Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

My new and improved wing is RTF (Take 3)

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Old 10-21-2009, 06:40 PM
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Mike Connor
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Default My new and improved wing is RTF (Take 3)

Rib caps did add a couple of hours to the build time but it was still an easy scratch build. While the rib caps did add strength and stiffness, making the equipment compartment a part of the airframe made it very rigid. Maybe it will hold together well past 100 mph.

The airframe ended up at 14.5 oz and the RTF weight is under 2.75 lbs. Not too bad for 500 sq in. and a 42 in. wingspan

Maybe a maiden this weekend if I can get my crew together. Hopefully I will catch any excitement on video.
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Old 10-21-2009, 06:43 PM
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Default RE: My new and improved wing is RTF (Take 3)

WOW! I looks like it's already doing a 100 mph![sm=thumbup.gif][sm=thumbup.gif]
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Old 10-21-2009, 07:09 PM
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Default RE: My new and improved wing is RTF (Take 3)

That does look like a fast plane! Did you need to take out an electrical permit?
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Old 10-21-2009, 07:48 PM
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Default RE: My new and improved wing is RTF (Take 3)

When the motor system is wired with 3/0 cable you know there is some serious power happening.

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Old 10-21-2009, 08:20 PM
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Mike Connor
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Default RE: My new and improved wing is RTF (Take 3)

No electrical permit needed but the battery is capable of 120 amps continuous and 160 amp burst. The $60 motor is the limiting factor here but I should be able to push it around 1100 watts (about 1.5 hp) for a short period.

Actually those are 10 AWG wires but that is big enough to be a pain to solder.
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Old 10-21-2009, 09:49 PM
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Default RE: My new and improved wing is RTF (Take 3)

Looks real good, good luck with it!
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Old 10-21-2009, 10:17 PM
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Mike Connor
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Default RE: My new and improved wing is RTF (Take 3)


ORIGINAL: iron eagel

Looks real good, good luck with it!
Thanks, hope I do not regret not following more of your suggestions. [:@]
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Old 10-21-2009, 10:35 PM
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Default RE: My new and improved wing is RTF (Take 3)

Looks great Mike.
One comment, If you are thinking about anything near the battery capacity I would change those Deans plugs(?) to 6mm bullets
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Old 10-22-2009, 08:01 AM
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Default RE: My new and improved wing is RTF (Take 3)

He might need the voltage drop to keep the wings on..
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Old 10-22-2009, 10:10 AM
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Default RE: My new and improved wing is RTF (Take 3)

The Deans plugs are not the only thing that would have a melt down if I ran the battery at capacity. [X(] But they do keep you from plugging things in backwards.
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Old 10-22-2009, 01:57 PM
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Default RE: My new and improved wing is RTF (Take 3)

Niiiice plane Mike

You can always use two Deans in parallel.
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Old 10-22-2009, 04:49 PM
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Default RE: My new and improved wing is RTF (Take 3)

Two 6mm plugs on battery side use a female on red and a male on black - no chance for mistake - (as long as you don't plug the battery into itself - but we are smarter than that, arn't we?) Which ever way you decide make it the fleet standard.

I hate deans[:'(] The only thing good about them is the price. How many times I have tried to pull them apart inside a fuse and theyfinally let go and you break the plane or run a pushrod into your hand.

But they would be up to the task of a fuseable link, indeed.
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Old 10-22-2009, 11:06 PM
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Default RE: My new and improved wing is RTF (Take 3)


ORIGINAL: RocketRob

Two 6mm plugs ...I hate deans[:'(] The only...
My electric fleet is one so changing my standard wouldn't be too hard. Your bullet connector scenario sounds pretty good but 4mm would probably be fine for my setup. You could heat shrink the two battery wires together so you couldn't set off the fireworks. I noticed that over time the bullet connectors on my motor are showing a small amount of metal where they plug together.

