Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

Viper 500 flight problem

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Old 06-03-2007, 08:06 AM
  #1  
rchad
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Default Viper 500 flight problem

I am having a problem with my GP Viper 500 at high speed. It is very unstable. It will fly in a straight line hands off the controls and all of a sudden jump around like it just flew into a gust of wind. The v tail is aligned with the wing and the cg is correct. I have not had the problem at low speed. The V tail seems to flex could this be a problem? Do you think the recever could be getting vibration at high speed and causing this? I have read other threads and cannot find any other vipers having this problem. Any suggestions will be helpful. Thanks...
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Old 06-03-2007, 08:28 AM
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Default RE: Viper 500 flight problem

check for radio glitches.... trying to remember who makes the glitch counter device..
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Old 06-03-2007, 08:33 AM
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Default RE: Viper 500 flight problem

Sounds like either a radio, switch, or bad servo(s) ?

Viper should be hands off stable.
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Old 06-03-2007, 01:34 PM
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Default RE: Viper 500 flight problem

I had the same issue. I changed the rx to a PCM and the issue stopped. Never did determine the cause of the glitch.

Remember any metal to metal contacts can cause glitches. Is your throttle linkage using a metal clevis?

rcs
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Old 06-03-2007, 02:31 PM
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Default RE: Viper 500 flight problem

Make sure there's no metal to metal contacts like throttle clevis and maybe remount receiver with more foam, reroute antenna wire, check for pushrod flex. Is the prop balanced?
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Old 06-03-2007, 06:51 PM
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Default RE: Viper 500 flight problem

I know my throttle link is plastic. I dont think I have any metal to metal contacts. I think I will change my receiver that sounds like my best option for now. Thanks so much for all of your help.
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Old 06-03-2007, 07:14 PM
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Default RE: Viper 500 flight problem

Rchad, This seems to be typical with the Viper. It is funny I was just test flying my new Nelson powered Viper today and experienced the same thing. Does it look like a jump, up or down? Like it is unstable in pitch? My Viper with a TT .40 did this as well and moving the CG forward solved this. I had my CG at 2.75 from L.E. . I started off with my new Nelson Viper at 2.75 and it still did it though. I think at those speeds I need to move it further forward as well.
While you could be experiencing radio issues I think most likely it is your CG.
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Old 06-03-2007, 09:36 PM
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Default RE: Viper 500 flight problem

I'm on my third Viper and never had this problem. My CG's have ranged from 2 3/4 to present day at 3 1/8" due to different engines, Evolution 46 nt(heavy)or Webra 55 (light). Like the others have said, bad receiver, crystal, servo(s) or metal/carbon fiber thats making or breaking contact. Sloppy linkage or servo gear trains can do the same. That V tail Quickie can't have the control surface play that trainers or sport planes can live with. Just wondering if you are running JR sport series servos? They acted much as described and further distances total loss of control resulted (RF noise). Myself and 4 others had a bad batch..... two others weren’t so lucky.
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Old 06-04-2007, 12:12 PM
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Default RE: Viper 500 flight problem

I will noted this here because I ran across another "ARF pilot" this week that thought it was ok to velcro/rubber band the RX into an airplane (well powered airplane - you can get away with this for electric I guess...)

Ensure the receiver is well wrapped in foam, and not touching directly the airframe.
Make sure you have a good switch, and it is installed properly.

As others noted, the Viper is very stable. Make sure the pushrods are not bending, and ensure the radio installation is secure.

