Drag wont matter to much at those speeds....?

[Barrett]

I was flying one of my own designs a few weeks ago at the local field. Its a speed 400 flying wing foamie. Pretty thin airfoil, and its fast. Well fast for me anyway. But ive got the battery taped to the bottom and the servos sticking out quite a bit so I can make linkage changes easily.

Another guy was there with a gas trainer and a zagi. His son took the zagi up at the same time I took my wing up. While I was flying he made several remarks about how fast it was. It was much faster than the zagi.

After I landed I was telling the guy that on the next one I wanted to bury everthing below the surface and come up with a low drag cover for the motor. I mentioned that the plane would look a little cooler and maybe be a little faster. Then he say that at the speeds I am flying reduceing the drag wont make any difference.

My questions is this......... On my 36" span foamie wing, will burying everthing below the surface have an effect on top speed?
Or an effect on anything other than looks?
Top speed now is in the mid to high 50's. Flight time on 600AE's is about 5 minutes with a little left stick management.

[Sparky Paul]

It depends on what you consider "faster".. your mods will lower the drag, but enough to be noticecable??? Probably not.
Monster increases in motor power/efficiency are usually required to get a change large enough to be significant.
Flight times at full power should be longer.. that's about the only way to measure such stuff without a radar gun or some other method of determining speed.
The change in flight times at full power will give an indication of the percentage change in the drag.

[astroboy]

Originally posted by Sparky Paul
It depends on what you consider "faster".. your mods will lower the drag, but enough to be noticecable??? Probably not.
Monster increases in motor power/efficiency are usually required to get a change large enough to be significant.
Flight times at full power should be longer.. that's about the only way to measure such stuff without a radar gun or some other method of determining speed.
The change in flight times at full power will give an indication of the percentage change in the drag.

I'm not sure I'm following here. If the increase in drag would not be enough to be noticeable, then it seems that the speed increase would not be enough to significantly unload the prop and reduce current draw. So why would full-power flight times be any longer?

Jeff

[heli frapper]

http://213.84.42.244:8087/paulraaf/pr400.avi
to view vidio from paulus

last month there was a vidio put up from holland club af s400 6v with with 7*600 ae pylon racer plane and it was shifting estimate 70 to 75mph

to find vidio go to performance section and with search type in 400 and pick out the title vidio of s400

he supplies a pdf file which has a plan to make the racer

it suggests to me that as it is a very stramlined plane with thin wing that drag does affect performance as certiaNLY ITS THE FASTED S400 PLANE I VE SEEN

hope that helps


Stephen

[Sparky Paul]

Originally posted by astroboy
I'm not sure I'm following here. If the increase in drag would not be enough to be noticeable, then it seems that the speed increase would not be enough to significantly unload the prop and reduce current draw. So why would full-power flight times be any longer?

Jeff
.
Speed is subjective. An measureable increase in speed at the same power setting might be evident only in the change in flight times.
And probably won't be much, if the stated changes are made.
It takes a lot of power to go faster in a meaningful manner.. a speed change that's obvious.
These things don't fly in a straight line long enough for one thing. Zing over there, 180, zing back. There's few reference points in the sky to use for a qualitative observation of the actual speed.
.

[Barrett]

Thanks for the replies guys. I know that it would make some difference, and I know that unless the changes are drastic then it would be hard to tell. But I was just curious what you guys thought about it.

Stephen, I mentioned to this guy that if reducing the drag didnt make a difference then why are S400 pylon ships obviously faster than my plane, when they are running on the same equipment?


Thanks again!

[Troy]

I'd be curious how much difference it would make in the end but from my experience with combat wings on the slope, a few wrinkles here and there made a dramatic difference in performance vs when it was new. Having said that, things are a little different when you throw a motor on it to "drag" it around the sky. I'm sure you will notice it is flying nicer and possibly faster without the battery hanging out in the air. Though, you're not going to notice much when you fair in the servos. You can't even really tell the difference on an all out F5B planes doing that unless you're talking about splitting hairs on the stop watch. You're wing would have to be much thinner (airfoil thickness) and lighter to begin to reach the speeds of a S400 pylon plane. Some years ago my Skat with a good S400 set up on 7 cells, I was able to clock 113mph with a modest dive.

[Ollie]

The math goes like this. The drag force is proportional to the square of the air speed. Therefore, speed increase will be proportional to the square root of the drag force change, assuming constant thrust. For small changes in drag, the percentage change in top speed will be a little less than half the percentage change in drag. If the drag were reduced 10% the speed would be increased about 4.9%.

I'm guessing that you might be able to reduce drag somewhere between 10 and 20% by putting everything inside. That would result in a speed increase, roughly, between 4.9 and 9.5%.

As Paul has said, it will be hard to tell the difference by casual observation.

[Barrett]

Troy, I have got to get a pylon racer. Right now im looking at the sokol. Ive got a Mega 16/15/3 that ill put in it, and for power im thinking 9 or 10 of the new 950mah cells. In the last Quiet flyer mag Steve says that they perform very similar to the old red 500AR's.

Ollie, thanks for the numbers. Now I can "see" what reducing the drag on my wing might accomplish.

Thanks again guys.