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Old Dec 02, 2003, 04:00 PM
AustinTatious
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Hurst, Texas, United States
Joined Jul 2003
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Got me Bushnell Radar gun!

I finally got my bushnell speedster. We had a crummy day to try it out. Wind was light and glancing hard. The M60 was barley gettin around and we were guessing around 20 moh speeds. We were surprised to see speeds up to 45 mph when the plane was jsut crawling. We have been estimating speeds in good conditions to be around 100. We did a few bungee launches and at a 10 degree angle got a 90 mph reading off the line. We regularly flutter the m60 while DSing so at this point we are pretty certain we are clearing 100 mph with it. cant wait to clock it when the winds are good.

A quick Q... I have been told the radar works better when the plastic lens is removed. If this is correct, which lens? There is a tinted outer lens and then a thick domed lens inside that one. I tried different configurations and even with no lenses the speed is accurate, however what will give me the best sensitivity?
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Old Dec 02, 2003, 06:03 PM
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Newcastle Australia
Joined Nov 2002
894 Posts
I have heard about people just taking the tinted lens off to give you a tiny bit more range.

Interesting you say you have had your M60 Fluttering.

I would like to start a thread for this and invite you to explain your experiences. Please Consider.

I like my bushnell too and have clocked a 54" Electron at 100mph. It had a lot of legs left in it too. With no hint of any instability or control surface distortion.

Keep up the good speeds.
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Old Dec 02, 2003, 06:47 PM
AustinTatious
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Hurst, Texas, United States
Joined Jul 2003
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Ohh yea, we flutter it regularly. I would like to mention as i have before, The guy who built this M60 is very meticulous. I am sure he followed the instructions to the T and probably did a little more as far as structure is concerned. Its hard to see Exactly what flutters first because the thing is screaming, it apprears the whole wing flutters and not jsut the elevons. We got into a long discussion about how to make the wing not flutter by adding weight along the leading edge to make the whole wing dynamicly stable. The problem is that the CG is being forced forward only at the fusalage, the length of the wing has an aft cg if you remove the fuse. This is no biggie if your wing is REALLY rigid. But if your wingis kinda flexable then eventually it will flutter from the tips having an aft cg. They will try to "peel" up and aft. If you weighted the length of the leading edge of the wing so as to balance the wing at the proper cg WITHOUT the fuse being attached, then you could prevent the tips from trying to "peel" and thus eliminate flutter of the wing.. ailerons are in need of this balancing too.

This is a difficult concept to grast especially without an in person demo or run down.. Imagine taking a bare wing with no fusealage(model A) and holding it by the tip and swinging it around yourself. What will happen? it will wither pitch upwards or downwards voilently if you turn fast. Now lets say you add a fusalage/pod and balnce the plane properly(model B). Now the plane has a good cg. Spin around fast and it will track well and not pitch up or down violently. The fuse is forcing the cg of the wing forward, BUT only at the center. You are relying on the rigidity of the wing to carry that CG outwards to the tips and prevent them from fluttering. The tips however try to behave like the entire "model a" which tried to pitch violently. If you were to first balance the entire length of the wing to the proper cg, then add your "pre balanced" fusalage, you would have a wing that woudl be VERY flutter resistant.

To the guys Breaking records and snapping wing roots, Why not add balast out at the leading edge tips of your wings, this would prevent flutter as discribed above, and also it would reduce the bending load at the center of the wing and prevent it from folding. think about it.. if needed ill explain that one further.
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Old Dec 02, 2003, 07:39 PM
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Lakewood, Colorado
Joined Aug 2002
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You don't add weight at the tips of the wings because
1. it screws with your yaw inertia which means much slower yaw damping when going through ugly shear, and it makes low speed maneuvering a real bear.
2. it's not the strongest part of the wing, nor should it have to be.

I'm not sure I'm buying the whole wing flutter thing as the maiden of a 4 servo M60 managed 116mph and fatboywings is claiming he's fluttering it at 90mph. I know I've had my 2 servo M60 faster than that, by a lot. If there's a problem here, it's gotta be starting in the elevons, and meticulous build or not, I still often see a little bit of play in the servo arms/horns/pushrods which needs to be addressed first. If the play is absolutely eliminated, then going to 4 servo wing is the next step, and that allows for shorter control surfaces. Get half the twist and twice the torque.

ian
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Old Dec 02, 2003, 09:21 PM
AustinTatious
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Hurst, Texas, United States
Joined Jul 2003
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Ian,

I have experimented with puting weight at the tips with great success in a small glider. 38 inch span 6 ounces, I ballasted it up to 15 oz by putting 4.5oz halfway out in each wing. The small plane had a Vtail, and i could not tell the weight was out in the wing.