Bob
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Old 06-04-2007, 06:49 PM
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Default RE: Viper 500 flight problem

Vertical grimmace, that is exactly what it was doing. It looked like it would jump up and down. I may not have had enough foam around my receiver. Though I did send the receiver off today just to be tested. I will check the CG again also. I have a 50sx on my Viper. When I get my receiver back I will wrap it in more foam just to make sure. Thanks for everyones help.
RCHAD
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Old 06-05-2007, 05:30 PM
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Default RE: Viper 500 flight problem

rchad: my Viper also had a touch of this problem at high speed, I cut my throw down just a little and used a lighter touch on the sticks and cured my problem. Just a thought.----------------Revver Bro #164
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Old 06-05-2007, 06:36 PM
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Default RE: Viper 500 flight problem

Yes, the amount of control travel can also be an issue. I am on my 3rd Viper as well and never really had a problem with the 424 (Thunder Tiger .40) powered variety but when adding a Nelson to enter 428 this is where it has really appeared. When swet up to Race we usually have no more than 1\8" ofr trqavel up and even less down. This with -%45 expo (with Futaba).
One thing I am noticing, is flex in the v-tail. I am extesively fiberglassing mine to stiffen this area up. I am scrambling to get this squared away for a race we are having in 2 weeks.
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Old 06-05-2007, 08:38 PM
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Default RE: Viper 500 flight problem

Mine did the same thing: CG at 3" and a Jett Q500 engine made for a very interesting first flight... As long as it was tracking straight, it would keep on doing so, but as soon as I touched the stick it would start to jump all over the place. It really looked like it got into some sort of oscillation.

After the Jett engine "removed" the firewall, I moved the engine 1/8" forward, moved the battery into the tank area and glassed the tail surfaces.
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Old 06-05-2007, 08:51 PM
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Default RE: Viper 500 flight problem

Very interesting.

I just assembled my first viper a couple months ago, and have flown it with a TT .40.

So far, it has flown very stable.
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Old 06-06-2007, 01:36 AM
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Default RE: Viper 500 flight problem

Rchad
I was flying my Viper last week and the elevator was not responding very well.I had to put it on high rates to get it down.Took it home and there was a big crack in the fuselage in front of the v tail.Actually I can't believe it did not crash.I ended up fiberglassing to fix and reinforce.Flew it again yesterday and everything is good.
John
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Old 06-06-2007, 09:55 AM
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Default RE: Viper 500 flight problem

With the Thundser tiger .40 I never hade a problem either. It seems to be when you get it going really fast. One of our local racers loves his Vipers for 428 and they will work fine. I think it is a tail CG issue more than anything. I have stiffened up my tail and will test fly it today. I will post back with my results.
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Old 06-06-2007, 12:06 PM
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Default RE: Viper 500 flight problem

I think people forget that the Nelson/Jett race engines are fairly light compared to some of the sport engines that are being used.. Sure it may only be a half ounce but at the increased speeds and higher than needed control throws it can make them a bit unstable.. This of coarse only applies if you take off the sport engine and throw on a Nelson without making the needed changes..
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Old 06-06-2007, 01:45 PM
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Default RE: Viper 500 flight problem

Well, I know the Texas guys are running Jetts/Nelsons on Vipers for most of their local racing, and I don't remember hearing about issues like this.

Just a little surprised.
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Old 06-06-2007, 05:41 PM
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Default RE: Viper 500 flight problem

I was unable to test today as it got really windy. Maybe on Friday afternoon.
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Old 06-06-2007, 07:57 PM
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Default RE: Viper 500 flight problem


ORIGINAL: daven

Well, I know the Texas guys are running Jetts/Nelsons on Vipers for most of their local racing, and I don't remember hearing about issues like this.

Just a little surprised.
Well, me too!
that's why I bought the Viper in the first place: as a cheap, cost effective spare plane. I did the basic strengthening of the airframe... I even went the extra mile and re-did the aileron torque rods properly, used real hinges (no gaps), sealed up the hinges gaps (just to be sure)... So I was kinda surprised to see this kind of behaviour.

