alasdair

Last weekend I saw a lovely scale jet spiral dive into the ground, and the verdict from all the jet fliers present was that the tailpipe collapsed, causing hot gasses to melt the compositerear fuselage.

The tailpipe consisted of a bellmouth, followed by a parallel portion about 6" long with a single thickness, followed by double walled parallelportion about 20-24" long. It was only the first, single walled, part that had collapsed, behind the bellmouth that was still intact. It was squashed completely flat, with sharp edged creases.


I am vaguely aware of the cause - reduced pressure of the very high speed gasflow within the duct compared to the ambient pressure outside, within the fuselage.
But
Does anyone know what factors are involved? Why might this particular duct have collapsed while thousands of others do not.?
What can be done to avoid/prevent such an occurrence?

RC Larry-RCU

My Feedback: (1)

My first questions would be:
Was he running a by-pass Unit?
What was the spacing between the end of the Turbine Exaust Nozzle and the front of the Pipe itself? (Not the bellmouth.)
What size Turbine?
Were the pipe mounting straps still attached to the pipe?

David J Ruskin

Rather depends on what the pipe is made of and who made it. If its Chinese.......well throw them away and get a real one from Grumania or similar. Single walled for any length.........well I think the most generous point is that they are 'old school' for little turbines. All pipes need a good airflow, like a bypass or similar, which takes heat from the inner wall. Thats what the outer wall is for, to focus a cooling airflow over the inner.

So a well ventilated double walled, well made stainless or titanium pipe, from a reputable source, is the best way to prevent such an incident.

David

alasdair

I saw the prepared model, and the takeoff (only his third flight) and I saw some of the spiral dive.

I don't know if the pipe was in a full bypass. What effect would that have?

I don't know the gap either. I am aware it should be around an inch, but I didn't see, or ask. Again why? Is collapse more likely with too small a gap?

The engine was a 160

The pipe mountings were still attached to the pipe. It collapsed in situ, not as a result of moving out of position.

powerjets

My Feedback: (1)

Turbine tailpipe too close or in exhaust pipe with bellmouth will create heat and underpressure in pipe and sometimes collapse (implosion) 160 size needs more than an inch distance to bellmouth

Vincent

My Feedback: (61)

It would be helpful if we knew what type of jet and who made the pipe?? I friend of mine just had a chinese pipe collapse (total loss) and we believe it had to do with running a P180rx in a 160 size pipe.
Vin...

tamjets

My Feedback: (2)

Had done alot duplicated pipe for customers. Most common pipe I had see is not done strong enough.
When engine running. The inner pipe can reach 200-300C. With lack of airflow can suck the pipe collapse. Many of these case happen.
With any prior wet start. These straight don't have a chance if wasn't done correctly.

basimpsn

My Feedback: (5)

I experience collapse pipes on two occasion one in-flight and the other on the ground

https://www.youtube.com/watch?v=bPF3hI1wpt8

Dave Wilshere

I flew up to test fly this model a while back. It had more than three flights and we had run the turbine when I was in Aberdeen a few times., the installation was fine, researching now it seems a known issue on this pipe. It's quite long and basically too thin a gauge material was used for the set up. Long small inlet too.

Dw

mikedenilin

My Feedback: (67)

Hi Vin,

I heard that incident. Basically the airframe was bought used and it's over 3 to 4 years old and had been running flawlessly with a P160SX. The new customer bought it and put a 180RX in a 160 pipe that's over 3 years old. To add fuel to the fire, the 180rx has much higher exhaust temperature, 700C. So basically, the extra heat couple with extra hot air flow are choking and softening the exhaust pipe and causing the collapse.

I have a 190R on the same type of airframe, but I use a custom made single wall pipe and a really big Bell mouth to draw sufficient airflow to keep cooling down. It's been 3 years now and running flawlessly.

Like Tam said, a wet start will weaken the pipe. I had a Germany pipe collapsed on me while doing ground test. I had a wet start before, so it might have been damaged.

By the way, I replace my exhaust pipe every 50 flights or so. As one exception just replace one on my F-15 after 200+ flights. It's a Chinese pipe and holds well because I kept 1" distance, and use a factory specified engine size. It's up to the pilots to use common sense not to over stress these pipes by using oversize engines for an extended period of time.

Mike

tamjets

My Feedback: (2)

If the pipe done correct. It should last as long the airframe.
Just watch out for wet start. Any wet start happen. Pay attention to the color of the pipe. If it turn dark purple.
That must replace right away. That the sign of pipe goes to fail any moment.
Golden brown color is normal.

