Viperjet vertical stab shears on maiden
 

Finally got the Viperjet ready after going over it and over it for a long time. With the kind assistance of one of the most experienced pilots in turbines at the controls for the test flight all went pretty smooth until about 3 minutes into the flight the vertical stab and rudder decided to depart the airplane. Still controllable, a flapless emergency landing was made. It actually flew for two laps around the pattern that way before landing. The seperation occured in straight and level flight at a very modest cruise speed. Power never exceeding 40% except for takeoff. No inverted or crazy stuff just plain gentle flying. No signs of flutter were ever evident and no gaps between the stab and rudder to create flutter. Controlled by a $100 JR 9411 servo with lots of torque and no slop in the linkage.
Cause is not known but the stab and rudder were located after the landing and all that is in it is a balsa spar. The stab sheared just above the carbon fiber reinforcement that is used on the interior sheeting. Nothing is used above that but balsa. Further examination leads to believe the spar failed but we'll never know for sure. Just want to get the word out about a possible weak point. A phone call to Cermark ordered a new vertical stab and thought it was going to be no charge....turned out to be $95 plus the $100 servo I lost in the field somewhere that could not be found. The new one has been opened on the bottom and reinforced the spar to sheeting seams with carbon and all weak areas strengthed with thin CA. Hopefully this will prevent another incident of the same. Fortunately I had the bolt on version of the stab that I had not glued and it was easily removable. However the new ones are now designed to be glued on. So I hope it holds together this time for a long time. For those of you still building or have the stab removable I would advise strengthening the spar of the vertical stab and just making everything as strong as you can including servo mounting and linkage as well.
Thank goodness the Viperjet has winglets and tail strakes along with the portion that was left, the airplane was still controllable. Many thanks to the skill of a well known test pilot as well. Without them it probably would have gone in.
Hence the name ....Black Cloud:D

RE: Viperjet vertical stab shears on maiden
 

Another photo

RE: Viperjet vertical stab shears on maiden
 

First of all, congrats on getting most of the viperjet back safely...

I have a question....where was the rudder servo mounted?

RE: Viperjet vertical stab shears on maiden
 

This is absolutely incredible (absurd, more like it). You would think they would cover such an incident especially considering it could have cost you the entire set-up. I hope your incident will help others out there because Cermark definitely will not. Their products and customer service have much to be desired in my book.

I'm glad you got it back in 2-3 pieces. You really should think about a name change ;)

George

RE: Viperjet vertical stab shears on maiden
 

Cermarks planes are only good after you seriously modify them (some ARF huh ? ) .. I have been happy with my bm339 for a while, but if it had not been modified in several areas, i would have ripped the eings and tail off in flight a long time ago .... I have seen numerous threads here on RCU about cermark stuff coming apart in flight ... its a shame, because a little more attention to quality on Cermarks part would have made for a great product ... its crap like this that has kept me away from the Viperjet, even though it is a cool looking , well priced, well performing jet ..


Wojtek

RE: Viperjet vertical stab shears on maiden
 

Just got back from Best in the West where we flew the Viperjets non-stop for three days and never had a mechanical issue. Ehab's viperjet had a deadstick on Saturday when he ran out of fuel and he lost his Viperjet on Sunday due to a radio lock out (confirmed by the ECU). The three Viperjets were all built stock as per instructions with no modifications to the rudder or elevators. My Viperjet is absolutely original with over 150 flights, no problems and looks as good as the day it came out of the box. It has truly been a "gas-n-go" jet for me. In addition, I know for a fact that the new shipment of Viperjets have been re-engineered in key areas with vast improvements. Back at Tamjets, we have put the Viperjet through all possible flight manuevers, conditions, G's, etc. and have purposely "broken" a few to learn more about the plane and to improve the next generation. It is unfortunate what happened to your Viperjet, but the incident is not common.

As always, we are very interested in learning more about the situation as we are conscientious of design safety and integrity.

I will have Tam read this post and comment.

John Orito
Tamjets rep

RE: Viperjet vertical stab shears on maiden
 

I will be more than happy to send you a free vertical fin and rudder for free....just call Tamjet at 408-2247600 between 8 am to 5 pm PST and we will take care of you.

It is possible that the cause is still unknown or it is a quality control problem at the factory. Tam will be personaly inspecting the factory, when they build the next batch of Vipers, for quality and consistency in the weeks to come.

RE: Viperjet vertical stab shears on maiden
 

Thanks John and Ehab for the offer on the stab. We had already talked to Cermark and Tam at the time it happened. We thought Cermark was sending a replacement to the hobby shop but they were billed for it and in turn passed it on to me at 89.99 plus tax. I had already sent the photos to Tam earlier. He is always willing to help. I guess that is just my usual luck. Hopefully round two will be better.

Ehab sorry to hear of your loss.

Mark

RE: Viperjet vertical stab shears on maiden
 

Mark,
I had look very closely to the photos.
Here is what I think what might happen.
How you mount and glue the servo? Where is the servo? Could it happen the servo plate came off during flight and take the half fin with it?

Usually the fin only can break off if you got flutter. Unlikely it will break for no reason. Even the spar are made from balsa.
The structure of the fin is seal balsa skin composite. That is strong enough.

