Tailpipe Collapse
 

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?

RE: Tailpipe Collapse
 

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?

RE: Tailpipe Collapse
 

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

RE: Tailpipe Collapse
 

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.

RE: Tailpipe Collapse
 

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

RE: Tailpipe Collapse
 

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...

RE: Tailpipe Collapse
 

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.

RE: Tailpipe Collapse
 

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

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

RE: Tailpipe Collapse
 

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

RE: Tailpipe Collapse
 

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

RE: Tailpipe Collapse
 

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.:D

RE: Tailpipe Collapse
 

;):D

RE: Tailpipe Collapse
 

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.;):D

RE: Tailpipe Collapse
 

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

RE: Tailpipe Collapse
 

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.

RE: Tailpipe Collapse
 

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..

RE: Tailpipe Collapse
 

True Tam, and 1% is fair,

RE: Tailpipe Collapse
 

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

RE: Tailpipe Collapse
 

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.

RE: Tailpipe Collapse
 

RE: Tailpipe Collapse
 

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

RE: Tailpipe Collapse
 

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

RE: Tailpipe Collapse
 

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

RE: Tailpipe Collapse
 

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.

RE: Tailpipe Collapse
 

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.

RE: Tailpipe Collapse
 

Tam,
My tailpipe only last one flight! Unfortunately, it was in my FEJ F-18 when it crashed on it's first flight. I was able to get some money for it at the scrap yard. It seems that a custom bifurcated pipe after 1 ride in a FEJ plane is worth about 3.00

RE: Tailpipe Collapse
 

I should twist your arm harder to throw out that pipe.
Sorry to hear that.

RE: Tailpipe Collapse
 

What a life saver this thread is. I was going to fly tomorrow for the first time this season. I was checking over my viper and after reading this thread I decided to pull my pipe out and give it a good look over. To my dismay I discovered that my pipe had failed and had a 2" long opening in the seam. I'll be calling tam tomorrow to order another pipe, but thankyou for the save.

RE: Tailpipe Collapse
 

Smart move.
Pipe need to check regular to see any open seam or dark purple spot.

RE: Tailpipe Collapse
 

I think FEJ did the same thing as CARf. My f16 pipe is very heavy.

I had a MB f86D and the pipe in that was very light, very small. I had some wet starts. Never collapsed after 100 flights.. Must of been luck?

Would love to see some ideas on how to align the pipe and turbine.

RE: Tailpipe Collapse
 

Would love to see some ideas on how to align the pipe and turbine. Good eyes are all that's needed...

RE: Tailpipe Collapse
 

Gotta admit, I was wondering if someone had a better way to do it than using the good ol' Mk1 Mod0 Eyeball :D

Sluggo

RE: Tailpipe Collapse
 

Sluggo and All,
Several (many) years ago I designed a simple tool to align the turbine to the tailpipe. This was documented the JPO newsletter, CONTRAILS, Volume 18, Issue 1 /Winter 2006, pages 9-10.The article is entitled "Turbine Alignment Tool". Fortunately, this issue is available on the JPOwebsite, www.jetpilots.org. Scroll to: CONTRAILS and open the Winter 2006 issue forthe article, found at the 2nd year up from the bottom and on the left.

While you're at the site check out some of the other issues for valuable jet tech hints and consider joining JPO, an application is located within.

Art ARRO

RE: Tailpipe Collapse
 

Thank Art!

RE: Tailpipe Collapse
 

In terms of a hot start, if you get a blue flame out the back of the pipe for a few seconds, kinda like a butane wind proof lighter, is that considered a hot start?
Also, with most pipes today, would you guys agree that smaller turbines (100N or less) are probably ok assuming there are not numerous hot starts or severe misalignment? Seems the issues come with bigger turbines these days with modern pipes.

BTW The FEJ pipe I have is very thick, and very big. It always weights a ton. Hoping it doesnt leave me burnt.

RE: Tailpipe Collapse
 

How are jet legend pipes? I have a 1/9 GJL F-15 should I be concerned other than checking it? Thanks

RE: Tailpipe Collapse
 

George,
I just binned the OEM Jet Legend pipe in my ongoing JL Mirage2000 assembly and replaced it with a new Tam pipe.
Never even installed the JL one; it "appears" to be constructed OK (decent looking welds and reasonably heavy gauge inner sheet) tho there is no way to know the quality of the steel.
I went with Tam's pipe because:
1) unknown quality of JL pipe
2)<span style="background-color: rgba(255, 255, 255, 0);">the JL one was a tapered (convergent) design 85mm tapering to 75mm at the exhaust which can up the temps and hurt thrust.</span>

<span style="background-color: rgba(255, 255, 255, 0);">Tams is a straight parallel wall front to back, weighs within 3 grams of the JL, and is a known quality.</span>

-<span style="background-color: rgba(255, 255, 255, 0);">sorry......probably doesn't really answer your question.</span>
<span style="background-color: rgba(255, 255, 255, 0);">Mike Warren</span>

RE: Tailpipe Collapse
 

Hi George

Yours is fine. I have over 200+ on each F15 before I replace the pipe.

Check the divergence Y for any holes or crack and replace the pipe if you find them.

One of the outer wall pipe sections at the junction will break loose if there is a leak of hot gas. Then it's time to replace it right away. This acts as a telltale for me to replace it before it fails.

Also put some heat shield around the servos and top section of the rear fuselage as precautions.

Out of hundreds of F15 we have sold so far we have no report of pipe collapses so far.

Mike

RE: Tailpipe Collapse
 

Thanks Mike The pipe looked good and the thickness was fine.

RE: Tailpipe Collapse
 

Was he injecting smoke into the pipe mouth?  That can cause premature failure as well...