tamjets

My Feedback: (2)

Hi everyone,
I would like to share important information about the Viper Jet.
This weekend we had 3 Vipers flying. My friend who flew my Viper, did a high speed pass and pulled hard straight up. The wings flexed and bent the the aluminum spars. He was able to land her safely.
I had many flights on my Viper, but never pushed her to the limits. Now we know the wings spar can't hold high speed G force manuever.
If some of you have your Viper ready to fly,PLEASE DO NOT pull a high G manuever. Be best not to fly her until I find the solution to the problem.
I already spoke to Cermark about this. They are waiting for me to fix mine with better wings spars and do some high G test. If everything goes well, I'll take some photos instruction to show step by step how to remove your original spars out and replace with stronger spars. Cermark will supply the new improved wing spars and some compensation for the trouble.

Sincerely,
Tam
www.tamjets.com
Cermark customer support

tamjets

My Feedback: (2)

The spars can easy remove out in 20 min.
Heat up the spars to loosing the glue. Pull it out with plier.
To put the new spars back in and alignment both wings for the expossy to dry can take up to 1 hrs.
With my detail photos instruction. I don't think anybody having problem doing it.

Here are the photos of first 3 step.

JohnVH

My Feedback: (38)

Wow! looks like the wings are built very strong if they held better than the spars!! Nice.

I see what looks like Johnny's bird in the background, is this his doing? hehe j/k

SAP_2000

This does not look good.....[]
A thought that just struck me, is that the wing spars looks to be the same as on Skymaster F-15. Maybe the Airpac guys should check this out...?

Looks like I have a few problems to solve, since I own a ViperJet, and the F-15 that should be here in few days......[&o]

tamjets

My Feedback: (2)

Staale,
The F-15 is O.K. It had flying fusalage. So the wings just carry 40% of the load.
The Viper had long wing. 90% of the weight all shift to the tip of the wings. That why the spars can't handle the heavy G manuever.
I'm go hunting for new spars tomorrow. I thinking using 304 stainless steal spars.
Hope that will take the spars problem.
Even with new spars change. I still would not fly high G manuever. This plane are not design to fly like that.
This plane design to fly smooth and gentle. So flying this plane just like flying the real scale. Beside, what the fun from pull high G manuever. Just asking for accident to happen.

John,
The F-15 on the background are my now. Is orginaly from Dave Fusiano. It had long history go thru many different owner. Now is in my hand. I just give her inside out service.
Brg,
Tam

SAP_2000

Hi Tam!

I understand that the wing loading on the F-15 is lower than on the Viper because of the flying fuse. But the F-15 is imo. a plane that is designed to do some tight high G maneuver's, and I do plan on doing some pretty hard G-turns with it, but now I will probably worry every time I am pulling some G's with it....[sm=crying.gif]

Can you try to describe exactly how hard the pull-up was? Do you think it is possible to bend the spars on let's say a hard landing?

I do hope you get some sort of compensation from the the manufacturer/ distributer for all your work reg. the Viper's control surfaces, gap sealing, and now the wing spars
Theese things is most definitely something they should have caught up with when they tested the prototype, so we as customers would not have to be test pilots!

I am starting to be a little tired of theese tings that need modification, and I wonder what's next..........

Keep up the good work Tam [sm=thumbup.gif]

Woketman

My Feedback: (6)

WOW!!! Nothing like landing with more dihedral than on takeoff. The photo from the back, now that is scary looking. As John said, it really is a testament to the wing's construction that they held, yet the spar yielded. Looks like Tam is gonna have an easy mod for this. I'm keeping an eye on this stuff cause eventually, I want one. Great job Tam. Any video available of the pull-up?

Aero65

My Feedback: (2)

Hello Staale

We have put the F-15 through some pretty high G, maneuvers, It will take some very hard maneuvering and come out OK. We have flown 3 of them here and none seemed to have any issues with pulling high G's. I have done high speed low passes to the vertical with no problems at all with 40 oz of smoke oil, tams smoke system, and 3/4 fuel. I would not worry about pulling High G's with the F-15.

We know of a F-15 that has a 28lbs turbine that is reported to have gone over 200 mph. This person also balanced his stabs because he knew he was making a very high performance F-15. This aircraft has flown well.

I'm sure that Tam will have this fixed in a very short time with a strong and logical solution. Thank you Tam for the good explanation of what happened and letting people know.

Vincent

My Feedback: (61)

Staale,

I would not be concerned with the 15. The AvondsF-15 uses a similar single alum spar and no where can i ever remember one of those being bent up like that.

Tam,
Good job with the flight testing and the heads up on this. As stated in this thread, the wing must be very strong to hold up as the spars were bending like that.
V..

Johng

My Feedback: (4)

Sorry, but that comment is just over the line in this case. No plane in existence, model or full scale, is built to withstand every concievable elevator deflection at any possible speed.

