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Old Jun 28, 2014, 05:29 PM
Registered User
United States, AL, Auburn
Joined Feb 2011
11 Posts
Question
Beaver Servo Mounting

Hey Everyone,
I'm building a 8' Unionville Turbo Beaver kit. This will be my first big and complex build.

I've got the wings built and am making my way through the instructions. They use control rods to right angle clevis's in the wings for the flight surface control. To me this will result in a lot of setup and messing around, and another possible fail point in the aircraft.

I've chosen some stout HS-645MG's which are probably overkill but I've already got them. They weigh ~2oz a piece but I don't think i'll ever has problems with overloading them. I'm concerned about mounting:

1. Which direction in the wing should I mount them? Should the control horn be forward or aft of the servo body.

2. Should the servo be as close to the CG in the wing as possible? Should the servo be a bit aft to allow shorter linkages.

3. How can I assure the proper control horn mount geometry?

4. What about access hatches?

I've included some pictures of the wing. (I'll be mounting both alieron and flap servos in the wing)

Thanks Guys.
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Old Jun 28, 2014, 08:22 PM
Mark LSF # 3792
United States, TX, Garland
Joined Nov 2008
521 Posts
If you are referring to the bell crank on the plans in the pics, you have made a wise choice in doing a direct linkage dual servo system, IMOH. Also, it will allow you much more radio programming capabilities using dual servos for both ailerons and flaps.

Sure have the servo output aft if you don't have clearance problems. If possible, without cutting holes in the spars, I'd put them in front of the CG. The further forward the less nose weight required. Mounting them on hatch covers that are removable, but rigidly mounted is also a good idea for future maintenance. If you set up your aileron linkage so the push rods and horns are at 90 degrees at neutral I would not worry about pushrod length, if your rods are a large enough diameter.

Flap servos are another type of animal. Being a sailplane flyer predominately I try to get 80-90 degree flap deployment. This requires adjusting horn angles and biasing servo centering, using sub trims, to maintain trailing edge precision at neutral. Depends on your set up, but for bottom output/bottom drive flaps I bias the servo horn toward the LE of the wing. Just my $.02.
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Old Jun 28, 2014, 10:00 PM
Registered User
United States, AL, Auburn
Joined Feb 2011
11 Posts
Flaps and Ailerons

Soarmark,
Thank you for the info. Those are the answers I needed to move on with this. Yes I was referring to the bell crank but had forgotten it's name. The programming aspect is important and I have both the channels available and radio which will work well to setup the model right.

I will have problems with clearance if I put the servos further forward than the shear webbing. I've decided through some other research to go with like you say a hatch cover design, which looks to be the most versatile and easiest to maintain in the long run. It will take a bit of time to get situated now but I think it'll be worth it.

The manual for the Turbo Beaver states that the flaps should be set at a maximum of 50 degree's deflection. This shouldn't be a problem to setup as it is no where close to the 90 degree demands of your sail planes. I try to keep in mind that the turbo Beaver is a fairly forgiving airframe which will make this build a bit easier. (read still will fly while learning the building techniques)

Quote:
Originally Posted by Soarmark View Post
If you are referring to the bell crank on the plans in the pics, you have made a wise choice in doing a direct linkage dual servo system, IMOH. Also, it will allow you much more radio programming capabilities using dual servos for both ailerons and flaps.

Sure have the servo output aft if you don't have clearance problems. If possible, without cutting holes in the spars, I'd put them in front of the CG. The further forward the less nose weight required. Mounting them on hatch covers that are removable, but rigidly mounted is also a good idea for future maintenance. If you set up your aileron linkage so the push rods and horns are at 90 degrees at neutral I would not worry about pushrod length, if your rods are a large enough diameter.

Flap servos are another type of animal. Being a sailplane flyer predominately I try to get 80-90 degree flap deployment. This requires adjusting horn angles and biasing servo centering, using sub trims, to maintain trailing edge precision at neutral. Depends on your set up, but for bottom output/bottom drive flaps I bias the servo horn toward the LE of the wing. Just my $.02.
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Old Jun 28, 2014, 10:39 PM
Art Schmitz
United States, TN, Crossville
Joined Jan 2012
392 Posts
Built the 6' recip. version probably seven years back.
Used the single servo , 1/16 M.W. to belcranks with Z bends . Fair leaded the wire using 1" inner Nyrod sections. I threaded the Williams Brothers nylon belcranks pivot hole 6/32 and threaded them on to 6/32 bolts mounted with double nuts through a 1/8 ply base. Triangle gussets. No slop. So much for the ailerons.

