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mikenjulie.parkin(at)btop
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 Posted: Sat Jun 23, 2007 10:49 am Post subject: Tailplane flutter & trim |
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Mark,
I think you have some false assumptions in your message. The increase in
forward stick force to maintain the high speed/dive is because more
tailplane 'leading edge up' is required to counter the increase in mainplane
lift - if you don't hold the forward stick pressure, plainly, the nose will
rise. Aircraft decellerates and the required forward stick force will
reduce.
It follows then that the required tailforce in high speed flight is the same
whether the aircraft is in trim or not - if the speed and aircraft attitude
are to remain the same. The actual way the tailplane generates the required
force will be slightly different because in one situation the tail is
positioned by a constant control input force, while in the trimmed situation
the force (for want of a better word) is provided by the trim tabs. The
real academic answer is probably too complex for me, but I am sure our
aerodynamicists could enlighten us.
By holding a control force the only slop that is being countered is that
from the cockpit to the torque shaft horn. I think that flutter is an issue
between the aerodynamic centre of pressure, the centre of gravity of the
control surface and its hinge line. I think that slop in the control system
leading back to the tailplane is largely irrelevant.
As far as trimming out the aircraft at high speed, it is a non event - old
habits die hard - and I always fly the aircraft in trim within the
capabilities of the trim system itself. I consider that doing a Vne test
holding a huge forward stick force presents a few problems, not least of
which is the possibility of a PIO developing. It is not the way to fly any
aeroplane.
(my 2 cents worth, for what its worth)
regards,
Mike
Do not archive.
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Mark Burton
Joined: 10 Jan 2006
Posts: 74
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| Posted: Sat Jun 23, 2007 11:16 am Post subject: Re: Tailplane flutter & trim |
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Mike,
The way I see it, either the trim tab provides the force or the pilot does through the stick (or a combination of the two).
If the pilot provides some force, that force goes all the way from the pilot's hand to the tailplane - all slop will be taken out while the pilot is pushing.
If the trim tab provides the force. The tailplane is "balanced" and so no force is needed through the control system and the tailplane will "float" compared to the pilot's hand and all the sloppy parts will clunk about.
Your point about PIOs is good.
Cheers,
Mark
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rlborger(at)mac.com
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| Posted: Sat Jun 23, 2007 11:59 am Post subject: Tailplane flutter & trim |
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Fellow Europaphiles,
If the tailplane moves outboard and disconnects from the TP14 pins something else happens that's very bad. The anti-servo/trim tab comes free from the control "T" rod. You now have a free-floating tab hinged on the front edge with CG well back from the hinge. You now have the perfect setup for a fluttering trim tab. Matter of fact, it will probably flutter at a much lower speed than you might expect. Flutter the tab and you are surely going to flutter the stab. We all know how powerful the stab is. You will have to make the aircraft get real slow real fast or it's going to come apart. Maybe you can't even get slow enough to stop it.
Good building and great flying,
Bob Borger
Europa Kit #A221 N914XL, XS Mono, Intercooled 914, Airmaster C/S
http://www.europaowners.org/N914XL
(90%) tail kit done, wings closed, cockpit module installed, pitch system in, landing gear frame in, rudder system in, outrigger mod in, Fuselage Top on, lift/drag/flap pins in, wing incidence set, tie bar in, flap drive in, Mod 70 done. Baggage bay in. Flaps & Main Gear complete. Mod 72 complete. Instrument panel complete, except for testing. Rotax 914 installed (for the 3rd time). Airmaster Prop installed. Electrical complete, except for testing. Fuel system complete except for testing. Working in - 32 Tail, 34 Door Latches & 35 Doors, 37 Interior & Finishing. Airmaster arrived 29 Sep 05. Seat arrived from Oregon Aero. E04 interior kit has arrived and is being installed.
3705 Lynchburg Dr.
Corinth, TX 76208
Home: 940-497-2123
Cel: 817-992-1117
[quote][b]
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