Pulling a cornering maneuver with this plane( as with most planes) at full speed is not the smartest thing to do - and obviously wasn't intended by the designer. The plane didn't even come apart, fer chrisakes!

If I was with Airpac/Cermark/Tam's garage, I'd be willing to sell new replacement spars - same as the old - and tell people to dial down their elevator rates or restrict thumb motion at max speed. The fact that Tam works on improvements to a perfectly good design does not mean that there is somehow a defect in the original.

warbird51

My Feedback: (12)

Tam,
The current spars are most likely 6061-T6 aluminum. That is the standard aluminum available commercially. If they were made out of 7075-T6, they would be more resistant to bending

jetdriver

My Feedback: (1)

I own both the F-15 and the Viperjet. I have not flown the Viperjet yet, but I have 6 flights on the F-15. I have a BMT 120 KS for power and I assure you I completelly trust the integrity of the F-15 after the way I have flown it so far. I don't "jerk" it around but I don't "baby" it either. Tam, have you looked at replacing the spars with 6061 T-6 aluminum? I am going to compare the hardness to the origional spar with some T-6. I will let you know what I discover


Mickey

SAP_2000

John:

I was not only talking abut the wing spars here....
I was as close as you can possible get to loose my Viper and all the gear in it totaling about 6 -7.000$ on the very first flight, because someone at the factory did not bother to use enough glue on the control surfaces... I was very lucky to get my plane down in one piece so the the cause could be confirmed once and for all, and that the other planes out on the market could be reinforced before they started falling out of the sky.....

That's why I feel like a test pilot.....

I agree that pulling lots of elevator at something like 200 mph. is not the smartest thing to do, but IMO this is seems to be to weak.

aparchment

John I respectfully disagree with you on your statement that the modeler shouldn't be able to pull a max elevator turn or pull up from top speed. Unless the manufacturer has recommended against such a maneuver, I personally would assume that it is within the design limits provided everything else on the plane has been set to manufacturer's specs.

I think we have seen several issues with these planes. I respect Tam for really hammering through all of the problems with the manufacturer. Unfortunately many of these problems are being discovered after models have shipped and are flying. It's too bad, because it is a cute airplane, but it clearly needs much refinement.

I guess it boils down to choice. I don't want to stick my expensive gear in an airplane that has not been tested to the max. I guess that's why I feel so comfortable with BVM. I know that when I get my stuff it has been put through the ringer by BVM test pilots BEFORE it is released to the modelers. Am I willing to pay a premium for this peace of mind? Yes I am.

Remeber back two years when people were crucifying CAI for not properly testing planes before releasing them to the public? It strikes me as the same issue here only slightly worse because the engineering seems rather more lacking.

Anyway, that's just my opinion and my preference not to jeapordize expensive equipment on aircraft that aren't fully tested.

Antony

Turbulence

My Feedback: (76)

O.K. Guys let's back up a second here. The planes are made overseas, you all know that. Cermark is the main supplier, we all agree here so far. Testing and instructions, photos where done by TAMJETS after the factory had done their testing. So take it like this. Part of the factory (TamJets, yep even though he does not make them himself.) is NOTIFYING all of you the limits of the plane. If you want to listen that's fine if not then you all know the consequences. This is not a Bandit and if you want to fly it like one, well go buy one (a Bandit that is) if you still want to push the Viper Jet to its limits, then you know what you have to fix.

I also wanted to buy one really bad after seeing it fly at Fresno, but decide to wait it out a bit until many others where out there and I tested. I made my decision to purchase one around March of Next year when I know all the hoopla will be done and I will get a second or third generation Airplane.

[:@]Last but not least, this is NOT a BVM airplane so why must everyone try to compare it to such. Look at the price of a King Cat (the only ARF Plane from BVM) and then look at the price of Viper Jet. For under $1000.00 if I have to pull the Wing Spar out then so be it, or I can go buy another plane or you can pay over $4000.00 for a King Cat that has been flight tested and all.

On another Note nice to see how This thread shows you how to FIX things, and STAYS HERE. I wonder what Happened to the other thread where some other manufacturers plane chrashed and it got deleted so quickly.

Turbulence

747drvr

My Feedback: (5)

I agree with Johng. This isn't a 3D aircraft. How many people fly their jets like that ?! I'll reserve further comment because I wasn't there and didn't see the pull up. If fellows truly do fly other similar aircraft like that and they hold up just fine, I'll eat my words . Isn't it a little smarter to fly with a little finesse and respect the limitations of the airframe ?

seanreit

My Feedback: (60)

The Isobar is.......

I personnally flew the model straight down the runway at full speed and pulled straight vertical. The computer profiling of the spar sytem indiates it's rated at least to 14 G's. I've seen the graphical analysis. The isobar with 8411's on the elevator is completely capable of this manuever. Also, I'm not sure, but David Reid's bobcat appears capable of doing this as well at or above 200 MPH.

