ludfleet

My Feedback: (10)

Trying to check and set the incidence on a bi plane with the above airfoil need some ideas. thanks guys in advance

Tall Paul

Find the most forward part of the leading edge. And the rear of the trailing edge.
A straight line between those points is the chord.
Then determine/adjust the difference between those end points on each wing.

J_R

Your concern appears to be about the camber. It makes no difference if the airfoil is symmetrical, semi-symmetrical, or under-cambered. As Paul said, use the foremost part of the leading edge and the rearmost part of the trailing edge to set the incidence.

After the plane has the static incidence set, you should check it dynamically. That is done by taking the plane up high, and putting it into a power off vertical dive. If the plane pulls to the canopy, it needs negative incidence. If it pulls to the wheels, it needs positive incidence. Having the power off removes the thrust of the engine as a factor. Test it in dead air several times before making changes.

This assumes you have an incidence meter and know how to use it. If not, Robart and Great Planes both make one and have manuals on their sites explaining the use.

Edit: Be sure to maintain the suggested incidence difference between the wings on a bi-plane.

MinnFlyer

My Feedback: (4)

Paul is correct, and an Incidence Meter will automatically figure that out for you. If you don't have one, they're not too expensive, or see if a club member will loan you one.

Ed Smith

You may want to enlarge on that "Dynamic" theory a bit. C.G. and trim will affect how an aircraft reacts in a dive. Both of those two cause what one thinks incidence is doing. If the low throttle dive speed is different from the level full throttle speed the influence effect will be different.

Use of an incidence meter is undoubtedly the best method. I use three of them. Engine, wing and tail. I set them all at once. Having three removes the danger of jogging something while moving a meter.

Ed S

J_R

Ed

I am always hesitant to get too deep into trimming planes on any of the forums. Eyes glaze over, even at the field when folks realaize that there is more to trimming a plane than the trim tabs on the Tx.

Here is my favorite trim chart, for those that are intersted it getting the most out of a plane. Although it is for pattern, in particular, it works on all planes, although those doing 3 d will want the cg back fruther... after the plane is trimmed.

http://www.wtp.net/DBEST/trimchrt.html

Ed Smith

There is? You mean my super gizmo switch infested beeping transmitter with the little red light will not do all that for me?

Ed S

J_R

It always amazes me how many people absolutely, positively will not move the CG. "It's where the plans call for. This plane is a dog". Next thing you know they sell it and someone else loves it after trimming it out. Some never learn.