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Small single seat 3 surface concept

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Tiger Tim

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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.
There are almost certainly things you would learn by flying a Cessna Skymaster that would improve your experience in an Apache... or an RV... or a Quicksilver. Diversity of experience is a good thing.
 

Riggerrob

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Look at Grumman A-6 Avenger before designing your yaw brakes. The farther outboard, the smaller your wing brakes can to minimize yaw after one engine quits.
 

jwmflying14

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One thing I haven't seen mentioned is a small amount of stall safety of a 3 surface design like the Avanti or the OP. The "canard" or forward surface is still flying at a higher angle of attack, and thus more loaded, than the main wing. As such the canard will, or should, stall before the main wing. This moves the center of lift back, making it act as if the center of gravity is at, or exceeding the forward limit (on a normal aircraft). This means that you can design it to "mush" and not fully stall as the horizontal stab effectively runs out of authority.
 

Vigilant1

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If the H-stab was lower and fully in the propwash of the two wing-mounted engines the interactions would be interesting. With power on, the effective AoA of the rear surface might be largely independent of the AoA of the foreplane and main wing.
 
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Wild Bill

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One thing I haven't seen mentioned is a small amount of stall safety of a 3 surface design like the Avanti or the OP. The "canard" or forward surface is still flying at a higher angle of attack, and thus more loaded, than the main wing. As such the canard will, or should, stall before the main wing. This moves the center of lift back, making it act as if the center of gravity is at, or exceeding the forward limit (on a normal aircraft). This means that you can design it to "mush" and not fully stall as the horizontal stab effectively runs out of authority.
Yes...
I admittedly don’t have enough aerodynamic knowledge to properly design something like this. My background is more structural/mechanical.
I’ve tried to think about the interaction between the 3 surfaces but it seems complex. The reason I delayed building the test model is because I didn’t think that the elevator would have enough authority at landing speed. This turned out to be a non issue even with a relatively small elevator and a heavily loaded canard. I loaded the model just like you would a typical canard design without factoring the aft tail. But if I’m thinking about it correctly I would think you could reduce the load on the canard. By how much, I don’t know.
One issue with this design is the fuselage volume/surface area forward of the CG. The pictures probably don’t give a good representation of how fat the fuselage is. But for a small airplane, the forward section of the fuselage can only be so small.
All of that fuselage out ahead of the cg is trying to destabilize it in all axes.
Seems like I remember a thread about whether or not the tail of a 3LS ever actually produces lift...
For the model I wanted the fuselage to not be at a really high angle of attack during takeoff/landing... So from the zero line of the fuselage itself I put the main wing at +4 degrees of incidence, +4.5 on the canard, and +2 on the tail.
This worked out well but I don’t know what an optimal incidence for the tail would be. I guess a full flying stab might be better aerodynamically???
The positive incidence in the wings also leads to good visibility at cruising speed. At least it appears that way looking at the model fly.
 

rbarnes

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I've been dreaming about this same concept. Except a little bigger. Two person side-by-side, with a cockpit about the size of an RV-14. Easy entry through a clam shell door just infront of the wing, similar to a Velocity. With a pair of turbo Rotax's or Yahama snow sled engines everyone is excited about right now. 3 lifting surface design with the front wing stalling before VMC is reached. If you could make it work, it should be safe (no VMC), relatively fast, and fuel efficient, with good single engine performance from 150-200hp on each wing.
 

jwmflying14

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Yes...
I admittedly don’t have enough aerodynamic knowledge to properly design something like this. My background is more structural/mechanical.
I’ve tried to think about the interaction between the 3 surfaces but it seems complex. The reason I delayed building the test model is because I didn’t think that the elevator would have enough authority at landing speed. This turned out to be a non issue even with a relatively small elevator and a heavily loaded canard. I loaded the model just like you would a typical canard design without factoring the aft tail. But if I’m thinking about it correctly I would think you could reduce the load on the canard. By how much, I don’t know.
One issue with this design is the fuselage volume/surface area forward of the CG. The pictures probably don’t give a good representation of how fat the fuselage is. But for a small airplane, the forward section of the fuselage can only be so small.
All of that fuselage out ahead of the cg is trying to destabilize it in all axes.
Seems like I remember a thread about whether or not the tail of a 3LS ever actually produces lift...
For the model I wanted the fuselage to not be at a really high angle of attack during takeoff/landing... So from the zero line of the fuselage itself I put the main wing at +4 degrees of incidence, +4.5 on the canard, and +2 on the tail.
This worked out well but I don’t know what an optimal incidence for the tail would be. I guess a full flying stab might be better aerodynamically???
The positive incidence in the wings also leads to good visibility at cruising speed. At least it appears that way looking at the model fly.
A few assumptions here, that I feel a change in how you look at aircraft design might be a better approach. First off it appears you are "stuck" in the conventional aircraft design mindset. This is evident in the way you describe the short lever between the wing and horizontal stab, and the assumption it wouldn't have enough authority. A better way to think about it is completely forget about where the main wing sits, and instead focus on the center of lift and center of mass (cg). You'll notice that aesthetically the lever arm from the center of mass/center of lift is much farther than that of the main wing, which at first glance is counter intuitive from what we have been programmed to recognize.

