HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Feb 15, 2013, 10:00 PM
Registered User
Joined Nov 2005
1,927 Posts
Airman, thanks for the link. Very cool. I have always wondered how to size servos.

I have an idea on the crash. I discovered during setup that the horizontal control rod will flex internally if you push on the elevator hard. It will bow out with enough force in a "pitch down" deflection. I wonder if the speed caused the control rod to bow, and this caused the nose point down no matter how much the servo was pushing. It is like trying to push a noodle at that point.

When I first experienced this during my checkouts, I thought "it would have been nice to secure the control rod at the mid point." But there is no way to get into the tail.

I would be curious if other folks can repeat the elevator control rod bowing inside the fuse when pushing the stab TE down? But dont push so hard you break something, just enough to simulate a firm air load at high speed.
tclaridge is offline Find More Posts by tclaridge
Reply With Quote
Sign up now
to remove ads between posts
Old Feb 15, 2013, 10:08 PM
Registered User
ddruck's Avatar
Canada, ON, Pickering
Joined Nov 2006
679 Posts
Thanks, that is exactly what I was talking about in my previous post, slop in the control system, I would be very interested for more people to check for this on their machines.

Quote:
Originally Posted by tclaridge View Post
Airman, thanks for the link. Very cool. I have always wondered how to size servos.

I have an idea on the crash. I discovered during setup that the horizontal control rod will flex internally if you push on the elevator hard. It will bow out with enough force in a "pitch down" deflection. I wonder if the speed caused the control rod to bow, and this caused the nose point down no matter how much the servo was pushing. It is like trying to push a noodle at that point.

When I first experienced this during my checkouts, I thought "it would have been nice to secure the control rod at the mid point." But there is no way to get into the tail.

I would be curious if other folks can repeat the elevator control rod bowing inside the fuse when pushing the stab TE down? But dont push so hard you break something, just enough to simulate a firm air load at high speed.
ddruck is offline Find More Posts by ddruck
Reply With Quote
Old Feb 15, 2013, 10:55 PM
Proud member of LISF and ESL
LI, New York, USA
Joined Mar 2003
24,476 Posts
That is why we always do the dive test very high. I usually start at about 500+ feet. But yes, if you get it going AND it starts to tuck it will REALLY pick up speed.
aeajr is offline Find More Posts by aeajr
Reply With Quote
Old Feb 16, 2013, 07:22 AM
Registered User
ddruck's Avatar
Canada, ON, Pickering
Joined Nov 2006
679 Posts
By the way there is a way to lock down bowing or loose control rods inside a composite fuse impossible to get to. I am assuming tube in a tube type control rods here. I have used the pressurized foam insulation can from your local building center used for sealing door and window frames. It comes with a plastic tube to direct the flow. I have extended this tube with couple of fat, strong drinking straws to get to the spot where I needed support and just shot some of the expanding foam in there. This stuff is sticky and expands locking the rods permanently. Caution here, do not use too much, like filling the whole tail, during curing process this can build up a lot of pressure and even pop open the fuse joint. Spray a small amount every 2 to 3" as you pull it out creating foam 'ribs' locking everything down. Works great. Test it on paper towel tube to practice, just to see how much spray you need.


