stunthanger.com
Electric Stunt => Gettin all AMP'ed up! => Topic started by: Andrew Borgogna on June 28, 2012, 09:06:05 AM
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I ask this question because my Continental has/had a slight hunt to it and nothing I did seemed to affect the problem. While looking carefully at the plane I realized I had very long struts and very wide wheels. It occurred to me that the landing gear could generate a pitch down force from drag and leverage. So I cut the gear struts by 1 1/8" and replaced the 1" wide wheels with 1/4" wheels and also removed .6 ounces from ahead of the CG. In still air the plane now tracts very well in gusty air there is still some bobble but I wonder how much of that is in the 1960's airfoil design. When the motor quits the plane remains level and settles to the ground with no noticeable handle input, so I think the CG is correct. All the surfaces are at 0 degrees and so is the motor. Has anybody else ever experienced this kind of symptom?
Andy
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If you are using aluminum or carbon gear, yes it can effect the flight of the plane. The gear has to be in line with the flying surfaces(incidence). I had a fuse mounted gear I had to put shims under trailing edge to get the plane to fly level with out hunting. H^^
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Well Andy it seems you have answered your own question! You have certainly removed weight and "windage", and you have achieved a perceptable change. As I recall the original Continentals were "low riders" with long & SKINNY wheelpants. Did you keep the wheel pants or fairings on the new gear?
I have heard of what Doc described happening on Pylon Racers. While our speed & forces are much lower, its still plausible that there is cause/effect for the change you described.
So is that the "silver bullet" you have been looking for?
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Thanks Doc for you input. The gear are 1.8" wire and the wheels were about 2" diameter and 1" across. The length of the struts were 5 1/8" from the bottom of the wing to the axle. Now the wheels are 2"diameter and 1/4" across and the struts are 4" long. Dennis I am not sure because I also went to a lighter battery, from 3300mha to 2600mha and I added more tail weight. Each thing I did had an affect, but so did changing the wheels and struts. Maybe you are right and I did answer my own question. I just never had a plane that was affected by landing gear.
Andy
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Andy
It affects 100% scale planes pretty dramatically. It will also affect our models. If you go to retracts, be ready for another est of changes.
bob branch
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Why not try wheel pants, that's what they were designed for - cutting drag.
Or conversely increase the windage above the thrust line with something like a bigger canopy, fake radio mast behind it, or even just a removable and adjustable spoiler to see if it has any benefit?
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The original Continental design called for wheel pants and strut covers, but because I need longer struts for prop clearance and in an attempt to save some weight I left the wheel pants and strut covers off. I just never considered wheels could be the cause of trim problems.
Andy
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You can drastically cut the drag of the wires by adding a very simple fairing of about 3/8" to 1/2" width behind the wire, tapered to a point. Put shrink tubing on the wire to provide a good gluing surface for the fairing. It will look cool, too!
The fairing can cut the drag of a round wire to under 20% of an unfaired one! That would require about 1/8" ahead of the wire also, and then sand the whole thing to a teardrop shape.
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Do you think the vertical cg might have also entered into the formula a bit? You did change it when you made your switch.
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We did check the vertical CG before and after and could not visually tell a difference. But you are correct we did reduce weight that would affect the vertical CG. I guess the bottom line is by changing the LG configuration a number of things were changed and they all could change the performance.
Andy
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On real planes that go over 100 MPH, retracts as needed to achieve acceptable performance. On slower airplanes, the gears are usually fixed to save cost and dedicate more weight capacity to payload. In some Cessna products, fixed gears are actually FAVORED for mountain flying.
Stunt planes want to fly at 50-55 MPH. Landing gear drag and other parasite drag is beneficial in that it allows more power to be added without increasing speed. This is one reason Al Rabe's bulky models were able to defeat most of the streamliners.
The drag of undercarriage is an even trade vs the offest rudder. Also, a common design factor is the entire fuselage offset upward vis-a-vis the center of the wing. Prago! It's in there.