newman

When climbing and intruducing down elevator my plane seems to react too quickly. Would a bigger stabilizer be better or is this just based on the amount of throw on the elevator.

Also, how many degrees should the rear elevator travel for a beginner or intermediate plane? And rudder too?

newman

newman

Oops... that should say REAR stabilizer.

A1RENCH

All manufacturer's that I know of have control throw recommendations included in the plans
or assembly instructions. Most even have "first flight" or "beginner" control surface deflections
and "advanced" or "expert" settings. If your model did not have these recommendations, contact the customer service department of the company that makes or distributes your airplane.
Also, recheck the center of gravity. Your plane maybe nose heavy. Then again, it may be that the particular model you are flying is just very responsive.
Good luck
Bud

newman

I forgot to mention that this is a scratch built plane. I will check deflections on another plan and start there.

CG is another problem I am working on too. I think I had it close on the first flight but set it too far back the second time out and had big problems.

Jason Beach

My Feedback: (4)

Some specs and pics of the plane would probably help us answer your questions.
The size of your stabilizer plus your control surface should be a certain percentage of the area of your main wing. However on our smaller planes, there's usually plenty. As for the amount of throw, your elevator shouldn't have much throw on it to begin with. Since the elevator is usually the most senative control surface on the plane, small throws are generally plenty.
Another thing to think about would be your experience. If you're learning to fly, you may be over controlling it.

If all else fails, turn the throw on your elev way down and take it for a test flight, then tune it in to where you're most comfortable over the next few flights.

A good place to start with CG is 1/3 the distance from the leading edge to the trailing edge. If you're not sure, it's always better to go a bit nose heavy.
Good luck

Jason

newman

Thanks for the reply.

I will try to post a few pics up here this weekend. It would be nice to get as much feedback as possible so this project doesnt get too expensive.

3DFanatic

My Feedback: (5)

I like my 3Der's rates "Fun" and "Expert" (that goes for balance point too). If being an "Expert" gets in the way of having "Fun" then I want to stay "Advanced"

newman

Here is a picture of when it was first built. I have since added dyhedral and reinforced the front area due to some "incidents" but for the most part its the same.

Any feedback would be appreciated.

Thanks

john 8750

Your stab area looks a bit to small. It should be 30% of the wing area. Not much elevator is needed. Check the incidence and the CG.
John Smith

feihu-RCU

newman:
Seems like you've flown the model with some success but have a problem with down elevator during climb. If that is the case, then you probably have too much elevator throw. Normal elevator throw on conventional models are about + and - 15 degrees or less for beginners, and more like 20 and above for the more experienced.
BTW, the horizontal and vertical tail is (conventional) is made up of a fixed and a movable surface. The horizontal fixed surface is called the stabilizer, and the horizontal moving surface is called the elevator. The vertical fixed surface is called the fin, and the movable surface is called the rudder.
From your photo, I find it difficult to judge the size of tail surfaces. Size does matter but it varies depending upon the distance between the wing and the tail.
Again, since your model flies, you might first try just reducing the elevator throw and go from there. Just be sure the CG is somewhere around 30%. If a modification is a must, then you will have to give me the dimensions of the wing and horizontal tail and the distance between the trailing edge of the wing and the leading edge of the stabilizer, before I can recommend any modifications.
Hope things work out for you.

john 8750

I have not heard of the distance between the wing and stab making a difference of the related areas. Could you please explain.
Thanks.

feihu-RCU

John:
The size of the horizon tail contributes to the static longitudinal stability of the airplane. For positive stability, a thing called "tail volume coefficient" (Vbar) is used in determining the size of the horizontal tail. Vbar varies depending on the airplane configuration, such as wing/tail angles, airfoil downwash, location of stab relative to wing (T-tail), etc. For model airplanes, I use a Vbar of somewhere between .33 and .43.
The Horizontal tail area can be computed fron the Vbar equation:
Vbar = St/S x lt/cbar ( eq. 5-18, Stability and Control by Perkins and Hage)
Vbar = tail volume coefficient
St = area of the horizontail tail
S = area of the wing
cbar = average chord of the wing
lt = distance between 1/4 chord of the wing to the 1/4 chord of the horizontal tail
Really, what all this means is that a short coupled airplane (short fuselage with wing and tail close together) needs a large tail area, and a long fuselage can use a smaller tail and still have positive pitch stability. As you can see, lt ( l is for length and t is for tail) is the distance between the wing and tail, and it does make a difference.

john 8750

So that explains why my old timer has a small looking tail.
Thanks for the crash course!

Gklugie

My Feedback: (1)

You also have a short moment arm. ... the relative distance from the trailing edge of the wing to the stab. Short moment arms make planes extremely sensitive on the pitch axis.

Scale back elevator deflection... trial and error in this case.

Fred DCRC

Has any one mentioned Engine thrust angels depending upon the
Type of aircraft, prop & RPM you may need as much as 3 degrease
Down and 5 right not having this correct will make the elevator
React differently than expected and give the affect of turning left
With no right turn capability or worse a snap roll followed by
Ground penetration

feihu-RCU

Fred:
The question by Newman was about stabilizer size and throw; however, by his description of having to give "down" elevator does leave one to question engine thrust. But "down" elevator to decrease the climb angle can be caused by a number of different things such as an improper elevator trim tab setting or excessive power, or engine thrust angle. Yes, all these things vary with different airplanes, and some will react as you describe.
feihu