I had test the model over the speed limit and pull until it break. The stabs and verticle fin stay in one piece when I pick the salvage.
Ehab plane pancake hard to the ground and tumble 200ft away. The stabs and verticle end up with some scracthed. No structure damage at all.

But I do got other two customer reported to me that they got flutter with they verticle fin.
After they landed and find the flutter cause by the servo stripping gear. The servo they using is not metal gear.
Stripping servo gear can cause by few things. Overdrive the servos, bump servo during transport and sloppy installation also cause flutter until the servo gear give up.

Mark,
If you return the fin back to Cermark. We can give you Ehab verticle fin no charge. If you have any problem return the fin.
Give me a call. I'll fix that.

The next shipment of new improve Viper Jet is coming late June.
I be flying to the factory few weeks before to do quality inspection before is final.

I do put alot time and investment to Viper Jet. Bad rumor do destroy my business.
So I only ask one big favor from everyone of you. Please take resposible for your post.

Goodnight,
Tam

RE: Viperjet vertical stab shears on maiden
 

Black cloud

Good job bringing back your viper. Some guy at FJ4 lost is stabilizer and some other guy is aileron rip open but still able to fly around and land safely. Not many jet out there for the same cost can do that. There is some modification that need to be done to this jet and I think tam is on top of it. ;)

RE: Viperjet vertical stab shears on maiden
 

If the next batch will have a lot of these issues fixed, i might think of getting one .... I have just always been afraid of the aileron ripping off, or issues with the stabs ... It is a nice looking and flying plane , and the price is just right ...


Wojtek

RE: Viperjet vertical stab shears on maiden
 

Tam,
Thanks, no harm intended. I am definately not trying to hurt your business as the next one will be from you. New colored Viperjet or whatever else. I just didn't want anyone else to encounter the same problem and lose theirs.
Thanks for the offer on the stab but I already have the new one intalled.
On the broken one the rudder servo was mounted in the stab using the plywood blocks with the kit using hysol to the interior of the stab to the opposite fully sheeted side. I have heard the stories of having it mounted to the hatch. This was not the case. The servo is long gone out in the pasture. I looked for two hours. Every piece of donkey dung looks like a servo case!
Again I do not know what the cause was, just a few things to look at when assembling to make sure it is good and strong.
It may have been my error or maybe it was not. I don't mean to point fingers or place blame.
I am not starting rumours and do not have that intent. I just hope it doesn't happen to anyone else. That is the whole intention of the thread. Let others learn from my misfortune.
Mark

RE: Viperjet vertical stab shears on maiden
 

The question about the servo location is extremely important.
If by any chance you mounted the servo on the hatch cover, there is the answer for the problem. The stabilizer skin is too thick to be held in place by 4 screws and at the same time holding a servo.

To mount the rudder servo, I glued a plywood plate of 1/8", about the size of the servo and provided with 2 blind nuts to hold the aluminum servo's mount...

A few weeks ago I tried to do a few knife edge with my Viper at full throttle and the vertical fin remained there....

So far my only complain with my Viper is the landing gear [>:], (actual "bended aft by your self" from Robart don't resist a hard landing at all) but the new Vipers generations are coming for use straight struts. Just hope Cermark take into consideration$ all the guys like me that supported them buying the first generation's Viper (....the lab's rat ;) ) giving good price for the new set of wings....[sm=drowning.gif]

Ehah, sorry to for your lost.-

Regards,

Miguel

RE: Viperjet vertical stab shears on maiden
 

BlackCloud were do you fly your jet (Markam park) ?. I was there last sunday and saw a couple of viper jet flying. Where you flying sunday????

RE: Viperjet vertical stab shears on maiden
 

First: Great job done by your test pilot getting it down in one piece:D

I too was a nanometer away from loosing mine on the maiden when it ripped LE of a aileron open in flight. Later it de-laminated one aileron and the metal mounting blocks for the wings got loose from the former in the fuse. There has been far to many *incidents* with the Viper by now. Too bad, because it is such a beautiful plane.

Would I buy it again....? -H*** no![&o]

RE: Viperjet vertical stab shears on maiden
 

[quote]ORIGINAL: SAP_2000

[ the metal mounting blocks for the wings got loose from the former in the fuse.
Did you check and tight this block before install?
Even is an ARF'S. It still need some experience to assemble. Check thru everything before install.
That why all my ARF'S kit I built never fail inflight.
Tam

RE: Viperjet vertical stab shears on maiden
 

This isn't the first Viper jet verticle stab problem. Ask the BarryMan!

RE: Viperjet vertical stab shears on maiden
 

Guys,
Any jet that flies at 200 mph need SERIUS assembling....
The smaller assembling details become big problems at hight speed if over looked.
As an example...I tested all brand of clevises [sm=bananahead.gif] before choosing one, and find out that only Dubro full metal clevis have no play at all into the horns....cracy ah?! but the only way to have peace of mind flying a US$7000.00 toy is that....at least for me.
Regards,
Miguel

RE: Viperjet vertical stab shears on maiden
 

Bill
Barry was one of report I mention.
It was comfirm servo strip the gear to cause that.
Tam