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Old Jun 28, 2009, 07:32 PM
...in the skies...
Cats Eyes's Avatar
Ottawa, Ontario
Joined Apr 2003
888 Posts
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Newbie question about pitch attitude, airspeed, etc.

Hi, guys

OK, I finally had my first FPV flight! It was short and featured an unscheduled landing. No damage, fortunately.

It all seemed to be going very well until I suddenly realized that I didn't have much altitude left. I increased the throttle, but that wasn't helping much. At about that time I also realized I was holding full up elevator. It was jammed against the stop and I couldn't get the nose to go up! At the time I thought that there was some problem with the R/C link. Anyway, I knew something was wrong and it seemed to be making a controlled descent, so I figured the best thing was to just let it land at that point. I had a bit of a walk, but the plane was still in one piece.

Upon reflection, what I figured happened was that I was slowly, gradually, increasing the up elevator as I was flying, I guess to try and compensate for what I thought was a nose-low condition. I was completely unaware I was doing this until I ran out of throw. I now realize something I never thought about, that is, that you don't have the same visual cues flying FPV as flying normally, and no way to really gauge airspeed.

I also now know what I should have done in that situation, which is to put the throttle wide open. During a subsequent "normal" flight I tried this. I slowed the plane down by gradually putting in more and more up elevator until it was near a stall, then jammed the throttle on. It did what you'd expect: it nosed up and started climbing. Just back off the elevator at that point and no more problem! Lesson learned.

Next time I try an FPV flight, I will also be a lot more aware of where I'm keeping the elevator stick, obviously. It's a slow, stable plane and it flies "hands-off", i.e. it's stable in the pitch axis. So here's the question:

Is it best to just leave the elevator alone (unless needed to correct for gusts or on turns) and let the plane find it's own pitch attitude, or is it better to line up the horizon at a certain spot (some marking on the nose, etc.)?

Here's the video of the flight. Note that the video camera is mounted underneath the nose, so what you are seeing is the bottom of the nose in the top of the frame. It's just foam so I could easily stick something in it to use as a horizon reference.

First FPV flight (1 min 18 sec)

Thanks in advance for any and all help!

-- Kevin
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Old Jun 28, 2009, 07:40 PM
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trappy's Avatar
Austria
Joined Feb 2007
6,411 Posts
mount your camera facing upwards a little more. If you over-compensate your elevator, you're trying to "look up" If your CG is right, you should not need elevator unless going in and out of turns or the usual acrobatics and minor corrections.

Edit: after looking at your video for a bit, it seems the camera position is fine... you'll just need to get used to it a bit it might help just forcing yourself not to touch the elevator for a while while in flight. Go a little higher up then try that. do a couple of turns, see what's needed. Always remember: Go 3 mistakes high ... especially when practicing "stalls" or "stall avoidance"
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Old Jun 28, 2009, 09:27 PM
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Joined May 2007
2,530 Posts
Im guessing flat lipo and downwind stall in the end.

Either your esc started kicking into softcut on low voltage, or maybe even the esc went into thermal prottection.?

Was looking fine until the end.

What
motor and KV
ESC size
prop size
Lipo size

Are you using ?
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Old Jun 29, 2009, 12:50 PM
...in the skies...
Cats Eyes's Avatar
Ottawa, Ontario
Joined Apr 2003
888 Posts
Thanks, guys.

So the answer is, leave the elevator alone except when needed for corrections or turns, and let the plane find it's own attitude. Right?

The lipo was fine, actually. I flew another 5-minute (or so) flight (non-FPV) just after and no hint of trouble. I probably did stall the plane, as I was holding way too much up elevator. Fortunately the plane stalls gradually and gracefully.

The video doesn't really convey what was going on very well. It doesn't show the low airspeed (which I must have had with that elevator position). What it does show is that, after the initial climbout and throttle back, I started losing altitude right away, which I wasn't aware of either during the flight. Something else to watch out for.

To answer the questions:

Motor: AXI 2808/24, KV 1190 RMP/V
ESC: Jeti Spin 22
Prop: APC 9 X 4.5 thin electric
Lipo: 3C 2200 mAH "LiPower Extreme"

This setup draws about 20 amps WOT on a fully-charged pack. I realize I'm cutting it a little fine with the ESC, but I've never had any trouble, and I've flown this plane with this combo quite a bit, including two non-FPV flights the same day. If you listen to the audio on the video you'll hear the motor is steady until near the end, when I decided to just cut the throttle and land. I'm 99% sure the problem was "pilot error," not any mechanical or electrical problem.

Thanks again for your input.

-- Kevin
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Old Jun 29, 2009, 08:16 PM
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Joined Feb 2009
194 Posts
Well, as a flight instructor I always teach

Pitch + Power = Performance.

You were probably on the back side of the power curve due to the flat lipo.

It just happened to work out for you that you had enough thrust left on the back side to land well.

Here is a quick explanation that I just looked up.

http://stoenworks.com/The%20Power%20Curve.html

You can search for aviation and power curve for more info.
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