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Old May 28, 2012, 02:43 PM
3DHOG
jcdfrd's Avatar
USA, CA, Aromas
Joined Sep 2010
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well Nick followed the assembly instructions and had this thing assembled long before and elevator stab issued came to light and the only reason he had used nylon pinned hinges was because I told him to throw the ca hinges in the round file just because thats what I do with those. the problem is he had the stab and elev installed and epoxied on before I could have any input on servo installation. this is a hard lesson for Nick and I feel bad for not getting in front of it, I should have because I have built a Het F18 and it said the same thing, epoxy the elev servo's to the inside of the fuse and I would never do that and didn't on mine, I mean what do you do when your buddy says I think its ok that what the instructions said to do and so its glued in and clamped down and it seemed ok and now with hind sight its soo not ok. oh and by the way all the servo's in the wing are even weaker if you pot them like the instructions state as your bond is only as strong as the foam your gluing too and every one of the four servo's in the wing had separated in the crash at the foam to fiberglass skin........ just a little heads up for ya
if we were to do another one I would do them just like the Bu32, mounted to the hatches and hatches screwed down to hard points
John
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Old May 28, 2012, 02:58 PM
BVM Viper Fever
pdawg's Avatar
United States, OH, Dayton
Joined Apr 2004
5,521 Posts
Hey Cn.
Just curious, are you commenting as a consumer or as a EJf sponsored pilot?
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Old May 28, 2012, 02:59 PM
DELTAS RULE
corsair nut's Avatar
tehachapi, CA
Joined Jan 2006
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well i never read the instructions lol. just built it the way i knew would work.
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Old May 28, 2012, 03:01 PM
DELTAS RULE
corsair nut's Avatar
tehachapi, CA
Joined Jan 2006
22,251 Posts
really bret? im commenting as somebody whos tired of people beating a dead horse. tam doesnt even own one and hes jumping all over ejf. they are working on it. but i think weve already proven if its built right...it works as is. optimal? by no means no. does it work? yes. it does.




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Originally Posted by pdawg View Post
Hey CM.
Just curious, are you commenting as a consumer or as a EJf sponsored pilot?
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Old May 28, 2012, 03:17 PM
3DHOG
jcdfrd's Avatar
USA, CA, Aromas
Joined Sep 2010
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Tam does have one I'm building it for him
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Old May 28, 2012, 03:19 PM
Registered User
Tamjets's Avatar
San Jose, CA
Joined Jun 2006
5,453 Posts
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Originally Posted by corsair nut View Post
really bret? im commenting as somebody whos tired of people beating a dead horse. tam doesnt even own one and hes jumping all over ejf. they are working on it. but i think weve already proven if its built right...it works as is. optimal? by no means no. does it work? yes. it does.
What are you talking about?
I got one of the kit had same issue with elevator
Now I know what to do...
Made the mod and fix the problem.
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Old May 28, 2012, 03:37 PM
Robert Wagoner's Avatar
Tucson, Arizona, USA
Joined Dec 1999
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Quote:
Originally Posted by pdawg View Post
Not trying to be negative but didn't the same issue of a tail flutter come up several years ago with the original super sniper 90mm? Now with a "new" composite version with the same issue of flutter??? The single hingeline is a good idea for lower speed models but at a certain point you can't cut corners anymore. Instead of changing the stab design just make 2 hingelines (instead of 1) so the elevators taper towards the tips and use a servo for each surface. That would more than likely solve the problem.
Thanks for taking the time to comment and discuss. Yeah I saw the CN / EJF sponsored comment. Really this about making everyone happy and to clear up any future problems and concerns.

This stab design has carried on since the 70mm Sniper and it's seen 160+ during the speed craze days. (all wood) stab. The 90mm Sniper V1 had an (all wood) stab and worked fine. then the factory made a V2 composite version that the control surface layup was thought the problem and made the V3 that was stronger and has been that way.

The 90mm Sniper XL was done the same as V3 and the shape of all these has never changed. This elevator discussion is pointing out that the aerodynamics of the control surface shape is the culprit causing higher loads thus stressing the components. albeit beefing it up with hinges and servo mounting does show a fix and makes it flyable, the loading is higher than it should be and that can be fixed.

The center XL stab area has room for two servos and the shape can be changed along with adding two hinge line redundancy that also lowers the loading. I'm all for it to get this done once and for all.

Are we all on the same page?

Regards,

--RW
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Old May 28, 2012, 03:57 PM
"Take Off" eh!
vettster's Avatar
Canada, ON, Beeton
Joined Aug 2008
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Originally Posted by SCALEFAN View Post
Well, as I assemble mine, I thought I would read the manual which is on a disk included with the kit. OMG guess what it said? Perhaps we all should read the manual more often.

