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Old Feb 17, 2013, 07:08 AM
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This concern about flex in the push rod seems a very real and very likely issue if there is no intermediate support. On a normal thermal type flight it would never show, but in a dive it could be a serious issue.

Airman, I think you found your smoking gun.

I have several 3M gliders and they all have the tail servos in the nose, but the pushrods all have intermediate supports on the elevator and rudder push rods.

EVERYONE PLEASE CHECK FOR FLEX IN THE ELEVATOR PUSH ROD.

Hold the elevator centered with your hand.. Now slowly apply up elevator from your radio. Probably don't need more than 1/4 elevator stick movement. You should fell the elevator trying to move.

If the servo can move than a degree, you have a flex problem or a LOT of slop in the linkage.. That needs to be addressed.
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Old Feb 17, 2013, 09:16 AM
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Mystique elevator pushrod linkage flex.

Quote:
Originally Posted by aeajr View Post
This concern about flex in the push rod seems a very real and very likely issue if there is no intermediate support. On a normal thermal type flight it would never show, but in a dive it could be a serious issue.

EVERYONE PLEASE CHECK FOR FLEX IN THE ELEVATOR PUSH ROD.
.
Agreed. My Mystique showed very much flex in the elevator pushrod linkage.

I happened to notice during assembly and bench checkout that moderate
finger pressure on the elevator bell crank arm allowed it to move forward
more than half an inch (13mm). I could hear the elevator pushrod flopping
around loose inside the fuselage when finger pressure was applied.

My fix was to apply Amazing Goop (TM) glue (available at
hardware store) in three places using a suitable length dowel.
Now, no more elevator pushrod linkage flex.

(I glued the rudder linkage, too.)
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Old Feb 17, 2013, 09:39 AM
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Just checked my Mystique linkage as well and found no considerable slop or bend which would make me agree to the "linkage failure theory".

However, returning to this forum, Air bender`s post and pictures astonished me very much! Therefore I would like to ask you folks to look into your fuselages with a torch and check if there is that additional former halfway down between the former behind the servo position and the the former at the fin - as in my fuse?

Looking at this crash from very far away , I could imagine wing torsion as a point to be considered?

Herbert
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Old Feb 17, 2013, 10:10 AM
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Quote:
Originally Posted by Air Bender View Post
Agreed. My Mystique showed very much flex in the elevator pushrod linkage.

I happened to notice during assembly and bench checkout that moderate
finger pressure on the elevator bell crank arm allowed it to move forward
more than half an inch (13mm). I could hear the elevator pushrod flopping
around loose inside the fuselage when finger pressure was applied.

My fix was to apply Amazing Goop (TM) glue (available at
hardware store) in three places using a suitable length dowel.
Now, no more elevator pushrod linkage flex.

(I glued the rudder linkage, too.)
That is freightening!

Are the pushrods in the fuselage when you get it or do you have to install them?
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Old Feb 17, 2013, 10:37 AM
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That horrible sound of the linkage flopping around

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Originally Posted by aeajr View Post
That is freightening!
Are the pushrods in the fuselage when you get it or do you have to install them?
The outer (flexible plastic) tubes for rudder and elevator are installed at the factory.
Each tube is glued to bulkheads at two places: the extreme ends of the tubes,
near the servos in front and near the bell crank in back. In between, the tubes are
unsupported for about 31 inches (80 cm). The builder installs the wire pushrods.

What is truly frightening is the =sound= the unsupported tube and wire assembly
makes when you press on the end before it's glued down. It flops around inside
the nicely molded fuselage, flexing enough to touch the other side of the fuselage.

I was happy to catch this on the building bench, and figure a way to fix it.
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Old Feb 17, 2013, 10:42 AM
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No halfway former on mine

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Originally Posted by h.eberbach View Post
Therefore I would like to ask you folks to look into your fuselages with a torch and check if there is that additional former halfway down between the former behind the servo position and the the former at the fin - as in my fuse? Herbert
Mine does =not= have a former halfway down.
I think that a halfway former might be enough to prevent the tube flex and flop.
I also think the "expanding spray foam" fix mentioned earlier would work very well.
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Old Feb 17, 2013, 11:10 AM
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Quote:
Originally Posted by h.eberbach View Post
Just checked my Mystique linkage as well and found no considerable slop or bend which would make me agree to the "linkage failure theory".

However, returning to this forum, Air bender`s post and pictures astonished me very much! Therefore I would like to ask you folks to look into your fuselages with a torch and check if there is that additional former halfway down between the former behind the servo position and the the former at the fin - as in my fuse?

Looking at this crash from very far away , I could imagine wing torsion as a point to be considered?

Herbert
Sounds like the problem may have been identified and later production added a former there to support the pushrod.

If it is hard to get into the fuse, past the front or back former, the use of that expanding foam with an extension on the tube sounds like a great idea. Or use the Goop, getting it about halfway down if you can.