Quote:
Originally Posted by tclaridge View Post
When I first experienced this during my checkouts, I thought "it would have been nice to secure the control rod at the mid point." But there is no way to get into the tail.
ddruck is offline Find More Posts by ddruck
Last edited by ddruck; Feb 16, 2013 at 07:32 AM.
Reply With Quote
Old Feb 16, 2013, 08:24 AM
Registered User
Joined Nov 2005
1,927 Posts
ddruck, excellent idea. I am going to do that. I am sure it only needs a few daps on the control rod sleeve to hold it down from flexing. This may be an important mod!
tclaridge is offline Find More Posts by tclaridge
Reply With Quote
Old Feb 16, 2013, 08:53 AM
Registered User
Red Bluff CA
Joined Sep 2001
242 Posts
Airman
Sorry for the loss.
Randall
RTaylor is offline Find More Posts by RTaylor
Reply With Quote
Old Feb 16, 2013, 10:31 AM
Registered User
USA, CA, Chico
Joined Feb 2011
3,212 Posts
Yes,, when I first saw those loooong thin pushrods,, I was thinking at the time : looks like a very sloppy system,,, but I never checked it under pressure!! Silly me!! I've never liked that kind of set up,,, now that I think of it,, I remember one other slope plane I had with a similar system,, noticed the flex and slop right away, and changed to straight carbon large hollow pushrods( more direct ) for me personally that's why I've always preferred tail servos IN the tail with short direct pushrods I can easily see,, like on my 3D planes,, and like on sailplanes like the AVA and the pulsars. Speaking of which,, I went ahead and ordered the sailplane I was first considering BEFORE the mystique which is the Pulsar 2M REF along with the Hacker BL20 to go with it,, I know,, different kinda of plane. Eventually ill come back to rebuilding the mystique,, but not now.,, but I am interested in others experience with this plane. When I think back on ALL the flights I've had with mystique ( about 5 ) I'm pretty convinced it was lack of control authority in elevator system that was my mystiques demise,, cause on other flights I remember in a fast dive there was a distinct lag in elevator response,, but I was soooo busy sorting out other things,, I forgot to check elevator system under pressure,, also on my mystique my elevator bellcrank was totally jammed up against inside front of vertical stab,, I had to pound it loose quite hard to break it free,, so its possible I might've messed up the joint of bellcrank a little doing so. When you think about it,, that whole elevator pushrod, bellcrank system has ALOT of things to go wrong,, not a very directly connected system,, especially considering how much load that full flying stab must take.,,, so others out there,,, learn from my tragedy,, check your elevator system out COMPLETLY!!! AND with pressure against horz stab,, if I get another mystique I think I may consider replacing the stock elevator pushrod for a direct hollow ( not in a sleeve) carbon pushrod,, seems less friction/resistance..
Another thing to consider is I don't believe you'd EVER see an elevator control system like this on ANY serious 3D plane,, which is another type of plane that experiences high loads on an elevator with a large surface area. Hmmmm
Airman74 is offline Find More Posts by Airman74
Reply With Quote
Old Feb 16, 2013, 10:40 AM
Registered User
USA, CA, Chico
Joined Feb 2011
3,212 Posts
Thank you all for your kind words and sympathy!!
I REALLY appreciate that. :-)

Jerry in Chico
Airman74 is offline Find More Posts by Airman74
Reply With Quote
Old Feb 16, 2013, 10:49 AM
Registered User
USA, CA, Chico
Joined Feb 2011
3,212 Posts
Ok,,,, so now I'm curious,,,, others out there who have this plane right now,, go an check your elevator systems under pressure,, then look to see how much flex and or slop in pushrod,, and notice if elevator servo can exert/ overcome much force in horz stab. And report back if you don't mind. :-)
Cause now that I'm thinking back again I distinctly remember just how quick and immediate elevator response was at SLOW speeds but not as quick in a high speed dive,,, guess I'd gotten soooo used to the slow response of elevators in the flexy foam sailplanes,, I didn't set off any alarm bells in my head when this happened in the mystique. Long ago when I had my heavily ballasted Mueller 3m slope plane on the bluff,, I remember on particular day fully ballasted screaming along the slopes doing 800ft full on dives and having instant elevator response on a plane MUCH heavier and faster than mystique!!
Man!! I feel like an idiot!!! Why didn't I think of this before ??? :-(
Airman74 is offline Find More Posts by Airman74
Last edited by Airman74; Feb 16, 2013 at 10:56 AM.
Reply With Quote
Old Feb 16, 2013, 11:31 AM
Registered User
USA, CA, Chico
Joined Feb 2011
3,212 Posts
Quote:
Originally Posted by tclaridge View Post
Airman, thanks for the link. Very cool. I have always wondered how to size servos.

