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07-18-2006 05:04 PM  14 years ago
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workerant

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MN - USA

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Throttle curve questions
Using throttle curves and stick at half (zero deg) should I be able to leave it at half stick and keep my desired head speed, or will it tend to over speed? In other words, should I have my mid stick throttle setting set so if I am at half stick on the ground, the head speed holds at 1830.

Do I want to run the head at 2000, or about 1900 so I have a little buffer when the head over speeds during a decent or something?

I'm flying a Rappy 50, OS 50 Hyper, about 1.5-2 gals run through. Using throttle curves, no governor or limitor.

Thanks!
Raptor 90, Raptor 50
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07-18-2006 05:18 PM  14 years ago
ptarp

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IL

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From my experience, there will be no way to prevent some overspeeding without a governor. If you reduce throttle enough around mid stick to prevent this during descents, then you'll loose some power when doing flips/rolls etc. I became so tired of worrying about overspeeding I bought a rev-lock: a governor is easily the best upgrade I've made so far.
Philip
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07-18-2006 05:20 PM  14 years ago
jsenicka

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Eagle River, WI

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your zero pitch needs to be a chunk lower than your hover points or it will over speed passing through zero.
I have around 55% at hover points and somewhere in the 45 range at zero pitch.
Jim Senicka
Team Manager, GrandRC Flight Team
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07-18-2006 06:49 PM  14 years ago
Leif

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I second what Philip said. You CAN set up a nice V-curve for aerobatics and it'll do pretty well for sport and basic aerobatic flying. However, once you start doing maneuvers that involve knife-edge orientations you'll start to run into problems.

If you set the mid-point of your curve for a constant headspeed at no load, you'll find that you lose headspeed during vertical maneuvers such as stall turns, tailslides or death spirals. This is because you typically use additional energy from either cyclics (rolling or flipping) or the tail (piros or backwards flight) during these maneuvers. You'll also lose headspeed during flips.

It is even more difficult to avoid overspeeding for maneuvers that call for negative pitch while upright or positive pitch while inverted. Pogos and "the wall" result in overspeeding unless you have a governor. Even tumbleweeds are hard to keep consistent.

With all that said, if you aren't doing any of these maneuvers yet by all means set up a nice v-curve and have fun. You'll want the mid-point to give you a bit higher RPM than normal under zero load and try to avoid fast descents under power.

Leif
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07-18-2006 06:52 PM  14 years ago
jsenicka

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Eagle River, WI

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I disagree. You can easily mix in throttle correction for flips and rolls, assuming your radio supports it.Jim Senicka
Team Manager, GrandRC Flight Team
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07-18-2006 06:54 PM  14 years ago
jsenicka

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Eagle River, WI

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I run 40% swash mix in idle up on my 9Z. I can roll from one end of the field to the other on the R60 with no headspeed change, and still not overspeed on high hover. My only issue is if I jam collective opposite my direction of hover, in which case I will over speed. There I could use a gov.

Trying to maintain rotor speed without swash mix would be hard...
Jim Senicka
Team Manager, GrandRC Flight Team
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07-18-2006 07:13 PM  14 years ago
Leif

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You can easily mix in throttle correction for flips and rolls
Yes, you can and most guys doing aerobatics without a governor use cyclic to throttle mixing. I still found that stall turns, tail slides and death spirals will load the head at zero pitch unless I program the throttle midpoint for a slightly higher headspeed "unloaded on the ground at zero pitch" than my target RPM. Also, some radios are limited in the number of available mixes, so you might not be able to correct for all the artifacts (such as tail loading).

My point is that there are a number of aerobatic moves that really bring out the benefits of a governor over a standard 3D curve. Vertical moves are one category, and any moves that intentionally use "negative" pitch relative to the direction of travel are another.

Leif
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07-18-2006 08:25 PM  14 years ago
jsenicka

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Eagle River, WI

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I hear ya.
I want one on my 60 at some point. But then again, I had a failing clunk line yesterday that would have had the gov masking the RPM changes that let me know I was leaning and overheating
Jim Senicka
Team Manager, GrandRC Flight Team
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07-18-2006 08:50 PM  14 years ago
workerant

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MN - USA

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Thanks for the feedback. I have a 9C so I'll be able to use the cyclic to throttle mixing.

I just want to clearify the zero pitch a little more, I hope this makes sense...

Is it acurrate to say that no matter what, the throttle curve should not push the head speed beyond let's say 2000rpm, but it is understood that the head speed may increase slightly do to, for example, descents?

Am I going about this the right way? Should I even be trying to set the head speed at half stick while on the ground? If so, if I shoot for a head speed of 1900 at hover, and I find that the engine bogs during manouvers, I might want to increase the mid stick to compensate.

To summarize, it sounds like I want to use cyclic to throttle mixing, perhaps as much as 40%, and be prepared to run the head at zero pitch higher in the unloaded state to compensate for the load from maneuvers in the air.

Thanks
Raptor 90, Raptor 50
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07-18-2006 09:00 PM  14 years ago
Leif

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USA

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You've got the gist of it. I never set RPMs on the ground... in fact I don't like to keep my helis on the ground any longer than I have to.

Set your headspeed for hovering and forward flight, then add cyclic to throttle mixing for rolls and flips. I would recommend using stall turns to set your zero-pitch throttle point, as this places some tail loading on the engine.

2000 RPM is generally considered the top safe sustained RPM for the larger helis, although I've run over this many times on my old Concept VR and my current Evo without any disasters. As long as the head holds together and you have thrust bearings in the grips a short overspeed event shouldn't result in an explosion. Of course, all bets are off if you're running wooden blades.

Leif
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