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Old May 31, 2011, 11:44 PM
peace love and RC
tonywayne's Avatar
United States, NV, Las Vegas
Joined Jan 2007
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Help!
strange phenomenon Crash!

So late last year i bought the Fox epo 2.3 meter glider from Hobby King here http://www.hobbyking.com/hobbyking/s...dProduct=17413 . It was my first glider and has been a joy to fly. Today i had it out in strong winds 15 mpa+ i have flown it in strong winds befor and it handled them well. I caught a strong thermal and befor i knew it she was climbing out of sight so i raised the spoilerons and put it in a slight noes down attitude. I got within a few hundred feet of the ground headed into the wind and pitched the nose down some more. all of a sudden the glider pitched hard nose straight down into a dive, I tried to pull up but elevator control was infective. i know i still had an rc link because i could see the elevator trying to pitch the tail back somewhat. Smack nose first into the ground at at least 60 mph +. Of course the model was totaled but i was able to salvage all the electronics and carbon fiber lol. I have been flying rc for many years and have hours of exp but like i said this was my first glider and i dont understand exactly what happened. Again the spoilerons were up full deflection about 40* and i just gave a little down elevator to pitch he nose down some more to get better penetration and the bird just went into a straight down dive and picked up alot of speed and ignored my elevator commands. its like the elevator compressed and didnt have any authority. Can someone please explain to me what exactly happened and if this is a common thing for a glider to an inexperienced glider pilot. Thank you
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Old Jun 01, 2011, 04:03 AM
the answer 42 is
Switzerland, AG, Lenzburg
Joined Jan 2006
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well you just explained how spoilers work, the increase the angle of decent and can reduce your elevator effectiveness, next time let go the spoilers and apply them in short periods. I am sorry for your lost but that is not an strange phenomena, I know it from experience of course, that is how spoilers work. on the good side you live to learn

regards

EZ
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Old Jun 01, 2011, 04:14 AM
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You dont use spectrum radio gear do you?
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Old Jun 01, 2011, 04:54 AM
Per Ardua Ad Astra
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Australia, VIC, Rosebud
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Did you cut power to the motor?

Kev
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Old Jun 01, 2011, 07:50 AM
prop wash
biggy boy's Avatar
North of Toronto in Ontario
Joined Dec 2002
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The elevator servos is no that responsive on the Fox. I'm thinking it due to the fact the servo linkage is so long maybe too much flex. And once you start going fast the elevator servos has a hard time battling the force.
I'm thinking of replacing mine, already replaced and relocated the rudder servo.




Glen
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Old Jun 01, 2011, 08:43 AM
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Quote:
Originally Posted by biggy boy View Post
The elevator servos is no that responsive on the Fox. I'm thinking it due to the fact the servo linkage is so long maybe too much flex. And once you start going fast the elevator servos has a hard time battling the force.
I'm thinking of replacing mine, already replaced and relocated the rudder servo.




Glen
I agree with Glen. I replaced my servos with tower pro MG90's. The Fox will build speed quickly even in a shallow dive.....Ive caught myself more than a few times thinking it would respond quicker to pulling out of a dive. It takes some room to rotate if its really moving.
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Old Jun 01, 2011, 09:14 AM
prop wash
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North of Toronto in Ontario
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Originally Posted by rhawk1967 View Post
I agree with Glen. I replaced my servos with tower pro MG90's. The Fox will build speed quickly even in a shallow dive.....Ive caught myself more than a few times thinking it would respond quicker to pulling out of a dive. It takes some room to rotate if its really moving.
whats the torque rating of the Tower pro servos?



glen
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Old Jun 01, 2011, 10:09 AM
Tailspin
Grand Blanc, Michigan
Joined Feb 2006
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Do not know about this particular plane but foam is not the strongest material in torsion and I have had planes that depending on airfoil and polar moments will tuck with speed, this usually happens when the moment caused by the increased lift due to speed bends the wing, almost always in a way that causes washin. One plane did this on winch launch if I hit it too hard in the zoom, it would not recover and the only way out was a shove the stick to full down and pray the outside loop would clear.

Another is my Super AVA electric. It will tuck if climb too fast or come down too fast without spoilers. That one is very controlable and gives a lot of warning. It has strong digital JR servos and no slop so either the wing is twisting (most probable) or the boom is bending.

So this is another thing to think about in a long skinny wing, torsion is nasty.

Jack
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Old Jun 01, 2011, 10:23 AM
Ant
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T-Pros

The T-Pro's are listed on HobbyPartz's website as having a stall torque of 2.0kg/cm(4.8V )2.4kg/cm(6V).
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Old Jun 01, 2011, 12:37 PM
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don't know the sailplane, but could be stalled servo. If the servo didn't have enough torque, could have stalled, then overloaded ESC too.
My son had a DG-1000 epo sailplane, that locked up and crashed last summer. I think the motor, to retract the remote power system jammed, then high current load caused the ESC to fail. All controls froze, sailplane crashed, with motor partially retracted into fuse.


