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wing flap servo suggestions for Bix.

#1
Need advice b4 buying 2 servos for a Bix2 for flaps, mainly to improve Vs and minimize gravel rash. What is recommended for the Bixler 2 ?. Would like to know who uses which and any pros and cons if any.
thanks
 

quorneng

Well-known member
#2
My own view is that flaps are by definition low speed surfaces. You don't need or want to deploy them at full speed.
The object is to reduce the stall speed so you can safely fly slower for landing. A planes stall speed is a function of its weight so the less you add with the flap servos the better.
The logical conclusion is to fit the lightest you can get away with along efficient linkage and free moving hinges. A 5g servos should be adequate and probably even smaller.
I have a several planes with flaps and even the biggest (each flap 18" x 2.5") only uses a 5g servo to move it.
 
#3
I just used the same servos in the flaps as the ailerons. Cost difference between 5 and 9 is peanuts. However, I agree with quorneng that 5G would probably suffice. However, you may need to shim up the hole as they have pre-cut holes in the wings for 9G servos. 5G servos are smaller.
 
#5
My own view is that flaps are by definition low speed surfaces. You don't need or want to deploy them at full speed.
The object is to reduce the stall speed so you can safely fly slower for landing. A planes stall speed is a function of its weight so the less you add with the flap servos the better.
The logical conclusion is to fit the lightest you can get away with along efficient linkage and free moving hinges. A 5g servos should be adequate and probably even smaller.
I have a several planes with flaps and even the biggest (each flap 18" x 2.5") only uses a 5g servo to move it.
Would this one do the job? Its the slimmest I can find so far.
http://www.trademe.co.nz/Browse/Listing.aspx?id=869296519
 

saf99

Junior Member
#6
I would check Hobby King for servos if you don't have a local shop. Same servo at HK http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=7475 .

Just check shipping cost and use Hong Kong post, they have quite short shipping time now (around 7 days to Sweden) and try to use your shipping cost full out, they charge for every 100g so if you order 2 servos and shipping weight is 62g then you can try to find lets say a prop or something to get close to 100g.
 

quorneng

Well-known member
#7
One point to consider is how much movement you are going to have on the flaps. The greater the flap travel the lower the effective 'mechanical advantage' for the flap servo.

How will your flaps be controlled by the Tx?
If by a simple one position switch it is best to limit the flap movement. Suddenly applying even 30 degrees of flap whilst travelling at any speed is going to result in a trim change. Best to start small and slowly increase it be experimentation.
Even with a 3 position switch the first step should be fairly small (10 degrees?).
Note the trim change actually occurs in two situations.
a) Whilst the flap is travelling and the plane is slowing down.
b) Any residual trim change once a new steady state has been reached.

My old Futaba Tx has a dial knob for the flaps so they are infinitely adjustable. I am thus quite happy to set them up for a full 90 degrees travel although it would never be applied all at once but only in gradual stages as the plane actually slowed down.
 
#8
I'll never buy from the states if I can help it as it will double or treble the cost with their postage, I learnt that one the hard way. Ozzie if possible and yes, you are right if possible from HK as its free normally (OK so they stack the price) But finding a really small servo for in wing is harder than originally thought. Thanks for all the advice. it all helps
 

joshuabardwell

Senior Member
Mentor
#9
The pre-cut slots are set for 9 gram servos, and the weight difference between 5 gram and 9 gram is negligible on a frame the size of the Bix. Just get any generic HobbyKing 9 gram servo and call it a day. The Bix is not a high-performance airframe where high-end servos are necessary or desirable.
 
#11
OK will do, Thanks guys. I was given an old Bix II and have absolutely no gear (or idea) what so ever (apart from a runway and the gutted plane). Thought I would get the Bix going first , then shift the gear to a nice high performing 2m glider.