shorty55

Im following this thread with great interest,the chap from australia seems to be doing a fine job!
Jason yours does seem to be running very hot, if I were you Id contact Knobby1 and see what he recommends.
I wonder whats causing your engine to run so hot?
Regards Nick.

jason

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Nick

yes it is a little warm.. Hopefully Smithy will chime in with some advice but my problem is the balancing equipment I have will not get it anywhere near where he says it should be. So for that reason, I'm a little stuck as soon as I take it apart.

Jason

knobby1

Hi Nick and Jason,
Thanks for the kind words. The Junior is indeed a fickle creature, everything needs to be "just so" for them to run at a reasonable temp.

Jason, might I suggest you remove the front cover, the engine will run fine without it, it's just cosmetic and serves no real function, this way we'll be able to determine if there is any "cold air leakage", by this I mean an air leak from around the outer case and the inlet housing "O" ring joint. I feel the "O" ring fitted originally isn't thick enough in it's cross section to be effective, any amount of leakage here will dramatically detract from the engine performance and running temps. With the engine running at idle, just wave your hand around the front of the engine and feel for any air leakage. Also while at idle, place your index finger on the front top part of the engine just in front of the glow plug, it should be smooth with no buzzing at all, if any buzzing is noticeable the balance it not correct and the bearings will not last.

A nicely running Junior will idle with an EGT in the 530c range and during a salm accel should peak at around 660c and settle to a nice 610-620c at full noise.

We're all aware that these engines are nowhere near the quality of the beautiful little Lambert Kolibri, but they can be made to run reasonably well.

Balance is indeed critical for any turbine engine but especially for such a small rotative as these have. I did experiment with tolerances in the 5mg-in range but found the engines still "buzzed" at higher rpm settings, this leads to premature bearing wear and eventual failure and poor engine performance.

The only real successful way to balance them is as an assembled engine sans exhaust, essentially as a "core" similar to how turbochargers are done, a tolerance of 1mg-in on both planes is the only way to get them to be relatively "buzz free" and as smooth as a baby's bum!! There are of course dynamic changes as the engine accelerates/decelerates etc, but we have little control over this. The best we can do is to get them as good as possible, it takes time and patience to arrive at the desired result.

If anybody wishes to speak to me privately please feel free to drop me an email to: [email protected] and i'll do my best to help you out.

Cheers and all the best,
Smithy.

jason

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smithy

thanks for that, I'll see if the case is sealed tomorrow and report back.

Jason

i3dm

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Jason,

Send it to Knobby1, he will fix it up for ya.

jason

My Feedback: (1)

Smithy was right, the case was leaking around the diffuser but also where the fuel and gas fittings are and where the RPM sensor fits. I sealed it all up and it is runing much cooler at 650 ish at idle with the thermocouple in 3mm so it's a good 150 deg cooler.

Any other ideas to get it running even cooler Smithy?

jason

jason

My Feedback: (1)

By the way, this engine came back with a new chamber, NGV, wheel and compressor on it's last trip to the JJ factory.

shorty55

Thats a great improvement, the air leak I presume caused the engine to run hotter due to a leaner mixture. How did you seal the leak, new O ring or sealent?
Regards, Nick.

knobby1

Hi Jason,
Good work finding those air leaks, it is often useful to take a small amount off the tailpipe, use small increments at a time, the ones I have played with usually respond well with ~2mm taken off the total length of the pipe, this will reduce the total thrust somewhat but only by a few %. Don't be misled into thinking a cool engine is best, to make a decent amount of thrust...a decent amount of heat must be produced, so cooler isn't necessarily better...however there are limits imposed on the components for a reason.

Also the thermocouple for these engines is not the same as the 1200/1400, the sensor itself is very thin, insert it into the exhaust 1.5mm max,.... and around the 9 to 11o'clock position when looking from the rear if possible, this may help somewhat.

Do you have the pump "by-pass" restrictor fitted? Could you post a photo of your setup? If so I have a nice set of ECU parameters which have the tiny beast running very sweetly, acceleration from idle to max in ~2.6secs without any temp problems, the throttle response is markedly improved.

All J-Juniors delivered by Ausjets.com will now have my new inconel combustion chamber design and preload systems fitted and balanced to under 1mg-in. A shameless plug for Ausjets.com.. ;-)

Cheers,
Smithy.

knobby1

Hi Nick,
You're right on the money, the compressor map for these little engines is very critical and is obviously most efficient when there is as little "leakage" as possible, any leakage within the "cold air" regions of the engine reduces the efficiency dramatically. Leakage of "hot air" has a similar result but we'll not worry about this today.

