Typsy junior

[geoff wise 1]

life used to be simple, single channel, valves a escapements powered by rubber, models lasted quite a long time as long as you didn't turn the radio on, then came galloping ghost, by this time you didn't need a 22 volt battery to power the might midget motor, then came pulse proportional, using 2 bellamatics which just about had the power to work after they had overcome the tension on the centering spring, then came my first 4 channel tx and rx and proper servos which came in one size which went in to every thing from a cox o49 to a sixty powered aerobatic. Then came a small servo FD 30M, which i used in club 20, now my question is, how much torque is actually required for some thing like the above? ie, servo in each wing, rudder and elevator, some of the torque on these small sevos seem pretty high, if you actually tried to stall them, chances are you would probably pull the servo mount out.

Comments welcome, Geoff

[FlyinBrian]

Geoff

I often wonder this too as some of the servos used in average club models seems like overkill to me.

In the 70's I had a SkyLeader SLX set with SRC1 servos, I doubt if these were much more than 1Kg/cm but happily flew piped OS 60 FSR powered aerobatic models such as the Wolfgang Matt Super Star.

I now have servos with three times that power in small electric models as, in general, even mini servos have tons of power. I have a couple of tiny models in which I have used 9 gram servos but even these give more than 1kg/cm torque.

I guess we should be glad that such power and reliability is available to us at a fraction of the price servos used to cost.

[geoff wise 1]

Hi Brian,

Thanks for your reply, i noticed somewhere in here a newby asked the same question and the replies left a lot to be desired, its a valid question, how much power is required to operate a surface of x square inches, speed of model will obviously have an effect, but saying that my fast models have very little deflection, think i'll just go down the route of small metal geared servos and see what the results are. I notice that you asked a question, do you use a modern transmitter or 35 megs, the answer is i prefer the weight of 35 megs, i only want rates and servo reversing. I couldn't remember what all the switches were for and would be more likely to crash. I do have a spectrum as well and i have to admit that being able to set the throws up etc.is handy

Now another question, alleron differential, i've only ever used it once intentionally and that was on somebody elses piper cub thing which basically gave you aeleron reversal differential made it flyable, so as the junior has a wing section very similar to a super 60, very Clark Yish, do you recon differential might be a good idea? If so, what percentage? Peter does say in his article that the rolls weren't very good. You mentioned servo prices, i think my first small servos were £30 each.

Geoff

[Charles Smitheman]

Hello Geoff,

I have just completed one of these Tipsy's, with modest electric power. It had cheapo 9g servos on the ailerons, and Towerpro 9g mg servos on ele and Rudder. I have now changed the elevator servo to a Hitec HS65hb, which has better resolution than the Towerpro's.

I think you can get away with cheaper servos for electric, but the elevator did not feel nice, hence the change. If I was doing it with i.c. I would have used better servos throughout, such as the Hitecs. Saving weight with lighter kit is important in my view with a small model, the lighter ones fly much better.

This model needs bags of elevator travel to stop it tipping on its nose on takeoff (well my one does) , but therefore is a bit touchy on elevator in the air. So this showed up the sloppy-ness in the lower quality servos. I have yet to try it again, it was a bit windy last weekend!

[Piers Bowlan]

Geoff, differential aileron is used to counter adverse yaw. If you witness a model that tends to 'drag it's tail' when turning, this is a symptom of adverse yaw. It is caused by the down going aileron producing more drag than the up going aileron so that it tends to yaw in opposition to the direction of turn. (a simplified explanation). Consequently this will result in poor turning ability even if the model rolls OK. Several design factors will affect how apparent this is. High aspect ratio, a short coupled fuselage, or a fin/rudder that is too small may exacerbate this characteristic. Other factors are the wing loading and the airspeed (angle of attack), I am sure there are others. Increasing the deflection of the up going aileron compared to the down going one should improve the handling of the model in this respect. Coupled aileron and rudder will also help counteract adverse yaw but, like differential aileron, it works best at one airspeed so is not the complete answer. I use it on all my gliders.

Regarding the model tipping on its nose, you could try raking the landing gear a little further forward and using bigger wheels, although this would spoil the scale effect.

Charles, if you are using 'bags of elevator travel to stop the model tipping on its nose for take off' then take off using high rate elevator for take off and switch to low rate once safely airborne. Alternatively use a mode switch if your Tx has one.

 

 

Edited By Piers Bowlan on 13/06/2017 10:30:34

Edited By Piers Bowlan on 13/06/2017 10:39:09

[Charles Smitheman]

Hello Piers,

Yup I have plenty of differential on my Tipsy.

Personally I don't like using rates as I like to keep it simple, less is better for me. I do use quite a lot of exponential though, depending on the model and how it feels.

I recall a club mate reaching for the retract switch on his F3A model, but operating the snap roll switch instead.... BAM!