Another issue, could be flexible pushrod to elevator. If that flexes, could loose power to move elevator, with high force (in dive) on elevator.
I use carbon pushrods now, in anything that I can't mount the servo in tailsurface.
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Old Jun 01, 2011, 12:50 PM
prop wash
biggy boy's Avatar
North of Toronto in Ontario
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Quote:
Originally Posted by 320pilot View Post

Another issue, could be flexible pushrod to elevator. If that flexes, could loose power to move elevator, with high force (in dive) on elevator.
I use carbon pushrods now, in anything that I can't mount the servo in tailsurface.
On the Fox the thin piano wire that goes to the elevator is run through a tub.
I would say there is definitely flex on mine.



Glen
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Old Jun 01, 2011, 09:07 PM
Per Ardua Ad Astra
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Quote:
Originally Posted by 320pilot View Post
don't know the sailplane, but could be stalled servo. If the servo didn't have enough torque, could have stalled, then overloaded ESC too.
My son had a DG-1000 epo sailplane, that locked up and crashed last summer. I think the motor, to retract the remote power system jammed, then high current load caused the ESC to fail. All controls froze, sailplane crashed, with motor partially retracted into fuse.


Another issue, could be flexible pushrod to elevator. If that flexes, could loose power to move elevator, with high force (in dive) on elevator.
I use carbon pushrods now, in anything that I can't mount the servo in tailsurface.
Do you have a source for the carbon pushrods?

Kev
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Old Jun 01, 2011, 09:14 PM
prop wash
biggy boy's Avatar
North of Toronto in Ontario
Joined Dec 2002
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3mmcarbon fiber tube, it is hollow so you can glue a threaded piece of piano wire 2mm inside or you can bend a piece of 2 mm wire at a 90 deg and use a keeper.
Or use a Z bend.


http://hobbyking.com/hobbyking/store...idProduct=6722


snap style keepers

http://hobbyking.com/hobbyking/store...idProduct=5119


Or any good Rc hobby shop should carry it.




Glen
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Old Jun 02, 2011, 11:49 AM
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you can also use solid carbon fiber rod, over short lengths, for pushrods. here is a flap linkage I made up for a Pulsar 2m. Clevis hardware is from
www.icare-rc.com
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Old Jun 02, 2011, 12:44 PM
B for Bruce
BMatthews's Avatar
The 'Wack, BC, Canada
Joined Oct 2002
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Quote:
Originally Posted by biggy boy View Post
On the Fox the thin piano wire that goes to the elevator is run through a tub.
I would say there is definitely flex on mine.



Glen
With a flexible cable or flexible rod in a tube style of pushrods it's incredably important that the ends of the outer guide tube be secured with glue to bulkheads or cross pieces at the servo end somewhere very close to the servo itself. On the other end the tube should be firmly secured to the fuselage material itself where it exits and the amount of unsupported rod or cable from the end of the tube to the control horn kept short as practical.

If the tube is secured it will support the inner cable or wire and it won't flex or collapse when pushing or pulling. But if the tube is not secured then the whole setup will flex and collapse like a soggy spaghetti strand.

The beauty of flexible cable or thin solid music wire in support tube systems is that they can be flexible and curve and S bend around to pass by things and aim at the control horn the right way. But it's very important to realize that this "trick" only works IF the ends of the support tube are solidly secured.

Now the issue in THIS crash may or may not be the elevator since he says he could see it moving and trying to pull out the model. A number of other possible causes may be at play here.

First, spoilerons add drag but they also strongly reflex the airfoil shape and at the same time the wing incidence angle is altered around the portion with the spoilerons. Since this Fox is made from EPO foam it's possible that the outer wing panels could be flexing downwards under the effect of the dive speed and twisting at the same time to produce angles between the wing and stabilizer that are so extreme that the elevator wasn't able to make the model pull out of the dive. The only way to test this will be to get the repairs done get the model up about "4 mistakes high" and try it. If you find it tucks again then pull the spoilerons back in so the elevator can make the model pull out. That's why you want to do this 4 mistakes high.

Once you have some idea of this critical flexing and tucking speed you'll need to avoid this situation in the future.

All full size aircraft have limits that are much like this one. There's speeds that are never to be exceeded and some aircraft have restrictions on types of maneuvers in order to avoid situations that may result in dropping off into spins and such antics. We modelers don't run into these situations very often but it can occur. THis may be one of those.
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