Only caution, as stated earlier, if you use the foam, don't use too much. That stuff expands like crazy and it does have weight. Any weight added behind the CG has to be offset by weight in front of the CG, but in this case, that is weight well justified.

I have never used this method. Those who have used this method, how much would you use? Let's get some how to tips.

Or, using goop, how do you get it down there, 12 to 15 inces in?

How to you apply it? Do you put the fuse on its side and hit each rod or do you try to fill the fuselage tube for a short space?
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Old Feb 17, 2013, 12:01 PM
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Quote:
Originally Posted by aeajr View Post
This concern about flex in the push rod seems a very real and very likely issue if there is no intermediate support. On a normal thermal type flight it would never show, but in a dive it could be a serious issue.

Airman, I think you found your smoking gun.

I have several 3M gliders and they all have the tail servos in the nose, but the pushrods all have intermediate supports on the elevator and rudder push rods.

EVERYONE PLEASE CHECK FOR FLEX IN THE ELEVATOR PUSH ROD.

Hold the elevator centered with your hand.. Now slowly apply up elevator from your radio. Probably don't need more than 1/4 elevator stick movement. You should fell the elevator trying to move.

If the servo can move than a degree, you have a flex problem or a LOT of slop in the linkage.. That needs to be addressed.
Bingo AEAJR !!!!! I DID find the smoking gun!!! Finally got up the heart to examine the wreckage ,, fortunately elevator system fully intact,,, I don't know WHY I didn't check this in the very beggining!! The elevator pushrod is only tacked down in ONE locatation about midway waaaaay down the fuse,, the pushrod is rather small diameter and flexes quite easily,,, so I hooked up horz stab,, pushed elevator pushrod and no problems under light loads,, but as soon as it reaches a certain point it just flexes outward instead of moving elevator
Waaaaay to much flex,,, in fact I saw that servo was still in full up elevator position cause its wire was ripped out on crash,, so the servo WAS giving FULL up command,, but flex in pushrod was absorbing it. I tried this several times, every time same thing happened,, light back pressure on stab normal movement,, heavier back pressure and pushrod flexes Absorbing ALL the servo movement with ZERO elevator movement. That's why on first flight when I HAD elevator to camber mix on,, when I pulled up elevator it was actually the increase in camber that pulled me slowly out of dive,, my clue should've been that it was SLOWLY pulling out even with FULL elevator,, on my 2nd ill fated outing I turned elev to camber mix OFF,, thereby nullifying ANY means I had to pull out of high speed dive!!! I had unknowingly sealed my fate!!!! And as Timography said ,, she picks up ALOT of speed VERY quickly. Soooooooo,,,, EVERYBODY out there PLEASE PLEASE check your elevator pushrod system completely AND with back pressure on stab,, look down the fuse with a light,, if you see its only tacked down in only one spot waaaay down the fuse like mine,, I strongly urge to to use one of the above suggested methods to tack it down in more locations along inside of fuse,,,,, otherwise I can almost guarrantee this will happen to you at one point!! I still can't believe I didn't check this when I was building!!!
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Old Feb 17, 2013, 12:22 PM
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I don't Wana rag on design of this plane,,, its a TOTALLY AWSOME flying plane,, speed range is very very good,, flying charcteristics with proper CG are very friendly , looks AWSOME in the air,, landings very very easy and smooth with right amount of flaps with elevator compensation,,, just be SURE you check your elevator pushrod system under load and fix it if you have my issue. I LOVED flying this plane!! I miss her :-(
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Old Feb 17, 2013, 02:03 PM
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Every design has weak points and it looks like the early versions had a lack of support in the support of the push rods as some report that they now have a mid point support for the push rods that was missing from the earlier birds.

Unfortunate, but it happens. Those who buy the Rev 1 version help create version 1.1 that has some of the bugs that the early buyers found.
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Old Feb 17, 2013, 04:16 PM
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Control Rod Flexes Even with Mid-Fuse Former

OK, this is not good. I checked my horizontal, and there is A LOT of control rod flopping around when I push on the tail. I DO HAVE the mid-fuse former, but the horizontal still moves at least 1/4 on the TE and it does not take much pressure. The tube is flexing between the mid bulkhead and the servo. I can hear it scrubbing around on the fuse as it moves.

So I have the mid-fuse bulkhead former, and the horizontal control rod is still flexing with just a reasonable amount of pressure. It looks like I can get a blob of epoxy/micro balloons on it with a dowel. I am glad I found this now and not in a high speed dive.

Horizon needs to put out a bulletin on this before we lose more planes!!!
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Old Feb 17, 2013, 06:19 PM
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Quote:
Originally Posted by tclaridge View Post
OK, this is not good. I checked my horizontal, and there is A LOT of control rod flopping around when I push on the tail. I DO HAVE the mid-fuse former, but the horizontal still moves at least 1/4 on the TE and it does not take much pressure. The tube is flexing between the mid bulkhead and the servo. I can hear it scrubbing around on the fuse as it moves.

