ORIGINAL: Ed_Moorman

My buddy, Flaps Laffert, and I are on our 8th canard, all of them his designs. We have done pushers, tractors, a pusher twin, a tractor twin and a flying boat. We use positive 3 degrees in the canard.

My advice is to use a large canard (25%-40% of the wing area) and make sure the plane isn't tail heavy.

ORIGINAL: Ionikios

My twins are about 3.75 inches from the CL in yaw.

What do you think about engine loss p-factor? The only vertical stabilization I am having are the exhaust stacks being vertical and in sym. airfoil shape. Rudder is extensions from inside the outer portions of the wings (flat plates introduced downward into the air stream) what does your intuit say?

Thanks a million for the input, information and help.

Ionikios

The thread you've got going elsewhere mentions that your design is for OS46 engines. The props they run are in the 10-12" range. Placing engines like that 7.5" apart is what you plan?

What do you mean by "engine loss p-factor"?
The thread in the other forum gives the impression you've got engine out yaw confused with p-factor. You do understand that p-factor is something that happens when a prop encounters the airflow at some angle other than perpendicular. And the unbalanced thrust has way more effect than the incidental p-effect? The imbalance of thrust from the engine out is way more a problem than any extra effect from the p-effect that happens while the airplane is being yawed by the operating engine.

ORIGINAL: Ed_Moorman

Here's the twin tractor and the seaplane.

Designing a new plane takes a lot of engneering and a lot of "cut and try" type effort. I believe you must resign yourself to building a minimum of two planes, probably three would be better. This is especially true of the non-conventional designs, like canards and flying wings.

Take our flying boat canard, the Duck. Carl "Flaps" Laffert is the designer (with my input). Right now, it flies, but needs several changes. It took a lot of weight to get it to balance. The engine needs to be moved forward to alleviate this. Overall, it is heavy and has a fairly small wing so a larger wing is needed to lower the wing loading. In addition, the engine mounted on the fin with its high thrust line, we think is giving us a pitch down moment so I am compensating with up control trim. Then when I throttle back for landing, it tends to raise the nose. I can put in a landing program to have some down control switched in, but I'd rather have some up thrust.

As long as his designs fly, Flaps doesn't want to do too many changes. Generally, he wants to see them fly for 3 or 4 weekends and he is off to something else. I would like to see a new plane, slightly longer, with the engine pylon in the fuselage forward of the wing with more up thrust. Plus I want a much larger wing.

ORIGINAL: Ionikios

I thought when you loose an engine and the p-factor sum was change by the loss (change in p-factor) was what produced the yaw difference along with the thrust being of center. I understand what you are saying. I didn't express it correctly, because if I loose an engine where the p-factor is working against the other engines p-factor it will be a different yaw effect loosing visa-versa. Thank You for clarifying.

I am planning on 3 or 4 blade custom prop. (not blade overlap :-)

ORIGINAL: da Rock

p-effect is a force that comes from an unbalanced lift coming from a propeller that happens when the prop is pitched or yawed from straightline flight. It happens for example when a taildragger taxiis. Or when any airplane pitches up takeoff. If the airplane is a single engine, it happens to that one prop. If it's a multi, then it happens to both props equally.

ORIGINAL: Ed_Moorman

Here's the twin tractor and the seaplane.

Designing a new plane takes a lot of engneering and a lot of "cut and try" type effort. I believe you must resign yourself to building a minimum of two planes, probably three would be better. This is especially true of the non-conventional designs, like canards and flying wings.

Take our flying boat canard, the Duck. Carl "Flaps" Laffert is the designer (with my input). Right now, it flies, but needs several changes. It took a lot of weight to get it to balance. The engine needs to be moved forward to alleviate this. Overall, it is heavy and has a fairly small wing so a larger wing is needed to lower the wing loading. In addition, the engine mounted on the fin with its high thrust line, we think is giving us a pitch down moment so I am compensating with up control trim. Then when I throttle back for landing, it tends to raise the nose. I can put in a landing program to have some down control switched in, but I'd rather have some up thrust.

As long as his designs fly, Flaps doesn't want to do too many changes. Generally, he wants to see them fly for 3 or 4 weekends and he is off to something else. I would like to see a new plane, slightly longer, with the engine pylon in the fuselage forward of the wing with more up thrust. Plus I want a much larger wing.

ORIGINAL: Ionikios
I had just planned to take a 9X7 3 blade prop. and trim it to 7", I don't expect it to be the perfect fit, if there is a better answer, I'll listen.

IHow do you measure p-factor in relation to the gyro effect (of the prop/engine not wanting to change angle)?

off subj: I see you are a moderator. I can't find how to make the last messages come up to be the first on the list. Can we do that?

ORIGINAL: Ed_Moorman

Actually, no. We had first built a pusher twin. Photo attached. We had to add weight to the nose to get is balances right.

I wrote a program to find the CG of a canard using the formula published by a club mate, Ron Van Putte, when he wrote the pattern column for Model Aviation. It is fairly conservative, which is fine for me. I can handle a tail heavy 3D plane, but a tail heavy canard is something else. Send me your e-mail and I'll send it to you.

The twin tractor was my idea. I talked Flaps into that configuration when he was set to go with another pusher twin. This one balanced very nicely and we had to make no corrections after testing.

We have a little trick we use. After I calculate the CG point, Flaps runs a 3/32 ID aluminum tube through the fuselage at that point. When he gets the plane completed, we poke through the covering over the tube and run a wire through and pick up. This tells you right now if the plane is nose or tail heavy and makes it easy to fix and check. In the close up of the nose of the canard twin, you can see the hole for the tube. It is just about in line with the cylinder heads of the engines. Normally, no one notices the holes.

Twins get a lot of their performance from having much larger combined areas from two less powerful props. You're losing that right off the bat. If you need twins for any reason, you need the area their prop blades sweep for them to be an improvement over a single engine. You'd probably get better performance out of two engines that normally swing 7" three bladers.

ORIGINAL: Ionikios
I'll talk to the owner of the hobby shop that told me that it would be OK........ He's built a lot of planes.

The only vertical stabilization I am having are the exhaust stacks being vertical and in sym. airfoil shape. Rudder is extensions from inside the outer portions of the wings (flat plates introduced downward into the air stream) what does your intuit say?

ORIGINAL: da Rock


Did he sell you the two 46s?

Two 46s will give you more thrust than one engine of equal displacement (a 92 in this comparison). They do it with their fan area. The two blades cover a lot more air than the single blade.

Let's compare two OS46AXs to one OS91FX.

The 46s swing 11" props. Those props sweep roughly 265sq.in. of air. They weigh about 36 ounces combined.
The 92 swings a 15" prop. It sweeps roughly 177sp.in. of air. It weighs about 25 ounces.
Cut the props down on the 46s and the 7" props would sweep only 76sq.in. combined but still weigh 36 ounces.

There really are no advantages to using two engines instead of one unless you're using everything those two can give. And you're taking away their one advantage.

What is the design weight and wing loading of your model? Use that to determine for yourself what the power requirements are.

With a design that has so many unique features, it's better to use tried and true power systems.

ORIGINAL: da Rock

Look at all of the pictures of Ed's models. They all have vertical fins. And the pushers have exposed engines and exhaust stacks in addition to the fins. And those fins are much larger than the exposed engine parts.