Less Flap Same Elevator

[Motorman]

Here's one I couldn't find in a search. Flap/elevator is 1:1 right now. If you want to adjust the control system for less flap travel but you want to keep the elevator travel the same what would you adjust?


MM

[Brett Buck]

Here's one I couldn't find in a search. Flap/elevator is 1:1 right now. If you want to adjust the control system for less flap travel but you want to keep the elevator travel the same what would you adjust?

  Usually, you speed up the elevator by shortening the control horn (moving the pushrod attachment nearer the hinge line). That makes the elevator move more than the flap, and speeds up the response. If you want to slow it down, make the handle spacing smaller until it compensates.

    Brett

[Motorman]

Ok so there's no way to keep everything the same and get less flap travel? you have to make the elevator faster and slow everything down up stream.

MM

[RandySmith]

Ok so there's no way to keep everything the same and get less flap travel? you have to make the elevator faster and slow everything down up stream.

MM

Yes you can, Some people use 2 rods off the bellcrank, one to the flaps and one to the elevator, I have seen people use R/C type flap (aileron ) horns and you slide the flap horn attachment up and down to slow or speed ( change ratio). However the answer that Brett gave would be the way to setup your ship. much less trouble and easier to work with, and has been proven in 1000s of ships.
Most ... modern stuntships will work best at 1 to 1 ratio, unless they are really light, then you add elevator throw because they do not need as much flap travel.

Randy

[jfv]

If you install the controls with separate push rods from the bellcrank to the elevator and to the horn such that you can adjust the horn height independently then you can do what you want.

(I guess Randy and I both pushed the button at the same time.)

[Randy Powell]

Like anything in trimming, you change one thing, you often have to compensate somewhere else. You change the CG you will usually have to change the leadout location, etc. What Brett notes works fine to change the ratios between the flaps and elevator, but, as he also notes, you will probably have to change the line spacing at the handle to compensate for the now faster controls. It's a system and all trim is a matter of balancing one thing against another.

[RandySmith]

I have one plane setup with two rods going to each control surface and the output distance of the rods coming out of the bellcrank can be screwed/slid in and out to vary the control rod speed.
 You can slide the flap horn attachments up and down to vary the speed/ratio, as well as the elevator has a slide adjustment too, this setup came from an idea Scott Bair gave me when I saw his dual split flap horn slide adjustments on his Stuntfire.
 Scott could adjust how much flap he wanted, and also adjust the elevator speed/throw from one of the split flap horns, by sliding the connection up and down.
by the way he also had another pushrod going to the nose of the ship to operate an exhaust throttle on the engine!

Randy

[Tim Wescott]

Ok so there's no way to keep everything the same and get less flap travel? you have to make the elevator faster and slow everything down up stream.

With the quoted method, yes.  But if you slow down the flaps you're going to have to adjust the handle spacing anyway.  Everything interacts.  The reason that so many people leave the flap to bellcrank ratio nailed down while adjusting the flap to elevator ratio is because it's just easier to build in access to the elevator horn.

[Brett Buck]

Most ... modern stuntships will work best at 1 to 1 ratio, unless they are really light, then you add elevator throw because they do not need as much flap travel.

   Two interesting points about that. You can play the flap area and flap travel against each other and get more or less the same overall response with a wide range of flap size and travel. But most of the time, it seems to work out best if you hold the 1:1 ratio and adjust the flap dimensions to get the desired response.

    Another interesting thing is that a lot of classic planes (like and Ares or Nobler) want drastically less flap travel. That's a combination of everyone building much lighter than in the old days and generally having much better engines. Ted built a really light Ares (kit version) and as built, with 1:1 it would barely turn. He had to cut into it, but he changed the elevator to something like 2:1 elevator/flap, and then it turned great. Part of the Tucker Special lead experiment was the reverse - as the weight went up, the turn balance got much better (in addition to the many other drastic improvements).

