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Throttle knob friction
Here is another aussie complaining about the throttle set-up. I hate the throttle creep too, but dont want to blame the springs necessarily. They are just part of a poorly designed sub-system (sorry Vans) which puts unnesessary stress on the pilot. I reckon its a safety issue.
Are the springs too strong, or is the friction mechanism inadequate? I have tried out a few things eg put a little leather dressing on the dry-as-a-chip leather washer to make it more pliable - no change. Greased the knurled knob thread with nickel antisieze - no difference. The next idea is to cut leather washers from better leather, of greater diameter to improve the friction . Maybe I will try a synthetic material washer. After that I plan to get a knurled knob with larger diameter (x2) from the manufacturer, or make a adaptor that does the same thing. I dont buy the argument that you need a strong grip and bulging forearm muscles to set the throttle (or hold it on idle on late final). My partner wants to learn to fly this plane, and I doubt if she could fly it safely as it is, with the current throttle design. Not good enough. Has anyone managed to solve this throttle problem from the cockpit end? Rod |
Lighter is Better
Rod, I think you may be over thinking, and over engineering a fix. Instead of more resistance, use less spring. Van has designed a very smooth and friction free throttle system, as is typical for most RV control systems. Rotax, on the other hand, installed heavy throttle springs, to compensate for throttle systems that are less free. The goal is to have enough tension to safely move the throttle to the full power position, in the event of cable breakage. We don't need these strong springs to accomplish that goal. So.....
Tom |
The throttle spring is the fault of Rotax, not Van's. If Van's made changes to the engine, they would be liable for any mishaps. Rotax does not know how their engines will be installed. In this litigious society, Rotax has to make sure that the throttle will fail open regardless of the throttle linkage. So they used very strong springs to cover their A $ $.
Increasing the holding power of the friction knob is not a solution. If the friction is great enough to hold those two powerful springs, weak hands or fingers will not be able to move the throttle. I see two possible solutions: use weaker springs, or replace the throttle cable assembly with a different design. For RV-12s that are currently flying, replacing the very strong springs with weaker ones is the easiest fix. The replacement springs that I used are still strong enough to open the throttle in case the cable breaks, even though the springs are only half as strong as the originals. When I loosen the friction nut completely, the throttle knob is still pulled fully forward. And that is without any vibration, the engine off. Companies that make springs are willing to make custom springs with any desired characteristics. However, they charge a setup fee. If Van's ordered a large quantity of custom springs, the setup cost per spring would not be much. For individual purchases, it is more economical to purchase stock springs and shorten them to fit. Joe Gores |
Tom - I want a set please. billhollifield at iname dot com
Bill Hollifield |
I'll 'spring' for a set!
Tom - PM'd you.
Thanks for putting this together! |
Has anyone considered leaving the original Rotax springs in place but adding counter balance springs from the same fixed position to the opposite end (aft) of the the throttle arm 'bellcrank'?
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springs
Tom,
I sent you an email. Hal-san |
Springs Vs friction
Tom and Joe, thanks for your comments. Joe, I take your point that even with the friction easier to set, you still have to pull against the friction + spring tension to reduce revs. That is the nub of the problem. Reduce the spring tension and you can operate the throttle with a lower and safer level of friction. Got it. Shame Vans doesn?t see it that way.
Tom, I would like to join the list of builders buying replacement springs from you. I will PM you. Rod |
Been flying a lot with the original springs. NO PROBLEM here. Just something you have to get used to. Not hard to pull to the min RPM when landing. Consider this another user preference.
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Another user preference...
Agree with Marty, no problem here either. The stock springs can be counted on to deliver power when needed.
Exercise care, it is not a push/pull throttle system. Tony |
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