I didn't like Deans at first but now they seem ok. My setup allows me to pull the wires out of the fuse to connect and disconnect.
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Old 10-24-2009, 11:56 PM
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Default RE: My new and improved wing is RTF (Take 3)

I did get a 5 minute maiden in today and the airplane came home in one piece. While the launch and flight characteristics through 100+ mph were good, there were some problems at higher speeds. Despite my mods to stiffen the airframe, there was a high speed oscillating wing twist that was obvious from the ground. There was significant outer wing movement at a frequency too fast to count but still visible to the eye. The entire airframe was probably flexing to some degree allowing the motor to work it's way 3/4" forward in a tight clam shell motor mount.

I hate to give up on the project at this point because of all the pluses but not sure why this design is doing this and what I need to do to correct it. I think it will take more then just extending the spars out or something simple like that. I may throw this problem to the guys in aerodynamics to see if they have any thoughts to WHY. Any thoughts from anyone here is also very welcome. I may end up with a park flyer that looks like it should go fast. []
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Old 10-25-2009, 12:12 AM
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Default RE: My new and improved wing is RTF (Take 3)

Mike, I've been against notching the spars at all..putting filler back in is no substitute, I don't think.
You're concern with thickness might need to be relaxed a little. Remember that the observations of some say that a certain amount of thickness is OK, the important thing is the smoothness of the shape with the fewest imperfections. We still want thinness, but you might have reached the point where the whole wing was flexxing/ fluttering? If you run out of options, more glass work on the surface should stiffen it up more.
The wing has to be able to keep those wingtips stationary, too..
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Old 10-25-2009, 12:28 AM
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Default RE: My new and improved wing is RTF (Take 3)

the winglets are your issue, unless you are totally anal, and are willing to use extreme measures to make sure the winglets are in perfect aligment you will have this oscillation, the simplest solution would be to chop them off and use a single rudder fin in the center FWIW
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Old 10-25-2009, 12:29 AM
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Mike Connor
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Default RE: My new and improved wing is RTF (Take 3)

It would seem that thicker wings are just full of air but I guess you must consider the leverage advantage of the rib caps and skin.
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Old 10-25-2009, 12:35 AM
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Default RE: My new and improved wing is RTF (Take 3)

I think there is a point with thickness where you don't improve the drag reduction enough to justify the built in weaknesses. The surface area drag remains the same and all those air molecules might actually like clinging to a long, flat surface better than one with a "crafty shape"?
The air doesn't meet all the head on view "frontal" area at once like hitting a wall, so a good flowing design has a way of diminishing the effects of some of that frontal area. The drag formulas could only ask you to assign an arbitrary number to reflect that. If what you experienced today was excessive wing flex, a sharp eye while doing some head on looping will reveal that.
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Old 10-25-2009, 12:48 AM
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Default RE: My new and improved wing is RTF (Take 3)


ORIGINAL: lfinney

the winglets are your issue, unless you are totally anal, and are willing to use extreme measures to make sure the winglets are in perfect aligment you will have this oscillation, the simplest solution would be to chop them off and use a single rudder fin in the center FWIW
Most flying wings use winglets without problem and it does help with the vertical fin volume coefficient numbers. Moving the fin to the center would be a lot of work but moving them in some woud be fairly simple. I was thinking that mid way out the fin could be used to also stiffen the wing much like the equipment compartment did in the center.
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Old 10-25-2009, 12:53 AM
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Default RE: My new and improved wing is RTF (Take 3)

cp, The flat plate was as much for building simplicity as it was for frontal area. I may need to go with a real slightly thicker airfoil
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Old 10-25-2009, 01:06 AM
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Default RE: My new and improved wing is RTF (Take 3)

Mike, if you can put a wing tip between your knees and twist the other tip with your hands [and using little effort], it's probably met it's match for the power you put on it.
I agree that the outboard fin allignment is critical, it needs to be very well supported too. It can act against the wing if the wing is too flimsy.


