Anyway, the Viper is still good value IMO. Now that I know where to devote my attention, these make very good spare-practise planes. It does fly well once it is sorted out.
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Old 06-06-2007, 10:35 PM
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Default RE: Viper 500 flight problem

Yes I absolutely love how they fly and I did the same as well. I glassed the fuse, and epoxy bedded the tourqe rods. I have gone back and fiberglassed the tail and epoxied it to the fuse. It really seems pretty weak in the area of the joint between the 2 stab\fins. I really believe this is where the flex is.
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Old 06-06-2007, 11:00 PM
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Default RE: Viper 500 flight problem

one of the texas guys here. tho i am not and expert by any means and have only raced 2 full seasons 3 this year.

i have 5 viper ready for the racing season. the problem described is related to the cg i have seen it on all 5 after setting the plane up first with a tt pro40 then going to a nelson.

put the cg at 2-3/4".

mods that i now make the viper last a little longer

2 inch wide fiberglass tape top to bottom and side to side over the firewall extending at least 3-1/2 inches back on the sides

1/2 inch fiberglass tape 3 inch's in front and behind on the side of the fuse at the le of the v tail.

3/4 oz cloth top and bottom of the vtail to stiffen,

3/4 oz cloth down the length of the fuse both sides

double the thickness of the wing mounts front and rear then tap for a 1/4 nylon bolt. get rid of the metal screws they willllllllllll vibrate loose with a nelson or jett engine

get a good set of wheels from jett or performance hobbies

use a bladder c/g tank from jett i stops the trim issues during a race

putt the throttle servo and batt pack in the nose

with these mods i have been getting 3lbs 10 oz consistant weights

once you have gotten the feel of the airplane and are looking for more speed cut off the outer 1/-1/2 inches each side of the v tail it will give you about 1 sec extra speed but it is slightly less stable so be ware.
control throws with nelson/jett setups on the ailrons is 3/16 up and down low rate 1/4 high rate, vtail is 1/8-3/32 up 1/32 down low rate 3/16 up 1/16 down on high rates both with 45%expo.

90 % of the vtail brakes are caused by just slightly pressind down on the fuse during launch 10% on a skidding landing.

the firewall problem has been solved by many by the extra fiberglass tape over the outside of the fuse as mentioned. the 3/4 oz cloth applied by the factory just is not enough and the fiberglass in side the firewall is useless it adds no strength to the twisting on a nose skid landing which most do.

another problem that i have personally experienced on 2 vipers (before reinforcing) was wing/ fuse seperation with a nelson engine in the turn. wing mounts plain flat ripped out. each time both were airframes with only 8 flights 2 with a nelson and both not dumpd on landings.

the viper has been found to be only about 1 to 2 sec slower in a race over the 600 dollar super composit airframes.

when doing the fiberglass and epoxy work remember less is better using epoxy. thin only 10% with alcohl (sp) squeege off the excess with an old credit card and then using toilet paper roll with paper get the excess out with the super absorbant paper. this is why it does not add much weight 30 minute epoxy works best.

enjoy the racing go fast turn left go faster.

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Old 06-07-2007, 12:21 AM
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Default RE: Viper 500 flight problem

Thanks for the info Resoucecapital. I have been getting my tips from Kurt Bozarth and he really likes these planes. It is also great how you can get replacement parts. The one thing I need to do in the future is put my battery and servo in front of my tank. I actually needed to add weight to get my to balace after the extra weight I added to the tail.
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Old 06-07-2007, 12:25 AM
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Default RE: Viper 500 flight problem

This is where the fuselage breaks at the front edge of the V tail mount. This can happen sooner or later to many of us if you don't take steps to strengthen it as suggested. This was found new in box this way, I think it had a rough trip from China. It's an easy fix. Remove the covering, drip in some thin CA, glass it all around and re-cover.
If this happens in flight, most of us won't have to worry about repairing it. I think this is what happened to my Viper #1 several years ago. Despite the Viper's shortcomings, it's still a great deal if you take the great advice on RCU.
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Old 06-07-2007, 02:27 AM
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Default RE: Viper 500 flight problem

Freakingfast
That picture looks identical to were my plane was cracked.
John
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