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Old Nov 18, 2012, 08:21 PM
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snap flaps

Ok, so i was curious how you guys use snap flap mixing (elevator to camber). Is this something that would be used for normal flying? I have been flying with a small amount of mix, I don't have any issues just wondering what is better. I figured that with alittle mix it would require less elevator to get a certain pitch effect. With that thought I figured that flying with alittle ele-camber mix would create less drag then having to use more elevator to get the same pitch effect. So, am I on the right path or way over thinking things?
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Old Nov 18, 2012, 08:51 PM
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It's not about getting a quicker change in pitch. For normal, thermalling use, it's a way of adding camber for thermalling. Steep banked turns mean more lift needed to maintain flight, you usually hold up elevator in a steep turn so you get that. Another thing you get from it is a lower stall speed so the plane handles better, less chance for goofing up.

Dennis
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Old Nov 18, 2012, 09:48 PM
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I've only played around with it a little bit on the slopes, and haven't done much experimenting with throws. Perhaps I had too much flap mixed in, but with bank and yank flying, it tremendously reduces the turning radius for high-G turns, yet with a notable slow-down. In other words, it initiated the turn vastly quicker (sayyy, up to the first 90° of a 180° turn) but it also slowed down notably during the second half of the 180°. A bit of flap travel reduction did help, but I didn't care at all for how it flew whilst not bank/yanking.
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Old Nov 19, 2012, 10:55 PM
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Some (IMHO most) planes benifit greatly from snap flaps. The biggest difference I have felt is DS'ing a Destiny. They and I think most slope rockets turn harder with snap flaps. The added camber increases the wing AOA and takes some load off of the elevators. Many of the DLG guys are also using it for the reasons stated above.
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Old Nov 20, 2012, 05:00 AM
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Woodstock 1's Avatar
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Quote:
Originally Posted by txg8gxp View Post
Ok, so i was curious how you guys use snap flap mixing (elevator to camber). Is this something that would be used for normal flying? I have been flying with a small amount of mix, I don't have any issues just wondering what is better. I figured that with alittle mix it would require less elevator to get a certain pitch effect. With that thought I figured that flying with alittle ele-camber mix would create less drag then having to use more elevator to get the same pitch effect. So, am I on the right path or way over thinking things?
Your'e on the right path (although I'm not sure about the drag differences).

It's not about adding camber to get added lift - it's all about angles of attack and stuff that I can't remember ...

One of the most useful things I find with snapflap is in a plane that is set up with as near a neutral CoG as possible, you start approaching the conditions where too much elevator input can cause a vicious snap / spin (particularly with the somewhat nervous V-tailed racing planes). Snapflap allows you to limit the elevator travel right back so as to prevent that scenario, but to then still keep a decent pitch response.

Chris
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Old Nov 20, 2012, 06:11 AM
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I've never thought of snap flaps that way, interesting. I use snap flap in an F3B plane for the speed task and have always just thought of it as a way of preventing a snap/spin from an accelerated stall if I pull a tight turn. I prefer to carve a turn without any flap and I have s/f set on programmable mixes so it doesn't come in until after 7/8 stick travel. So, it gives protection and an increased pitch control, how about that.

Dennis
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Old Nov 20, 2012, 08:05 AM
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I might owe you an apology Dennis: I have never thought of snap flaps in a thermal context. I see in other places that is mentioned also. I just know that many moons ago I was severely chastised for mentioning anything about "increased lift" in connection with snap flaps. As I said, I forget the rest, but it was a long thesis all about angles of attack and stuff that I'm too lazy to get really excited about ... I just stick with what I find works for me !

Chris
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Old Nov 20, 2012, 05:09 PM
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The reason for using elevator to camber mixing is to minimize the drag for a given Cl. Cl is a function of the angle of attack and camber. For a given Cl, the airfoil has a camber setting that provides the lowest drag. So, by using elevator to camber mix correctly, you ensure that the wing is generating the desired lift as efficiently as possible (lowest drag). Fortunately, it works out that the correct ratio of elevator to camber is fairly linear for most modern airfoils so it is relatively easy to set up. For a typical F3B model, for every mm of elevator movement there should be around 1 mm of camber movement. This goes for both up and down (positive camber for up elevator and negative camber for down elevator). The ratio for camber/elevator is actually a little less than 1, but when you include compliance of the linkages, the 1 to 1 ratio works out to be about right.

Note that when you start using elevator to camber, you don't need as much elevator throw to get the desired result (as the OP suggests). I think this is why some people write elevator to camber mixing off - they use the same throw and pull the same and the model turns tighter for the same input creating a higher Cl and the model slows down more than it did for the same elevator deflection without the mix. If you compare the same turn radius with and without the mix, you should find the turn with the mix to be cleaner.

I use elevator to camber mix for all flight modes (except launch and landing) and it is on all the time.
FWIW
Tom
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Old Nov 20, 2012, 11:36 PM
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I agree but must ask if this is as true for slow thermal flight as it is for high speed flight? I have used the mix for my DLG's and I don't know if I feel much difference. With the higher speed slope ships and even lead sleds you can feel the difference.
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Old Nov 20, 2012, 11:46 PM
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alot of great points, Thanks guys
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Old Nov 20, 2012, 11:46 PM
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Good question.

Of course, the faster a plane goes, the greater the effect of its surfaces.
Previously, I hadn't even considered "snap-flaps" for slower flight.

Hmmm...Methinks I'll be re-visiting my mixes and tune (reduce) the throws and experiment.
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Old Nov 21, 2012, 12:30 AM
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Quote:
Originally Posted by davidjensen View Post
I agree but must ask if this is as true for slow thermal flight as it is for high speed flight? I have used the mix for my DLG's and I don't know if I feel much difference. With the higher speed slope ships and even lead sleds you can feel the difference.
Yes, it is true for slow speed flight as well. The difference is the ratio may be a bit different if you are using a camber preset. So if you have some initial camber you might not need as much elevator to camber mix. I haven't looked into the exact ratios. I typically use the same 1 to 1 ratio with good success in my thermal mode which may have 2 to 4 mm of preset camber. The nice thing about using the elevator to camber mix is you don't need to have camber on a slider. The camber is automatically tuned appropriately with elevator input.

Tom
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Old Nov 21, 2012, 06:16 AM
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Someone who knows way more about this than I do, asked me the perfect question, "...which wing do you want doing the work, the small one or the big one, especially with respect to reynolds number." And that is how I look at it, I do set it up so that very small elevator throws do not have the mix, but at about 20% throw, it kicks in and as Tom said, by dumb luck in my case, I had about that 1:1 ratio and I really like it.

Marc
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Old Nov 21, 2012, 07:50 AM
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Originally Posted by Kiesling View Post
The reason for using elevator to camber mixing is to minimize the drag for a given Cl. Cl is a function of the angle of attack and camber.
Tom
So, what IS CI? I'm trying to get my head around this...

Chris
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Old Nov 21, 2012, 12:52 PM
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So, what IS CI? I'm trying to get my head around this...

Chris
Cl = coefficient of lift
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