Flap and Elevator percentiges?

I read the angle of flap deflection is to be equal to that of the elevator.

Is this alwayes the case? One would think the flaps wouldn't have to deflect as much?

Good rule to follow when setting these up?

Thanks in advance,

Charles

Well, I am by no means an expert, but the flaps effectiveness are generally dependent on weight to wing area. I believe the current thinking is still 1 to 1 flap to elevator, and if the flaps are to effective, they should be cut down in area to match the weight/area of the plane. If they are not effective enough, they should be increased in area keeping the 1 to 1 ratio. There probably are exceptions though.

Thanks for that invo, I will preceed along those lines.

Bellcrank wire to flap lower control horn hole. Top hole of flap control horn to lower hole on control horn hole.

This should do it!?

Right?

Charles

Flap/elevator horns vary. A 1:1 ratio simply means the wire (pushrod) from flap horn to elevator horn must be exactly the same distance from their respective axis (the horn connecting wire). This is usually 1".
Floyd
AMA 796
SAM 188
LSF 020

I'm of the opinion that smaller airplanes, 1/2A size say, do better with leas flap deflection. Perhaps flap deflection increases drag, and that may be a problem on an airplane with not much power to begin with.

>I'm of the opinion that smaller airplanes, 1/2A size say, do
>better with leas flap deflection. Perhaps flap deflection
>increases drag, and that may be a problem on an airplane with
>not much power to begin with.


Makes perfect sense, because the scaling effects mean that the wing loadings are much lower the smaller you go. I am far from an expert on 1/2As but it makes some physical sense it would be that way.

Brett

There you go. I would agree with the 1/2A thing. We have an exception already.

I should have given this information:

The wing root cord is 9.75" and the root flap measurement is 2.5".

Hoz. stab is 2.5" and the elevator is 3.5"

Could be of use. Any issues here?

CB

>Thanks for that invo, I will preceed along those lines.
>
>Bellcrank wire to flap lower control horn hole. Top hole of
>flap control horn to lower hole on control horn hole.
>
>This should do it!?
>
>Right?
>
>Charles

NO! For example: Start with a 4" handle spacing, 4" bellcrank, and 1.25" or 1.5" horns. Handle/BC is 1:1, right? If you use the 1.25" flap horn and connect from the 1.25" hole on the flap horn to the 1.25" hole on the BC arm, you are still at 1:1 rato, right? Continue on aft, trying to keep the horn arms as long as possible. It gives better control response as the line tension drops, because all the power to drive the controls comes from line tension.

You really do NOT need more than 15 or 20 degrees up and 15 or 20 degrees down, regardless of what is shown on the plans. Use an adjustable elevator horn. Increasing the elevator (shortening the lever) actually reduces the flap input. You will probably want to narrow your handle spacing. Reducing the elevator (lengthening the elevator horn lever) increases the flap input, and you will probably want to widen your handle spacing. HOWEVER...tho the change can really mess up your feel of the plane, and might take awhile to get accustomed to, it will probably be pretty obviously better. Tricky, eh? Steve

Steve Helmick
Renton, Washington
USA

>I read the angle of flap deflection is to be equal to that of
>the elevator.
>
>Is this alwayes the case? One would think the flaps wouldn't
>have to deflect as much?
>
>Good rule to follow when setting these up?
>
>Thanks in advance,
>
>Charles

It is always true that if you ever use the word "always" or "never" you are sometimes wrong. (This is sort of like the rule of Lating that "There is an exception to every rule except for this one for which there is no exception.")

Anyway, back to seriousness: For a "normal" design of "normal" weight, the 1 to 1 ratio is a good rule of thumb with which to start.

Many of the top flyers (maybe most) will use adjustable elevator horns with which to adjust the ratio as needed. An airplane with a lighter wing loading needs less flap (area or movement) and an airplane with a heavier wing loading will need more flap (area or movement). Thus, if you start with a 1 to 1 ratio and your airplane has too much flap because you built it too light (?), you can either trim the flap or, if you have an adjustable horn, increase the elevator movement in relation to the movement of the flap. You can see the logic here. It is easier to adjust the horn in the field to get proper trim than to constantly trim the flap and then have to refinish that part.

I would not advocate using more flap movement than elevator movement. In this case adding flap area would be the solution. Bob Gieseke builds extremely light. His Nobler and Bear designs use very thin flaps toward the tips because of this. I have known instances where people have built his designs "normally", had the wing loading come out heavier than his, and had to increase the size of the flap to get it to turn properly. So, since we never know how heavy we are going to end up, I would advocate starting with larger flaps and an adjustable elevator horn. And here is where an adjustable handle comes into play because we can adjust the sensitivity here as this will certainly change as we move the ratio on the elevator horn.

