put my biggest one in a tree and don't exactly know why!? (Full Version)

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fozjared -> put my biggest one in a tree and don't exactly know why!? (5/9/2008 5:18:31 AM)

i have a big spad that i built specifically for a 30cc weedeater engine, i have flown it quite a bit, but the elevator has never had the authority that i like, so i made the plane very slightly tail heavy and that seemed to help for a long while, but today i flew her for about 10 minutes, everything seemed fine until about 10 minutes in and suddenly the plane stopped responding to elevator input, well it did respond to the input, but i had full up elevator, and the plane just acted like i had about 1/4 stick or less pulled back, it slowly sank i continued to hold full up, but the plane was about to get over a thick forest and then out of sight so i banked and in doing so it lost enough altitude to catch the top of a tall pine and there is where it is sitting right now.. it weighs 15.5 lbs and has over a 7ft wingspan but for some reason it took more than 1 hour to find, and when i did it was lodged in the top of a very tall pine so i don't know what to do about that, but i am sure i can figure something out for that, but what i cant figure out is why when i held full up for about (absolutely conservative figure) 10 seconds, probably longer that it just slowly sank!? this is the second time that this has happened, but i couldn't get the plane to repeat any issue.. the only thing that i can figure is that the coroplast elevator is flexing out towards the ends and not giving enough surface deflection during higher speeds.. although it didn't seem that it was moving that fast when it stopped responding, but i guess it was moving pretty fast, i bought some music wire and tomorrow if i can get it down somehow i will run the wire through the length of the flute in the center of the elevator and see if that helps. any other ideas?



aussiesteve -> RE: put my biggest one in a tree and don't exactly know why!? (5/9/2008 6:16:43 AM)

Do you have any photos of the plane to post?
Preferably at least one prior to it getting "treeborne"



gboulton -> RE: put my biggest one in a tree and don't exactly know why!? (5/9/2008 12:20:06 PM)


quote:

ORIGINAL: fozjared
but what i cant figure out is why when i held full up for about (absolutely conservative figure) 10 seconds, probably longer that it just slowly sank!?


Almost certainly because it was stalled.

We'd need more specifics about the flight profile prior to the behaviour to be certain, of course, but I'd wager several cold beverages that that's the answer.




gunfighterII -> RE: put my biggest one in a tree and don't exactly know why!? (5/9/2008 12:53:41 PM)

I would agree with the stall. Might have got caught going downwind to slow. Don't ask how I know this.[:)]

Get out your fishing pole and put a large hook on it. Good Luck.[:D]

Let's see some pics when you get it down.



fozjared -> RE: put my biggest one in a tree and don't exactly know why!? (5/9/2008 3:15:40 PM)


quote:

ORIGINAL: gboulton


quote:

ORIGINAL: fozjared
but what i cant figure out is why when i held full up for about (absolutely conservative figure) 10 seconds, probably longer that it just slowly sank!?


Almost certainly because it was stalled.

We'd need more specifics about the flight profile prior to the behaviour to be certain, of course, but I'd wager several cold beverages that that's the answer.




you would definitely lose the beverages! hehe.. but seriously, there is no way it was stalled, it was scooting along at a good click, that is why i think that the coroplast elevator was flexing out at the ends and not providing quite enough deflection. it was definitely not stalled though, it was moving far too fast for that and this wing, as ugly as it is, has a tremendous amount of lift at low speeds and has a very low stall speed, and it was moving at almost its fastest speed (~40-50mph is as fast as she'll fly weighing 15.5lbs with a 30cc trimmer engine) i think that either the two times it has happened thus far, the servo didn't reach full deflection, or the coroplast flexed enough to not be at full deflection.. i bought some music wire and plan to strengthen the coroplast and maybe it will move all as one now. (that is when and if i get her down from the great heights of the mighty pine holding her!) will post pics later as i am on a work pc.



gboulton -> RE: put my biggest one in a tree and don't exactly know why!? (5/9/2008 4:08:58 PM)

quote:

ORIGINAL: fozjared
you would definitely lose the beverages! hehe.. but seriously, there is no way it was stalled, it was scooting along at a good click
...
*snip*


Airplanes can, and do, stall at any speed. Despite popular (and sometimes vehemently argued) belief, an airplane does not stall because it is too slow. It stalls because its wings have exceeded their critical angle of attack...a situation that can occur at full power in a dive as easily as it can occur with power off.

