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

Heavy or Light

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Old 12-16-2007, 10:40 PM
  #1  
colbourne
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Default Heavy or Light

The aim of this group as far as I can tell is to make the fastest model through a speed trap.
Has it been decided yet whether it is best to use a light model which accelerates quickly or a heavy model which can build up momentum in a dive.
If the aim is to achieve 200mph I reckon this could be obtained fairly easily with a high performace (low drag glider ) with only a simple low power engine to get it to height. (Then either dropped /folding prop /retracted).

Designs based around pylon racers are designed for quick turns and will therefore have more drag than is really required.

My assumption is that a heavy model will be fastest.
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Old 12-16-2007, 11:18 PM
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Default RE: Heavy or Light

The heavy model won't be able to sustain speed very long in level flight. For those of us who don't see much value in purely gravity assisted speed records, the European format is the definitive way to measure a prop driven planes' worth.
If you do your best to scratch build a sleek model out of the best materials and make it just strong enough to withstand the forces of flight, the end product will probably be a speed plane that you wish could have come out even lighter if some things were done differently. Building heavy is easy, it is something that anyone can do.
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Old 12-16-2007, 11:59 PM
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Default RE: Heavy or Light

It's a combo of drag and surface loading of the wing. If you have more wing area than needed to maintain lift, it's just extra drag. But if you're wing is too small then it flies at too high AOA and you loose efficiency. To figure it out to the enth degree requires a degree I don't have. I say more power and make sure you can land it to do it again.
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Old 12-17-2007, 12:54 AM
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Default RE: Heavy or Light

From what I have seen of the European's speed attempts, they do use gravity assist (dive) to achieve their high speeds. Otherwise they would never get the engines on the pipe with the heavy props used. Since most of them tend to use the FAI guidelines, they are somewhat weight limited to 75 grams/dm^2. That puts it around 24.57 oz/ft^2

I reject the idea that a span limited airframe will be the fastest in their operating format, as the induced drag when pulling out of the dive will be significant and they do need to carry the speed through the traps which is a distance of 656 ft.
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Old 12-17-2007, 02:06 PM
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Default RE: Heavy or Light

Colborne:

The aims and goals of this group vary somewhat for each of us. It is much easier to determine the common goals rather than the various avenues to reach those goals. First and foremost is to build and fly something fast for the same reasons some would drive a Hugo while others perfer a Corvette, Fararri or Porshe. To attain their goals, some would stuff a 90 into a sleek 40 size airframe and power their way to speed. Suttle others will design there own sleek birds looking to go fast with a reasonable size engine and get their speed through airframe design. Othere are simplty lost souls not completely at home with the pylon crowd who are generally limited in dimensions, and seek the pure bird design capable of both speed and turning/flying ability, sort of the best of all worlds. Then there are the rules pushers who club race and are looking for ways and means to go faster within the given rules and specifications. Its sort of hard for the rules committee to outlaw a sleek airframe that they see doing torque rolls after practising on the pylons with the same airplane. The same group will jump all over the guy who claims the improbable, yet will praise the outstanding work and concepts of others with equal gusto. Yes, the brotherhood is a group of missfits, strange and unusual, yet wonderful people who share the common bond of speed from all over the world. Enjoy the diversity.
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Old 12-17-2007, 04:43 PM
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Default RE: Heavy or Light

It really depends on How Much Heavier, and where is that weight coming from?

If your trading a few ounces for a stiffer airframe, it may be beneficial to do so.

I agree, Slightly Heavier may be faster, but only if that extra weight is used in a manner to deaden the vibrations of the motor through the airframe.
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Old 12-17-2007, 07:36 PM
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Default RE: Heavy or Light

I went to the local auto body shop after work to buy a couple of pounds of lead stick to try out in my Diamond Dust, but the sales clerk said, "Why don't you just buy a Whiplash?"
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