LN,

Thanks for taking the time to explain this. I appreciate it.

OK, so, the only horn to be adjusted is the elevator, correct?

I've looked real well at some of these high tech stunt models, and I see no hatches that can be removed for horn adjustments.

Am I missing something?

This particular model I'm working on, has a split elevator and the horns are exposed. SO, your suggestion for elevator adjustment won't be an issue.

How are these guys adjusting the flap horn?

Thanks,

Charles

>LN,
>
>Thanks for taking the time to explain this. I appreciate it.
>
>OK, so, the only horn to be adjusted is the elevator,
>correct?
>
>I've looked real well at some of these high tech stunt models,
>and I see no hatches that can be removed for horn adjustments.
>
>
>Am I missing something?
>
>This particular model I'm working on, has a split elevator and
>the horns are exposed. SO, your suggestion for elevator
>adjustment won't be an issue.
>
>How are these guys adjusting the flap horn?
>
>Thanks,
>
>Charles

Adjusting at the elevator changes the ratio, and that is all you need.

I don't know what horns you are using, but there are several varieties. The one Matt uses is made by Tom Morris and has a slider that is adjusted by a ball wrenchy. He merely has a vertical slot in the side of the fuselage at the point where the horn is and uses a ball wrench through the slot to adjust the horn up or down. Others will use a hatch of some sort, or, if they have a take apart plane may have a tail section that comes off and gives access to the horn adjustment.

You might note that they also use an adjustable length push rod and this gives one more adjustment without having to lock the controls and try to bend the elevator or flap horn to achieve neutral. The more adjustments you have, the better.

I have to admit that we hadn't even thought of trying this until we ordered a set of horns from a person who made these and ordered a "standard" elevator horn. Well, he sent an adjustable one saying we would probably prefer this.

OK, one more confession. Matt used this on his plane that he was building but we never thought too much of adjusting it. He just flew it "as is" and we did the normal other trimming. Then one day we got to thinking about seeing what it would do. Surprise! Hey, this really does work. So now he wouldn't build one without one.

It is like adjustable leadouts: Don't build a plane without one. (And why someone doesn't get the idea to include these with the ARFS (along with bushed belcranks) I don't know. So simple to include them. And at a dollar a day wages, it isn't going to add that much to costs.

LN,

OK, great! Thanks.

<>

Does anyone have photos of this adjustable horn?

Charles

>I've looked real well at some of these high tech stunt models,
>and I see no hatches that can be removed for horn adjustments.


Removable wings and tail planes?

[photo not recovered: 40121.jpg]

This has got to be the ultimate in adjustability though!
(From http://www.holdfastmac.com.au/controlsys.html)

Attachment #1, (jpg file)

Thanks for the photo.

I must say I didn't expect that.

Looks to me that there's a pushrod missing?

CB

>Thanks for the photo.
>
>I must say I didn't expect that.
>
>Looks to me that there's a pushrod missing?
>
>CB
Nothing is missing mate, the two rods you see are for the elevators and the flaps and they are driven from the bell cranks central shaft.

Just check the supplied link for more info.

Look at the math.

Assume the flaps are 6" behind CG and the elevator is 18" behind CG. The elevator has 3 times more leverage than the flaps.

Assume the flaps have 3 times more surface area than the elevator. The flaps have 3 times more leverage than the elevator.

If elevator and flap both move at identical angles the (+3)+(-3)=0

Did I do my math right or did I make a mistake? Anyway you get the idea.

About 5 years ago I built and airplane from old MAN PLANS and the first time I flew it, FULL UP on the control handle and the airplane just barely went UP and FULL DOWN on the control handle and the airplane barely went down. Flap and elevator moved at about the same angles one was canceling the other. I made several adjustments and finally ended up with the flaps at about 15 degrees and elevator at 35 degrees. After that I'm not sure if it flew MORE BETTER or LESS WORSER but it flew GOODER. It was a good learning experience for me. Each airplane is probably different.

>Look at the math.
>
>Assume the flaps are 6" behind CG and the elevator is
>18" behind CG. The elevator has 3 times more leverage
>than the flaps.
>
>Assume the flaps have 3 times more surface area than the
>elevator. The flaps have 3 times more leverage than the
>elevator.
>
>If elevator and flap both move at identical angles the
>(+3)+(-3)=0
>
>Did I do my math right or did I make a mistake? Anyway you
>get the idea.