I would bet the weight at the wingtips actually stabilizes the plane going thru the ugly sheer. Think carefully abotu what happens! The high wing hits the oncoming wind before the low one, the xtra drag slows that wing and yaws the plane. Well if you put weight out there, then when that high wing hits the sheer, it has more enertia and wont slow down as much, thus the plane wont yaw as much.

Im not sure what the wingtips not being the strongest part of the wing has to do with what i am talking about.

Im not discribing anything new to aerodynamics, im jsut trying to help the guys trying to set records. THe reasoning behind what i am trying to explain is difficult to convey over text... think about this for a second. Yall are fluttering very strong wings around 200 mph speeds, However on .60 sized choppers the tips are going over 380 mph and they dont flutter. This includes flimsy wooden blades that twist like never before. The reason for carbon blades it to keep them from twisting so much in 3d flight causing a loud BRRRR sound, not to prevent flutter. This is because the blades are balanced CHORDWISE along the length ( especially near the tip) by using heavier wood and weight at the leading edge. Yall should treat your wings like rotorblades and balance them accordingly. Then balance your ailerons similarly and flutter wont be an issue. Also moving balast out to the tips will decrease the load at the center of the wing.

So now you have elimintated a problem of too much "twist" in the wing, and you have taken a big load off the center section. Now all you need is a tail that wont come off and wing skins that wont seperate at the new speed record your gonna set. BTW if someone employed these teqniques, they could do so on a large(more than 2m) plane and it would hold up and maybee set some records.

Bigger is better so i hear ;-P

Anyway about the m60, the fact is at some speed the wing WILL flutter. I believe ive found that speed and have no doubt I will flutter it again, but this time ill have a radar gun on it and ill report that speed. If you dont balance the entire wing, then the speed at which it will flutter is dependant upon how resistant to twist the wing is.
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Old Dec 02, 2003, 09:27 PM
Brett
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So Cal
Joined Apr 2002
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Just FYI, the last 4 or 5 records set have not involved wing flutter. Kyle had some control surface flutter, but the wing itself was solid. Gary's wing snapped at the spar.
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Old Dec 02, 2003, 09:36 PM
AustinTatious
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Hurst, Texas, United States
Joined Jul 2003
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I am aware, I believe balancing the wing like this is more benificial to the twisty foamies. The weight at the tips will hep prevent spar failior in the record setters. Of course if their spar dosent fail and they go faster, they may jsut hit the wing flutter speed.
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Old Dec 03, 2003, 01:36 AM
Vitruvian JART
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San Francisco
Joined Mar 2003
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Mass balancing the wings in this way has been considered and employed by at least one DS record-chaser that I know of (with a larger than 2M plane).

Balancing control surfaces is problematic - we've all seen weights out in front of an aileron on a full-size plane but that isn't practical on a sloper. Often an aluminum tube is laid in the LE of the control surface of a bagged wing to add torsional stiffness. Biased layups can also be important for the wing and control surfaces of a bagged or molded plane.

re: that M60: Those balsa elevons aren't always light enough or rigid enough to control fluttering. Some folks lay a light layer of cloth on them (on the bias) to keep them from twisting so much. If it's the whole wing then it can't hurt to try the mass balancing, IMO. This assumes (as Daemon suggests) that the usual culprits (weak servos/horns/slop, etc.) have been ruled out.

My 2 cents, FWIW, and all that jazz...
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Old Dec 04, 2003, 03:31 AM
speedfreek
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Newcastle, Australia
Joined Apr 2003
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Question

Hey AustinTatious,

If Im not mistaken, this can only applied to a wing that has a mean chord that runs perpendicular to the centreline of the plane. The reason for this is that on some tapered or swept wings, the COG at the wingtip could be way behind the COG at the root. Any weight added to balance the wingtip COG will put weight behind the roots COG, hence making it tail heavy. This would compound the weight required to balance the plane in a big way wouldnt it?

I agree with your theory as it seems quite logical but it may have limitations on its application.



Waz
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Old Dec 04, 2003, 09:13 AM
AustinTatious
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Hurst, Texas, United States
Joined Jul 2003
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Thats right,

I intended to use this teqnique on an M60 which has a strait leading edge and a forward swept trailing edge. My electron will not have this wing flutter problem, as the eading edge is tapered as well as the trailing edge being forward swept.
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Old Dec 11, 2003, 07:03 PM
AustinTatious
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Hurst, Texas, United States
Joined Jul 2003
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Hey guys,

I finally got my Bungee launcher site up and going, This is what we used to get 100 mph out of the M60 on the calm day.

http://webpages.charter.net/austinswill/
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