I have an idea on the crash. I discovered during setup that the horizontal control rod will flex internally if you push on the elevator hard. It will bow out with enough force in a "pitch down" deflection. I wonder if the speed caused the control rod to bow, and this caused the nose point down no matter how much the servo was pushing. It is like trying to push a noodle at that point.

When I first experienced this during my checkouts, I thought "it would have been nice to secure the control rod at the mid point." But there is no way to get into the tail.

I would be curious if other folks can repeat the elevator control rod bowing inside the fuse when pushing the stab TE down? But dont push so hard you break something, just enough to simulate a firm air load at high speed.
Thanks TC!!! You made me remember something else,, on that 2nd ILL fated outing,, I checked and had CG at it most fowArd reccomended point about 117-118 mm ,, when I was first cruising around then had to add a tiny bit of up trim got her flying level by trim,, tested her out in turns ( excellent ) did some small tiny up and down elevator inputs no problems very quick and immediate elevator response. Then the ill fated dive test,, I was fully expecting her to pull up or at least gradually pull out with that fowArd CG,, but I was shocked when she started to tuck nose down instead ,, which TOTALLY didn't make sense to me,, but,,, if pushrod was bowing under pressure in a dive that would explain behavior,,, AND here's one other piece of puzzle I just remembered: on first flight I had elevator to camber mixing ON,, so if I pulled out of dive then increased camber when pulling up would've helped overcome lack of elevator response,, but I remember I didn't like the elevator to camber mixing flying slowly cause it made plane overly pitchy,, so I turned it off before 2nd outing!!!
Ding!! Ding!! Ding!!!! Think I've got it!!!!
Now if I can convince HH of this,,, maybe I can get a replacement at wholesale or better yet FREE!!! Don't know if they'll go for this.
I once watch a guy put his radian pro in the dirt in a high speed dive when fuse flexed ( it is foam after all ) he couldn't pull out in time,, destroyed it.
And remember Timography saying how he pulled out of high speed dive by
" popping the flaps"???
So EVERBODY EVERYBODY Please go check your elevator systems thoughly and with pressure exerted against horz stab and check for signs of flex and or slop. And yet another thing I remember while building : when breaking loose the frozen bellcrank I also managed to knock loose a little of very distal end of elevator pushrod probably contributing even MORE to slop,,WOW!! I thoughly checked elevator movement without back pressure,, but why didn't I check with. :-O
Airman74 is offline Find More Posts by Airman74
Last edited by Airman74; Feb 16, 2013 at 11:42 AM.
Reply With Quote
Old Feb 16, 2013, 11:53 AM
Cultural productionof ignorane
kcaldwel's Avatar
Joined Jan 2007
3,632 Posts
Sorry to hear about your airplane.

I'm not sure if this would work in this case, but it is common practice with DLGs to run a steel wire down the pushrod housing and then pull the housing against the fuse side with super magnets along the length. You can get thin CA to wick the entire length of the housing by putting a few drops at the top and letting gravity pull the CA along.

It doesn't take too much CA, and it is best to seal the pushrod ends to prevent it from getting inside the housing.

It shouldn't take much servo torque to drive a properly designed full-flying stab, much less than an unbalanced rudder or even a normal elevator. The lift on the stab should act at the 1/4 mean aero chord point. If the main pivot is placed there, there will be very little load on the servo. I'm not sure how the Mystique is designed.

There can be some load from the airfoil Cm if the stabilizer airfoil is not symmetrical.

It is also possible for the wing to twist during high speed flight from the wing airfoil Cm. The tips can twist downward, which is like lowering the incidence angle of the entire wing. That can also make dive recovery difficult.

