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Old Jan 27, 2006, 12:46 PM
Intermediate Pilot
preston_brown's Avatar
Chapel Hill, NC
Joined Dec 2005
338 Posts
Question
2nd outdoor flight, helicopter caught in wind/thermal?

Hi all,

Today has been the 2nd time I've flown a helicopter outdoors. Been flying since Christmas day, I got a Lama 2, and last week I finished building up a X400. I've test flown it inside a garage about 6-7 times, and I have hover and hover movement worked out.

Everything has gone well outside, although the rate of climb on the helicopter isn't that great right now (400DH motor is probably to blame). I get about 11 minutes of flight time on a 2100mAh battery pack.

Here's the question part: As I am a beginner, I have set up a fairly conservative pitch curve, and I'm flying with a CC35 in governor mode at about 2200 RPM. My pitch curve only has a very small bit of negative pitch at the bottom, and at mid stick, already has several degrees of positive dialed in. Still, hovering doesn't occur till I'm in the top portion of the stick.

I was flying around the big back yard, doing fine, and then I decided, hey, no ceiling! Let's fly a bit higher! I ascended to approximately 30 or 40 feet. Winds are calm to very low, and today is around 45-50 degrees and sunny.

All of a sudden, there was a LOT of additional lift on the helicopter. Even pulling the throttle WAY back (but I don't think I pulled it completely) the model was still climbing. Then, after a couple of seconds all of a sudden it started dropping of course, and I had to put in lots of throttle to keep it coming down at an alarming rate. I went through this for what seemed like eternity, attempting to bring the heli down at a controlled rate, cause it was really high now, almost higher than the tallest trees in my yard, and that's pretty high. I was getting really nervous and actually thought I was going to get disoriented and stuff it.

Eventually I had it under control and got it down, at lower altitudes (like 10-15 feet) the throttle behaved as I was used to.

Did I get caught in a thermal and thus the helicopter got extra lift? Did something else happen? Clearly I think the main remedy is to dial in extra negative pitch on the bottom, I guess it is time to set up an idle-up 1 curve?
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Old Jan 27, 2006, 12:53 PM
DRAGONUS
Cardiff, Wales, UK
Joined Jan 2006
1,150 Posts
Sounds more like radio interference to me

Butuz
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Old Jan 27, 2006, 01:01 PM
Intermediate Pilot
preston_brown's Avatar
Chapel Hill, NC
Joined Dec 2005
338 Posts
I doubt it was radio interference. I've got a Futaba 7CHP in PCM mode, talking to a R146iP receiver, and I have a noise filter between my ESC and receiver.
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Old Jan 27, 2006, 01:01 PM
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Motions's Avatar
Tallahassee, FL
Joined Nov 2005
480 Posts
It sounds very much like wind. Even small winds can cause a small heli to jump in altitude. You should definately be flying in idle-up and have at LEAST -5 degrees pitch. You don't want to fly at altitude you need to use idle-up because in normal you will loose head speed when you bring the throttle down.
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Old Jan 27, 2006, 01:04 PM
Intermediate Pilot
preston_brown's Avatar
Chapel Hill, NC
Joined Dec 2005
338 Posts
Thanks for the confirmation of the wind theory. I guess you are right about losing head speed at the very low end in normal mode (my gov. throttle curve for normal/hover is 0 80 80 80 80).

I'll set up an idle-up with more negative pitch and constant throttle across all 5 points.
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Old Jan 27, 2006, 07:29 PM
Registered User
Joined Jul 2005
200 Posts
At least you had negative pitch, my GWS Minidragonfly FP chopper goes for one heckuva rollercoaster ride when I get it up above our 2 story house. The only way to bring it down is to reduce the throttle at which point it becomes a heavy kite, soon as the wind dies or the rotor slows too much down she comes..........................and quick! Haven't stuffed it yet but I picked up an X400 for breezy days and I'll keep the lil guy for calmer stuff.
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Old Jan 27, 2006, 08:16 PM
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ukgroucho's Avatar
Stratford upon Avon
Joined Jul 2004
2,502 Posts
Quote:
Originally Posted by preston_brown
Thanks for the confirmation of the wind theory. I guess you are right about losing head speed at the very low end in normal mode (my gov. throttle curve for normal/hover is 0 80 80 80 80).

I'll set up an idle-up with more negative pitch and constant throttle across all 5 points.
That should work... you also want more headspeed. 2200 is a little 'light' for dealing with windy conditions on a small rotor disk... 2400 would be better as it reduces the impact of gusts and gives you more control generally. Better to fly for 1 minute less than to heap it 'cos you don't have control.... and it may not actually reduce flight time - depends on where the BL motor is in it's efficiency curve. If 2200 is 'inefficient' then 2400 might be in the sweet spot so battery life might actually improve.

Sounds like you're doing really well! Congratulations on getting it back in one piece!

Oh, one more thought... sounds like you have tall trees around. These can cause some funky wind effects. In general the wind will be a little more as you climb from 0 to 50 or even 100 feet but big trees can add to this by causing sheltered spots - and exagerated 'high wind' areas.
My flying field (an old airfield) has a set of trees about 100 - 150 yards from the RC fly zone and if the wind is in the right direction they cause some really odd effects where we fly..
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Old Jan 27, 2006, 09:00 PM
Chesapeake Bay RC Club
Gary Hoorn's Avatar
USA, MD, Annapolis
Joined Feb 2005
4,964 Posts
Quote:
Clearly I think the main remedy is to dial in extra negative pitch on the bottom, I guess it is time to set up an idle-up 1 curve?
Yes and Yes when flying outside and doing anything other than just low level hovering on calm days. If your Tx has more than 1 Idle Up postion set that up as well in case you push the switch too far in a panic! There have been Helis crashed by inadvertently switching to an Idle Up that was not configured.
Gary
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Old Jan 27, 2006, 09:48 PM
Registered User
San Carlos, California, United States
Joined May 2002
7,640 Posts
Quote:
Originally Posted by ukgroucho
...
Oh, one more thought... sounds like you have tall trees around. These can cause some funky wind effects. In general the wind will be a little more as you climb from 0 to 50 or even 100 feet but big trees can add to this by causing sheltered spots - and exagerated 'high wind' areas.
My flying field (an old airfield) has a set of trees about 100 - 150 yards from the RC fly zone and if the wind is in the right direction they cause some really odd effects where we fly..
That's called "rotor".

They're air eddies (not to be confused with EddieMoth or EddieNewYork) caused by wind blowing past obstacles.

We're very careful of them when paragliding.

Toshi
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Old Jan 27, 2006, 09:54 PM
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ukgroucho's Avatar
Stratford upon Avon
Joined Jul 2004
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OK Toshi.. I'm intrigued... eddies I understand but
EddieMoth?
EddieNewYork?
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Old Jan 27, 2006, 09:58 PM
Registered User
Joined Dec 2004
248 Posts
climb out rate not good? have you tried the 400dh without gov mode on your esc? I have read quite a few posts about gov. mode really decreasing the performance of the 400dh.
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Old Jan 27, 2006, 10:20 PM
Registered User
San Carlos, California, United States
Joined May 2002
7,640 Posts
Quote:
Originally Posted by ukgroucho
OK Toshi.. I'm intrigued... eddies I understand but
EddieMoth?
EddieNewYork?
Yes, those are Eddies, not eddies.



Toshi
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