|Aug 10, 2012, 12:28 AM|
Post Crash Inspection - Cheap Servos?
After deciding to dip my toes back into the hobby after a long hiatus, I grabbed my Brio 10 out of the ceiling and after spending a few hours over the course of couple of nights on repairs that were pending from a crash before I got out of the hobby, I took it and my trusty old Stryker to the park. I ultimately want to get back into 3D flying with helis, but before dumping that kind of cash I thought I better dust off the couple of models I kept and see how things went.
Didn't go too well.
I knew I should have started with my trusty old Stryker, but figured the Brio would be better as I was thinking it would take less space, the need for which might I add, I completely underestimated having been away for so long.
I had to fly way tighter circuits than I thought due to the trees and even on low rates I was banking the plane like a drunk on a teeter totter. I kept it up for a couple passes before tip stalling it and plowing the nose in the ground from 50-75 feet up. A pretty interesting sound, that. I've done most of my crashes with foamies and helis. A covered balsa model sounds more like breaking a tight drum head with a bundle of sticks: a much more satisfying spectacle for sadist spectators. Too bad repairing them combines tedium of tax preparation with the excitement of ironing.
Entertaining the denial of simple pilot error, the post-crash inspection leads me to blame the following as factors:
1. Aileron travel was too high on low rates. I don't recall the #s, but probably 30-40% higher than recommended.
2. Cheap and under-powered servos on the elevator and rudder (I feel I should have been able to recover from the stall).
3. Choice of flying field (too small).
I was using HK HS-55 knock-offs all around on the Brio and noticed it only took very slight pressure on the elevator to reduce its travel quite a bit. I'm working on a Fun Cub now, which is a similarly sized plane and noticed Multiplex calls for HS-81 servos for both rudder and elevator and 55's on the aileron. So this supports my theory, too. The 81's put out nearly 3X the torque and this is to support control surfaces smaller than the Brio;s. Needless to say, I'm building the cub with the recommended servos and won't go cheap on them again.
|Sep 07, 2012, 12:53 PM|
Joined Dec 2004
you wrote,"2. Cheap and under-powered servos on the elevator and rudder (I feel I should have been able to recover from the stall)."
An under-powered servo would not be the cause of being unable to recover from a stalled condition. When a plane is stalled, there is little to no airflow over the flight surfaces, and therefore, little to no response from the control surfaces. In order to even stand a chance at recovery, you must allow the plane to gain airspeed so that it is flying again, and only then will the control surfaces have an effect on the flight path. Rule of thumb is, when stalled, let go of the sticks and allow the plane to fall. Count, one, two, three and ease out with elevator.
Of course, it helps when you have altitude.
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