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Author Topic: Dope weight  (Read 1993 times)

Offline Don Hutchinson AMA5402

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Dope weight
« on: August 23, 2016, 06:55:04 PM »
I have over the last ten years built several Go-Devil Jr. models powered with Magnum 25 or equivalent engines. They required two to three ounces of lead in the nose to get them balanced. The last was done exactly the same as those I built in the fifties, no tissue except on the wings, no primer, just clear dope, then color. The new engines are also heavier than the Glo-Torp 29 I used to use. Back then it was "bolt in the engine and go fly!"  I could not figure out any reason for this until someone mentioned that he thought the dope we are buying today is heavier than that of the fifties. Anyone else noticed this?? Bill Byles, any comment?

Offline Steve Fitton

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Re: Dope weight
« Reply #1 on: August 24, 2016, 07:09:51 PM »
I don't think heavier dope is plausible.  Besides, if "heavier" dope had a detectable weight change to a small model plane, imagine the weight gain in your typical J-3.  It would never get off the ground.

Chemistry changes to dope over the years are relatively minimal compared to many other paint systems.  Big changes could have unintended effects and get people killed.
Steve

Offline billbyles

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Re: Dope weight
« Reply #2 on: August 27, 2016, 10:09:26 PM »
I have over the last ten years built several Go-Devil Jr. models powered with Magnum 25 or equivalent engines. They required two to three ounces of lead in the nose to get them balanced. The last was done exactly the same as those I built in the fifties, no tissue except on the wings, no primer, just clear dope, then color. The new engines are also heavier than the Glo-Torp 29 I used to use. Back then it was "bolt in the engine and go fly!"  I could not figure out any reason for this until someone mentioned that he thought the dope we are buying today is heavier than that of the fifties. Anyone else noticed this?? Bill Byles, any comment?

Hi Don,

The dope we are using now is the same formula that we used in the fifties with mostly the same pigments.  I have not noticed any weight increase in the dope. 

There has been, on occasion, attempts by various modelers to add additional color pigment to dope.  When this happens the ratio of pigment, which is non-binding, to the resin, which is the binder, becomes unfavorable to the point that adhesion of the dope is reduced.  Up to a point additional pigment can be added and the resulting loss of adhesion may not be noticed on our under 65 mph models.  However, I have recovered many fabric and dope covered control surfaces, especially rudders on P-51 mustangs used for racing at Reno that are affected by added pigment in the dope.  The highly modified P-51 Dago Red holds the course record for the gold race on Sunday at about 505 mph and the inhibited adhesion due to added pigment would definitely be a factor.
Bill Byles
AMA 20913
So. Cal.


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