I would really like to hear opinions about plane weight and how it effects speeds and 10 lap times.

I've had several high level racers tell me 3-4 oz heavy racing plane is NO big deal at all, and doesn't cost you anything in terms of speed or race times.

I really struggle with this, but would like to hear some opinions.

My take would be that you will lose time on your first lap getting up to speed, and bleed off more speed in every turn because of the extra control throw you will need to use to turn a heavier plane.

Has anyone ever done tests? I would think it would be reasonably easy to do. Take a 3 1/2# plane and run 5 timed runs of 10 laps. Add 4 oz of lead to the C.G., and do 5 more timed runs. Maybe not scientifically perfect, but should be adequate.

Anyone want to test this?

try attaching ,,, say a pound or 2 of lead to your machine Saturday and see what happens

Dave,

You seem to assume that I have an airplane that is NOT overweight.

Actually, my personal best time in QM40 was set with an airplane I later discovered was 7 ounces over. There may be something to that "more weight, less bouncing around in the wind" theory. But at most, that would reduce the amount of the handicap -- I can't see how it could possibly give you a net gain in speed. Otherwise you'd see the fast guys adding bricks.

Mr. Manifest Density

quoted by Splatt

"try attaching ,,, say a pound or 2 of lead to your machine Saturday and see what happens"

I know what would happen, you might be able to stay on the same lap as me.

I think what we are talking about is a compromised tradeoff between stiffness and lightness. They are both good, however, they are very ellusive as a mutal goal. So what is better... a stiffer airframe and wing that will be a good motor mount and will not flex during the highest flightloads or a lighter, but maybe more flexible airframe that gets up to speed a bit faster? I don't even try to build a 3.5 LB 428. I prefer a stiffer fuse and wing. I don't even use contest grade balsa anymore although I do have Lone Star hand select the weight woods I want. The only way I actively cut weight is to strictly limit use of glue and paints and carefully weighing the materials before use so I have the correct weight wood and other materials where it is needed. I generally stick to 7-8 LB balsa for the fuse and wing sheeting. My planes generally come out several onces heavy... but so do those $500 composites. IMHO.


Dan

Glad to see this has sparked some interest. I have started a link on the same subject here

http://www.rcuniverse.com/showthread...94&forumid=122

Weight has absolutely no effect on absolute speed but as Dave quite rightly points out it has effect on acceleration and as you scrub speed on turns, acceleration is a factor on lap times. I believe that anyone who does quick times with an over weight model may improve if the model was lighter. A lot depends on how smooth you fly and how many mistakes you make.

Justin Odelll

Just a few thoughs from my own personal speculation, I,am no aerodynamics egghead (Never met one that was not entertaining though because they can,t even agree with each other) nor am I an Ace pilot but I have to jump in on this one.

Justin, I believe its a bit of a reach when you say "weight has absolutely no effect on absolute speed". Suppose an airplane is two ounces overweight something has to hold that two ounces up, gravity never sleeps except maybe in the movies. If nothing else changes Like increased thrust that airplane is going to descend from a level flight condition with
those two extra ounces if the trim is exactly the same as it was at the lighter weight unless something else is done. The only thing left to do is increase angle of attack to maintain that level flight just enough to support those extra ounces. OK we have just increased lift by increasing A of A and with lift comes induced drag and with drag comes a speed reduction.

Yes and I do agree this differance is a tiny percentage and I seriously doubt anybody could tell much of a differance in flight.

All of the above is just my speculation and refuse to 'incriminate' myself any further

John

Haaaaaaaaaaaaaaaaaaaa



BV

I built 2 Sidewinders for a friend. One is heavier than the other because I got carried away with painting it. The heavier plane flew better, faster and almost didn't want to land.

I have, from time to time. Built race planes heavier than what I wanted. I have done wings 5-6 years back of a SIG Cobra. I used blue foam with wood glue and after that is completed. It weigh a ton and it actually perform better than a built-up one.

This doesn't mean I will add a brick into my plane. I still want to build planes lighter. And those heavy planes I've done were mistakes and never intentional.

Hudson

Bottom line IMO... if two planes could be built with the same strength and stiffness in all the right places for racing.... one is 3.5 LB's... the other is 2-4 OZ's heavy... I don't think there is anyone that would leave the 3.5 LB plane in the car given that they flew the same. However, 2-4 OZ's over seems to be about the norm for a real good woodie. Anybody have to add weight to a composite to get to 3.5? I haven't heard of anyone complaining that their composites were too light.

I added about 1/4 ounce to my Vortex in Phoenix at the Winterfest. Travis Flynn has by far the lightest composite that I've seen (shows how I rate).. I think his was about 1/2 oz under. But for the most part all mine are dead nuts 3 1/2lbs.

IMHO ... most people don't fly well enough to feel the difference of 2-5 oz's overweight.

Randy Bridge

The only benefit I can think of to adding more weight would be the increase in stiffness that has been mentioned. I don't know how big an issue this is, but my gut feel is that even the lightest plane allowed by the rules would be stiff enough that the extra stiffness you could add at the expense of a few ounces would not help you.

It is not true that added weight has no effect on absolute speed. In straight & level flight, the plane still needs to generate enough lift to support its weight. A heavier plane must generate more lift. Induced drag increases as the generated lift increases ( actually, it increases as the coefficient of lift increases ). In fast, straight, level flight, the coefficient of lift is very small, so the induced drag is also a very small fraction of total drag. Thus, between turns, this effect would probably be very small. One thing that might make this effect bigger is the habit of flying the whole course partially banked. A plane flying straight & level in a bank will need to fly at a higher coefficient of lift than one flying with its wings level, so the weight would be more important. The biggest effect of extra weight is in the turns. In a pylon turn, the coefficient of lift is fairly high, and induced drag becomes a significant, maybe even dominant, component of total drag.

I'm guessing that a bunch of extra, or unduly dense, material in the empennage would be the most wasteful. Since pylon planes likely have the CG located pretty close to neutral, the tailfeathers should not be too heavily loaded, and the fuselage behind the wing need not be extra heavy duty. If flexing is going to have adverse effects anywhere, I would guess it would be in the wing. In front of the wing, of course, is a heavy, furiously vibrating engine, which requires a nice stiff structure there.

banktoturn

Banktoturn,

Very well put. This sounds logical to me.

Dave, get the weight out of it! You need to end up with a 16 oz wing. Try something different to get the weight down. No suggestions here though. Try to find out from MDP his construction technique. He has always built light foam wings. Mike, any insight?

Dan

This was RB's quote


That should put this whole thread into perspective. I am a firm believer that lighter is better, faster, and can be the difference between really fast and really, really fast !!!!

Mikey D

I am now selling helium foam, only $19.99 per 52" panel. It looks and acts just like the regular stuff, but is guaranteed to reduce the finished weight of your wing by 2 oz.

It will also add 3 inches to your fuselage overnight.

Visa and Mastercard accepted.

"It will also add 3 inches to your fuselage overnight"

Now what you been buying off the internet?

Duane, the helium is better served with hollow molded wings. Better yet, hydrogen, it's lighter and will make for more spectacular crashes!
GS