Oh, and one more thing - propellers in air do not cavitate, that only occurs in a liquid not a gas. You can get blade stall though, particularly with high pitch propellers during static thrust tests, which is what I think you guys were talking about

Kevin

Edit:

Here is a post and some photos on the magnet pushrod method:

http://www.rcgroups.com/forums/showp...1&postcount=26

And another with way too many magnets!

http://www.rcgroups.com/forums/showp...&postcount=792
kcaldwel is offline Find More Posts by kcaldwel
Last edited by kcaldwel; Feb 16, 2013 at 12:05 PM.
Reply With Quote
Old Feb 16, 2013, 11:54 AM
Registered User
USA, CA, Chico
Joined Feb 2011
3,212 Posts
Quote:
Originally Posted by ddruck View Post
By the way there is a way to lock down bowing or loose control rods inside a composite fuse impossible to get to. I am assuming tube in a tube type control rods here. I have used the pressurized foam insulation can from your local building center used for sealing door and window frames. It comes with a plastic tube to direct the flow. I have extended this tube with couple of fat, strong drinking straws to get to the spot where I needed support and just shot some of the expanding foam in there. This stuff is sticky and expands locking the rods permanently. Caution here, do not use too much, like filling the whole tail, during curing process this can build up a lot of pressure and even pop open the fuse joint. Spray a small amount every 2 to 3" as you pull it out creating foam 'ribs' locking everything down. Works great. Test it on paper towel tube to practice, just to see how much spray you need.
I have actually done this technique on one of my slopers that had pushrods not tacked down against the sides well enough,, worked PERFECTLY ,, just be careful not to use too much,, I do remember that it did add a little tail weight that I had to compensate for though,, but not a big deal on a slope plane. :-)
Airman74 is offline Find More Posts by Airman74
Reply With Quote
Old Feb 16, 2013, 11:57 AM
Registered User
USA, CA, Chico
Joined Feb 2011
3,212 Posts
Quote:
Originally Posted by kcaldwel View Post
Sorry to hear about your airplane.

I'm not sure if this would work in this case, but it is common practice with DLGs to run a steel wire down the pushrod housing and then pull the housing against the fuse side with super magnets along the length. You can get thin CA to wick the entire length of the housing by putting a few drops at the top and letting gravity pull the CA along.

It doesn't take too much CA, and it is best to seal the pushrod ends to prevent it from getting inside the housing.

It shouldn't take much servo torque to drive a properly designed full-flying stab, much less than an unbalanced rudder or even a normal elevator. The lift on the stab should act at the 1/4 mean aero chord point. If the main pivot is placed there, there will be very little load on the servo. I'm not sure how the Mystique is designed.

There can be some load from the airfoil Cm if the stabilizer airfoil is not symmetrical.

It is also possible for the wing to twist during high speed flight from the wing airfoil Cm. The tips can twist downward, which is like lowering the incidence angle of the entire wing. That can also make dive recovery difficult.

Oh, and one more thing - propellers in air do not cavitate, that only occurs in a liquid not a gas. You can get blade stall though, particularly with high pitch propellers during static thrust tests, which is what I think you guys were talking about

Kevin
Wow!!! Fantastic idea!!!!
Airman74 is offline Find More Posts by Airman74
Reply With Quote
Old Feb 17, 2013, 03:00 AM
Electric Glider Nut
timography's Avatar
Australia, WA, Perth
Joined Feb 2012
350 Posts
Sorry about your crash Jerry

I've had a few more flights with the Mystique, and it keeps getting better. High wind? No problem for the Mystique. I found some wave lift [at least thats what i think it was] on the other side of one of my flying fields the other day - I usually never fly that side but the wind was strong from that direction so i just pointed her into the wind and powered on up to 600ft. Turned on Camber and started to fly back and forth on a straight line in the middle of the field and before I knew it my telemetry alarm was going off telling me I was over 1000 ft. Cool.

Had another flight in zero wind yesterday morning and oh my God - what a nice relaxing flight that was. Very happy. One note though - with the MVVS motor, I have found that I have to put a *minimum* 35C battery in her though. I mistakenly put in a 30C 2200mAH 3S in, launched out ok and started to climb, but after 20 seconds the low battery voltage alert on the telemetry started going off. Hmmm. Landed, checked the battery and it became apparent what had happened. Oops. Good to know for future reference.

