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Old Jun 04, 2012, 08:02 PM
Better then Sliced Bread!
NorCalMatCat's Avatar
United States, CA, Arcata
Joined Oct 2011
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Originally Posted by Eagle202 View Post
I agree that a P51 or for that matter just about any of the old war birds will easily stall.

I can testify that the SS can and does stall even with the wing dihedral. It will also recover from a stall better than most planes. You just have to learn to override your internal desire to power out of the dive and just let the plane's natural gliding ability to do the work.

It took me at least 2 OS stalls crashes to learn not to panic.
Oh believe me I know it can, here is a tip stall from earlier this year for those that haven't seen it, or haven't seen it in a while .

Bixler FPV CRASH! (1 min 13 sec)
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Old Jun 04, 2012, 08:09 PM
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Originally Posted by NorCalMatCat View Post
Oh believe me I know it can, here is a tip stall from earlier this year for those that haven't seen it, or haven't seen it in a while .

http://www.youtube.com/watch?v=zoH3U5olbCw
Ah yes. I remember the video of your Bix deciding to go on a month vacation.

I still think it hit the power line and lost it's memory or it would have found it's home a lot sooner.
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Old Jun 04, 2012, 08:11 PM
Better then Sliced Bread!
NorCalMatCat's Avatar
United States, CA, Arcata
Joined Oct 2011
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Quote:
Originally Posted by Eagle202 View Post
Ah yes. I remember the video of your Bix deciding to go on a month vacation.

I still think it hit the power line and lost it's memory or it would have found it's home a lot sooner.
We will never know But she flies great now, and with that FY31AP I don't really worry about it now .
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Old Jun 04, 2012, 08:14 PM
Row 0, Seat A
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Quote:
Originally Posted by Eagle202 View Post
I agree that a P51 or for that matter just about any of the old war birds will easily stall.

I can testify that the SS can and does stall even with the wing dihedral. It will also recover from a stall better than most planes. You just have to learn to override your internal desire to power out of the dive and just let the plane's natural gliding ability to do the work.

It took me at least 2 OS stalls crashes to learn not to panic.
ANY airplane will stall if the pitch authority or flight dynamics are sufficient to cause the wing to exceed it's critical AOA. What it does then is a function of many factors. Airfoil section, wing loading, g, wing geometry, wing twist (washout/washin), Reynolds Number, wing stores present or not, and maybe several other things I'm forgetting. Dihedral has no affect on stall. The only recovery procedure is to decrease AOA. That is done primarily by decreasing elevator input (even to full "down" as required) or by increasing power (airspeed).

What's an "OS stall"? I'm not familiar with that term.

Ted
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Old Jun 04, 2012, 08:22 PM
Why so serious?
2500GENE's Avatar
United States, FL, Cape Coral
Joined Dec 2007
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Originally Posted by G550Ted View Post
What's an "OS stall"? I'm not familiar with that term.

Ted
I believe it rhymes with "Oh Spit"
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Old Jun 04, 2012, 08:23 PM
Row 0, Seat A
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Originally Posted by 2500GENE View Post
I believe it rhymes with "Oh Spit"
Well then, PAHTOOHEY!

Ted
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Old Jun 04, 2012, 08:30 PM
Better then Sliced Bread!
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United States, CA, Arcata
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Spit happens...
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Old Jun 04, 2012, 08:33 PM
Limited flyer
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Some times i wonder if ted and AJ will ever bury the hatchet, but on a more upbeat note, i finally got the rythem to do fair to middling, stands in the wind, {no vid so belive what you will}, but i was timed flying in one spot for over 30 seconds,personal record.

B.T.W That felt awsome when i done it,l and it still feels awsome.
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Old Jun 04, 2012, 08:59 PM
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Quote:
Originally Posted by G550Ted View Post
ANY airplane will stall if the pitch authority or flight dynamics are sufficient to cause the wing to exceed it's critical AOA. What it does then is a function of many factors. Airfoil section, wing loading, g, wing geometry, wing twist (washout/washin), Reynolds Number, wing stores present or not, and maybe several other things I'm forgetting. Dihedral has no affect on stall. The only recovery procedure is to decrease AOA. That is done primarily by decreasing elevator input (even to full "down" as required) or by increasing power (airspeed).

