Elevator and Flap Angles?

[VA Flier]

Haven't flown CL since mid 90s, and then only 1/2A.

Want to build Flite Streak, then Fancherized Twister, but short on time these days so picked up a used Brodak Pathfinder w/OS 35 FP just to get flying ASAP.

In prepping for first flight I used epoxy to seal up some delamination cracks between ply, hardwood and balsa forward of wing in engine mounting area, built up some crushed wood under the engine mounting lug beds w/ epoxy-glass, glassed a cracked rudder, freed a binding pushrod, and other minor issues.

As a novice, and never having flown this model, one area of concern are the angles of the elevators and flaps.

It was set up with the forward (bell crank) pushrod in the top hole in the flap horn (fifth of five holes from the flap), with the rear pushrod in the next hole down (4th of 5). This initially gave 21* (degrees) of down, on both elevators and flaps, and 14.5* of up, which seemed unbalanced to me.

Adjusting the fork on the aft end of the fwd rod out 6 turns equalized the up and down angles at 17.5*.

But then I wondered if this was enough overall angle, so I tried the fwd rod in the 3rd hole on the flap horn. But this gave angles of 21* down and 26.5* up.

My questions are:
1) How much angle should there be on average?
2) Should the available angle be biased up or down, or just equal?

Any comments or advice appreciated. I'm excited about putting up a flight soon!

[Tim Wescott]

I think that 17 degrees of deflection will be plenty, but I'm kind of a bottom-feeder myself.

It should certainly be enough for round maneuvers.  So start by doing your first wingovers intentionally high, and watch how much corner you achieve -- if it's enough, you don't need to adjust anything.  If it is, you'll have an idea how much.

[Steve Helmick]

What you're really looking for is equal response on inside/outside turns. Best way to do this is the "Lazy 8". If the loops are not equal size with what you feel is equal input, then you need to adjust the controls in the plane.

As for the attach point at the flap horn, the flaps are the largest part of the control load, so it makes sense to have the pushrod from the bellcrank going to the top hole if you can...more leverage. The elevators are a smaller part of the control load, so that pushrod should be from the next hole down on the flap horn. Measure the hole locations from the flap hinge point to the hole where you have the pushrod to the elevator hooked up, and look for a similarly dimensioned hole on the elevator horn. That'll give you 1:1 flap/elevator ratio, which is a good starting place. You might move to a shorter location on the elevator horn if your plane is light. If your plane is heavy, 1:1 is good. The actual angle of travel used for a stunt flight is probably under 20 degrees up and 20 deg. down. Having more than 20 degrees just isn't needed. Smooth controls under tension is essential. Smooth controls without tension doesn't prove much.

The ratios are very important to the way your plane flies, because the force that moves the control surfaces comes from line tension. If the control loads are very heavy, your line tension is reduced by that amount, so when your model is running low on line tension, you don't have a heck of a lot of force available to operate the controls. Remember that when you adjust the controls, your neutral setting at the handle will then need readjustment. None of this stuff comes quickly, but fiddling with it flight after flight is important. Trying to compensate for the airplane's poor trim by using your vast pilot skill is a lost cause! Don't push the airplane beyond its abilities...keep trimming! The more experience you get, the quicker you can trim a plane.     Steve

[Tim Wescott]

What you're really looking for is equal response on inside/outside turns. Best way to do this is the "Lazy 8". If the loops are not equal size with what you feel is equal input, then you need to adjust the controls in the plane.

Steve, when I do a lazy 8 I never know which loop is going to be smaller.

[john e. holliday]

If you can't tell, then you need an observer.   

[VA Flier]

Thanks much to all for all the detailed info.
I'll go with the top hole for the most leverage and figure the 18 degrees is enough until I learn more from experience.
Good to know I'm at least in the ballpark prior to heading out for the first flight...

[Bill Little]

HI Mike,

I think you will be OK starting out wit the 18* movement each way.  Just do like Steve suggests and begin your learning curve about trimming.

BIG Bear
RNMM/AMM

[Steve Helmick]

Steve, when I do a lazy 8 I never know which loop is going to be smaller.

I'm skeered to try a lazy 8, because I am afraid I'll get (more) confused. I'd also like to learn to turn and face downwind to do the OH8's, but that's a tough habit to change, too.  I don't really remember the PA Pattern, I figure it out as I go! It's why I don't fly OTS. For all this effort and skill, I'm being "encouraged" to move up to Espurt (sp?)?  Steve