussion of that here, along with some follow on posts.

Looks pretty interesting. I'd probably go for two B&S 4 stroke engines for economy and reliability, but that may be heavier than you want to go and takes things out of the 103 envelope.
 

Wild Bill

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Single engine flight wasn’t really part of the original idea. It just needs to not go out of control in the event of failure. Shut the other engine down or throttle back and glide to the airport.
Even on a short flight to a nearby airport the idea would be to have a landing site within gliding distance.
That’s the appealing side of it being electric powered. Not only would reliability be better, but rearward folding props would be very practical. And glide performance would be exceptional.
Flights would be short but again long flight times wouldn’t be a major goal.
Four strokes or even more robust 2 strokes would get too heavy. Going that route would mean making the plane much larger.
No way to meet 103 except in the weight department.
I keep hearing different opinions on the regs regarding EAB and multi engines. Unless something has changed, my interpretation is that there are no specific pilot or aircraft requirements to operate this type of aircraft.
 

Vigilant1

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I keep hearing different opinions on the regs regarding EAB and multi engines. Unless something has changed, my interpretation is that there are no specific pilot or aircraft requirements to operate this type of aircraft.
If you learn anything about this, please chime in. Opinions are all over the map (as shown in the posts after the one I linked) and are not always in accord with the (to me) plain wording of the applicable regs. If (as some maintain) a DAR has the discretion, and is encouraged to, require an MEL rating for pilots operating a multi-engine E-AB in solo flight, then the whole enterprise loses a lot of its allure. In my case, having to spend thousands of dollars in an Apache to get skills that are almost entirely inapplicable to a small centerline thrust single seat aircraft would be a dealbreaker.
 

Victor Bravo

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A drag plate mounted at each of the wingtips could be deployed in the event of an engine failure. If the left engine fails, the pilot pulls a lanyard that deploys the right side drag plate. The pilot can now use full power on the right engine (without the airplane yawing uncontrollably left) to climb, or maintain altitude, or to "get to the crash site". All this would do is allow the pilot to use full power, it would certainly not increase the single engine performance (it would reduce the performence), but it could allow full power to be used where it might not be able to be used otherwise. I'm guessing the drag plate would allow the airplane to be designed with a smaller vertical fin and rudder, because you don't have to super-size the fin/rudder to handle an asymmetric thrust issue.
 

Vigilant1

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A drag plate mounted at each of the wingtips could be deployed in the event of an engine failure. If the left engine fails, the pilot pulls a lanyard that deploys the right side drag plate. The pilot can now use full power on the right engine (without the airplane yawing uncontrollably left) to climb, or maintain altitude, or to "get to the crash site". All this would do is allow the pilot to use full power, it would certainly not increase the single engine performance (it would reduce the performence), but it could allow full power to be used where it might not be able to be used otherwise. I'm guessing the drag plate would allow the airplane to be designed with a smaller vertical fin and rudder, because you don't have to super-size the fin/rudder to handle an asymmetric thrust issue.
Kudos on the out-of-the-box thinking, and I think the drag plate would do as you say, at least at one airspeed. But if/when we need to reduce power on that remaining engine, possibly at a critical time in the approach or when we decide we really need to lose altitude to "make" a favorable landing site, we'd have that plate out there. It's another thing.
I'd think a larger rudder and possibly together with canting the engines slightly to help reduce yaw in a single engine situation might be better. It's always good when the actions required in an emergency are as similar as possible to the ones the pilot uses every day. And a larger rudder comes in handy lots of other times--don't mash on the pedal if you don't need it.
 

Wild Bill

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If you learn anything about this, please chime in. Opinions are all over the map (as shown in the posts after the one I linked) and are not always in accord with the (to me) plain wording of the applicable regs. If (as some maintain) a DAR has the discretion, and is encouraged to, require an MEL rating for pilots operating a multi-engine E-AB
The DAR adding something to the operating limitations could be a real issue. Especially for a new one off design maybe...
But they can also do it on plans built airplanes. They could also just simply not like some minor issue and wash their hands of it completely.
This is where being somewhat political in how you approach it, and finding the right DAR can make or break things.
 

Vigilant1

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The DAR adding something to the operating limitations could be a real issue. Especially for a new one off design maybe...
But they can also do it on plans built airplanes. They could also just simply not like some minor issue and wash their hands of it completely.
This is where being somewhat political in how you approach it, and finding the right DAR can make or break things.
Agreed. But getting a feel for the issue and having an "If you saw situation 'X', would you include 'Y' in the operating limitations?" understanding would be useful. It would be a bummer to design and build a plane only to find out that flying it will require a few thousand dollars in inapplicable training.
I understand the DAR needs to have discretion to address unusual situations, but I don't agree that discretion should extend to over-ruling published guidance that specifically addresses an issue.
 

Wild Bill

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No argument there.
I’ve heard of a few sad stories.

@Victor Bravo
Those drag plates are something I’ve never heard or thought of. Seems like it should work. And being at the tip with all that leverage, they wouldn’t have to be all that large.
 

Vigilant1

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All past flying experience informs all future flying experience.
Good. Since, in the real world, time and money are finite resources, I choose to train first in a single seat centerline thrust twin as a critical foundation to someday flying an Apache.😁 Or not.
 
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