Jerry Sigur

I have quite a bit of floatflying experience but have run into something
which has me scratching my head.
A friend scratchbuilt an 80" Beaver, very nicely done. We first flew it
on wheels from our local flying field to check out trim and balance. It
flys very nicely with crisp control response on all axis.
So it was then mounted on floats, carefully, checking out the incidence
and step placement, balance, etc.
Well, today we attempted the first flight using the floats. After breaking
free from the water and climbing out I discovered a complete lack of roll
control using ailerons, I mean nothing, no response. To make a long story
short I used the rudder to turn it around and finally get it close to a landing,
finally dumping it from about 5". No damage. (rudder very sensitive)
Upon retrieval the ailerons worked just fine.
The Beaver is 80", powered by a 120 two stroke. Scalelike ailerons and flaps.
All up weight with the floats is 14lbs.
Any thoughts or input as to why there would be no response to aileron input
with the floats mounted on the aircraft?

Brian A

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Heres a few pics

michpittsman

My Feedback: (11)

Jerry-Sounds like the weight of the floats acts like a pendulum, resisting efforts to roll the airplane. I would either increase the throw of the ailerons or couple them to the rudder, or both. JIM

Ed_Moorman

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Jerry,

The first thing I'd do it to hold the ailerons in place and move the stick or move them to full deflection, then push on them. I have a buddy, flying partner, who builds scale. He has this tendency to put in belcranks and all sorts of hidden control systems that may work well on the ground, but fail under air loads. He also tends to use inexpensive, low power servos. None of these are conducive to good roll control in flight.

I don't know about seaplanes and pendulum effect, but I do know that an 80 inch plane usually has ailerons large enough to require high power servos and a good, stiff 4-40 hook-up.

Jerry Sigur

Well the ailerons are controlled by servos installed just directly ahead of
the aileron, so just a short direct pushrod.
Could be pendulum effect I suppose, altho the rudder spun it around
smartly, too smartly. :-)
We're gonna go back to square one by pulling the floats off and trying
it on wheels again, mixing in some rudder with the ailerons.
Thanks guys, all input appreciated.

polstery

Strange problem,You may be flying just a bit too slow, try flying faster that should do it.

Jerry Sigur

Was at full power and moving along very well. It's
not underpowered.

seaplane

Jerry, I just finished a 96" Beaver, only on floats, and it also has very slugish ailerons, especially when the flaps are lowered. Did you have the flaps down or up? Seaplane

Smoky

Hi! my manual say's to use lots of aileron throw, needed especially at low speeds! so I set it up that way. My bird has an 8 foot wingspan, and the roll characteristics are very slow. unless you use rudder and aileron at the same time. then it does nice snap rolls. Mind you not as fast as my bipe. but still a snap roll.

Adding floats, did slow the roll down a bit, but not overly slow. do you have water rudders installed. just wondering if mebbe something got mixed wrong. aileron/rudder offset instead of mix or something like that. another possibility, is some water spray from takoff momentarily killed the servo's. have they been waterproofed? I use vaseline on mine to seal the seams. and around where the gear sticks out the housing. My servo's get wet from a big splash, but it doesn't seem to bother em.

Smoky.

Jerry Sigur

The flaps were up. No mixes were being used at the time of the float test.
Both aileron servos are housed in small enclosures to minimize any water
intrusion.
From you experiences it sounds like most Beavers have very sensitive rudders.

JimCasey

My Feedback: (1)

Full-size beavers add vertical fin area when floats are mounted. Sometime's there's a separate fin under the rear of the fuselage. Another mod (Certificated by Kenmore Air) is to add small fins to the end of the fixed part of the horizontal stab. Apparently the side area of the floats in front of the CG is enough to make more stabilizer area behind the CG necessary.

Also: Flat-bottom airfoils tend to exhibit much more adverse yaw than symmetrical airfoils.

With inadequate stabilizer area, and adverse yaw, ailerons will make the plane yaw the wrong way and the dihedral will then cause it to roll the WRONG way. Apparently yours is juuust balanced and the adverse yaw/roll coupling is exactly the same as the aileron roll force.

I was there for the test flight of a 100" beaver, and it needed substantial rudder mix with the ailerons to fly properly.

Program/build in plenty of aileron differential, and mix in at least 25% rudder with the aileron. Add a little more fin area. Earlier remark about being sure the ailerons have positive motion under load is a good one. Be sure your servos are mounted solidly, and the aileron horns are mounted into a reinforced place on the aileron.

I got around the problem by fudging a Senior Telemaster to make it look (mostly) like a Beaver. It still needs rudder mix with ailerons. 96" Span, 10 pounds with floats. EEEEASY to fly.

Jerry Sigur

If you enlarge the pics Brian posted earlier in this thread you will see the
small fins added to horizontal stab.
Your thoughts on aileron differential will be tried and we are also going to
mix in some rudder, tho will have to very careful with this due to the
sensitivity of the rudder.
Thanks

PeterC

Iin reply to the problem of aileron ineffectiveness it could be that the pendulum effect of the floats is counteracting the ailerons. I'm not saying that the ailerons are ineffective it's just that the deflection of the downgoing aileron is creating so much drag that the weight of the floats is not allowing it to roll.
Two, or possibly a combination of solutions are possible. One, adjust the ailerons so that you get about three times as much up aileron as you do down, and two, couple your ailerons and rudder together. Down aileron drag is a reason that full size sailplanes always seem to use rudder and aileron together. It is particularily noticeable in slow flying airplanes.
I think you will find differential ailerons will solve most of your problems,
LOL, Peter

cf-drg

My Feedback: (1)

Sub fins and finlets ...The finlets on the stab tips help , but also try a big sub-fin under the tail. Same as what Jim mentioned...With all that float area ahead of the C/G, the sub-fin might help..And it won't do any harm... Plus also differential on the aillerons...
I had a 72" WS beaver that did the same thing..My only fix in the end was to mix aileron and rudder...

markebooboo

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hi was wanting to know the cg on 80 in beaver please. thanks mark