Your math is correct but the underlying concept is not. If it worked that way, you would find you have exactly zero control capability (since the pitch torque created by the elevator would be counteracted exactly by the pitch torque created by the flaps).


Brett

>>Look at the math.
>>
>>Assume the flaps are 6" behind CG and the elevator
>is
>>18" behind CG. The elevator has 3 times more
>leverage
>>than the flaps.
>>
>>Assume the flaps have 3 times more surface area than the
>>elevator. The flaps have 3 times more leverage than the
>>elevator.
>>
>>If elevator and flap both move at identical angles the
>>(+3)+(-3)=0
>>
>>Did I do my math right or did I make a mistake? Anyway
>you
>>get the idea.
>
> Your math is correct but the underlying concept is not. If
>it worked that way, you would find you have exactly zero
>control capability (since the pitch torque created by the
>elevator would be counteracted exactly by the pitch torque
>created by the flaps).
>
>
> Brett


I did have pretty close to zero control. Holding the control handle full up the airplane elevation only changed a few feet in one full circle.

First thing I though of was the bell crank is hitting or stuck on something if I give it full down it will probably nose dive and crash. After some experementing I realize there was almost no control on full down.

Math? Here's my math.

CG to flap hinge point is: 6.75". Flap is 2.5" at the root.

Flap hing point to elevator hinge point is: 13.25". Elevator is 3.5".

Good, bad or evil, this cannot be changed.

CB

Even if you did have zero pitch moment, it doesn't prove that moment is proportional to flap deflection * area * moment arm. That is a natural thing to assume: that's how a linear system would work, and lots of physical things work that way. You'd just superimpose the flap effect on what the rest of the wing is doing. However, in subsonic flow, the flap affects the flow upstream, hence the pressure distribution over the whole wing, so the calculation is more cumbersome. If I weren't so lazy, I'd run one of those free online aero programs and show the pressure distribution over a stunt wing at different flap deflections. Is anybody interested? Better yet, does anybody else volunteer to do it?

Howard Rush
Bellevue, WA

>Even if you did have zero pitch moment, it doesn't prove that
>moment is proportional to flap deflection * area * moment arm.
> That is a natural thing to assume: that's how a linear system
>would work, and lots of physical things work that way. You'd
>just superimpose the flap effect on what the rest of the wing
>is doing. However, in subsonic flow, the flap affects the
>flow upstream, hence the pressure distribution over the whole
>wing, so the calculation is more cumbersome. If I weren't so
>lazy, I'd run one of those free online aero programs and show
>the pressure distribution over a stunt wing at different flap
>deflections. Is anybody interested? Better yet, does anybody
>else volunteer to do it?

To disprove this one, all one would need is a pitching moment curve, I think.

Brett

>
> To disprove this one, all one would need is a pitching
>moment curve, I think.
>
> Brett

Cliff Lee has got a pretty good pitching moment curve. And a darn good slider too.

Go Phillies

Larry, Buttafucco Stunt Team

>>
>> To disprove this one, all one would need is a pitching
>>moment curve, I think.
>>
>> Brett
>
>Cliff Lee has got a pretty good pitching moment curve. And a
>darn good slider too.
>
>Go Phillies
>
>Larry, Buttafucco Stunt Team

Yeah, but the Cardinals beat him. Go Cards!

I miss Manny.

>>Look at the math.
>>
>>Assume the flaps are 6" behind CG and the elevator
>is
>>18" behind CG. The elevator has 3 times more
>leverage
>>than the flaps.
>>
>>Assume the flaps have 3 times more surface area than the
>>elevator. The flaps have 3 times more leverage than the
>>elevator.
>>
>>If elevator and flap both move at identical angles the
>>(+3)+(-3)=0
>>
>>Did I do my math right or did I make a mistake? Anyway
>you
>>get the idea.
>
> Your math is correct but the underlying concept is not. If
>it worked that way, you would find you have exactly zero
>control capability (since the pitch torque created by the
>elevator would be counteracted exactly by the pitch torque
>created by the flaps).
>
>
> Brett


Ron B.
F4Fguy

Brett,

I'm a little confused (not unusual for me). Without applying anything but my own twisted logic, it would seem that, if the pitching moment is exactly cancelled, the airplane would still have to respond in some way. Either it would climb or lose altitude (with down input) without pitch, or it would slow down due to induced drag, depending on the power available.

Ron B.