I used Fowler flaps with individual servos. Horns on top, Z bended wire from flaps to 2/56 brass Sullivan clevis's @ servos. Off set servo arms for max rearward travel. Flap hinges were from Hobby Lobby, two to a flap. ( the off set lower hinge points can also be done with two long control horns with 2/56 pivots )
Shape each flap to an air foil section rounding just the top leading edges. Mount to wing with zero gap at bottom. The gap at the tops will increase quickly as the flaps deploy, Go for 35 degrees down. Viola, the typical slotted Fowler effect happens ! High cool factor. Excellent performance enhancement. I used mine for both take off and landing.
My 72" used scratch built 32" G&S wood floats. Two water rudders via cables. Power was the OS .50SX, remote needle valve and fueling port.

Caution, keep all the equipment weight as far forward as you can. My rudder and elevator servos were on a slide plate that positioned them under the wind screen. These servos used the same 1/16 M.W. fair leaded with the yellow inner Nyrod sections as described for the ailerons.. Brass clevis's at surfaces, Z bends @ servos. Note: this linkage system was developed by R.C. pioneer Harold De Bolt. It gives a zero slop installation.

Keep the speed up when turning down wind / base / and especially final. These high aspect ratio wings like to stall when weighed down with floats, etc. I never raised the nose in any low speed turn. Best to avoid any inclination to use 'up' elevator. Give the rudder a little 'kick' in the turns. Worked for me.
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Last edited by lindart; Jun 28, 2014 at 11:50 PM. Reason: added info
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Old Jun 29, 2014, 02:16 PM
Registered User
United States, AL, Auburn
Joined Feb 2011
11 Posts
lindart,
Thank you for the post! Your setups sound masterfully designed and setup. Do you have pictures by chance? I trust you when you say they do not have any slop and work very well.

Not that I'm into scale, but the original Dehavilland Beavers did not have Fowler flaps. You are right, the kick ass cool factor does go up, but it isn't for me.

Since this is my first major build, complexity will stretch the amount of time that it will take to build this airplane with significant loss of interest following. That complexity will lead to failures if not properly done which is extremely likely. The additional setup versatility with the individual servos/control surface far outweighs the weight savings of the bell crank system and the constant maintenance of the more complex bell crank system. I'm under no illusion that this plane won't crash regardless of what I do, but I want to minimize the possibilities.

I know this will add momentum to the wings giving me a slower roll rate, but then again I am not trying to win an aerobatic contest with this bulky cargo ship.

Do you have pictures of the 72" with floats?

I will heed your warning about the weight as far forward as possible, as this was one of my concerns.

Excellent! The flight tips are exactly what I needed to keep this thing in the air.

Thanks Again,

Mark

Quote:
Originally Posted by lindart View Post
Built the 6' recip. version probably seven years back.
Used the single servo , 1/16 M.W. to belcranks with Z bends . Fair leaded the wire using 1" inner Nyrod sections. I threaded the Williams Brothers nylon belcranks pivot hole 6/32 and threaded them on to 6/32 bolts mounted with double nuts through a 1/8 ply base. Triangle gussets. No slop. So much for the ailerons.

I used Fowler flaps with individual servos. Horns on top, Z bended wire from flaps to 2/56 brass Sullivan clevis's @ servos. Off set servo arms for max rearward travel. Flap hinges were from Hobby Lobby, two to a flap. ( the off set lower hinge points can also be done with two long control horns with 2/56 pivots )
Shape each flap to an air foil section rounding just the top leading edges. Mount to wing with zero gap at bottom. The gap at the tops will increase quickly as the flaps deploy, Go for 35 degrees down. Viola, the typical slotted Fowler effect happens ! High cool factor. Excellent performance enhancement. I used mine for both take off and landing.
My 72" used scratch built 32" G&S wood floats. Two water rudders via cables. Power was the OS .50SX, remote needle valve and fueling port.

Caution, keep all the equipment weight as far forward as you can. My rudder and elevator servos were on a slide plate that positioned them under the wind screen. These servos used the same 1/16 M.W. fair leaded with the yellow inner Nyrod sections as described for the ailerons.. Brass clevis's at surfaces, Z bends @ servos. Note: this linkage system was developed by R.C. pioneer Harold De Bolt. It gives a zero slop installation.

Keep the speed up when turning down wind / base / and especially final. These high aspect ratio wings like to stall when weighed down with floats, etc. I never raised the nose in any low speed turn. Best to avoid any inclination to use 'up' elevator. Give the rudder a little 'kick' in the turns. Worked for me.
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Old Jun 29, 2014, 02:29 PM
Art Schmitz
United States, TN, Crossville
Joined Jan 2012
392 Posts
Hi, Mark. Actually both the flaps and the ailerons drop down on the full scale DH-2's.
Set a test linkage up on your bench and try to flex it. The fairleads are 6-7 inches apart, the pushrod exit counts as one.
The plane suffered demise when I was instructing a very experienced RC'r in water flying.
He just had to add 'up' in the last turn on to final...inside wing stalled. Two spins and that's all she wrote.

PM me and I will mail you some pictures that you can keep or post. I've never had much luck posting pictures.

Take care, art
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