Today was a beautiful day to fly my brand new Viperjet MK 11 powered by a simjet 2300.This was my second time flying this jet,when all of a sudden the whole back of the jet started to shake violently from FLUTTER.The back hatch flew off,the front hatch had pushed into the fuselage,I immediately went to idle on the throttle,made a left turn,droped the landing gear down,control of the jet was very mushy and the jet was coming down fast and very little control on the elevator.I managed to land the jet with one elevator servo working,breaking the brand new landing gear, bending the nose gear and bending the spars on the wings. After assessing the damage, the FLUTTER was caused by the RIGHT HORIZONTAL STAB coming loose, not from the screws but from the WOODEN BLOCK in the fuselage, this block separated from the fuselage while IN FLIGHT. Looking into the tail of the plane you cannot see this block as it is covered by the back former. I lost 4 digital servos,bent both wing spars broke 2 struts (mains),bent nose gear and 1 hatch latch, all caused from STRUCTURAL FAILURE. I will contact TAM tomorrow.

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A friends Vertical fin did the same thing on the first flight at 1/2 throttle with a Ram 750.

Hi.
Sorry to hear about your incident. You can consider your self lucky as flutter on a jet normally is fatal.
I have flown my Viper Jet (first series) for two years w/o any flutter issues at speeds upp to 330km/h on a regular basis (130N or thrust).

In my opinion the elevators and rudder of the Viper is sensitive to flutter if you don't take any precautions. By mass balancing the elevators (approx 20g in each tip of the elevators) and similar to the rudder you will reduce the models sensitivity to flutter.

The wooden part that came loose may be a secondary effect of a self induced flutter. The forces of a flutter when your jet is doing 150mph can easily rip out the servo of the elevator or fin or destroy a nylon gearbox of a servo. Always use metal gearbox.

I know the Mark II is a bit tail heavy an you may not want to add 50g of lead in the tail. However, if you do a proper mass balancing you can operate the elevators and rudder with a 24g Digital wing servo (Hitec HS-5125MG or JR DS161).

It would be useful to se a picture of the servo installation in the horizontal stab. Please check if the servo has come loose.

Also very important is to have a rigid an slope free linkage/control of the control surface.

/Johan

I can predict what he is going to say, save yourself the phone call.

"IT YO FAULT!" This has been his response after several of the same occurances.

Thank Mike,
If you don't have anything better to say.
Save it.

Now let me help out this customer and I find out what have happen.
If the stab fail due to manufactor problem. I'm sure I always take care of it.
But if it not. I'm sure no manufactor can replace every single jet each time customers have a problem.

Sorry for your flutter.
It would be nice if you have contact me first. Make a post on public forum try to get other opinion is bad. To many guys out there got nothing better to do than stir up stuff.

O.K.
Here is fews information I need from you.

1. What servo are you using?

2. How you set up your linkage?(show me photos)

3. Did you check the stabs for any sign of weaking after you finish the assembly?

Just purchased a viperjet kit, can you tell me where I might find a list of the equipment needs for the viperjet, I do not want to experience any of the problems I am hearing about so I want to use the best servo for each application. Also has anybody come up with a list of all of the mods that should be taken into consideration while assembling the viperjet. It strikes me as odd that if there are all of these problems with this kit then why is there not a complete list of what needs to be done to remedy these issues somewhere on the web or included with the kit from Tam.

Guys, just got off the phone with TAM, we both discussed how this could have happened, conclusion we both agreed on is a stripped servo gear. He has offered to help me with parts that I will need to repair the Jet for FREE, so I would like to say THANK YOU TAM for your support.


SS678554- Give Tam a call, he can give you the best servo selection. (408)2247600

Steve,
I got your message.
I left early to see my daughter. I'm here in the office. Stay up late to catch up some of the works.
You can call me if you still up.
But here the servos lists I promise to send you by email and forget.
Elevator: 2 JR 3421
Rudder: 1 Jr 9411
Aileron: 2 Jr 2721 or any good standard size servo.
Flap: 2 Jr 2721 or any good standard size servo.
Retract :Jr 341 or any mini size servo
Nose steering: Standard size servo

Remember to use the shortest servo arm (about 1/2" out from servo center). This will give more mechanical advantage.
Make sure everything is solid. Specially the elevator. Any sloppy play can cause major flutter.
During transport. Tape the elevator for safety protection.
Any bump to the elevator can cause the servo to strip gear without notice.

Tam, what about the servo for the brakes?

Also extensions, rf chokes, switches, can you give me the complete list of all the radio equipment I need to order? Thanks

This is a dead horse, how many of these have to come apart during flight to realize that its garbage ?

Charlie Beverson of SVF has had mucho flights on his Viper (believe over two years worth)
Semper Fi
Joe

Just received a e - mail that Charlie lost the viper @ AZ jets

There are obviously any number of reasons why a jet may flutter. While I can certainly appreciate WIDEOPEN'S problem and the excellent manner with which TAM is handling it (as expected IMO), I only ask that unless anyone has evidence that clearly illustrates poor workmanship, bashing will not be tolerated. Let's keep it professional and informative, as it should be. Thank you. Regards,

Richie

Richie,
Here are some examples of the problems, I suggest this track history should suffice to fulfill your request for evidence. It might be noteworthy that Tam is handling this in an excellent manner...but the plane was not totalled. If the plane was a total loss, his reaction could be much different.

http://www.rcuniverse.com/forum/m_27...iperjet/tm.htm

http://www.rcuniverse.com/forum/m_30...tm.htm#3001994

http://www.rcuniverse.com/forum/m_27...tm.htm#2783353

http://www.rcuniverse.com/forum/m_17...tm.htm#1724529

http://www.rcuniverse.com/forum/m_17...tm.htm#1717319

http://www.rcuniverse.com/forum/m_11...tm.htm#1128417

Video included:
http://www.rcgroups.com/forums/showt...light=viperjet

A tiny JR 3421 servo with just 60oz/in of torque on the unbalanced primary pitch control of a high speed jet !
Are you guys serious ?
Regards,
David Gladwin.