What's an "OS stall"? I'm not familiar with that term.

Ted
Ted

Maybe I have been led astray concerning dihedral. It was my understanding that wings that have more dihedral are harder to tip stall than those without any dihedral. Since I am not an expert, I learn to listen to those that I believe have more knowledge on this subject. The person on this topic happens to have flown and still fly's larger cargo jets for a living as well as having a couple of decades of RC flying under his belt.

I do know that the best way I have found to get out of a crash when my SS has stalled is to power down and let the elevator stick go. If it has enough altitude then it will flatten out by itself. When I have tried increasing power to pull up I have not had very good results.

As for the "OS stall". I believe Gene hit the nail on the head. That is why I try to fly 1 to 2 OS high when trying out a new maneuver. The old heart can't take too much excitement anymore.
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Last edited by Eagle202; Jun 04, 2012 at 09:01 PM. Reason: added info
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Old Jun 04, 2012, 11:46 PM
ICrashRCs
United States, TN, Memphis
Joined Jun 2011
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Re-Test

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Originally Posted by Scooch View Post
Just to add some info. It is the stock setup, engine, prop all stock. The ESC did start to get hot while on the bench. I was not moving any control surfaces while running the motor. I'm not sure why you would want to continually do that anyway. I don't think it is a control surface issue. The ESC was out of the plane at the time. After running it, I did feel the motor and found it to be hot as well. I pulled the fuse apart earlier and checked to make sure that the motor was not rubbing on the foam. It's all clear.
Could you do us a favor and run a little test?
Turn on your Tx.
Plug a battery into your plane.
Do not move anything and let it sit for 1 minute.
Is the ESC cold/warm/hot?

Now while still not moving any control surfaces,
run up the motor for 25 to 35 secs. Just running up and down with throttle, not a lot of full throttle.
Is the ESC cold/warm/hot?

Some may better suggest a different length of time to run the motor.

That would at least get everyone on the same page for diagnostics.
I'm guessing that it's perfectly fine as is. But let's see what we've got.
My thinking is that it was run too long and got hot like it's supposed to.
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Old Jun 04, 2012, 11:58 PM
ancora imparo
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Melbourne, Australia
Joined Jul 2005
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I know I wasn't supposed to read this but for those who are interested in the question there's bit more info in my post here

http://www.rcgroups.com/forums/showp...ostcount=14945

In summary 4x HXT900's stalled pull just under 2.5A.

All the 3A UBECs I tested could actually deliver 3A continuously but a lot of them got very hot at that current. None actually failed, but after 10minutes at 3A some were well over 80C (180F).

So in practice you aren't going to have problem with a 3A switched BEC on a Bixler/Skysurfer since the chances of running 4 servos stalled for 10 minutes AND staying airborne are zero for other reasons I would think.

Quote:
Originally Posted by ajbaker View Post
P.S. For you only, what do you think would happen if it is a control surface problem and he used an external sBEC? Would the ESC or sBEC still get hot? I do not know the answer to this hypothetical situation. I have never tested that thought before.
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Old Jun 05, 2012, 12:06 AM
Argue for your limitations
ajbaker's Avatar
Lincoln, CA
Joined Oct 2006
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hanging out

Quote:
Originally Posted by Eagle202 View Post
The best way to tell if you have a good or cheap meter is to check what the CAT rating is. A really good meter has a CAT III at 600V. A lesser meter has a CAT II at 600V but may have a CAT III at 200V. The really cheap units won't say what their CAT rating is....
So, since my HF meter does not have a CAT rating, is it a DOG?
Darn. I have been hanging around GENE too long.
AJ
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Old Jun 05, 2012, 12:29 AM
Argue for your limitations
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Lincoln, CA
Joined Oct 2006
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Quote:
Originally Posted by jj604 View Post
I know I wasn't supposed to read this but for those who are interested in the question there's bit more info in my post here

http://www.rcgroups.com/forums/showp...ostcount=14945

In summary 4x HXT900's stalled pull just under 2.5A.