I think the Viper will be capable as well with a beafier spar system.

Cool Pictures!!

DavidR

My Feedback: (1)

Actually there are quite a few airframes now that people DO fly this way. Over the course of the last few years I have seen more people snaping their jets, etc....If a spar will bend with a 90 degree hard pullup what's to say it won't bend in a high G 360, or during a snap roll? And just because the spar only bent and did not break this time does not mean it won't break the next time. People are yankin' and bankin' and they are going to do it with "scale" jets as well as sport jets.

AlW

My Feedback: (17)

Nice pictures but this could have been a major disaster. Manufacturers of turbine powered aircraft need to perform at least minimal stress analyses of critical components of the airplane as well as flight testing to the limits at which they expect the airplane to be flown. Looking at the pictures I would guess that the material used was 6061 aluminum and probably in the zero heat treat condition. In the aerospace industry we call that ornamental aluminum because of its poor mechanical properties. A simple beam stress analysis would have revealed the failure of the spar. What has been discovered here is the weak link in the system. Changing the spar material to 7075 aluminun or steel as Tam suggests will not necessarily fix the problem and may simply drive the failure to a different location ie What is the capability of the spar supporting structure inthe wing and in the fuselage? It is obviously better than the current spar material but by how much? Telling the user to not perform high g pullups is not the answer . The turbine powered models which we fly and love are serious flying machines and need to follow a design process similiar to their big brothers - structural design concept - structural analysis of critical components - well-planned flight test program. We are way past the point where someone with no knowledge of basic structural design and analysis can "design" one of these machines.

Al Watson

sandslx

My Feedback: (1)

Public flight testing is like Christopher Reeves judging a dance contest...it aint right.
I am amazed it bent that far...I'll bet it wasn't 6061 Aluminum, or 2024?

sincerely,
Justin Sands

tamjets

My Feedback: (2)

I only had few things said.
I fly very responsibily. I don't push the plane to the limits if I know was not design for it.
But I still try my best to help Cermark company to improve their ARF'S to the next level.



Safety is the first thing. That why I make this public annoucement. I know go to hurt my sale and Cermark. But safety is still our first priorty. We are on the case to make improvement.

So some of you like to chime in with helpful information to improved. I'm glad to take any advise. For other got nothing good to said. Please kept it to yourself.
I don't want this thread to be come manufactor wars. Whom is better or whom is cheaper. You can argue all years without any result.
Please kept this thread going to under respect and helpful to the jet community.
That is all I got to said.
I'll kept this project updated.
Brg,
Tam

Turbulence

My Feedback: (76)

So Al, let me go once step further because I feel you missed my point so let me be more blunt. If you buy a full scale Viper Jet (or any real plane for that reason) Then the manufacturer tells you not to loop the plane (you can pick any maneuver you like, just follow along with the loop for this example) Does that mean you are going to go ahead and loop the jet anyway?

I hate it when someone else compares any Jet to another manufacturer that does not sell the same kit at the same price and I must eat my words because I will do that know. Do BVM jets not have a VNE? For a while (I don't know if he still does or not, but pretty sure he does) He included a statement where He stated to you the VELOCITY NOT TO EXCEED for that plane because after that your plane has less chances of coming back in one piece. Now Tam Jets as the main vocal, or visual representative of Skymaster for the Viper Jet has told you what not to do with it the rest is up to you. He also has posted fixes for his plane if you fix it or not is up to you.

I personally Applaud Tam for bringing it out in a public Forum instead of trying to hide it and fix it on the other planes coming off the production line. He could of just as easily just stated "Do not fly this plane at certain Speeds or do no perform certain maneuver" and not said ONE word about the spar. He is in the business to make money and by bringing out these problems he only makes the planes Safer for you and the rest of the hobby. I am sure people have cancelled their orders from him regarding the mentioned problems, but we are all safer or at least will keep an eye out when we see the plane flying at a meet. A lot more people will be alert, I promise you that.

Turbulence

Vincent

My Feedback: (61)

Good post Tam, i never have "pushed" my jets to their limits and still have fun flying them. I keep my rookie flying within reasonable limits. I think stainless is overkill and would try a harder grade alum as suggested by the others. I believe those wings are very beefy including the mounts. I bet on a foam core wing the mounts would have split right out of the wing.

V..

Doug Cronkhite

My Feedback: (34)

Without knowing how fast this person was flying and how much control deflection was used when the spars bent, this is a pointless discussion. ALL aircraft have structural limits, and if those limits are exceeded by the user due to their own negligence or ignorance, you cannot blame the manufacturer.

There has to be some common sense applied. You cannot simply lump everything on the manufacturer and say 'bad design' if the pilot on the sticks failed to use the 8 pound mass atop his/her shoulders.

KFalcon

My Feedback: (18)

I agree completely. Thank you Tam for putting safety before the all mighty dollar! Looking forward to hearing about how the fix fairs out! I hear good things about the jet!