The closer we can have the compressor tip clearances the better also, I've experimented with this a little and find a comp blade to inlet housing clearance of 0.002" to be optimal.

The ECU will supply enough fuel for the engine to run at the required rpm, if the incoming air is a few percent less than it should be, the temp rise will be essentially a square of this percentage of loss...within reason!...so a combination of all these factors makes quite a difference.

jason

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Nick

I have some 1mm O ring cord so I made a new one. But the case is simply too big to the point where it takes the shape a a 50p coin when the screws are done up I used some RTV silicone to make the seals. I also had a leak on the NGV so I used some car exhaust sealer there.

Smithy

the thermocouple is currently at 2 oclock when viewed from the rear and that is obviously the hottest part of the engine because it was glowing at dusk tonight. I recon opening the tailcone a bit and moving the thermocouple to where you say will have it running cooler. I'll try again tomorrow night.

Thanks for the help.

Jason

jason

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It's getting better. With the tailcone opened up 1/2mm and moving the thermocouple out the hottest part of the engine it's 640 deg at idle and I never saw it go over 740 during slam accel. It's now time to stick it on a foamy.

Jason

shorty55

What "foamy" are you going to use Jason? Must keep us informed of your progress!
Regards,Nick.

jason

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Nick

I have a Twinjet here which seems to be the norm for the lambert engines.

Jason

shorty55

What about something like the eflite bae Hawk or 1 of the electric "bobcat" type of thing. For some bizzar reason I hate hand launching models, must be down to the fact, other than a dodgy launch, I do love take off and landing my models on wheels.
Keep us informed!
Regards Nick.

i3dm

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Get a Multiplex twister - its perfect for this application !

jason

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Nick

as it happens I flew one of these eflight hawks the other day and I was well impressed with it for a snotty electric model. It might be a good option if the engine stays together long enough.

Jason

Duncan

Jason

I'll bring my eflite over on Tuesday and we can measure the thrust to get some idea as to whether the jjj will have enough oomph

Dunc

knobby1

Well done Jason,
The temps are now getting into the normal range. The Inconel turbine wheel can take ~750c all day, when it starts getting up to and over 800c at full noise we need to raise an eyebrow or two. What is the "max temp" set to? I reduce them down to 800c, some of them come from the factory at 1000c, this is just silly.

As you're well aware, the tailpipe is very thin and will start to "glow" a dull cherry red at ~600c when not in direct sun light.....this is quite normal. If there's plenty of heat in there, (which you seem to have), you should be making ~3.6-3.8lbs of static thrust at sea level with ambient temps of 20c or so. Should push the Eflite Hawk around fairly well and will may tear the wings off a foamy Twister if it gets to full speed, should see well in excess of 100mph I imagine!! Be careful of the "flutter" factor.!

Cheers,
Smithy.

shorty55

Jason,
Been reading through alot of posts on rcgroups re the hawk. I you went for the hawk option make sure you fit the wing fences, some people have put in a little aileron up reflex, both jshould help the dreaded tip stall.
I have a J Perkins/OK Models L-39 hanging in my room, it has a 70mm edf unit, sorry for mentioning edf on here but it just slipped out, it could be another option as well as the hawk for you to consider,nice f/g fus and balsa convered foam wings, no u/c though Bonny plane,ideal for the jjj!
Nick.

jamiechip

the e-flite will suit quite well i am also doing one and pland to make some bae hawks for these turbines my jjj is pushingout just under 4 pounds anyone interested in purpose built fiberglass planes for the kolibri or the jjj pm me and ill keep you informed of when they are ready

jason

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Dunc

I recon the thrust will be about the same but with a EGV of 800 ish mph compared to your weedy EGV of about 120mph it will be awsome. I really hope the engine lasts though... I'll tear that hair dryer out that hawk if you bring it over Tuesday..

J

PigeonHawk

I want to try it on Sapac T-45 and L39. Where to get it in US?

Duncan

lol your not putting that china junk in my lovely hawk, although it's not as if i need a hair dryer is it

tonyjms2005

Hi

Can anyone tell me internal diameter of the exhaust cone on this engine, on the mounting flange end? I may need just the jet pipe for a project.

Kind regards

Antony




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