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Old Jul 26, 2003, 04:16 PM
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sizam's Avatar
Mountain View, CA
Joined Aug 2002
363 Posts
Help, CP hornet won't maintain altitude...

I'm flying a CP hornet with the Alu swashplate upgrade, Astro 10T 010, 3cell 1200 eTec, and the 12-tooth pinion. I'll get it up to about 6' in the air and it'll stay at that altitude for 10-15 seconds but then just drop altitude and if I don't throttle up it'll land and bounce back up, whats the problem? It must be losing RPM (the only reason I can think of) because shouldn't it maintain a hover as long as I don't drop the throttle, I shouldn't need to throttle up should I?
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Old Jul 27, 2003, 11:40 PM
It's a really big number.
Brisbane Intl, Australia
Joined Jan 2001
1,315 Posts
Remember that the hornet is a small heli, and that when it gets into its own turbulance, it loses a lot of lift. So once it starts to sink, it can get caught in the rotor wash and keep on going, getting faster and faster...

Mine will do exactly the same if I spill too much air playing with the cyclic when hovering around. Just needed a boost of power or nose forward slightly to break out of the bogging caused by decending in turbulence to break free.

Try nosing forwards slightly, and if you go back up, that's the problem....

I found backing off the throttle around hover smoothed mine out a bit too (less turbulence from the lower head speed I guess...)

-tim
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Old Jul 28, 2003, 02:47 PM
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sizam's Avatar
Mountain View, CA
Joined Aug 2002
363 Posts
That is _exactly_ what is going on! I found that if I moved forward or anywhere out of where the hornet just was it'd shoot up, which made no sense at the time. Would incresing the pitch (lowering head speed) help at all, I don't think it would since the same amt air would be moved..?
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Old Jul 31, 2003, 12:01 AM
It's a really big number.
Brisbane Intl, Australia
Joined Jan 2001
1,315 Posts
Sorry about the delay - been working ~

Its something you have to play with. I found that a lower head speed was better, but it might just be because the air spill as you move the cyclic to stay still is lessened due to lower velocity of the displaced air. Its a problem on short and wide bladed heli - they really throw air out to the sides as you deflect the cyclic.


Which body are you using btw? The s300 is a HORROR for this because of the big wide top section of the canopy for all the sinking air to press on. I have flown with both s300 and standard weighted to be the same - the s300 sinks a lot worse,...

-Tim
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Old Jul 31, 2003, 01:23 AM
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DELAWARE
Joined Mar 2003
846 Posts
If you are hovering in the house you are flying in "dead air". the rotor pushes all of the air out from under it and tube like pocket of dead air is forms. There have been instances where real helicopters get caught in this while hovering to low for to long an just fall to the ground. Take it out side and i will bet you it will hover up 20feet with less throttle.
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Old Jul 31, 2003, 03:58 AM
It's a really big number.
Brisbane Intl, Australia
Joined Jan 2001
1,315 Posts
Yes, I also have found outside better. When there is a roof it restricts the intake flow to replace the air undernieth and excassibates the problem. Inside, my hornet gets to about 8" from the roof and won't go any higher due to cavitation. Of course if I really hammer the collective and go up like a missile, it hits every time


-tim
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