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How to trim a free flight biplane?

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13 Oct 2018 19:17 #1 by Del Piero
How to trim a free flight biplane? was created by Del Piero
I have just built a 2x Ebenezer biplane, with a Mills .75 up front.
I have the correct downthrust, CG, incidences etc. but it still climbs under power and stalls on the glide.
Are the trimming rules the same as for a monoplane? IE pack the leading edge of the top wing or add some weight to the nose.
Or do you have to do something to the lower wing as well?
Any help would be much appreciated.

Regards, Del Piero.

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13 Oct 2018 19:37 #2 by Bryanair
Replied by Bryanair on topic How to trim a free flight biplane?
If it stalls on the glide it is over elevated or the cg is too far back. Packing the leading edge of the top wing will make the situation worse. I assume the tail is glued on? If so pack the trailing edge of the wing and try some test glides. With Ebenezers the glide is normally pretty steep - not floaty. Once the glide is OK only use downthrust and sidethrust to adjust the power phase of the flight.
Thanks: THE BLACKBIRD

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14 Oct 2018 14:28 #3 by Klipkopwildlife
Replied by Klipkopwildlife on topic How to trim a free flight biplane?
I would check the lower wing incidence against the tailplane. It should be no more than 2o, once you have that right set the upper wing to parallel to the lower or at most 1o negative. Once you have the incidences right set the CoG to 25% back from the leading edge of the top wing. Check the glide, as Brianair says it will be steep, adjust with elevator. once you have a glide start moving the CoG back until the glide looks right (not nose high or low). Once you have this right you can start playing with power. I find many so called recommended settings do not result in a good flight, they're what works for the builder of that particular model. Even the manufacturers are guilty of this!

Do it now, you may never get another chance

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15 Oct 2018 12:00 #4 by Del Piero
Replied by Del Piero on topic How to trim a free flight biplane?
Many thanks for your help. I will put your suggestions in to practice for my next test flights.
Unfortunately I now have another problem. The aluminium prop nut on the Mills .75 has lost its thread and I assume I can replace with an ordinary nut. Steel or brass and what BA thread is the crankshaft of an original Mills .75 please?
Hope you can help so I can go flying again.

Del Piero.

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15 Oct 2018 15:57 - 15 Oct 2018 15:58 #5 by Quorneng
Replied by Quorneng on topic How to trim a free flight biplane?
The crankshaft thread on an original Mills 75 is 4BA. On the Mills 1.3 it is 2BA.

The aluminium prop nut was used on purpose so that it would strip before the steel crankshaft thread which by the way is left unhardened, unlike the main bearing journal, so be careful using a steel nut that you don't wreck the crankshaft. ;)
Last edit: 15 Oct 2018 15:58 by Quorneng.

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15 Oct 2018 22:48 #6 by Del Piero
Replied by Del Piero on topic How to trim a free flight biplane?
Thanks for that. So would you recommend using a brass nut?

Del Piero.

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15 Oct 2018 23:00 #7 by Quorneng
Replied by Quorneng on topic How to trim a free flight biplane?
I would recommend using aluminium if you can get it but brass would be ok.
Also check the crank thread is ok.

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17 Oct 2018 12:24 #8 by Del Piero
Replied by Del Piero on topic How to trim a free flight biplane?
Thanks Quorneng. Great help.
Just as a matter of interest, what thread are the Indian Mills crankshafts, as I have a couple and I would like to be ready if a similar thing happens to their aliminium prop nuts?
Thanks a lot.

Del Piero.

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17 Oct 2018 14:59 #9 by Quorneng
Replied by Quorneng on topic How to trim a free flight biplane?
Del Piero
I don't have an Indian Mills but this site suggests it is 4 BA like the original.
It appears the threaded part of the Indian Mills crank shaft bends very easily indeed and if straightened to many times it simple snaps off!

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23 Oct 2018 02:34 #10 by one tenor
Replied by one tenor on topic How to trim a free flight biplane?
I have seen the broken shaft drilled and tapped to create a new shaft nose/thread. You can't see the join.

Anything will fly given enough power

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