Small balsa kit build - Aileron Control options?

[Andy C]

My build of my small Fly Baby has stalled recently, partly through time and if I am honest partly as I am at a couple of decision points (tricky bits) mainly around the electronics.  One of those is what to do about the ailerons.  The instructions are very limited and simply say stick a servo in centre and then drill through all necessary ribs for the control cable.

 

I guess my 2 options are:

1  Have a centre servo and then I assume snakes along wings to the control surfaces

2.  Go for a more modern set up with individual servos in each wing. 

 

I personally like the idea of option 2 as it seems easier and gives more flexibility when aligning, setting up etc.  So if that is my option, how do I choose servo size?  Those who have seen my other power source will know that it is an 049 to 090 (old money), 2217 (new money) size.  In my spares box i have some 9g size (HXT900) servos as well as some 4.3g MX-95E so would be great if one or other would be suitable.

 

Thoughts please.

Thanks

[Frank Skilbeck]

I would go for individual servos in the wing, you don't say the size of the model, but based on the power then it looks quite small and lightweight so the MX-95Es should be fine, you could check by using an online servo torque calculator, but if you are unsure then the HXT900s should be fine. For comparison my Saturn Skydancer, approx54" wingspan with a 400w power system (2650 mah 4s) has 9g servos all round.

[J D 8]

 Another option with a small model where fitting of even small servos in the wing may be difficult or not look to good is to have two servos in the centre each driving its own aileron via torque rods. 

[Andy C]

Thanks Guys.  I'll see if I can find a calculator to check.

 

FYI, this is the model in question......  

 

https://outerzone.co.uk/plan_details.asp?ID=7298

 

[Matt Carlton]

+1 for using torque rods and two tiny servos in the centre section. Keeps the weight in the centre and is a much neater and cleaner installation. The structure of some models doesn't always lend itself to wing mounted servos without a but of beefing up and as this is a small model, small bits of added weight can make quite a difference. 

 

To be honest though, I don't think a flybaby really needs two servos. Bend up the torque rods to give a bit of differential and it'll be fine, just like we have been doing for decades quite successfully. 

[Nigel R]

Barn door ailerons Matt, torque rods would be long.

 

You could use a long torque rod I guess, but a 9g on each would be the easy route.

 

 

[Matt Carlton]

Ahh gotcha, I didn't look if I'm honest. You're right though, long torque rods are not the best idea really. 

[leccyflyer]

With that set-up, given the outboard ailerons, I'd opt for a pair of 9g servos, mounted out in line with the ailerons. That said, my recent Mini Astro Hog refurb is the same configuration and has a single, centrally-mounted min-servo, with long torque rods, which isn't ideal as the space inside the fuselage for three servos is very tight.

 

[Piers Bowlan]

Yes two servos in the wings would be my option too; less slop and easier installation. Nothing wrong with using the HXT 900 servos you have, but I would ensure they are easily removable incase you are unlucky enough to need to replace one. The tiny plastic gears can get damaged in 'an arrival' or even transport 'rash'!

I have used quite a few of these Corona 929 servos from Hobbyking in small models. They are about the same size but with metal gears so a bit more robust - and they are in stock!! 

[Frank Skilbeck]

Using the servo calculator on Ecalc, assuming a 4g load and 30mph with a 30 degree deflection gives a total torque to move the control surface of 0.3 kgcm, so if your servo arm was half as long as the aileron horn that's 0.15 kgcm. Note the aerodynamic load is only 1/3rd of the total load.

rudermoment (2).pdf

Edited May 10, 2021 by Frank Skilbeck

[Nigel R]

3 hours ago, Piers Bowlan said:

Yes two servos in the wings would be my option too; less slop and easier installation.

 

I've said this before, but, 'two servos in the wing' is only quicker if you don't mind the things sticking out in the breeze. If you want it all tidy behind hatches, then torque rods are quicker / easier.