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Gordon Misch
02-01-2020, 06:38 PM
We're building an experimental PA-12, using Dakota Cub wings. The Dakota wings use ailerons with the PA-18 shape, and they also use the -18 actuation horns rather than the -12 bellcrank. I'm at the stage of rigging control surfaces so looked up the control surface movement specs in the PA-12 and PA-18 TCDS. I was surprised to see the aileron specs are quite different. PA-18 has considerably less travel.

PA-12 is 31 deg up and 25 deg down.
PA-18 is 18 deg up and 18 deg down.

I know we can't obtain the -12 up/down differential with this system, so here is my question:

Is there is any reason we shouldn't increase the aileron travel to 25 or 28 deg both up and down? 28 deg would be the average of the -12 spec.

Thanks - -

mike mcs repair
02-01-2020, 07:43 PM
Post pictures of aileron bay & aileron nose ribs. -12 would block gap in down position so it depends on shape of aileron bay false spar(flap shape on -18 flap)


Sent from my iPhone using SuperCub.Org

Gordon Misch
02-01-2020, 10:56 PM
Three pics here. One is the aileron / false spar interface. The other two are another issue that is arising, that is the lower aileron cable and drag wire are very close. Closer than I like. Is this normal for -18 cable runs? Ignore the misalignment between pulley and the cable run parallel to the spar - it's the way I was tugging on it. I haven't finished making up the cables yet - still roughing in.



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skywagon8a
02-02-2020, 07:41 AM
.... they also use the -18 actuation horns

PA-12 is 31 deg up and 25 deg down.
PA-18 is 18 deg up and 18 deg down.

I know we can't obtain the -12 up/down differential with this system, so here is my question:

Is there is any reason we shouldn't increase the aileron travel to 25 or 28 deg both up and down? 28 deg would be the average of the -12 spec.

Thanks - -
Gordon, The real limit is when the top aileron horn hits the trailing edge of the wing. However many degrees that may be. Since the length of both the up and down control horns are the same length from the hinge pivot the up and down travel will be the same. The down travel will be controlled by the opposite aileron hitting the trailing edge.

There is another limitation point. That is under the floorboards where the throw of the stick is limited. Maximize this as well. Use as many degrees as you can manage. The more up you can muster, the better your roll control will be.

I left the stops off my wings in order to maximize the travel.

supercrow
02-02-2020, 07:47 AM
No stops on mine either.

Gordon Misch
02-02-2020, 01:30 PM
Use as many degrees as you can manage. The more up you can muster, the better your roll control will be. I left the stops off my wings in order to maximize the travel. Pete, do you know how many degrees on yours? I'm wondering about any possible adverse effects from increasing the travel. Thanks.

skywagon8a
02-02-2020, 02:31 PM
Gordon, Aileron up and down 22.5 degrees each direction.

The only adverse effect would be a need for more rudder to compensate at full aileron throw. The more aileron throw the higher the crosswind capability. The only restriction would be your ability to keep your legs out of the way of the stick, which is one reason I chose the wide body fuselage.

BC12D-4-85
02-02-2020, 03:29 PM
Here's some opinions on differential aileron travel: https://aviation.stackexchange.com/questions/23392/why-is-there-a-difference-between-aileron-upwards-and-downwards-deflection-angle

Gary