@Jerry - on my first flight [with the CG @ 120mm, apparently a very rearward CG as it turns out] I too put it into a dive and wow did it tuck in quickly and picked up an enormous amount of speed *very* quickly. My outer wing panels started to flutter badly, enough to pull out the aileron horn on the left wing. I managed to land no problems with only one working aileron and the other flapping in the breeze like a rag on the clothes line. I never had a problem pulling out of the dive though - and the dive only lasted about 6-8 seconds. But fortunately I had enough time to pop the crow and pull up elevator at the same time and I pulled out with about 100ft to spare. Scared the outta me though and I still can't believe how quickly it seemed to reach terminal velocity. I'm not using the recommended elevator/rudder servos though, I'm using Hitec HS-5085MG digitals. Even flying yesterday in calm wind, I thought I'd try 'hands off' to see just how neutrally stable the Mystique is. So, straight and level flying along ok, flew through lift as the left wingtip popped up [as you do when flying through lift], the model entered a gentle right turn, slightly nose down, but the turn tightened and the nose kept dropping and the model started to speed up again, although not nearly as aggressively as on my first flight. Left unchecked it would have spiralled down into a fatal mess of balsa and fibreglass. This is a little bit annoying I have to say as I often take my eyes off my gliders while I'm flying around, to look for other signs of lift or what other pilots are doing. This doesn't bode well.

I am going to try a bigger battery and see if that helps, as it should move the CG forward past the 117mm mark meaning self recovery from a dive should be [in theory] inevitable.

Stay tuned - more to come. Oh, and like aeajr said, the second build goes a lot faster than the first one. Chin up and carry on!
timography is offline Find More Posts by timography
Last edited by timography; Feb 17, 2013 at 03:17 AM.
Reply With Quote
Old Feb 17, 2013, 04:03 AM
Airborne whenever I can.
PAT-T's Avatar
Canada, AB, Edson
Joined Dec 2006
549 Posts
Airman,
Very sad story it is. And you should ask HH for a replacement Mistique. This is a shortcoming that should have been found at the prototype testing level. Lucky for me and others, I am still working on my wings, and had only a quick look in the fuse so far, maybe I would have discover that issue, or only to late. If HH and E-Flite are correct, and I believe they are. You will get your new Mistique. This is a little of the backside with some ARF kits, that they have some shortcomings that will be overlooked by less experienced builders and even old veteran builders. ARF kits create some kind of "rush to get that plane airborne",
with all the problems connected to it. That is why I always go slow with stuff like this, and even then, I often see that something could have been done better.
Mistique is my 2nd ARF ever, never was a big fan of these kits. And except for some high end gliders, I only build from good kits, wood, foam and more.
I hope for you and others that HH will do what is right and replace your glider.
Be sure to check all your radio gear before using it again.

Thanks for sharing. Have fun and break a leg.

Pat
PAT-T is offline Find More Posts by PAT-T
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
For Sale New in the box E-Flite Taylorcraft ARF Kit plus High Performance E-Flite components Philscho Aircraft - Electric - Airplanes (FS/W) 4 Aug 19, 2012 12:25 AM
Sold E-flite Habu 32 ARF with E-flite Motor/Fan/Retracts/ESC/lipo ton2di Aircraft - Electric - Jets (FS/W) 3 Aug 16, 2012 07:42 PM
Sold (2) E-flite Power 32's, (2) E-flite 60a ESC, all NIB cybercrxt Aircraft - Electric - Power Systems (FS/W) 8 May 17, 2012 01:53 PM
Discussion E-Flite Taylorcraft 450 ARF Kit and High Power E-Flite electrical components $300 Philscho Hot Online Deals 1 Mar 02, 2012 08:11 PM
Wanted WTB Art Hobby 2.5M or 2.9M e-glider rrweather Aircraft - Sailplanes (FS/W) 0 Sep 12, 2005 11:09 AM