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Old 10-25-2009, 10:26 AM
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Default RE: My new and improved wing is RTF (Take 3)

The winglet is supported with tri stock on the inside base and the alignment is perfect by my ability to measure. While most of the winglet seems very rigid, the sweep does allow a small area of vertical grain balsa at the top rear to flex with little effort. That area should probably be laminated with 1/64 ply or horizontal grain balsa.

My thoughts at this moment is to move the winglets in to the first rib out from the wing taper change. This should make the wing much more rigid. Or I could just add something that looks like a wing fence at that location to stiffen it up and use it for a landing skid.
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Old 10-25-2009, 10:34 AM
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Default RE: My new and improved wing is RTF (Take 3)

Since you've got a throttle, you'll be able to observe it up close to get a better impression about what's going on. If you knocked some height off the fins and the problem changes, then you might get some idea about which way to go........
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Old 10-25-2009, 12:04 PM
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Default RE: My new and improved wing is RTF (Take 3)

ORIGINAL: Mike Connor

I did get a 5 minute maiden in today and the airplane came home in one piece. While the launch and flight characteristics through 100+ mph were good, there were some problems at higher speeds. Despite my mods to stiffen the airframe, there was a high speed oscillating wing twist that was obvious from the ground. There was significant outer wing movement at a frequency too fast to count but still visible to the eye. The entire airframe was probably flexing to some degree allowing the motor to work it's way 3/4'' forward in a tight clam shell motor mount.

I hate to give up on the project at this point because of all the pluses but not sure why this design is doing this and what I need to do to correct it. I think it will take more then just extending the spars out or something simple like that. I may throw this problem to the guys in aerodynamics to see if they have any thoughts to WHY. Any thoughts from anyone here is also very welcome. I may end up with a park flyer that looks like it should go fast. []
Mike,
I think your major issue is structural, but I will not dismiss issues caused by skin effect or airfoil shape entirely at this point.
I think your planeform is an excellent idea, and I have no doubt that it is way more than any parkflyer, so don't give up on it yet!
The fact that your wing is twisting tells me from a structural perspective that it is not stiff enough, and all you need do is give it some Viagra...
I still think that the LE must extend from the wingtip to the fuselage/battery box in one piece, with the front delta portion joined to it.
The spars do not carry much if any load I would eliminate them (and their weight) and go for a stressed skin approach. The spar being in the center of the wing does little or nothing for you strength as the drawing I have included shows graphically how the bending forces work in a piece of wood, but are present in the structure as well.
I would at this point go with a 3/32 skin, loose the spars, extend the LE from the wingtip to the fuse, and bring the LE and TE stock up to 1/2 X 1/4 to allow for more aerodynamic shaping to both the LE and TE as well.
Another consideration would be to taper the wing from the root to the tip (No big deal without the spars), this will stiffen the wing as well by laying the sheathing so they form a triangle shape out at the wing.
This would cut your frontal area of the wing by 50% as well. Granted a lot of work (not as much as capping the ribs was (which I would still do) but you wont have to deal with the spars at all.
This would put the grain of the sheathing into play to stiffen up the wing much more than your spars ever will. If you wanted to get real involved you could use some 1/2 oz glass on the entire exterior and rather than use covering, paint it.
I really don't get the feeling the winglets are the real issue, but they might be, I still think it is structural at this point.
Like CP says a little thicker is not all that bad of a thing, and he is right notching the spars is not my first choice either but the back of the wing exploding was an issue before, but you have resolved that one problem. I am fairly certain you got up to at least what your VNE was in the prior version, and it did hold together enough so that you could see something happening, so you are making progress.

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Old 10-25-2009, 12:45 PM
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Default RE: My new and improved wing is RTF (Take 3)

the way i have seen these wings flutter is the elevons fluttering applying torque to the airframe and an things amplify.. i'd stiffen the rons with carbon tape.. perhaps move the servos out midspan... perhaps diagonl strapping tape like the foamies use....
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