tamjets

My Feedback: (2)

O.K.
Fly lever at 190 mph plus. Full hard straight up.
This manuever was no no. But my friend use to fly bandit. He just got carry away.
Is not his fault. I forgot to tell him. But I'm glad it happen to me instead of cusotmer plane. No one got hurt. So now there is a warning for the public. I hope all you considering your flying manuever. Some aircraft are design to pull hard and some don't.
To be safe pilots. Fly it safe.
Brg,
Tam

AlW

My Feedback: (17)

Turbulence,
I make no comparison between manufacturers. I believe that mfgs should be responsible enough to perform analyses and tests of there products before they hit the market place. The future of turbine flying depends on it. We
need to do the best we can to keep accidents to a minimum- thats all Im saying. I applaud Tam for bringing this problem to everyones attention.

HotelSierra

My Feedback: (9)

Ralph, Doug and Vincent are right on. I was there when the incident occured. The plane was flat level near 200 mph when a hard up elevator pull was initiated, similar to performing a square loop. Remember, we are flying the model at 3 times scale speed to the top speed of the full scale version. Both of my BVM and Avonds jets have specific VNE and/or G-load restrictions from the manufactures. I have also seen the same plane that was damaged fly over 10 flights at much higher speeds with high G, but smooth manuevers without any problems. I have exactly 20 flights on my personal Viper and have had absolutely no structural problems. I have done just about everything within and slightly beyond the full scale version's flight envelope, both positive & negative G's. However, I did have one of my spars out for inspection and noted how "soft & malable" the aluminum was. I have spoken with Tam and know that he is working deligently on a solution. I am convinced that safety is his number one priority. Although the Viperjet was never marketed nor designed as a high dollar, composite, bandit style "...I dare you try and break-me" aircraft, this plane will satisfy 99% of the pilots out there. When the spar material/engineering are upgraded, go out & demo one of these aircraft, you will truly be delighted in its flight performance & envelope. If we manage to keep "slamming" the Viperjet and other aircraft manufactures during their developmental stages while they work out the bugs, only modelers will suffer. I would hate to see a great design like the Viperjet go away.

DavidR

My Feedback: (1)

Hmmm.......it does not appear that this is during the models design and developement stages if they are shipping them to customers. No doubt Tam is doing a good job keeping people informed. But a spar failure seems like a rather serious defect to me doesn't it to the rest of you guys?

David Reid

seanreit

My Feedback: (60)

There does seem to be a lot of buzz in a short period of time on failures of the aircraft and or pilot error. I was told on my first turbine jet (kangaroo) that I had to put a dowel in the spar if I was going to attempt any high G stuff. That was enough to scare me into doing it not knowing what the definition of high G moves was!! I was told some people's spars bent in the roo. I read the instruction manual that I was given, and it's not documented. Ya, a bent spar is a significant problem. Sounds like the system was given at or close to the highest G move the airplane is capable of. The spar didn't completely fail, as the plane came back in one piece. Problem here is you can't just put a dowel in it and fly with peace of mind.

I guess once they upgrade the spar material they'll run the plane to the edge again? Or at least do some computerized stress loads of the material and calculate what it's going to take?

To duplicate the move and conditions in the field may be difficult.

Might never see the problem again.................... Then again................. Time will tell.

You never know when someone's going to accidently bump the controls at full speed level flight, sneeze bump full up elevator, for a bullet proof RC Jet, I think this needs to be taken into account. []

I'm no expert. [&o]

Sean

Doug Cronkhite

My Feedback: (34)

As a friend once told me..

"Try to make something foolproof, and they'll only upgrade the fool."

The end user needs to be responsible for the way someone flies. Personally.. I wouldn't change a thing. This airplane responded to a VERY unusual high stress maneuver and didn't come apart. It DID however show a visible non-catastrophic failure that was easily identified, and apparently easily fixed.

Again.. without knowing exactly how much force was exerted on the airframe, you cannot make a valued determination of failure. How much control throw is used? How fast was the airplane actually going (not a guestimate), what does the airplane weigh?