No need for the speedbrake with the aileron/flap crow setup. Save yourself some work with a little radio programming. Sweetheart with crow. Never had the speedbrake installed and flew off 500 foot runway before the crow, now could probably do half of that.
Mark

David, yes I agree that it sounds fishy....but we have logged hundreds of flights each on at least 6 differant ViperJet kits set up how Tam suggests and flown full throttle for most of the duration, and all I can say is that it works. If I havent already seen with my own two thumbs that this is a reliable set up, then I may have been inclined to put larger servos in the stabs and not care that they stick out a bit. Tam has done so much testing with this plane to make sure that the customers have no problems, he has even went to the extent of purposely donating one of the kits to the full power dive and pull full up elevator with a G-meter just to see how strong the redesigned wings/spar system holds up. In our extensive testing, the flutter is non existant when installing the short servo arms and using all the torque of the servo. I believe the instructions describe this installation, and I have not heard of any customer's having a problem with their ViperJets when this system is implemented. Some may choose not to build this kit because of the "touchy" elevator set up, and that is their choice. However the problem has been identified and a fix is in place.
This kit is not manufactured by Tamjets, it is s Cermark product, but Tam has still treated it like it was his own to make sure that anything sold to his customers was trouble free. If there are still any questions/concernes please feel free to call TamJets for detailed pictures and instructions.
David, if you buy an airline ticket to San Jose California Tamjets will pick you up, feed you, house you, and take you flying. You will be handed the transmitter to our demo viperjet to fly, and if you can break it by flying full throttle with a JetCat P-120 (199.9 mph) TamJets will re-imburse you for your plane ticket.
Hope this answers some questions,

Dave

Heck of a deal .. all David has to do is fly it into a tree, and he gets a free plane ticket !!

I have had this argument many times before. Sure some guys, probably most guys, will get away with it but not every machine is identical . Some elevators wil have different mass and different mass distribution and the flutter characterstics will vary slightly just as the aeroelasticity of each fuselage will vary slightly according to the glass layup. There are four or five primary defences against flutter:
Mass balance
Stiff structure
Minimal control circuit "slop".
and on aircraft which have powered controls, model or fullsize, powered by hydraulics or powerful servos MORE than enough for the job.

To me a tiny servo like a 3421 is OK but marginal just as I said BVMs servo spec for his original Bobcat were poor. when he specced 3421s for the rudder, which I said were totally inadequate (they proved to be) and fitted 9411s from the start, and the 3301 servo for the elevators were marginal (as SOME fliers found, to their cost to be the case) and upgraded them also to 9411s. I have had many emails from around the world telling me that they have so equipped their BobCats and had NO further recurrence of elevator softness)

No, unless each airframe is IDENTICAL then the argument that because some, most, models have been fine then there cannot be a problem, despite SOME other models having problems is, in my opionion, flawed.

In essence I have never heard of a model being lost because the servo power was too great, on the other hand I have heard of many, many machines being lost because the servos were not up to the job !

High speed jets demand servo power which is right up to the job in the most adverse circumstances and there ia absolutely no room for compromise or corner cutting here.

I rest my case.

Regards,

David Gladwin.

David,

Unless the servo you use has a capacity of torque and servo gear strength which exceeds the theoretical maximum load that could be placed on it by a max speed max g load manuever, it will fail and quite possibly cause flutter in that instance. Hence your suggestion of using 9411 servo's instead of the smaller, less powerful, 3421, in fact accomplishes no more than your beginning statement "Sure some guys, probably most guys, will get away with it but not every" There is no system, currently that can feasibly be installed in our models which will give 100% protection against exceeding design limits. The 3421's work in most cases, as has been proven in the field and thru testing, but not all. Your suggestion will work in most cases, maybe even more cases, but not all. There's not a plane thats been built, that some fool pilot can't break! Given half a chance.

I rest my case.

David Searles

I entirely and absolutely agree, particularly your last sentence, but what ARE the design limits (have any been established) and how do we know when we are approaching or exceeding them? That is the dilemma. What I do say is that we can very easily improve, strengthen, our control systems and make them less, perhaps much less prone to flutter or failure, (but not immune), at very little weight or financial penalty, thereby further reducing, but by no means eliminating, the risk of failure of the control system in typical use.

Certainly, if I had a Viper (or any other type) and I had heard of more than one or two incidents of flutter (as I believe there have been, just as there were several BoBcat pilots who suffered pitch control problems) I would take all reasonable precautions to avoid a recurrence in my machine. The first step is to look at the specification of the servo used on that control surface and the associated linkage. That is exactly what I did when I heard of the BobCat problems two or three years ago and many pilots have spoken to me or emailed me and said they have done the same and have had absolutely no recurrence or similar symptoms of the problem in their BoBcats, a very fine flying machine, two of which continue to give me and many others superb service.

Regards, David Gladwin.

Hi, Are you refrerring to the same Charlie Beverson who built planes in Freeport, Long Island in 1957/58. I used to fly with him in "the "field" then. Love to chat with him again.