BTW,
Anyone had my pipe last over 200-300 flights.
Please send me my bounus check.

basimpsn

My Feedback: (5)

tamjets

My Feedback: (2)

I need money to spend for my vacation.
I know alot of you had my pipes over those number of flights.
Don't make me pick up the phone and call you for my bonus check.

Joe C

My Feedback: (23)

Your too funny Tam, send me my bonus check, LOL!!!!!

tamjets

My Feedback: (2)

Joe,
How many jets out there I have save from crashing to the ground with pipe failure.
All I need 1% from everyone is enough for me going vacation. Haha.

alasdair

Dave,
Thank you for chipping in with first hand knowledge of the aeroplane. I didn't know that you did its first flight.
Do you know if he used a bypass, or an exposed engine installation?
I wondered if having the whole pipe double walled would have helped?

We were at Machrihanish for the weekend. I think Graham said it was HIS third flight with the model. What a sad loss.

I assume that you can assure me that my CARF Lightning and Eurosport pipes will not suffer the same fate? That was my concern, that caused me to post the question. I didn't build either model, both are second hand but used original kit parts, and are powered by Booster 160 engines..

Joe C

My Feedback: (23)

True Tam, and 1% is fair,

HarryC

My Feedback: (1)

I lost a model due to the Aviation Design pipe collapsing on just the tenth flight. It was a twin wall pipe properly located and not subjected to a wet start. Most of my other pipes are Wren single wall and the oldest has done over 500 flights so there is no relation between the number of walls and the pipe collapsing. What I did find was that the Aviation Design pipe was about 30% thinner steel than my other pipes from Wren and Grumania

ron Sweeney

Alasdair, a timely and constructive topic.
I have an F15 eagle with a single outlet. I use a Wren single wall pipe. The model has over 600 flights logged. It does not have a by-pass or a bell mouth. Just the pipe entry turned out a little. The model has been mainly powered by a Wren ss and also by a Wren 70. I have never experienced the slightest problem..
I also have an ancient JMP Phantom with a bespoke bi-furcated pipe which I have just removed because the '' beak'' had a 'wrap around' folded cover which had become detached. Tam, you quoted for this pipe and I decided to buy a less expensive option which I now regret.
I also experienced some very hot starts recently with a Wren 44 gold due to pump problems which have now been sorted. As soon as I read Tams' post I checked the pipe and it was OK. It is also a Wren pipe with a single wrap of thin mineral sheet provided by Wren. I have no connection with Wren other than their close proximity and good customer service.
It would appear to me that the ever increasing use of larger turbines is exposing several vulnerable areas in the design of our jets. Some manufacturers seem to be ahead of the problems and others are trying to catch up at the expense of the customer.
I am curious to discover more about the subject you have raised, Ron.

rcand

dubd

Tam, I had planes with over 200+ flights with your pipe. Perhaps you should get into the replacement stab business too.

Dave Wilshere

Alistair

I had a couple of flights with it when new at Elgin. The pipe set up was for complete bypass, but from memory we left the top cover off. The PST turbine ran quite hot. It was a long tailpipe and a long inlet track that is not huge in area. Last time it was flown before last weekend, I understand it had a heavy landing, so who knows whether something started there or even if the turbine was still centralised in the tube...I didn't know he was taking it to Machrihanish, maybe I would have talked him out of it
Pipes run at all sorts of temperatures, with and without cool-wall outer tubes. Simple fact is a pipe that is too thin or made from the wrong material will fail with heat. Its amazing people don't centralise turbines and get the turbine at the same angle...and many people will never look at the alignment again after the build and some straps allow turbines to move with "arrivals"

CARF pipes are very unlikely to fail!!! Heaviest chunky (overweight ) pipes out there. My original Flash is something over 500 flights, CARF can't get the quality of thinner material in Thailand, so they went for meat...which is fine by me.

Dw

tamjets

My Feedback: (2)

If I was. You guys can't afford my hours rate.

tamjets

My Feedback: (2)

The higher thrust turbine require stronger pipe to be safe.
Some of the pipes send to my shop was made out of paper constructed and the factory included with the kit and kit require 36 lbs engine to fly.
How scary.[X(]
There will be more pipe collapes incidents coming.

tamjets

My Feedback: (2)

CARF pipes are very unlikely to fail!!! Heaviest chunky (overweight ) pipes out there. My original Flash is something over 500 flights, CARF can't get the quality of thinner material in Thailand, so they went for meat...which is fine by me.

Dw


Truth...CARF's is so heavy.
You can done with good material and constructed right to save 1/2 the weight.