    Brett

[RandySmith]

   Two interesting points about that. You can play the flap area and flap travel against each other and get more or less the same overall response with a wide range of flap size and travel. But most of the time, it seems to work out best if you hold the 1:1 ratio and adjust the flap dimensions to get the desired response.

    Another interesting thing is that a lot of classic planes (like and Ares or Nobler) want drastically less flap travel. That's a combination of everyone building much lighter than in the old days and generally having much better engines. Ted built a really light Ares (kit version) and as built, with 1:1 it would barely turn. He had to cut into it, but he changed the elevator to something like 2:1 elevator/flap, and then it turned great. Part of the Tucker Special lead experiment was the reverse - as the weight went up, the turn balance got much better (in addition to the many other drastic improvements).

    Brett

Yep  I've noticed  that , now  and back then, another example is the Mackey LARK , Bob Hunt and many other build them, they have partial span flaps, and work really well "as is" even ones with slider horns and such..

Randy

[Brian Hampton]

I set up my control system with individual sliders for both flap and elevator pushrods so either can be changed without affecting the other. On initial flights I set the flap to minimum possible travel and elevator to what I think will be OK or possibly a bit too much then start reducing elevator movement until I'm happy with both sensitivity and cornering ability. Rather surprisingly I found that best sensitivity came before any noticeable change in cornering. From memory I started with around +-30 degrees elevator and ended up with +-17 degrees. Flap travel wasn't enough because there was a trace of stall at the bottom corner of triangles so flap was incrementally added until any stall was gone. I ended up with only +-5 degrees of flap. Any more flap travel would just mean added drag right where you don't want it. Obviously these figures only apply to my model, others will be different.

So I guess the answer to the OP's question would be that if you're happy with elevator feel etc then adjust the flaps to where they just barely eliminate any stall.

[Motorman]

So I guess the answer to the OP's question would be that if you're happy with elevator feel etc then adjust the flaps to where they just barely eliminate any stall.

That's what I'm asking, how do you do it. I can't change the line spacing on my handle. It's 3-3/4" with a 4" Brodak bellcrank with the push rod in the middle hole and the push rod goes to the top of the flap horn. from there I could raise the elevator push rod on the flap horn or lower it on the elevator horn both of which will speed up the elevator so, there's no way to do it.

MM

[RandySmith]

That's what I'm asking, how do you do it. I can't change the line spacing on my handle. It's 3-3/4" with a 4" Brodak bellcrank with the push rod in the middle hole and the push rod goes to the top of the flap horn. from there I could raise the elevator push rod on the flap horn or lower it on the elevator horn both of which will speed up the elevator so, there's no way to do it.

MM

Is not that what your wanting? to slow the flaps and speed up the elevator?  move the elevator horn one hole closer to the pivot point, or move the elev, pushrod up one hole one the flap horn.
 This will have the effect of slowing the flaps , because you will use less movement with a faster elevator.
Also it is a bad idea to use a non adjustable handle, that is easy to remedy, just change to an adjustable handle

Randy

[Tim Wescott]

I can't change the line spacing on my handle.

That is a problem you really should fix.  Handles are dead easy to make -- a Paul Walker-style CF and balsa hard-point, adjustable-spacing handle takes me about half a day to make.  They're ugly as all get-out, but that's not what matters.

[Motorman]

My handle is a compromise on adjustability but I like the feel of having the hard points closer to the grip instead of out front. It's set to the minimum 3-3/4" for my size hand. Can't seem to warm up to a close spaced handle, can't feel up from down. It works ok with a Brodak 4" in the middle hole (3/4" arm) the flap horn is pretty tall though.

I've got the inner hole on the bellcrank to go to and that would slow it down enough after speeding up the elevator. I tried it before and it was too slow but I didn't shorten the elevator horn because I thought it always had to be 1:1, live and learn.

Good thread, I got it now, thanks for the advise, I can see you really have to design this stuff into the system from the start. On my next one I could go with a 4-1/4" bellcrank with an 11/16" arm and that would slow it down to give me some head room on the flap travel.

MM