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carson

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I bought a rocket and flew it with a B motor. Then I primed and painted it, even clear coated it. After I was finished I was proud of the job I did. BUT after launching it again after the paint job, it flew at best 2/3 the height of the first flight. I assume that the extra weight is a really big issue it rockets. Any comments??
 

Zippy

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That big a difference in altitude is probably more likely from variations in performance of the two motors even though they are the same type.

As far as paint goes their are two trains of thought I've heard.

A: Paint has weight so rocket goes lower.
B: Paint is smooth so rocket goes higher.

I think they are both right.
 

Silverleaf

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Unless your doing a massive bird, paint isn't that large of an issue - unless you use some older oil based paints from the 70's. Don't laugh, I've a whole basement full of that old stuff, and since its been kept cool and dry, it has excellent value and covers very well. 8)

I agree with Zippy though, odds are your second flight had a motor that varied greatly from the first. Try a 3rd motor, and I'll bet you'll come closer to your first altitude than the 2nd flight.

On a final note, did you double-check the launch lugs to be sure paint didn't clog them up ?

As to paint helping heigth, I've used Dope on many rockets and the finished outer shell was very smooth. One other thing that can help is to smooth a bit of baby powder over the rocket after a week of drying. Why ?..it helps you " feel " bad areas that may need extra sanding. With my Sandhawk, I sanded and sanded till I thought to try baby powder, and sure enough it pointed out one small area near the cone that I'd missed.

I reached 4712 with the sandhawk pre-painted and lost only 39 feet on the second painted flight. Granted both launches came on very calm almost windless days, but thats a positive example that paint doesn't add too much weight.
 

teflonrocketry1

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The paint job on a model rocket should only amount to a few grams at the most, unless you go way overboard with the number of coats. Even with a thick primer and heavy gloss coat, I expect an increase in weight no more than 5 grams on an average model. Did you weigh the rocket before and after painting?

The allowed variation in motor specifications is +/- 20%; which allows for cheaper manufacturing. You may have just picked the wrong two motors; the first one from the high end and the second one from the low end of the specifications.

Did you launch from the same field under the same ambient (wind, temperature and pressure) conditions? Was the launch rod corroded up from sitting around between the first and second flights? These amoung numerous other factors may have given you a preceptively lower second flight. How did you determine the second flight was that much lower? Are you sure it was 2/3 lower, or was it maybe 3/4 lower? It would be hard to tell these two cases apart without making some sort of measurement.

Bruce S. Levison, NAR #69055
 

carson

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The second launch may not have been that much lower.
The motors were from the same pack, I think.
How does temp affect a flight?
The second launch was on a day of about 35 degrees instead on the 60+ degree day of the first launch.
 

doxiedog315

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Air is much (thicker) when it is cold.and as you would expect,thinner when hot, Air is a fluid,in respect to are small rockets.
 

KermieD

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60 degrees to 35 degrees does not make for a 2nd flight that is only 2/3rds the altitude of the first one however. In fact, my personal experience with cold weather flights has been one of increased altitude due to the lower humidity compared to warmer flights.
 

astronboy

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I think that th boost glider guys have the experience in this area as weight vs drag is the key trade off with gliders. What I have read is that the gains made by less drag from a well finished model (ie: doping, or tissuing a glider) far outstrips the losses produced by the weight of the finishing. Non-glider rockets do not have the need for a super light finishing job, as they are boosted by the motor. During boosted flight, an unfinished rocket (fuzzy!!) will have far more drag than a finished rocket. The weight is pretty much negligible.
 
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