RE: JetJoe OWNERS thread
 

Combustion chamber – there are probably loads of different designs but again if made with the correct materials, and fuel needles etc all flowing properly should be not an issue.
The ends of some of my tubes are slightly burnt, I know now all the CC now have inconel tubes but strongly suspect my one dos'nt due to the burning, many homebuilt turbines use stainless for the tubes but obviously for longer life inconel is preferred.

The fuel ring was definatly a poor on my turbine and three needles were basicaly not working at all. After a lot of cleaning and poking and blowing I realised that the needles were bottoming out on the collector ring and being blocked that way. A little squeeze on the ring left them all working properly and it said to me they were probably like that from new and one of the reasons why I never had the full 14lb thrust with the origonal two piece tail cone.

This is definatly one of the quality issues and assembly problems where I belive the majority of the problems arise. There is nothing wrong with the actual part and it could have been sorted if checked.

RE: JetJoe OWNERS thread
 

Turbine Wheel and NGV
I believe these were very suspect in the past, still dont know if they are as they should be but my wheel looks very good after its use todate and I know they are using the proper material now but wether they are xrayed or not I dont know. Mine has been machined in the inside for balance. I am happy my turbine wheel is good, as if not it would have probably gone by now!

The NGV casting seems as good as my experience allows, as mentioned in posts when I stripped the turbine some of the stators have slight lips that should have been removed, as the rest of the machining is very well done.

RE: JetJoe OWNERS thread
 

Thats it there is'nt much to it, I have been told later 1400's are different from mine and I would assume that meant for the better.
So where are the problems, it has to be in the assembly, quality control and balancing, there appears nothing major wrong now with the actual parts now they are being made properly and with the correct materials.

For the next part of my "project" I am going to theoretically assemble a engine so we can identify where the faults can be.

RE: JetJoe OWNERS thread
 

Xairflyer

It appears from the photo that your NGV is cracked on the chamber side at the 10 o'clock position. Judging from the heat bluing on the outer rim of the NGV the chamber wasn't sealing well to the NGV.

RE: JetJoe OWNERS thread
 

The blueing is probably from the hot spot caused by the bad needles... Can't tell if that's a crack or not though.

RE: JetJoe OWNERS thread
 

Yes it is a hot spot because of the blocked needles, the colour rainbow extends around the collar for about 3/4 of the circum.
I'd say if it had a few more hours use before I stripped it then it may have cracked don't know, would this be the case ?

RE: JetJoe OWNERS thread
 

Ï know it would have. I have seen a jj ngv with holes in it. The metal at those points is just vaporized :)

RE: JetJoe OWNERS thread
 

Must have been an old NGV cant imagine a Inconel one doing that now

RE: JetJoe OWNERS thread
 

The ngv isn't inconel? It is RVS as far as i know...

RE: JetJoe OWNERS thread
 

What is RVS???

RE: JetJoe OWNERS thread
 

It is dutch ;) Rost Free Steel

RE: JetJoe OWNERS thread
 

316 Stainless Steel. What JJ actually uses is up for discussion.......

Dave

RE: JetJoe OWNERS thread
 

Ah, that is the right name.

A metal worker thought is was not inconel as it warped and craked to much. Inconel thould have been better and so he thought it was stainless steel.

RE: JetJoe OWNERS thread
 

RVS in dutch mean " roest vrij staal.

RE: JetJoe OWNERS thread
 

OK. In aerospace we call it 300 Series CRES (Corrosion Resistant Steel).

RE: JetJoe OWNERS thread
 

I'm sorry, these just make me cringe!

I would not stand next to that turbine while running.

RE: JetJoe OWNERS thread
 

Erazz, I'm not a JJ owner but what are you saying?

I should imagine most turbine wheels are not perfectly balanced out of the mould & would have to be balanced by grinding part of the wheel away.

It would be up to the manufacturer to decide which wheels need too much ground away, which would affect the integrity of the wheel, to achieve balance & therefore should be junked.

Has the wheel you show had too much ground away & would a more responsible manufacturer have just discarded this example? - John.

RE: JetJoe OWNERS thread
 

You're right. Every turbine needs to be balanced. This is usually done by grinding away at the sacrificial ring (the ring around the hub) which JJ so blatantly copied and the completely ignored! The milled out section introduces extreme stress points in the most highly stressed part of the engine. Think along the lines of grinding away at the hub of a propeller and then mounting it on a high performance engine.

The original turbine (when it's made correctly from the right materials) can withstand 1100C temperatures and is just strong enough to withstand the stress from running at full RPM. Remember that the turbine sees higher temps than the egt probe sees. When accelerating the egt can reach 800C. The le of the turbine can then easily reach 1000C. This is a very small margin. Frankly I'm amazed that JJ's turbines aren't exploding on every run. IMHO selling a turbine like that is irresponsible and downright dangerous.

Yes and yes. Actually the responsible manufacturer may discards the whole batch on a wheel this bad.

RE: JetJoe OWNERS thread
 

The NGV were is the past Stainless but I believe now they are inconel

Is this method of balancing any better

RE: JetJoe OWNERS thread
 

Both ways are good enough. Mine has the same balancing marks.

RE: JetJoe OWNERS thread
 

Yes. The ring is there especially for balancing. It does not provide any strength and therefore does not weaken the turbine when ground away.



Absolutely not!!!
One method severely compromises the structural integrity of the turbine.

There's a saying in Hebrew that translates roughly into "A successful folly does not wisdom make".

RE: JetJoe OWNERS thread
 

Hi chaps,
Heres a video of my mate flying his JJ powered TwinJet..he has opened the tailpipe up to 24mm and sealed the front of the engine alot better..engine runs nearly 300 degrees cooler. A nice running motor..he had 10 flights today with it.

Hope you enjoy the video


Regards Rich


www.youtube.com/watch?v=JNyMQumSGF4

RE: JetJoe OWNERS thread
 

Nice to see a junior powered twinjet :) I want to build the same combo next year :) Do you have more information?

RE: JetJoe OWNERS thread
 

Hi all

I have JJ1400, total run time is aprox. 14hours, so now my turbine have problem. i can't start turbine, i increase or decrease Pump start and fuel ramp dights. when i increase i have flame out on start and turbine doesn't going to idle rpm. max rpm on start 24-25k.
fuel ramp -2. pump auto-1. but after my turbine started i have wite smoke and kerosine from glow plug on idle rpm.
who can tell me what's a problem? My combustion chamber is down?
Can i change CC without balancing?

RE: JetJoe OWNERS thread
 

If you mark the position of the wheels so you can align them exactly the same way it won't be a problem. Just put a pin strip on both wheels (use the glowplug as a refference) and you should not have any problem. You can balance it by hand also, it is better then the jetjoe way if done with care ;)