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This is gonna be tough...

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This is gonna be tough...

Old 09-29-2010, 01:05 AM
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ptulmer
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Default This is gonna be tough...

I took a hawk silhouette and drew an airplane around it. It's more of a flying wing with an elevator. And it's gonna be tough to figure the CG! There is no telling whether I will build this next. A fellow club member wants to learn a thing or two about SWRs, so we may put our heads together for an afternoon build. Being one of the newly unemployed, time is all I've got. But I've got hand drawn plans of CP's original SWR and it's something I've wanted to build for a speed engine.

Sooo... what do you guys think of this with a surestart?
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Old 09-29-2010, 04:32 AM
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unclecrash
 
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Default RE: This is gonna be tough...

It looks birdy to me. I like it. Dan Savage over on rcgroups could cg it for you. He design edf jets and have helped out lots of people with cg issues.
Old 09-29-2010, 08:43 AM
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combatpigg
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Default RE: This is gonna be tough...

It looks like the CG would be a little bit aft of the spot where you show the wingtip seams meeting the leading edge of the main wing.
I've been thinking about a similar project but a little different. Capture a hawk or a eagle and rig up a harness to control it's head with a couple servos. It should work like steering a horse, it'll fly where it's head is pointed.
Once the bird gets all trimmed out and used to doing pylon laps, then the idea is to suit up little squirrel monkeys like jockeys to ride the birds around the poles..

so, you can see how we have basically the same idea going here........
Old 09-29-2010, 09:05 AM
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Mr Cox
 
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Default RE: This is gonna be tough...

How about retractable wings for a scale like dive...?
Old 09-29-2010, 11:10 AM
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ptulmer
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Default RE: This is gonna be tough...

CP, that IS very close to what I'm doing. It will surely pick up speed every time it turns back towards you. [sm=lol.gif]

Get this, those internal lines near the tips are the hawks wingspan. I extended it a bit for my own comfort. Those wingtip feathers must do a lot of stabilizing work! It also has a much shorter head than mine. And I'm probably going to need to move the engine out a bit further! How do they balance?! It's no wonder it took so long to invent manned flight. Working from birds would be extremely hard. They don't even have a vertical stab!
Old 09-29-2010, 11:15 AM
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Default RE: This is gonna be tough...

but they do have pretty impressive built-in gyros..
Old 09-29-2010, 12:51 PM
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Default RE: This is gonna be tough...

I actually built and flew a very similar design not that long ago. Was more of an eagle, but it handled just like a buzzard. Slow wheeling type flight.....yours may be a bit faster with less of a WS than mine. Flying wings need a slightly more aft CG...usually. I'd err in the aft direction and then move stuff forward as testing provides you with some data.

ZZ.

Was the loudest damn buzzard you ever saw though....lol! none of the others liked him very much.
Old 09-29-2010, 12:53 PM
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Default RE: This is gonna be tough...

If you watch birds in flight they flex the tip feathers to generate drag. They're using the same idea as the B2 drag rudders but done naturally. Also they twist their tail to some pretty radical angles to have a V tail like function but with one side only. All very complex and tough to do without a lot of controllers and built in high speed surface actuators (muscles)

Your birdie looks pretty good to my eyes other than the lack of side area. Some folks have gotten around that aspect by using a clear plastic belly or upper fin so it looks like there's nothing there in flight.

If the lines at the tips are your ailerons I think I'd suggest making the line run more span wise with the inner hinge line start at the mid span trailing edge break line and the outer hinge line about 1/4 to 1/3 up the tip curve. It'll work better at altering the wing tip camber and be a lot less likely to catch on grass and things and rip off during landings. And make the fuselage more tear drop shaped. Bird bodies are actually very wide for their length and a fatter more scale shape would help hide the engine.
Old 09-29-2010, 01:06 PM
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Default RE: This is gonna be tough...

With something that small just glide test to determine a workable CG.
Old 09-29-2010, 01:12 PM
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Default RE: This is gonna be tough...

Cutaway has a point. A little 8 to 10 inch version from some 1/16 sheet would soon find a balance point that is just barely stable, which is what you want for our style of flying. It would also quickly let you figure out how big of a clear cheater fin you need to achieve adequite yaw stability.
Old 09-29-2010, 04:54 PM
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Default RE: This is gonna be tough...

Bruce, you're a genius. There wasn't a fin in the drawing because I couldn't decide how to handle it looks-wise. I've got some plastic around here somewhere. This project just got more attractive! Plastic is pretty darn heavy, though. Hopefully it won't hurt it overall. My experience with flying wings is the opposite of ZZ's. CG's in the 10-12% range worked better. But even though the tail is small and short-coupled it may be enough to move it back. Toss-test it is!

One last thought on the vert stab. Do you think a bit of anhedral in the horizontal would reduce the size of the plastic vert?
Old 09-29-2010, 05:22 PM
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Default RE: This is gonna be tough...

If you go with swept wingtips [like a Taube] and angle them down somewhat, you should get away without using any vertical fin. I've got flying wings that have very small tip fins.
Are you using elevons, or elevator / ailerons?
On the tail, you could also trail and droop the outboard feathers to add some vertical area.
Landing speed will be slow, so the drooped parts are pretty safe with a strip of 2 oz cloth on either side of any angled glue joints.
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Old 09-29-2010, 06:53 PM
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ptulmer
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Default RE: This is gonna be tough...

Ahhh, I see what you mean. What do you think of these cut points? I definitely need to sit down and calculate the CG and make sure the tip area is behind it. A little trimming is going to be a must. But it's only a hundred sq in right now... The span is ~23"
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Old 09-29-2010, 06:55 PM
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Default RE: This is gonna be tough...

Either some anhedral and an upper plastic fin or some dihedral and a lower fin. One thing with the clear plastic is that it could be extended back behind the elevator so it can stay as small as possible.

The ideal material would be some lexan sheet. You could get away with a thin piece since it's so tough. Most plastics shops that deal with it should be able to sell you a scrap the size you need for a buck or two. Something in the .050 to .060 range would be aces.
Old 09-29-2010, 07:17 PM
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Default RE: This is gonna be tough...

That looks like a winner Patrick. You've got a very birdlike model there. It looks like you want it to be fast as well. If you can keep the weight under 10 ozs, that size will do OK, but if it's going to be more like 12 ozs you'll want 125 sqs, 14 ozs....150 sqs. A lot depends on how you rig it with hardware and equipment.
Old 10-01-2010, 11:13 AM
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JeffH
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Default RE: This is gonna be tough...

Are you going to install retractable feet?

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