I think people are a bit too quick to point their finger at the manufacturer in this forum instead of taking a hit to their ego and realizing the fault COULD be their own.

HotelSierra

My Feedback: (9)

David, I don't think anybody is questioning the serious nature of a spar failure. But can you tell me exactly when an aircraft is ever done with its "developmental stage"? Aren't D-version designated aircraft more evolved, developed and improved from earlier A, B and C versions? Or at least by design? I seem to remember owning three distinct versions of the BVM F-86. The first one with a weakly sparred one-piece wing & mechanical gear, the second with a one-piece wing, pneumatic gear and modified gear mounts, and the lastest version with a stronger two-piece wing and highly improved gear system. And we all know how much superior the new one tracks on take-offs & landings. And when was the last time you bought anything mechanical, be it automobile, VCR, stereo equipment, toaster, etc. that didn't have a defect, recall or failure. People are not perfect and we don't live in a perfect world, so it is unrealistic to think R/C jet industry would be any different. I lost my father a few years ago when the jet he was flying in threw a couple of turbine blades and disabled the aircrafts entire hydraulic system. Am I to blame McDonnell Douglas or General Electric for pre-releasing a commercial jet for public transportation before it was ready? The DC-10 had been operational for many years before this tradgedy occured. I am not interested in stirring-up the "which manufacture is better pot". We all know who you represent.
John O.

DavidR

My Feedback: (1)

JohnO,

I was not stirring up the manufacturer pot, and you are right there are no secrets here about who I represent. But suffice it to say that in the very short period of time that this particular airframe has been on the market, and obviously there are not a whole lot of them flying, there seems to be an overwhelming number of them failing for one reason or another. So you make the call.....who is doing the actual flight testing on the airframe?

David Reid

tamjets

My Feedback: (2)

Thanks for all with suggestion.
Just order the GPS system. You all know what I'm go to do with it.
This plane weight 30 pound wet.
Wings span 72"
Fuse 75" long and 11" wide.
Can someone give me the safe G force apply to this aircraft.
Don't compare with other aircraft. Not all aircraft has the same wing loading.
Some of you already know that.
I'm putting $7k investment to find out this coming weeken. So LA trip be plan in short period.
I taken to the desert to try it. Just incase things don't go the way is plan.

Brg,
Tam

DavidR

My Feedback: (1)

Tam,

One problem with the GPS systems is the refresh rate. Most that are currently available do not refresh fast enough to give you accurate results.

tamjets

My Feedback: (2)

David,
If pull hard loop is that enough to give the reading.

Brg,
Tam

mr_matt

My Feedback: (10)

Hi Tam,

The GPS updates once per second. If you download the positional data after the flight, you should be able to figure out the G forces. As close to a round loop as you can fly would be best.

From the looks of those spars the aluminum was unhardened. Bob parks should be able to spec the right material for those spars. At least it looks like the mounts held well, that is a big step.

tamjets

My Feedback: (2)

I just run around to find the spars. But no luck.
Here is what I looking for.
1/8" thick by 3/4" wide and 9" long
1/8" thick by 1/2" wide and 9" long.
I refer stainless steel.
As right now no time to machine. So I like something exact size to do the quick change for testing.
Could some one point to the resource.
TIA,
Tam

tamjets

My Feedback: (2)

Matt,
The mount was bolt with 4 4mm screw and nut on each mount. I had good comfident that be O.K.
Tam

hanna

My Feedback: (3)

The fact that the spar bent instead of breaking might be ok. If you make a stronger spar you are moving the failure to another part of the wing. You know now that the plane can be brought back. I have no idea how the wing is made and submitted fyi. If you install stout spars they could turn into knives that slice the wing. Good luck Mike Krizan

DavidR

My Feedback: (1)

Tam/Matt,

I have been flying the GPS for months and have not seen consistent readings. I have seen up to a 19 G high. Average would be somewhere around 9 G's for my "normal" flying style. A refresh rate of 1 second is a long period of time considering the amount of distance we can cover with our planes. I'm not knocking the system but do question the accuracy of the results we are obtaining with it.

