Tail Pipe length
 

Hi Jet-Fans

I was wondering if the length of the pipe, longer or shorter affect the thrust lost of the turbine ?

I finally flew my Tamjet's F-16 with a JF50 Bee 14 lbs. turbine, mind you ,I have not checked my engine max thrust yet
But my takeoff was very sluggish ( used up the full length of the runway 240 ft and almost took the top of the cactus for a ride ) and the loops at the top had barely enough speed. I saw some f-16 video online but mine was not nearly as fast [:o]
Landings were great though, you can actually aim for the X-point you want to land !!!

My Y/A A4 skyhawk with the same turbine was a lot more spirited ( shorter pipe length )

I have seen turbine at the tail ( no pipe )

Comments ??????

C Lim
www.ArubaRCClub.com

RE: Tail Pipe length
 

How did the weight of the A-4 and F-16 compare...that can affect acceleration. Also the gap between the engine and tailpipe could possibly affect the thrust also. Not only length but pipe inlet and outlet diameter can also affect thrust.....see where I am going, it could be alot of things.

RE: Tail Pipe length
 

Hi Lim,
With for 14lbs should move very fast.
Check your engine. It might not produce the thrust you think. I have see all my customers plane fly with P-60, Simjet and Bee 50.
It move pretty fast.
BTW, I'm waiting for few case of green bottle.
Special summer. I drink more.:D

RE: Tail Pipe length
 

Hi Tam

Can't make it to the west coast this year , my daughter wants a Orlando/Disney vacation in the summer and my wife wants a European vacation end of the year but the green bottles are still in the colder for next year:D

But out of curiosity ,would you lose more thrust on a long pipe as oppose to a shorter one ???

I'll check on the turbine if the programming is wrong. Tomorrow is Labour Day and a good day to fly[8D]

THanks

C Lim

RE: Tail Pipe length
 

The lost is un notice. We talking about ounces.
Not enough to slow down the airplane.
Good luck tomorrow flying. I'll do some flying after works too. The sunset around 8. So I got over an hour for flying.

RE: Tail Pipe length
 

what is the outside temperature?? that can affect things too...............

RE: Tail Pipe length
 

Hmmmmm Calvin -- I didn't see any of those Balashis when I visited the field.

See you in the Fall.

Antony

RE: Tail Pipe length
 

Hi Antony

How are you ?

Shhhhhh ,please antony ,don't tell Tam about the brown bottles ,He will probably ask for those also.
Did you see who is actually flying Tams planes lately ????? ( It's his special summer , you know :D )

THanks guys for the infos

C Lim
www.ArubaRCClub.com

RE: Tail Pipe length
 

Brown bottle. If taste as good. I'll take that too.

RE: Tail Pipe length
 

I have a Wren MW54 Mk II (12 lbs. thrust) in my '16. Due to the fact that the Wren is a bit longer than the P-60, I had to mount the tailpipe with no gap between the tailcone of the engine and the bell-mouth of the pipe. I couldn't get the engine any further forward without hacking up the inlet duct. I was amazed at how quiet this setup was. On the test flight, it sounded like it was only at half power on takeoff. In the air it was a pooch! I was somewhat disappointed. I contacted Wren and explained the particulars and they suggested that I move the pipe back a minimum of 10 mm... about 3/8". I did this and I just let the pipe hang out the end of the airplane. Now it is about twice as noisy on takeoff and it performs much better in the air. These tests were done on very similar days...same temp, humidity and Baro.

I hope that this helps,

John

RE: Tail Pipe length
 

What is the "ideal" dimension?? Seems to me i read somewhere that if the turbine pipe is set aprox. 1/4" in (or forward) of the fuse tail pipe, that was "ideal" for creating a venturi effect, and the supposid "ideal" setting for the turbine is to set the end of the turbines tailcone a 1/2" ahead of the bellmouth. Does this sound about right?? Asuming you have the space ........

RE: Tail Pipe length
 

That sounds right. I was concerned about having the tailpipe hanging out of the airplane but I haven't seen any ill effects...yet.

Tailwinds,

John

RE: Tail Pipe length
 

LOL! Just caught your response. Sorry C -- the cat is out of the bag!

Antony

RE: Tail Pipe length
 

Of course pipe length affects thrust. The wall friction slows down the airstream drastically, so the longer the pipe the more you loose along the way. With a good pipe design, this can be minimized. I use pipes with a golfball surface to create a turbulent boundary layer and reduce the overall loss. Works excellent, it is just really noisy (My MW puts out quite a lot more sound than any 160 class i've seen).
The optimum solution is to mount the turbine directly in the airplanes nozzle. That way you have set your fire hazard down to almost zero (if it burns it will simply burn behind the airplane), plus you will get true turbine thrust. I'm doing that in my Avonds F-15. Batterys all up in the radome and CG should come out all right.

As to the gap between thrust tube and engine: there is no "rule of thumb". How far is drastically affected by turbine mass flow, nozzle design and exhaust gas characteristics......in simple words: it varies from turbine to turbine. Best way is to build a test stand on which you can adjust the gap with a screw. Run up your turbine, and turn the screw until your thrust scale peaks, that way you will get optimum (static) performance from your turbine.
Also, have the thrust tube end before the airplane nozzle ends. Depending on the "space" around the thrust tube about 1/2" to 1". That way you will get a venturi to suck the hot air around the pipe out of the plane when sitting on the ground, plus static thrust is also increased slightly.

Regards
Hank

RE: Tail Pipe length
 

Best way is to build a test stand on which you can adjust the gap with a screw. Run up your turbine, and turn the screw until your thrust scale peaks, that way you will get optimum (static) performance from your turbine.

OR.............You can refer to the turbine manufacturer's instructions.............Wren specifies 10 mm for the MW-54 MK I and MK II. For the super Sport, it's 25 mm.................

Tailwinds,

John

RE: Tail Pipe length
 

Well, i have a MK1 with a modified NVG, combustion chamber and vaporizer system, and have found the best distance with this setup to be at 47mm aft of NVG, translating to 36mm aft of outer nozzle end. As soon as it's not stock, things change....
Regards

RE: Tail Pipe length
 

Hello Jet_fans

Well I discovered one problem for the slow acceleration takeoff. When I installed the main retracts I did not check
the angle ( toe-in at more than 6-7 degrees) of the wheels which I think causes drag as you try to speed up on take-off.
I fixed it and taxing / take off was a lot better.
Still playing around with the pipe / turbine seperation to find the optimum trust range ( large loops still a bit sluggish.

Hi antony.
If you visit us this year Tam's Brown bottles (Balashi ) are still in the colder ,we can always open some ( Tam I hope you don't mind ):D

C Lim