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Old 02-18-2014, 10:40 PM   #1
pattern14
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Default Flaps on tailless aircraft

After retiring my last combat plane, I've been building a Lippisch Li 10, which was a contemporary of the Me 163 Komet. It is a swept wing (36 degrees) with a pusher prop, typical of the early 1940's German mindset. I've already flown it several time now, and it shows great promise as an all weather plane. The question is;

I want to fit flaps to it, as it currently has full length elevons. Is there a recommended length ( or formula) for flap size relative to the elevon? It snap rolls very well, and is extremely aerobatic; I just want to try something unknown, and possibly improve on landing in a restricted area. I fly on the beach regularly, and being able to bring it down quickly in light winds would really help. It tends to glide forever....It would be very simple to set up, and return to standard if not successful. Any advice is welcome
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Old 02-18-2014, 10:50 PM   #2
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The "flaps" will have a large pitch authority on a flying wing... you'd need to mix to the elevons to essentially have a "crow" setup. % relationship depending on sweep angle of the TE and relative areas of the surfaces.
This does give the effect you are after, adding significant drag to allow a steeper approach without building speed. It also makes the plane less likely to drop a wingtip in a stall.

I'd do a variation on the 4-servo sailplane wing mix, allowing flaps to follow the elevons, elevons oppose flaps.

When we did wings using separate elevator vs ailerons it was appx 60% aileron, 40% elevator in the center.

Experiment with LOTS of altitude... When you put flaps down the nose will go down.
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Old 02-18-2014, 11:01 PM   #3
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Very Interesting, I was Just wondering if you could mix flaps with elevator, flaps down and elevator up, that may keep the nose from going down and add a lot of drag to slow the wing down, with wings that dont like to slow down, i spiral them down in a circle to land, that seems to help a lot, Take care and have fun, Chellie

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Old 02-18-2014, 11:07 PM   #4
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Um, wouldn't lowering flaps on a flying wing be that same as 'down elevator'?

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Old 02-18-2014, 11:12 PM   #5
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Originally Posted by FlyWheel View Post
Um, wouldn't lowering flaps on a flying wing be that same as 'down elevator'?
Yes and i think you would need up elevator to counter it, hence, lot of drag to slow down IMHO with both.

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Old 02-19-2014, 01:13 AM   #6
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Originally Posted by pattern14 View Post
After retiring my last combat plane, I've been building a Lippisch Li 10, which was a contemporary of the Me 163 Komet. It is a swept wing (36 degrees) with a pusher prop, typical of the early 1940's German mindset. I've already flown it several time now, and it shows great promise as an all weather plane. The question is;

I want to fit flaps to it, as it currently has full length elevons. Is there a recommended length ( or formula) for flap size relative to the elevon? It snap rolls very well, and is extremely aerobatic; I just want to try something unknown, and possibly improve on landing in a restricted area. I fly on the beach regularly, and being able to bring it down quickly in light winds would really help. It tends to glide forever....It would be very simple to set up, and return to standard if not successful. Any advice is welcome
Hmmmmm Just an Idea, how about split flaps That open up and down at the same time Just my 2 cents worth see video below

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Old 02-19-2014, 01:22 AM   #7
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Old 02-20-2014, 01:25 AM   #8
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That's called 'crow', or a drag rudder and is used as an air brake, or individually as yaw control on a rudderless craft. Flaps are used to reduce the stall speed, not just reduce speed or control yaw.

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Old 02-20-2014, 02:57 AM   #9
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Crow is flaps down with ailerons (elevons) up

Split flaps come in 2 'flavors" Fixed upper surface and the upper surface moving opposed to the lower for dive brakes. (As on the SB2C Helldiver)

Split ailerons typically get used for airbrake effect (As on the A-7 Corsair II) and occasionally for yaw.

Several years ago RC Pattern competitors were experimenting in split rudders for airbrake. Mixed results generally seen as not worth the weight when the planes have a hard time meeting the 2 kg (11 lb) max allowed in competition.
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Old 02-20-2014, 03:15 AM   #10
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If you wanted to get fancy, you could try adding slats. not sure how that would work though.

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Old 02-20-2014, 05:33 AM   #11
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With this style of body you will only be able to use min flap degree. With to much flaps you will get a ballon affect when flaps are lowered to heavy. This affect will make it hard to land in small areas quickly. I see some sail plane set ups to be abetter choice on a min base say 15 degrees to start and go up slowly from there.
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Old 02-20-2014, 12:04 PM   #12
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The real Me163 had flaps, so if it were me I'd copy the design from those used on the real one. the flaps were unusual in that rather than being mounted at the trailing edge they were on the centre of the wing, close to the CG. This was no doubt to minimising any pitching effect.

here's a photo:


I'd avoid the idea of using crow because if you did you would end up running out of up-elevator and aileron authority. Your elevons would already be fully up just to offset the downward pitch caused by conventional flaps, leaving little available movement for elevator or roll control.. A sure recipe for a crash if you ask me!
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Old 02-20-2014, 12:29 PM   #13
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Mixing flaps to follow elevons would leave elevator authority available. The flaps would come up as you pulled more.

Ailerons work fine in crow mode on sailplanes. I don't forsee a problem there.

I'm not sure... but the 163 picture looks like they might have mixed up "elevons" with the flaps even with the more forward split-flap location. We'd need a tail-on view with those flaps down to verify it, since that could just be the yoke hard over to the right.
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Old 02-20-2014, 12:41 PM   #14
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It's hard to compare a conventional sailplane with a tailess.

Ailerons on a sailplane work in crow because you can lower one of the ailerons, causing a bank, and losing only a little drag. If you tried that on a tailless the model would dive when you lowered the elevon with potential disasterous results.

If you used worthwhile flap angles then the elevons would inevitably end up virtually hard up against the stops. Maybe with complex mixing you could get something to work, but it would be very hit or miss.

IMHO following the method used on the full size plane would be the way to go. The same idea with flaps located mid-chord at the CG position is used on other tailess and delta wing aircraft, the Gloster Javelin being an example I can think of right away. The simplest solution is usually the best:
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Old 02-25-2014, 10:38 PM   #15
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Thanks for all the feed back everyone I'll try several configurations and see what works best. Being an all EPP and tape finished combat plane makes this kind of experimenting painless, so I should be able to get away with sorting things out and not destroying the plane cheers...
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