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All my F1B models use Vivchar front ends. At the Pan Am, on the 4th flight, I had both blades land on the wings. With a V formation and it’s enormous drag, the model landed in 81 seconds – placing me dead last.
How can something like this happen? Well , first there was friction in the main shaft, requiring the replacement of the ball bearings. The higher friction and maybe dirt delayed the deployment of the Montreal stop, at which point the right blade hit the top of the right wing. The impact might have caused the front end to pivot forwards around the bottom of the fuselage tube. If the rotation of the front end is just right, the left blade is folding in a tilted plane and might end up resting against the left wing, forming a blade V-formation. Although a wound down motor is stretched (the motor tube’s is 20” and the raw motor about 13.5” before the wind, plus the length the bobbin reaches in plus the rear aluminum hook used for external winding) the impact shock of the first blade was evidently sufficient to pivot the front end. This is a most unusual occurrence, and it happened to me!
How can this be avoided? (Besides assuring a clean front end and a proper alignment of the main bearings.) The key seems to be the overlap between the front end and the fuselage. In older Vivchar front ends, this overlap is 4 mm, while in the newer front ends it’s 5.5 mm. Inserting trim rings will reduce the overlap. Although the difference between the two is not large (.060”), the gap between the front end and the motor tube might be sufficient to allow the front end enough space to pivot.
The fix is to add an aluminum ring that will increase the front end’s overlap to 5.5 mm. Such a ring will be epoxided to the front end. [I’m considering ordering a few of these extension rings, and would like to ascertain whether other F1B fliers using older Vivchar front ends might be interested in buying them as well. I don’t yet have a price quote and will probably get have them by April. (I’m traveling part of March.)]
Dont know wherther this applies to other front ends, but it might be worth checking.
I had trouble with a Vivchar front end about 5 years ago,but I suspect it was the opposite of yours.There was too much tension in the spring which made the plane shake when the rotation stopped.Maybe the tension in yours is too little causing the blades to fold when rotating slowly,rather than after rotation has stopped.
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