quote:


it slowly sank i continued to hold full up


Thus, aggravating the stall

quote:


but the plane was about to get over a thick forest and then out of sight so i banked


Thus FURTHER increasing the angle of attack AND drag on one wing, AND increasing the plane's weight
================

You believe, as many do, that if airspeed is over X, there's "no way it was stalled". That belief will cause you to stall airplanes and wonder why the elevator wasn't working. :)





Nathan King -> RE: put my biggest one in a tree and don't exactly know why!? (5/9/2008 4:41:28 PM)


quote:

ORIGINAL: gboulton

quote:

ORIGINAL: fozjared
you would definitely lose the beverages! hehe.. but seriously, there is no way it was stalled, it was scooting along at a good click
...
*snip*


Airplanes can, and do, stall at any speed. Despite popular (and sometimes vehemently argued) belief, an airplane does not stall because it is too slow. It stalls because its wings have exceeded their critical angle of attack...a situation that can occur at full power in a dive as easily as it can occur with power off.

quote:


it slowly sank i continued to hold full up


Thus, aggravating the stall

quote:


but the plane was about to get over a thick forest and then out of sight so i banked


Thus FURTHER increasing the angle of attack AND drag on one wing, AND increasing the plane's weight
================

You believe, as many do, that if airspeed is over X, there's "no way it was stalled". That belief will cause you to stall airplanes and wonder why the elevator wasn't working. :)





I love 'ya Gboulton! [image]http://members.cox.net/scaleaviator/love.gif[/image]

That's precisely what I was thinking as I read the post. I'd bet anything that's what happened.



Villa -> RE: put my biggest one in a tree and don't exactly know why!? (5/9/2008 10:13:39 PM)

What size elevator servo were you using?



fozjared -> RE: put my biggest one in a tree and don't exactly know why!? (5/10/2008 3:00:50 AM)

villa, you are right on!! i swapped to a stronger elevator servo and it flies so much better!!

i cut the tree down to get the plane, it came down on a pile of saplings i had cut and piled up for it to fall on, it rested so softly i was amazed! i got it up to the shed, swapped the rx battery and held a little pressure on against the elevator and it struggled hard to deflect so i think that was the problem.. swapped to a stronger servo and it deflected even against me pushing hard on it, so i flew it and was much more pleased..

Mr. Boulton, in your quote where you said that me holding full up furthered the stall, well normally that would definitely be true, but in this case me moving fast evidently put to much stress against that servo and it wouldn't move to its fullest.. as i said before, this wing has a great amount of lift and a very low stall speed, the nose was pitched down slightly so i severely doubt that it was caused by stalling, but thanks for all the info sir!



Villa -> RE: put my biggest one in a tree and don't exactly know why!? (5/10/2008 2:47:41 PM)

Hi fozjared
You mentioned using steel music wire to stiffen the horizontal stab. Recently I used a piece of carbon fiber tubing purchased from the LHS to do the same job. It is a very snug fit inside the coroplast flute. It weighs very little and it is amazingly rigid. However, it is very pricey. On another plane I simply used two layers of 4MM coroplast CA glued together and some bamboo skewers. On my J3 COROCUB I had to add flying wires to the hor stab. I will replace them with carbon fiber tubes the next time I'm repairing that area.



fozjared -> RE: put my biggest one in a tree and don't exactly know why!? (5/11/2008 5:27:12 AM)

sounds like a great idea villa, but pulling the steel out now would be a little difficult, but i will definitely keep that in mind for any future build!



kid chuckles -> RE: put my biggest one in a tree and don't exactly know why!? (6/30/2008 8:09:51 PM)

And another one bites the dust, Then gets up dust's off and fly's again. Great story with a nice middle and a great ending. You sir are quite the story teller. Glad your plane lived to see another cloud. There sure are alot of planes that get lost because of the feared stall. This makes you wonder if some were actually stalls or the electronics might play a part. I have dove my planes at very fast speed and pulled slight elev. and they all have came out of the dive smoothly. Some more than others lol. Have also lost a very good plane not thinking and flying real slow (thought it was very cool) and just turned and expected the wind to pick up the speed and it fell like a rock. That was a stall lol. Or so i was told. I thought it was just going to slow. lol.



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