All the 3A UBECs I tested could actually deliver 3A continuously but a lot of them got very hot at that current. None actually failed, but after 10minutes at 3A some were well over 80C (180F).

So in practice you aren't going to have problem with a 3A switched BEC on a Bixler/Skysurfer since the chances of running 4 servos stalled for 10 minutes AND staying airborne are zero for other reasons I would think.
Ah. Got it. That is what I was wondering. My question was supposed to be -> If I had a heat problem with an external linear BEC, would an external sBEC minimize or stop the heat problem. If I am reading your post like you wrote it, it appears that the heat problem would still be present. Am I reading your post correctly?
In my experience of installing sBEC's, the BEC "seems" to be cooler compared to other linear BEC's. As stated before, I have yet to an sBEC vs linear BEC controlled experiment to see what difference there is in heat and and amp draw, voltage differences.
I started out looking at this situation as an off topic discussion. However, if there is a huge difference (like the sBEC running cooler) in our Sky Surfers/Bixlers, I think it would be well worth a Page #1 posting. So, any input (tests, experiments, accurate numbers on the SkyS/Bix) would be appreciated. Full credit to the pilot will be given on page #1. TIA
AJ
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Old Jun 05, 2012, 01:14 AM
Limited flyer
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So are you talking about just testing seperate bec's or ones that are built in as well? What about swtch mode?
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Old Jun 05, 2012, 01:40 AM
ancora imparo
jj604's Avatar
Melbourne, Australia
Joined Jul 2005
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I looked only at separate switched BECs initially then compared them to a couple of ESCs I have with "2A" integrated linear BECs. Typical HobbyKing/HobbyWing 30A ESCs.

The integrated BECs I have run VERY hot at the same current as a switched BEC.

It will obviously depend on your battery voltage as well as the current you are pulling - I tested these at 12V which is as high as I would want to use an integrated linear BEC.

In summary:

1) An external switched BEC will always run cooler than a linear BEC at any reasonable load.
2) A switched BEC will handle higher applied voltage than a linear BEC (normally limited to 3S) since the linear BEC dissipates ALL the unused power as heat.
3) Even the cheapest switched BEC I tested kept working at high temperatures.
4) Don't believe any label that says more than 3A on a cheap switched BEC unless you actually test it. I have a "5A" one which shuts down at bit over 3A
5) The advantage of a linear BEC is that it generates much less electrical noise than a switched one - didn't look at that this time around. That's why the designers have to put a big ferrite ring on the servo lead of the switched BEC because they did fairly poor job of minimising the electrical noise it generates.
6) The only advantage of a linear BEC integrated into an ESC I can see is convenience and minimum weight for small planes.
7) If your ESC craps itself there is a fair chance your inbuilt BEC will too and you are cactus. With an external BEC connected to the flight battery you have a fair (but not guaranteed) chance of retaining flight control even if your ESC fries or the LVC cuts in at a very low value.

When I say switched BEC I mean an separate external switch mode BEC - the sort of thing you can buy for $5-$10 from HK. Typical of what a Bixler/Skysurfer/Easystar would use. There are fancier high quality ones, high voltage ones and specialised fail safe versions.

All my integrated ESC BECs are linear as far as I can tell.

I haven't looked at separate external linear (which are less common but have a good rep if used within their specifications) or switched BECs integrated into an ESC.

FWIW, I wouldn't use an integrated linear BEC on anything but a weight critical or small plane any more.

aj, the answer to your question ,"My question was supposed to be -> If I had a heat problem with an external linear BEC, would an external sBEC minimize or stop the heat problem. If I am reading your post like you wrote it, it appears that the heat problem would still be present. Am I reading your post correctly?"

is that an external switched BEC will normally run cooler than a linear BEC at almost all voltages since it is more efficient at turning input power into output power. There are a few cases where the linear BEC might be better when the input/output voltage is small but in practice it would only happen on 2S batteries I'm guessing. Haven't done the calculations.

So in one word, yes.

John
Quote:
Originally Posted by Limited flyer View Post
So are you talking about just testing seperate bec's or ones that are built in as well? What about swtch mode?
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