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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Engine Manufacturers Direct Support Forum >> Jett Engineering Support >> Sport Jett seems 'rich'?
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Sport Jett seems 'rich'? - 11/13/2007 8:46:44 PM   
J.T. Hammer


 

Posts: 68
Joined: 6/14/2003
From: Belleville, ON, CANADA
Status: offline 		In spite of frigid temps here in Canada, I've got 3 flights on my new sj .50 Arrow Tiger, and a total of about one hour running on the engine. Am using the apc 10/6 prop (down from the 10/5) using for most of the initial running, and a Mccoy 59 plug. Performance seems right there, and vertical is unlimited. However it doesn't sound 'quite' on the pipe - like there's more rpms wanting to turn. There is also a heavy vapor/smoke trail. I landed twice to tweak the needle just a bit, and it comes on the pipe. After taking off, it really goes, but after a minute or so it coughs/falters for a split second (it doesn't sag, just coughs). So I land, not wanting to risk a lean situation. Don't know it was lean, or a bubble in the fuel. The tank instillation is very good and there is no evidence at all of bubbles while running on the ground - right down to almost empty. Should I fly it on the rich side of lean for a while, go down to 10/5 , try a different plug? Suggestions are welcome and thx.

Hammer

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Let's see; how could I make it go a little faster?
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RE: Sport Jett seems 'rich'? - 11/13/2007 9:26:00 PM   
bob27s



Posts: 4637
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: offline 		Question up front... is this aircraft the Lazer Arrow delta wing ? (copy of laser arrow?) or the Laser Tiger sport plane by Vmar ? (ultrasport clone)


first... a rich engine is a safe engine. But too rich is not good either.

Let make sure you are not setting the engine rich to cover up an underlying problem.

Your story is not unique.... something we hear all the time

Plug you have is fine. Glow plugs blow primarily for one reason --- lean run --- usually an air bubble causing a temperature spike will do it too.

Sounds like you may have a fuel system issue. Those tend to get worse as the tank empties.

Make sure the fuel tank is 100% foam padded, and does not touch ANY of the airframe. A bouncing clunk risks drawing air into the system too. Over 90% of the trouble calls we get end up traced back to the fuel system and tank installation.

Fuel foam is a killer, and at these rpms and power levels, it is a different ballgame from the usual sport engines.

That cough you hear is the engine sucking a big fat air bubble.

What you are seeing, is when you lean out to grab those last 800-1000 rpm the engine is hitting a frequency that puts the fuel toward foaming. You many not see foam at first on the ground, often it is micro-bubbles. As the engine unloads in flight.... you are getting even more rpm - makes the energy and frequency climb ..... the tank is likely foaming, and thus the engine will draw air, go lean and blow the plug.

By setting the engine rich as you have now, you mask this situation by lowering the engine rpm into a range where the airframe is not buzzing and the tank is not foaming. But that is not the right approach in the long run.

Fixes:
1) confirm/correct the tank installation. MUST be padded as above. Check all of the fuel feed and pressure lines - no holes, no kinks.

2) If you cant fix it or improve the tank installation due to space limits, replace the fuel tank with a bubble-free tank. Bubble Jett tank or Tetra tank recommended. Essentially zero chance of fuel foam or air in the fuel --- consistant needle right to the last drop.

3) If you have not done so.... consider removing the needle valve from the engine, and mounting it on the airframe. On the .50 its usually not that big a deal either way..... but something to check. We have found that sometimes doing this will help prevent the microbubbles from becoming bigger bubbles.

Start there.....

Let me know how tyou make out...
Bob

< Message edited by bob27s -- 11/13/2007 9:27:38 PM >


_____________________________

Bob Brassell
Jett Engineering - Engine Mfg Support Forum Host

(in reply to J.T. Hammer)
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RE: Sport Jett seems 'rich'? - 11/14/2007 1:33:25 AM   
J.T. Hammer


 

