Throttle springs

N800LH (120052) took her first flight this morning under my command! Everything worked great! Only one thing I am not particularly fond of on the whole plane is the sprung full open throttle cables. Maybe it will just take a fair amount of getting used to for someone who has for many years only flown standard push pull throttles. What do the rest of you think of just removing the open throttle springs so the darned thing doesn't charge forward if you take your hand off for a split second if you don't have it locked yet? I know that I would be removing a supposed safety feature, but most aircraft don't have this and seem to work just fine.
Larry

Hi Larry.....

...I'm not familiar with the -12's throttle setup but it sounds almost indentical to the Zenith 701s. A guy removed the springs and bought weaker ones for his 701, from an auto parts store.

On the first flight, he was short and added power but nothing happened! Into the trees and a totalled airplane. I'd really reconsider,

Best,

Larry,

For one thing, Rotax will void your warranty if you take it off. They would rather you have full power if it breaks than no power. Not a bad idea. What I have learned as the thing gets used a lot....there is a "just tight enough" position on the lock where you can comfortably push it in and out and it doesn't move. Works good for landing. You just have to experiment. Then on long flights you just set it at your RPM and lock it tight. You'll get used to it. Mainly because you'll keep saying "wow, what a view".

Pete

HOW ABOUT INSTALLING A VERNIER THROTTLE AFTER THE 5 HOURS ARE FLOWN OFF? MY 12 HAS A LONG WAY TO GO BEFORE FLIGHT BUT I HAVE FLOWN A FRIENDS AND AGREE THIS IS NOT A COMFORTABLE SETUP. MY CTSW HAS THE SAME ENGINE WITH THE SAME SPRINGS BUT WITH A DIFFERENT THROTTLE SETUP. THE THROTTLE IS EASY TO MOVE AND NEVER STRAYS FROM WHERE I PUT IT. THERE IS NO IN FLIGHT ADJUSTABLE FRICTION EITHER. FRICTION IS ADJUSTED DURING MAINTENANCE AND RARELY NEEDS FURTHER ATTENTION.

Reiterating what Pete had said, a change is not necessary here. You will very easily get used to the way the throttle lock works. It is VERY easy to manipulate with your right hand any time a RPM change is called for. Try it before installing something different!

I would NOT change the spring, nor change the throttle cable arrangement. Van's made a wise choice here. Change the spring arrangement......If the throttle cable has a problem, would you prefer to land in a field or land at the next airport and then shutdown the engine when on final?

I admit I know very little about a vernier throttle, nor do I particularily like them, nor would I advocate doing away with the carbs being spring loaded to go full throttle. But, would a vernier throttle change that? Seems the safety feature would work the same either with the stock throttle or the vernier throttle. If my thought is correct, then it comes down to a matter of preference and would not affect safety.

Why change it!!!

With over 50 hours on my RV-12 I find the friction nut and spring to open throttle easy to use and have have had no problems. I have had more problems with a vernier throttle on a Eurofox, with quick throttle application, maybe it is the cheap vernier they use.
I believe if it aint broke don't fix it or when you are on to a good thing stick to it.
Tony

Weaker Springs

I searched though online spring catalogs to find a suitable, but weaker, replacement for the Rotax throttle springs. The Century the 6049 came closest, but it does need to be shortened by 1/4". There is a picture of these springs in my previous post about modifications after certification:
http://www.vansairforce.com/community/showpost.php?p=492537&postcount=51
I am resurrecting this thread because of this email that I just received from a builder who also replaced his throttle springs with the weaker ones.

