siddus74

Hi guys,

I have an old P80 which on the test bed is good as gold, when installed I am getting over temp cut outs - moving the thrust tube forward towards the back of the jet I though sorted the issue, but 3 minutes into the flight it went out with an over temp again :-(

Look at the jet cat manual, they suggest the inner thrust tube diamter shoule be 85mm with the out intake cone being 107mm mine 74mm and 84mm ish ... could this be the reason?

Anbody has these experiences?

Regards,

Scott.

Dave Wilshere

Scott


What length pipe? Single or double walled??

Which P-80? SE or twin cone older?

What gap do you have?

Dave

siddus74

Hi Dave

Its a twin walled pipe, the 74mm is the internal Diameter ... its about 380mm in length, its ina skymaster gripen - flew great for about 2 minutes flat out ... reduce the throttle to 3/4 for a circuit and then it cut stopped with the over temp ...(23lb glider ... nice)

Its an old P80 with the inner cone and outer ring.

I had the gap set to 30mm as per JC instructions and it over tempted at that before it got to full throttle ... I then moved the trhust tube closer to the engine and all seemed ok on the ground on idle and flat out ...

Do you sell thrust tubes?

Jim Cattanach

Tailcone looks too far into the thrust tube. I would seperste them by at least another half inch.

siddus74

Thanks Jim, but that would take me back to where I was when the turbine would over temp before reaching full throttle on the ground in testing.

Scott.

Dave Wilshere

OK, it is too close. Ground/flying situation is different you need to move the turbine forward. Can you also photo the outlet end? The tail pipe is a litle on the small side, but I have used 75mm/3" tubes myself. I would say 15mm between the outer cone and the start of the tail pipe.
The tailpipe position is normally fixed-the turbine should be moved.

Dave

jzuniga

My Feedback: (7)

How far in, is the temp probe? Could that be a possible culprit? I know I was having very high temps (no cut outs) on a brand new P60se, come to realize, after consult with jetcat usa and experienced jet guys, that my temp probe was too far in! Once I took it out about a 1/4" it read normal temps... mine was about 1/2" into the exhaust cone! Maybe a possibility? Just saying...

Z

Dave Wilshere

Different probe types on different size JC turbines need a different approach. The P-80 unit uses the last 10mm or so for readings

Dw

siddus74

Thanks Guys, this P80 was taken from a Boomerang sprint where it enjoyed hours of fun and ran on the test bed with out fault before the installation. The temp at idle is around 600 if I can recall.

I agree that the tube looks to close to the jet, but any further and it doesnt even reach full throttle and the out side of the fuselage gets very very warm even to warm to touch, which is surprising because the inside of the fus where the jet sits has reflective tape installed.

Could it be a combination of too smaller thrust tube and it being in a very enclosed area? Does it not follow that the turbine has to work with a too smaller exit? Im leaning towards the thrust tube size due to the recomendation of the sizes stated in the manual?

Scott.

Dave Wilshere

Need a picture of the outlet end....

Dave

siddus74

Dave,

Here are some pictures of the exit ... its 74mm internal Diameter, a guy on the Jas thread give me a link to a JEt cat document .. what do you think?

Best regards,

Scott.

Dave Wilshere

Scott

OK, just wanted to see that the inner pipe was short of the outer. Can't really see from the pixs, is the outer tube level with the back of the fuselage?
The pipe is smaller than ideal, but it should run at acceptable temps. 600 degrees is hot for a P-80

Dave

siddus74

Dave,

The thrust tube does not extend out past the end on the fuselage (see pic) 600 is hot? what should it be ideally at idle etc? Ill run it up and check it ... (maybe the higher idle temp is due to the installation)

Thanks for the advice, do you sell thrust tubes?

Scott.