Posts: 68
Joined: 6/14/2003
From: Belleville, ON, CANADA
Status: offline 		Bob

Thx for the prompt reply. What you explained about the tank about the tank installation makes sense. I have padding all around except where it exits at f2 I used a bit of hot-melt glue at the bottom edge to keep it from sliding further back into the fuse. Based on your remarks this is likely where the vibration and foaming would start. So I will enlarge the the hole in f2, remove the glue and put some good quality foam around the tank there; and yes the hicuping began about 5 minutes into the flight. The airplane is the VMAR Tiger Arrow. I was a bit disappointed when I received as the fuse is quite big and bulky, and the Jett .50 had to be rotated to about 10 o'clock so the muffler would lay alongside the fuse. Furthurmore I had to add 1 pound of weight at the front to achieve the CG making it 6 and 1/4 pounds!. However, it flys veryt well with the Jett and doesn't seem to mind the weight. I really bought this model as an inexpensive bird to break the Jett in, late in the season (only too a week to put it all together). Am looking to put it in a light prop jet for next spring, perhaps a Shrike, but would prefer something a more realistic. Had a Direct connection f-20 a few years ago with an os .46. It went pretty well, but am getting lazy, so am looking for an arf. The Pheonix f-20 looks intriquing but seems a bit large in some respects, and the silver canopy doesn't turn my crank (I like clear or tinted). Anyway, thx again, weather permitting I might get one more chance to try before our field is closed. If so I will let you know how it goes with the changes.

Hammer

_____________________________

Let's see; how could I make it go a little faster?

(in reply to bob27s)
       Post #: 3

RE: Sport Jett seems 'rich'? - 11/14/2007 3:07:34 PM   
bob27s



Posts: 4637
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: offline
good deal..... let me know how you make out...

also, since you are just getting time on the engine.... once the fuel system issue is resolved a bit.... fly the plane with a 9x7 out front. Let the engine spin up a bit in flight.

a pound of lead ????
what do they make the tail surfaces from !! ?

Hey... something to look at for a jet,
Hobby People is importing the VQ aircraft now .... look for the T-45. Retract ready. Not too bad of an aircraft.


_____________________________

Bob Brassell
Jett Engineering - Engine Mfg Support Forum Host

(in reply to J.T. Hammer)
       Post #: 4

RE: Sport Jett seems 'rich'? - 11/14/2007 8:46:15 PM   
J.T. Hammer


 

Posts: 68
Joined: 6/14/2003
From: Belleville, ON, CANADA
Status: offline 		I got out for one quick flight with the VMAR this morning. Improved the tank installation and wanted to try it. Got 7 minutes full bore, and no hiccups so that was nice. Flew in extremely high wind so going downwind was quite speedy even with this bird!. Had to land when it started to rain, but lucky it wasn't snow. The temp peaked upwards today above freezing which is uncommon for this area .

Will check out Hobby People for those VQ Arfs you mentioned. You will notice in the other forum I am considering another Kougar. A bit more work involed but quite an easy build.

Hammer

_____________________________

Let's see; how could I make it go a little faster?

(in reply to bob27s)
       Post #: 5

RE: Sport Jett seems 'rich'? - 11/14/2007 9:08:59 PM   
rmenke


 

Posts: 1684
Joined: 6/25/2004
From: Merced, Ca., CA, USA
Status: offline 		JTH:

So, wanna make it go a little faster. OK, get the Jett 60 LX with black pipe, will fit right in existing mount and gives you mo power+ more prop = more speed, little more fuel. Some claim their 50LX's will run with the 60. Poo, bah, humbug!!!!!Thats one you just gotta show me on. ENJOY

(in reply to J.T. Hammer)
       Post #: 6

RE: Sport Jett seems 'rich'? - 11/14/2007 9:14:26 PM   
bob27s



Posts: 4637
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: offline 		Good to hear....

stay warm ! or at least try to...


_____________________________

Bob Brassell
Jett Engineering - Engine Mfg Support Forum Host

(in reply to J.T. Hammer)
       Post #: 7

RE: Sport Jett seems 'rich'? - 11/14/2007 10:48:56 PM   
J.T. Hammer


 

Posts: 68
Joined: 6/14/2003
From: Belleville, ON, CANADA
Status: offline 		Rmenke

Hey, now there's a great idea a .60lx in a Kougar - I'll check out the Jett site for pricing; maybe there's time to get a quick letter off to santa! You think the difference in speed would be worth it?
How do they sound when going full wide open. The sj .50 gets folks attention when she's up there!

JTH

_____________________________

Let's see; how could I make it go a little faster?

(in reply to bob27s)
       Post #: 8

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