So I have the mid-fuse bulkhead former, and the horizontal control rod is still flexing with just a reasonable amount of pressure. It looks like I can get a blob of epoxy/micro balloons on it with a dowel. I am glad I found this now and not in a high speed dive.

Horizon needs to put out a bulletin on this before we lose more planes!!!
That is EXACTLY what mine is doing TC,, flexes between servo and mid fuse former,, unfortunately I didn't check and lost my plane. :-(
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Old Feb 17, 2013, 07:10 PM
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United States, WA, Bellevue
Joined Oct 2010
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Originally Posted by Airman74 View Post
Bingo AEAJR !!!!! I DID find the smoking gun!!! Finally got up the heart to examine the wreckage ,, fortunately elevator system fully intact,,, I don't know WHY I didn't check this in the very beggining!! The elevator pushrod is only tacked down in ONE locatation about midway waaaaay down the fuse,, the pushrod is rather small diameter and flexes quite easily,,, so I hooked up horz stab,, pushed elevator pushrod and no problems under light loads,, but as soon as it reaches a certain point it just flexes outward instead of moving elevator
Waaaaay to much flex,,, in fact I saw that servo was still in full up elevator position cause its wire was ripped out on crash,, so the servo WAS giving FULL up command,, but flex in pushrod was absorbing it. I tried this several times, every time same thing happened,, light back pressure on stab normal movement,, heavier back pressure and pushrod flexes Absorbing ALL the servo movement with ZERO elevator movement. That's why on first flight when I HAD elevator to camber mix on,, when I pulled up elevator it was actually the increase in camber that pulled me slowly out of dive,, my clue should've been that it was SLOWLY pulling out even with FULL elevator,, on my 2nd ill fated outing I turned elev to camber mix OFF,, thereby nullifying ANY means I had to pull out of high speed dive!!! I had unknowingly sealed my fate!!!! And as Timography said ,, she picks up ALOT of speed VERY quickly. Soooooooo,,,, EVERYBODY out there PLEASE PLEASE check your elevator pushrod system completely AND with back pressure on stab,, look down the fuse with a light,, if you see its only tacked down in only one spot waaaay down the fuse like mine,, I strongly urge to to use one of the above suggested methods to tack it down in more locations along inside of fuse,,,,, otherwise I can almost guarrantee this will happen to you at one point!! I still can't believe I didn't check this when I was building!!!
Thank you sooooooooo much Airman. And a big shout out for all the other guys here...

I tested this on my mystique and ***exactly**** the same issue. I have the former about midway down the fuse but apply a bit too much pressure and the pushrod and tubing both flex like crazy. I'd never have thought of doing this on the workbench if it had not been for your warning and in all likelihood would have found about it in mid-air

Anyways, I built a long stick by CA'ing popsicle sticks together and then applied epoxy graciously to the outer tubing and fuselage somewhere between the 2 formers. Check again after a few hours and viola - problem solved like a charm!!

Btw, I'm missing a pushrod holder - the black part that snaps in on the pushrod to keep it from sliding out of the rudder or elevator control horn. Any chance anybody would have a spare that they'd be willing to help me with? If not where can I get one?
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Old Feb 17, 2013, 07:29 PM
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I've put both the servos in one wing, now need to do the other. One thing I may share with others:

I found it easier to bend the pushrod for the flaps in a z shape, with both angles being about 100 degrees, rather than doing an S-shape. Its very hard to get the S-shape perfect. BUT - and heres the advice - whatever you do, do NOT bend the pushrod further than about 115 degrees - it may start breaking if you do. It can surprisingly withstand a bend of 115 degrees (maybe even slightly more, but I'd say 115 is the safe limit) without problems. The angle I'm talking about is as measure between the arms of the bend (if you were to bend it further, you'd get a 90 degree angle).

If you do accidently bend one a little beyond its limits you may notice a small break starting to appear in the rod. If that happens stop bending further (obviously) and you can try filling in the gap with some solder. I've done that earlier and its worked for me. It regains its strength this way. Anybody else have any experience with this? I'd like to hear what others have to say on this. On this plane, I added some solder to one joint anyways because I was paranoid...
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Old Feb 17, 2013, 07:37 PM
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Wow!! I'm glad that my tragedy is at least helping others avoid the horrible crash I had that destroyed my plane. And even IF you have the fuse former halfway down,, please check your pushrod system anyways as I and a few others here have discovered it doesn't seem to be enough to keep elevator pushrod from flexing ALOT!! On mine it was like the pushrod works fine up to a certain amount of back pressure , then it will just suddenly pop out to the side causing loss of elevator control. Very risky indeed
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