DR

P.S. Tam have you considered using carbon fiber spars? Relatively easy to cut and they are pretty rigid.

Thud_Driver

My Feedback: (1)

Maybe try McMaster-Carr (www.mcmaster.com). Here's what I found after 5 min. Search on steel or stainless steel.

Item# 8131K141 nickel coated 1018 carbon steel 1/8" x 3/4" x 12" @ $4.94
Item# 8131K131 nickel coated 1018 carbon steel 1/8" x 1/2" x 12" @ $4.06

Stainless was about double in price. I'm not much on alloy's but these might work for you. Could have them in ~2 days for $18 + tax + shipping. Warehouse in LA don't know about the bay area.

lov2flyrc

My Feedback: (24)

David,
I agree, the G load results are questionable, I have also recorded a 18G high on my Euro and I highly doubt I have ever put that kind of load on the airframe (I believe the airframe would fail well below 18G ). The speed readings do appear to be accurate though.... BTW....I do feel this airframe should not fail regardless of G's pulled at the manufacturers suggested VNE. Sometimes you just have to pull hard to avoid others in flight. The aiframe should be able to withstand the max flight loads possible when equipped with the thrust output that is suggested....
Todd

mr_matt

My Feedback: (10)

You could also try Online Metals

http://www.onlinemetals.com/

tamjets

My Feedback: (2)

Thanks. I did check for stainless steel. Their don't had the size I need.
How strong is the carbon steel? Are their able to bend in heavy load?
I want to be able to bent instead breaking clean.


David,
Carbon fiber can't be use. The set screw to tight the spars will eat up the carbon fiber.

Brg,
Tam

Ehab

My Feedback: (44)

I am using the GPS system by Jetcat too. It is very inacurate if you do not give it enough sampling time. If you fly a Bobcat at 119k rpm (P120) and do a big sweeping circle, you will pull about 13-14.5G's and that seems to be consistant. The speed is around 190-200 mph.

I think with proper methodical testing of the viper jet, more data can be collected to find a good reliable solution. There are situations where ANY plane will go thru high G manouvers, for example if you are trying to avoid another plane or a bird you can easily pull 10 G's. Hence the mfgs should consider these cases in their R&D and proto testing. A successful solution in this case is good for all of us customers and yes for ALL other mfgs too.

tamjets

My Feedback: (2)

Thanks Matt,
I just place an order.
I hope it here in time for the weeken.

O.K.
Whom like to gamble?
Failer or Pass

Tam

Ehab

My Feedback: (44)

Tam:

We need to test the spars on a test bed first, then in flight. In flight we should moniter each flight and increase the G forces till we pass at least 12-15 G's. Then go and put 40-60 flights on it and then you should have a high level of confidence.

Tom Antlfinger

My Feedback: (24)

Geez, that first photo of the Viper on the stand looks like an ornithopter ready for launch...

Not the first spar problem for jets......

Nico offered machined steel spar replacements for the soft, short aluminum spars in his early SJ-16 kits.....these were very nicely done and light due to the lightening holes....

I still own Ron Ballard's SJ F-16 which he upgraded to full length, solid steel spars, good for probably 50 G's....but they are heavy...

PA F-15's not indestructible either....if any of you guys noticed one of our club members dogging his two PA F-15's at SM 2003 from dawn to dusk every day with lots of high G stuff(20 flights on Thursday), he experienced a wing failure during repeated high G turns and pulls to vertical a couple of weeks ago on PA F-15 #3.....I know of 2 other wing failures on PA 15's.....no bent spar....wing actually fails in an unusual fashion, obliquely from root to tip, just behind the aft spar.....very little meat in this area....so even if you go to solid steel spars, best to do at least one static ultimate G failure test on the wing with new spars to be sure the failure point has not moved downstream....


Tom

tamjets

My Feedback: (2)

I agree Tom
I'll put some hole to the spars to make it light. The weak point of the spar I leave it along.
Brg,
Tam