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Jun 13, 2007, 09:34 AM
Registered User
Quote:
- instead of the "airfoil only" best L/D ratio I think that the whole wing L/D ratio must
be taken into account. The influence of induced drag is not neglectible so the optimum camber is depending of the aspect ratio and is lower than expected with an X-foil analysis only.
Yes. But you want to use a turn CL which gives the fastest lap time. This is not necessarily the same as the CL for best L/D in the turn. My simulations indicate that the best CL is approximately 0.4 to 0.6, depending on the level-flight CL and the aspect ratio. Once the best CL is chosen, then picking the best turn camber is only a 2D airfoil problem.

Quote:
- I am always surprised by static margins of 10% or more because the real margin that we can measure on F3B or F3F planes are close to 0%. Our plane are very neutral.
I think that a margin of 10% is evaluated from a calculated neutral point.
If the airplane has a significant amount of dihedral, like my Supra, then the neutral point location and hence the static margin also depends on the CL. At high speed (low CL), the airplane is almost neutral. But at low speed (high CL), it is relatively stable. This effect of dihedral is difficult to predict using classical methods, but AVL can do it relatively easily.
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Jun 13, 2007, 02:41 PM
Registered User
<<< Yes. But you want to use a turn CL which gives the fastest lap time. This is not necessarily the same as the CL for best L/D in the turn. My simulations indicate that the best CL is approximately 0.4 to 0.6, depending on the level-flight CL and the aspect ratio. Once the best CL is chosen, then picking the best turn camber is only a 2D airfoil problem.>>>

I agree with you. My simulations give also an optimum Cl around 0.4 to 0.6 (of course very depending of wing loading). But it is supposed that the turn is perfectly anticipated. I am not such a good pilot, optimum Cl may be higher when the anticipation is not so perfect.

I am not used to AVL . Does AVL take the fuselage lift into account ?

Thierry
Jun 13, 2007, 07:10 PM
Registered User
Hi Guys
I have some of questions with regard to snap flaps. Not sure if it's been answered in the forum.
1. I have 4 wing servos, do I setup snap flaps for all the control surfaces or just the flaps?
2. Snap flaps goes down when elevator goes up, but what about elevator goes down do you add reflex?
3. Do you have deadzone on elevator or the moment you move elevators the flaps move?

Thanks
Jun 13, 2007, 07:30 PM
Detail Freak
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Quote:
Originally Posted by chiadennis
Hi Guys
I have some of questions with regard to snap flaps. Not sure if it's been answered in the forum.
1. I have 4 wing servos, do I setup snap flaps for all the control surfaces or just the flaps?
2. Snap flaps goes down when elevator goes up, but what about elevator goes down do you add reflex?
3. Do you have deadzone on elevator or the moment you move elevators the flaps move?

Thanks

1. All the surfaces, some like the ailerons set a bit less.

2. I don't. Some do, but I think it is more for aerobatics.

3. Some like a dead zone where the elevator moves a bit before the snapflap comes on, and some like the snapflap to be all in before the elevator sick is all the way back.

Target
Jun 13, 2007, 10:57 PM
Registered User
I think I'll stick to TE (Trial and Error) or KT (Keep Tweeking) method.
Jun 14, 2007, 09:35 AM
Registered User
Quote:
optimum Cl may be higher when the anticipation is not so perfect.
True. But the choice of CL in the calculation has very little effect on the best amount of snap-flap mixing.

Quote:
I am not used to AVL . Does AVL take the fuselage lift into account ?
It uses slender-body theory. But the effect of the fuselage on lift and moment is almost negligible. On the AVL Supra model, adding the fuselage shifts the neutral point forward by 0.9mm. This is for any chosen CL. On a non-pylon wing mount the effect will probably be stronger, but still very small I think.
Jun 14, 2007, 03:04 PM
Registered User
<<< True. But the choice of CL in the calculation has very little effect on the best amount of snap-flap mixing. >>>

I suppose you want to say a very little effect on dCamber/dElevator ?

Thierry
Jun 27, 2007, 07:26 PM
Just chillin @ 403 MPH
Jantar2A's Avatar
every plane I've flown takes a diff amount of snap flap,,,#'s might get ya close,,but in the end you will be tweeking by trial and error..

Nick
Jun 28, 2007, 03:15 PM
Chuck it and see!
Wing-span's Avatar
Does anybody out there not use snap flap (in F3F) and feel they are not at a disadvantage?
Jun 28, 2007, 06:45 PM
around Colombia
ShredAir's Avatar
Quote:
Originally Posted by Wing-span
Does anybody out there not use snap flap (in F3F) and feel they are not at a disadvantage?
Why do you ask? Do you think that snap flap is over-used and over-rated and that we should focus more on basics such as CG and decalage?
The thread is titled "how much and why." So far we have posts responding to the how much. Would anyone wish to address the why?

Dieter Mahlein, ShredAir
Apr 22, 2014, 11:04 PM
Eagle Butte User
PDX Slope Pilot's Avatar
Here's a great topic I just had to dig up from the RCG record files. Still an interesting topic and I'm curious if there are other practical, plain speak thoughts out there on dialing in elevator to camber throw or snap flap. I'm no engineer so some of the academic discussion on the subject matter is hard to wrap my brain around.

From what I can gather from reading posts by the experts - elevator to camber mix should be linear and at a 1:1 ratio. Here's my question. What's the best process or steps one should take to get to that point? Do you first adjust elevator then start dialing in elevator to camber mix then slow back off on total elevator throw ? Because as you dial in more camber you need less elevator, etc. Then fine tune until total elevator throw equals total camber throw?

R,
Vic
Apr 23, 2014, 08:09 AM
Detail Freak
target's Avatar
Snapflap is what really makes planes work in F3F. I think most people use either to much of it, our to much elevator and too much snapflap.
And the planes will happily fly tight corners setup that way, but what happens is the plane shows more in the turn, and you'll lose some speed without realizing it. That's when you back off on the elevator throws, which usually reduces snapflap also, on most tx's. This is what I do anyway.
Often the tightest turn doesn't equate to the fastest run time, all things considered. Things like ballast come into play as well. More ballast requires a more open carving style turn, IMO.
As stated above by a few, trial and error come into play. Just remember that to much deflection of surfaces is more drag usually. Not enough can be disastrous on a lip slope. It's a balance you need to find for your style.
Apr 23, 2014, 08:42 AM
Registered User
Avaldes's Avatar
I miss Tom Copp. His posts were awesome and his support of the hobby was great!
Apr 23, 2014, 08:48 AM
F3B
satinet's Avatar
Is he just out of the hobby or what? He was a good rcgrouper.
Apr 23, 2014, 08:59 AM
Registered User
Avaldes's Avatar
Yes, I have not seen Tom at an event in a long time. I know he is working a LOT. Did not mean to imply any health issues...at least none that I am aware of!


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