Being that you loaded the canard like a true canard, you completely unloaded the horizontal stab, meaning the horizontal stab is only acting as pitch control, and not pitch stability - IE it could be extremely sensitive. By splitting pitch trim with the canard and tail you vary how much either is loaded, and that becomes a favorable design aspect that you can play with depending on aircraft requirements. There is no written in stone "split" between the forward and aft surfaces, and how much they share the same job.
 

Wild Bill

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I do tend to get a case of “tunnel vision” when it comes to certain things.
I guess you could call this a biplane.. Because really it’s just that. A biplane with a LOT of stagger and a big size difference between the two wings.
You could move the CG location depending on the size of the canard. Not by a huge amount though.
The CG is less than one root chord ahead of the leading edge of the main wing. So the CG is around the middle of plane for reference.

Some ball park numbers might be useful. The main wing of the model spans 68” with a 6” mean chord.
My original idea for the full scale, was to be in the 16-18’ span range depending on various factors.
150lbs pilot weight. 500lbs +- gross weight.
 

WonderousMountain

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You could use a cam so that the drag flap engages rapidly on full length rudder presses. Light application would get only rudder. Then adjust like a trim tab so you can go back to normal controls.
 

daveklingler

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Wild Bill, if you haven't already done so, you might want to sit down with an onion sandwich and read up on John Roncz's Eagle 150.

I believe there was an article on it in Sport Aviation, in addition to several threads on the various Quickie email lists on Yahoo (which I hope have been archived elsewhere). The Eagle 150 also gets attention from time to time on HBA.

One of the counterintuitive innovations about the Eagle 150 is that the rear surface unloads the wing in such a way that it lowers drag. There was talk on the Q-Performance list for a while about adding a third surface to the regular Q1 and Q2 designs, and at least in X-Plane, the results were very promising.
 

daveklingler

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The Quickie Q1 comes in around 240 pounds empty. Looking at your design, it doesn't seem to me that it needs to be twice as heavy if you're not using large engines.
 

Riggerrob

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You mean the WW2 era Grumman Avenger torpedo bomber, or the Vietnam era Grumman A-6 Intruder jet attack bomber?
Sorry about using the wrong name.
I was referring to the Viet Nam era Grumman A-6 Intruder ground attack jet. I f you watch video of Intruders landing on aircraft carriers, they usually approach with wing-tip drag brakes open (draggy) and a little extra power. Since drag brakes/spoilers can be closed in a second, they help when flying precision approaches. They also help during missed approaches/bolters since they can be closed in a second and engines can be throttled up quicker because they are already producing some power (above flight idle).

A few airplanes also use roll spoilers mounted on outboard wing panels. Roll spoilers are tougher to design because they depend upon smooth boundary layer airflow ... which is difficult to control at the small chords of light homebuilts.
Which gets us to the biggest problem of small 3-axis airplanes: Reynolds numbers. Since it is difficult for amateurs to build precise wing ribs - less than 3 or 4 feet long (1 metre), efficiency suffers with small wing chords.
If you go read some of Barnaby Wainfain's articles about his Facetmobile, you will understand how large Reynolds numbers (wing chord) help make his crude, faceted airfoil waaaaay more efficient than conventional curved airfoils.
When you get down to the size of one or two-seater airplanes, then deltas make more sense than two or three surface configurations.
 

fulcona

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Dec 20, 2004
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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.
Burt Rutan designed a similar plane many years ago. I believe it was showcased in Popular Mechanics magazine. It was a 2 seater with staggered seating but did not have a horizontal surface atop the vertical. It used (2) 40 hp rotary engines, the landing gear was on the centerline as sailplanes use.
 

fulcona

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Burt Rutan designed a similar plane many years ago. I believe it was showcased in
Popular Mechanics magazine. It was a 2 seater with staggered seating but did not
have a horizontal surface atop the vertical. It used (2) 40 hp rotary engines, the
landing gear was on the centerline as sailplanes use.
 
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