stunthanger.com
Design => Stunt design => Topic started by: Scott Jenkins on January 24, 2007, 11:48:30 AM
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Hi all I am getting ready to set up another production run of bellcranks. Normally I make only 2 inch bellcranks for the racing side of the hobby. but thought I would make and test some larger bellcranks for Stunt and combat and possibly some for 1/2 A and speed. Question is I know that most stunters are fond of 4" bellcranks but I do not know what the throw is on the pushrod end. One more thing my bellcranks are made from Carbon Graphite 2 and 3mm sheet. The 2" bellcrank will pull test at over 150 lb. I have yet to have one returned or hear of one failing. I will replace any bellcrank of my manufacture due to defect or failure of the bellcrank itself.
Scott
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Tom Morris bellcranks are typically not drilled so the user can locate the push rod as it suites him. Probably your best bet would get hold of 3 and 4 inch bellcranks from Brodak or SIG and copy the measurements. All of mine are in airplanes, makes it a little hard to measure.
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Fox 2 in. .325 .540
Fox 3 in .375 .6 .825
Brodak 2 in. .425 .610
Brodak 3 in. .470 .7 .935
Brodak 4 in. .470 .680 .920
The Fox bellcranks are moderately soft aluminum. Never seen one break, but they can bend, which actually is a plus, since it acts as a cushion.
Just got some of John's bellcranks in. The 2 in. one looks like opaque nylon. The 3 incher appears to be straight, unfilled nylon, and the 4 incher appears to be a fiberglass-filled black nylon, similar to many plastic motor mounts. Haven't pull tested any of them to destruction. The most likely problem with any molded crank would be internal flaws that won't show up until it is pulltested. The 4 inch one is certainly stiff and strong enough by a quick hand pull test.
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Phil,
Thanks for the info what is your favorite size of Bellcrank. PM me and I will send you a sample as soon as the next production run is complete. Better yet if you have a particular style drawn up and want to try send it to me with dimensions and I will add it to the cut list. scojen@earthlink.net
Scott
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Phil,
You have mail here at stunthanger.
Scott
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Personally, I favor bellcrank throws equal to the height of the used flap horn. In the case of Tom Morris's flap horn, 1 1/4". Tom's bellcranks have enough material to drill for 1 3/16", but 1 1/4" gets too close to the edge of his material. Bellcranks with large throws are needed when particular designs depend on large control movement for lift. I like the thought that Tom will drill his bellcranks for any throw possible within the physical limits of his bellcrank profile. Replacing defective bellcranks? After the crash?
Al
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I make my own.