Possibly the calculator is haveing a problem with the extreme
deflections of the flap function,(90 degrees).
I also think that you are using some unresonable numbers as far as
speed. 75mph is not an unresonable number as far as speed of some
planes, but I know when I pull flaps on my TD ship I am not normally
going anywhere near 75mph. I do sometimes dive down from altitude but do
not come screaming in and drop the flaps at that speed.
If I have time and have planned things right I may pull on flaps first
and spiral down slowly. In this case the flaps come in with very little
speed and then pull out and off the flaps.
Also when making the landing approach it is not at the extreme speeds
you are referring to.
I am using Hitec HS-225MG servos, one on each flap and as you have said
they are up to the task for a 65 - 70 oz. Unlimited plane.
Try inputting some smaller value for speed and see where the torque
values come in about 45 oz.
RB
Bill Johns wrote:
>
> Greetings!
>
> One of the really neat things about the Multiplex web page is the
> calculator that will help predict the right sized calculator for an
> application. check out:
>
> http://www.multiplexrc.com/calcservo.htm
>
> OK, given that it is an approximation at best, I still get some really
> strange numbers. I'm probably using it wrong.
>
> Given your basic 125" sailplane. weighs say 70 oz, flaps are 2x25 inches,
> they deflect 90 degrees, the wing has a 10" chord and the plane is moving
> at say 75 mph. Yes, this is fast, but not unreasonable for a dive. For me
> the servo calculator gives a required servo of 112 in oz. This is a huge
> servo. Most of us would find a Hitec 225 MG with 55 in oz adequate.
>
> On the other hand, given an aileron on the same plane, again say 2"x25"
> that moves only 30 degrees then the required servo must carry only 37 in oz
> and an HS 85 at 42 in oz.is more than adequate.
>
> Am I doing this right? Whenever I try to come up with a value for flaps,
> it always seems about twice as high as folks use successfully. What am I
> missing?
>
> Thanks,
>
> Bill
>
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