HIGH PERFORMANCE TIP --- Testing of this airframe has demonstrated that the stock Cloth Hinges are sufficient for “Sport Flying” but suffer from fatigue when repeated fast passes and High-G manuevers are performed. If you intend to fly your Sniper XL90 aggressively, a stronger hinge-type (i.e. nylon pinned hinges) are strongly recommended
Im sorry... I just cant buy that. I have fiber hinges on my 25lb turbine that is moving well over 160mph in a dive, and with almost 200 flights they are still perfect. Blaming the hinge type is not valid. Not installing them into a block of wood is a serious problem.
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Old May 28, 2012, 03:58 PM
Fly allot, Crash allot, next?
United States, CA, Corona
Joined Feb 2006
7,235 Posts
CN,

What servo are you using on your elevator?

Al
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Old May 28, 2012, 04:02 PM
3DHOG
jcdfrd's Avatar
USA, CA, Aromas
Joined Sep 2010
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Originally Posted by vettster View Post
Im sorry... I just cant buy that. I have fiber hinges on my 25lb turbine that is moving well over 160mph in a dive, and with almost 200 flights they are still perfect. Blaming the hinge type is not valid. Not installing them into a block of wood is a serious problem.
I dont think all CA hinges were created equal, are you using Het ca hinges?
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Old May 28, 2012, 04:03 PM
"Take Off" eh!
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Canada, ON, Beeton
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Point taken
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Old May 28, 2012, 04:12 PM
Registered User
United States, TN, Jackson
Joined Mar 2007
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Robert---The problem is with the outer part of the elevator being larger than the elevator is at the root...Seriously, I've seen this type of design flutter due to the way the air comes off of the tips of the stabs...If you do manage to get the stab in the wind tunnel---It doesn't matter that the tunnel won't blow fast enough to get the stab to flutter---With smoke you WILL see a couple VERY turbulent vortices coming from each tip..The votices will act upon the larger outer portion of the elevator, acting like a lever...Get them out of sinc with each other and you now have a twisting motion on the entire elevator...DEFINATELY---A straight across elevator will stop this...Testing will prove whether or not the reduced elevator area will need to be lengthened for adequate pitch control, especially during the landing flare...

When you get to the tunnel---I'm 99.9% positive you will see what I've described...Get a high speed camera to see the vortices..And make another stab of the same size but of weaker material to get the lower air flow tunnel to get enough airspeed to cause flutter/tip vortices..Again, I can just about guarantee what you will see...

Hoping to be helpful and not critical!!!

Kevin
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Old May 28, 2012, 04:18 PM
Robert Wagoner's Avatar
Tucson, Arizona, USA
Joined Dec 1999
1,552 Posts
Quote:
Originally Posted by Kevin Greene View Post
Robert---The problem is with the outer part of the elevator being larger than the elevator is at the root...Seriously, I've seen this type of design flutter due to the way the air comes off of the tips of the stabs...If you do manage to get the stab in the wind tunnel---It doesn't matter that the tunnel won't blow fast enough to get the stab to flutter---With smoke you WILL see a couple VERY turbulent vortices coming from each tip..The votices will act upon the larger outer portion of the elevator, acting like a lever...Get them out of sinc with each other and you now have a twisting motion on the entire elevator...DEFINATELY---A straight across elevator will stop this...Testing will prove whether or not the reduced elevator area will need to be lengthened for adequate pitch control, especially during the landing flare...

When you get to the tunnel---I'm 99.9% positive you will see what I've described...Get a high speed camera to see the vortices..And make another stab of the same size but of weaker material to get the lower air flow tunnel to get enough airspeed to cause flutter/tip vortices..IAgain, I can just about guarantee what you will see...

Hoping to be helpful and not critical!!!

Kevin
Thanks for explaining.

--RW
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Old May 28, 2012, 04:55 PM
BVM Viper Fever
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United States, OH, Dayton
Joined Apr 2004
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CN,
My comment wasn't meant to be a passive aggressive attack. We've known each other for years and I know you will toss out the instructions and make things work simply based off previous experiences. So when your having success when others might be failing I believe its important to note that your coming from the perspective of a sponsored beta testor and not someone following the instruction manual.

Robert,
I believe we are are on the same page according to your description.
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Old May 28, 2012, 05:45 PM
deltas are cool
AIR SALLY's Avatar
Tehachapi ,CA.
Joined Apr 2006
20,862 Posts
Robert if you need help molding a new Stab let me know ,and i'll try and help.just build a balsa one flight test it and i could used the tested stab as a plug .i agree with kevin ,the load at the tips could cause a twisting ,the load may have broke Nicks servo loose too .Brent has VG's on the stab tips ...but Vic' did'nt so not sure if the vg's are helping ,but brents is flying well .it was the only plane up today ,and you could hear it well .i herd no flight control flutter.and it was moving out with 6000 8s set up .he used silicon to bond the elev to the fuse .
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