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hgmckay
Joined: 23 May 2006
Posts: 397
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 Posted: Mon Mar 22, 2010 3:49 pm Post subject: Negative Flaps |
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When I built my Allegro 2000 E-LSA the instruction manual stated that the flaps in the "0" position (cruise) were to be four and one half degrees above the neutral position of the ailerons (I.e. a slight negative flap position). I have set my flaps this way. I have since seen other Allegro 2000 SALSA planes that do not have this negative flap position. In those planes ("0" flap position) the flaps are even with the ailerons in the neutral position. Which is correct? In what position do others have their "0" flaps set?
Hugh McKay
Allegro 2000
Rotax 912 UL
N661WW
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brad(at)vision-technology
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| Posted: Mon Mar 22, 2010 5:06 pm Post subject: Negative Flaps |
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As I recall mine are even with the ailerons. It may be nice to have a negative setting if that makes running at cruise speed a little more efficient. I'm not sure, however, that I would want to cruise much closer to Vne. There isn't a large margin as it is.
On a different subject... any Allegro owners near Spokane WA? I'm in town for a couple days and am always interested in catching up with other owners and seeing their planes.
Brad Kramer
Allegro N221FA
Bismarck ND
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jlhazen(at)copper.net
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| Posted: Mon Mar 22, 2010 6:13 pm Post subject: Negative Flaps |
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My factory built Allegro 2000 has -4.5 reflexed flaps.
Jim Hazen
N44469
From: Hugh McKay <hgmckay(at)bellsouth.net>
Sent: Monday, March 22, 2010 16:49
To: allegro-list(at)matronics.com
Subject: Negative Flaps
When I built my Allegro 2000 E-LSA the instruction manual stated that the flaps in the "0" position (cruise) were to be four and one half degrees above the neutral position of the ailerons (I.e. a slight negative flap position). I have set my flaps this way. I have since seen other Allegro 2000 SALSA planes that do not have this negative flap position. In those planes ("0" flap position) the flaps are even with the ailerons in the neutral position. Which is correct? In what position do others have their "0" flaps set?
Hugh McKay
Allegro 2000
Rotax 912 UL
N661WW
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aerosiam
Joined: 26 May 2008
Posts: 59
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| Posted: Tue Mar 23, 2010 1:01 am Post subject: Re: Negative Flaps |
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My 2006 Allegro has negative flaps. A few thoughts....
The design is for neg flaps. If the flaps are set 0, then about 5 degrees is added to the flap settings (unless the microswitch positions are altered). That means take off at 20 deg not 15 which may lengthen the run. Also full would be 53 deg which suggests the Vfe should be reduced. Are the hinges etc designed to allow for that extra force with 10% more full flap?
Neg flaps improve the performance by reducing drag ( exactly in the opposite way to having flaps down.) Climb, cruise, glide and economy will be better.
Althoug neg flaps are more associated with gliders, more SLAs have them such as the good-performance Virus and CT2
One downside is that neg flaps reduce the washout. In theory, the aileron span will stall earlier (in a clean stall) than the flapped span because it is at a higher angle of attack. In practice, the Allegro design has enough washout built in so this does not happen. However, I fitted vortex generators to my plane with closer spacing outboard and this noticably reduced the wing drop at the stall.
My suggestion is don't alter a basic design parameter.
Paul
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Thom Riddle
Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)
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| Posted: Tue Mar 23, 2010 3:54 am Post subject: Re: Negative Flaps |
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Brad,
Have you actually measured the flap position when set to "0"? When I owned N221FA I checked the flaps in "0" position and they looked slightly reflexed to me, but I didn't actually measure them. 4 1/2 degrees is pretty small amount visually on a short chord flap but enough aerodynamically on a clean airframe to make a difference.
If you decide to measure them, you might want to consider putting a little upwards pressure on them when measuring to take out the slack in the control system. Not sure which way the aerodynamic forces will push them in the "0" position but a little bit of slack would affect the measurement noticeably. Unless the manual says to make this measurement by comparing to the ailerons, I think it would be more appropriate to measure against the bottom camber of the wing just ahead of the flap. One reason for this is that the aileron rigging could be uneven from one side to the other for fine tuning of roll trim.
Thom
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Thom Riddle
Buffalo, NY (9G0)
Don't worry about old age... it doesn't last very long.
- Anonymous |
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brad(at)vision-technology
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| Posted: Tue Mar 23, 2010 8:01 am Post subject: Negative Flaps |
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Hi Thom,
Somehow I just KNEW I should ask you about our plane, instead of firing off answers when I'm in a hotel and not at the airport. You're right... 4.5 degrees is very little to see given the length of the flaps. So... Hugh, let me retract my answer and defer to others who have actually made some measurements.
Thom... hoping you make it to OSH. I'm 80% sure I'll be there working departure briefings and being a tent rat again. (Hopefully with the Allegro, instead of Delta Airlines).
...brad.
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Thom Riddle
Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)
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| Posted: Tue Mar 23, 2010 11:39 am Post subject: Re: Negative Flaps |
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Hi Brad,
Now my curiosity has been piqued. When you get back home and have a chance, it would be nice to know if your Allegro does have reflexed flaps as I suspect it does.
Without a digital angle instrument it is very easy to determine the reflex (if any) by simply measuring the distance from the top of a straight edge laid along the bottom camber of the wing up to the trailing edge of the flap. That divided by the chord of the flap gives you sine of the angle you are looking for. Arcsine of that number gives you the angle. It would not surprise me to learn that there is some difference between the two flaps because that is another way to adjust roll trim.
Thom
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Thom Riddle
Buffalo, NY (9G0)
Don't worry about old age... it doesn't last very long.
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ray
Joined: 26 Apr 2006
Posts: 6
Location: australia
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| Posted: Tue May 18, 2010 5:26 pm Post subject: Re: Negative Flaps |
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Hi
I built my plane about 2 years ago and set my flaps at 3deg neg, works fine. I believe that 0 deg would give you a little more lift in flight, more lift more drag, thats why they specify the neg degrees at the back of the wing.
Ray
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