Joe, I installed the reduced-force throttle springs on my RV-12 several weeks ago and they work great. No more throttle creep. Thanks for this wonderful mod. Denny Myrick

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Another builder, Wayne, is installing the weaker springs. He has not flight tested them yet due to illness and cold weather. I am anxious to hear how he likes them. I know that I do.
I have read the warnings posted above and realize there is a danger whenever a significant change is made to an aircraft. It is definitely safer to do nothing and use the well proven stock springs. On the other hand, we are flying experimental airplanes and are allowed to experiment and to make improvements. If no one ever experiments, then progress will never be made. I definitely did not like the original springs. Even with the friction lock fully tightened, the throttle would creep forward. Some of you do not have that problem. But you are most likely younger and bigger and have a stronger grip to tighten the friction knob. I prefer a throttle that stays where I put it without gremlins pushing it in when I am not looking. My new springs are not purchased from a hardware store. I have done my homework and chosen springs with the desired properties: 4 pounds of tension compared to 8 pounds for the original springs. With the friction knob unlocked, the new weaker springs will still open the throttle, overcoming the friction of the cable. With a broken cable, it will be even easier for the springs to open the throttle. Theoretically, weaker springs are less likely to break because they are under less tension. And likewise, the little plastic bushings are less likely to wear out. I admit that there could be problems that I am not aware of. Time will tell. Meanwhile, I like having the throttle staying where I put it.
Joe

Throttle Springs

I am not a fan of the springs either, but with the flexible cables that cannot be "pushed" they seem necessary

I would pefer to replace the entire throttle assembly with a solid core wire like the conventional throttle systems, so that you can push forward instead of relying on the springs. That would seem to be a relatively easy modification. Has anyone tried that?

Joe,

Thanks for bringing this up again. I only have 3 hours on N37JP, but the one thing I haven't gotten used to yet is having that throttle jump wide open if I set the friction too light. If I can't overcome my old habits and this continues to be annoying I might just relieve you of a couple of those springs. How hard was it to modify the ends to get the right length?

John

Shortening springs

How hard was it to modify the ends to get the right length?

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The nice thing about springs is that they stretch. It is better to cut the spring slightly short and not to worry, it will stretch to the required length. Extension springs have a certain maximum extended length. This particular spring can be extended way more than needed, up to 2". Bending the end hook can be done by holding the spring against the work bench while using needle nose pliers.
Joe

Had the same revulsion for the first few flights. After about 10-12 hours in the plane it seems normal (and is quite convenient on take-off roll, since you just let it loose and concentrate on other things like flying the plane). And now I can't figure out why I have to push the throttle forward on the big Lycoming in my RV-10!

-Dan Masys

Mich48041 said:

Even with the friction lock fully tightened, the throttle would creep forward.

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Certainly, if you are not comfortable you can change out the springs, but if the friction nut cannot be tightened by hand to stop 2 little springs there is something wrong with the throttle friction control. The only time mine creeps forward is when I have it too loose. It is second nature now to set it right and not an issue at all. I don't even think about it when flying and taxing.

Your post is well thought out and logical. These are experimental aircraft so you can change them. I was going to change out the springs until I got used to the stock ones and it is no longer an issue at all. Keep us posted on how it turns out, but I would take a second look at your throttle set up.

email from happy builder

Today I received an email (quoted below) from a RV-12 builder to whom I had sent weaker throttle springs.
Joe

Joe, Installed the springs per your instructions yesterday. Resisted the temptation to duplicate exactly the complex profile of the Rotax originals. Figured the less cold-working the steel, the better. Used some needlenose that I had rounded off the serrations and straight edges, avoiding stress risers on the springs.

Well...what a revelation. *This* is the way the 12 *should* be! Set the friction lock so throttle action is like a normal plane. Now I can set an RPM and it will stay there and if I have to jam it forward (e.g. imminent bird strike) it'll go.

Of course it makes ground handling a lot less stressful but the absolutely nicest thing is landing and immediately after touchdown when you want to get that RPM back up to 2000.

Please feel free to share my comments but please don't use my name.

I sure appreciate your work in finding and developing this "common-sense" solution.

Oh, one other thing. When I had installed one spring and the other was on the bench, I cycled the throttle cables and sure enough, the one spring easily moves both cables in and out. I realize this might not be the case if the cables were old and fouled but it was nice to see.

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