mirce

Today I got new thrust tube from IQ Hammer for my smaller 1/5 scale G2.
http://www.rcuniverse.com/forum/rc-j...serbia-12.html

First one I got month ago was 87 mm inner diameter, but with outer wall for cooling, total diameter was little bigger than 95 mm (diameter of hole on last rib), so I can't install it in fuselage.
On IQ Hammer web site this tube size is for turbines from 80 - 160N.
http://www.iqhammer.de/schubrohre/10...160n-schubrohr

Thrust tube I got today is with smaller inner tube, 68 mm in diameter.
On IQ Hammer web site that tubes are for turbine from 40 - 80N.
http://www.iqhammer.de/schubrohre/10...-80n-schubrohr

For my model I want to use IQ Hammer 90 turbine.

I have now few questions, what do you think, is this tube maybe little smaller than I need?
What smaller diameter of thrust tube can made, bigger temperature in thrust tube, less thrust, faster exhaust gas and faster model...

Please tell me your opinion about this situation.

Guy from IQ Hammer told me that this tube can work, but it is on little critical size, what ever it mean...
I don't want to check knowledge of IQ Hammer guys, I'm just curious...

BTW, I got this tube for free, pay just shipping... Thanks IQ Hammer...

Thank you in advance on answers...

Mirce

Justflying1

What I have found is if your pipe is to small you will get excessive heat problems.
I had this problem on two of my jets. Once I replaced the pipe to a more appropriate size my problems where solved. In my opinion stick to the manufacturers recommendations and stick with quality pipes. I personally love Tams pipes. Quality made and the rite size for the turbine.

Jgwright

Mirce

The pipe you have will probably work. There are plenty of Wren engines out there 54 to 100 size with pipes that have exit pipe diameter of 71mm. I would have thought your pipe will work ok but if the engine or pipe gets hot you may have to change it for a slightly larger size.

John

Dave Wilshere

I'd say at the long length you need, its too small and hyper critical.
John's 3mm increase in diameter is almost a 10% increase in area...odd mm makes a big difference!

Mirce
What is the largest outside diameter your airframe will take? Then allowing for 'cool wall' space you can see what the largest pipe you can fit is. I'd look for 75mm personally.

Didi can make, or Grumania

Dave

mirce

That was my idea also, to make me just little smaller pipe than made first time.

First time inner pipe was 87 mm and outer is 95 mm on the end, but 100 mm in front. That make me problem, because I must put pipe in fuselage through last fuselage rib and hole on that rib is 95mm.

Dietmar from IQ Hammer was very kind, told me no need to send thrust tube back, he will made me new for free. I payed just shipping.
I got now this small tube...

I'm afraid that wasn't solve my problem, because now tube can fit, but its too small (my opinion).
Diameter of inner tube is 68 mm...
BTW, length is 800 mm.

I can try model with this smaller tube, just don't know what to expect (big temperature, low thrust, or some other problem...).
Who know, maybe it work fine...

On my first G2, two years ago, I use Jet Cat 80 and thrust tube with one wall, 95 mm in diameter.
When I try how it work, in my back yard, fuselage was warm.
Conclusion was to must made outer thrust tube wall.
I wasn't fly that model, maybe in the air, because air steam during flight, fuselage temperature will be normal...

Dietmar told me that he can made 95 mm two wall tube full length. In that case thrust tube can fit.
I don't know can they produce smaller diameter tubes 80/90 mm, or they have tools just for 68 and 87mm inner tube...

Watching on internet, same diameter can use turbines from 80 - 160 size. That is big span.
Because that I hope that my smaller tube maybe can be good for 90 turbine. Original, it's for 40 - 80 size turbine...

How much thrust tube length have influence on performance?

Thanks for answers, maybe after text you can have more information. Any conclusion?

Wait for your opinion

Mirce

mirce

One more cogitation, if I take down outer wall on my first tube, I can in that case, tube fit in the fuselage.

Question is now, how much that outer wall is important for fuselage heating...

Little discussion on this thema maybe can help to other and future jet pilot also...

Mirce

mirce

Questions, questions...

Outer tube, some firm made as long as it is inner, other made it about 2/3 or even 1/2 long as inner tube.
Is there some rule about length?

On rear fuselage rib some time is outer tube as wide as hole on rib.
Some time is outer tube smaller than hole.
In that case there is gap, so air from fuselage can go outside between thrust tube and fuselage. Is that better option?

Mirce

Dave Wilshere

OK.
Outer wall on pipe is important to keep fuselage side temperatures lower.
If there is a lot of space around the tube (6cm plus all around) then the outer pipe can be reduced in length. Normally it is weight related, I prefer the complete (or near) outer tube. The short inner tube on exit is the key to dragging heat from the fuselage. Static air gets hot, drag in cool air and take the heat away is best.

It is best if the outside of the cool wall pipe has air that can move, but air is moving on the inside of this tube, so not 100% critical

Dave

Didier

Hello,

I've got a question as wel regarding thrust pipes.
Is there an "ideal ratio" between the diameter of the end of the exhaust nozzle of the turbine and the inner diameter of the thrust pipe?
For example:
-My thrust pipe is 45 mm in diameter (area 159 mm2)
-My exhaust nozzle is 33 mm in diameter (area 85 mm2)
That makes a ratio of 1:1,85
Looks to me there is enough room for cool air to mix with the exhaust gas but I might be wrong.

Thanks!

Shaun Evans

Hi,

The pipe diameter matters. I didn't think so for many years, but I saw an undeniable performance difference with my P-60 when I went from a straight Tam pipe to a Jet Tech 'Augmenter' pipe in my Y/A F-16. I could get the plane off in a third less distance (with the other variables being the same).

Erik R

My Feedback: (32)

Beyond everything said so far, I have had an engine violently compressor stall and flame out, due to a too restrictive tailpipe. This happened shortly after takeoff, full of fuel, with little altitude and airspeed. I was able to save the jet, but it wasn't pretty.