Jab Plenum Chambers

[derekliston]

Couple of screenshots of my temps. Only circuit flight but one at, as you put it WOT and one on downwind. Tried to load them, but it says ‘uploaded files do not have agreed extension’ Computer geniuses, what the hell does that mean? One day I’ll end up in the nuthouse and it will be due to computers!

 

 

[derekliston]

Since I can’t seem to post the screenshots, numbers are as follows:- CHT @ WOT 115, 110, 125, 139 and EGT 621, 609, 685, 611. Cruise, ie downwind CHT, 110, 106, 117, 125 and EGT 679, 692, 658, 710. All in Celsius, Oil temp 96 and Ambient 27 also Celsius of course.

 

 

[biggles]

Derek , I'm no expert either, but all I do is click on the box that says "attach files" which takes you to your photo library . You then select a photo then click " done" and it appears into your reply. I am an Apple user...... Bob

 

 

[derekliston]

Derek , I'm no expert either, but all I do is click on the box that says "attach files" which takes you to your photo library . You then select a photo then click " done" and it appears into your reply. I am an Apple user...... Bob

Yes mate, that is what I did, I-pad! Never seen that message before.”The uploaded file does not have an allowed extension”?

[derekliston]

Yes mate, that is what I did, I-pad! Never seen that message before.”The uploaded file does not have an allowed extension”?

I have previously uploaded pictures, only this time, first time ever, it gives that message?

[Paul davenport]

Paul,If this is your aircraft , you can easily adjust the instrument to give you an almost full scale deflection. I have my EGT's set to 750 degrees and CHT's set to 160 degrees, like this....... Bob[ATTACH=full]54082[/ATTACH]

That’s a mighty fine set of numbers you have there. Yes I am aware that I can set it up a little differently. Went for a fly the other day and what was 127 is now 134, have not done a thing ,maybe ambient was slightly higher. Does yours vary from day to day.?

[Paul davenport]

Let try that again with the attachment

 

 

 

[Paul davenport]

Does having the high tension leads angled up or down off the spark plugs have any effect on CHTs

 

 

[biggles]

That’s a mighty fine set of numbers you have there. Yes I am aware that I can set it up a little differently. Went for a fly the other day and what was 127 is now 134, have not done a thing ,maybe ambient was slightly higher. Does yours vary from day to day.?

Yes , ambient temp. does have an effect on CHT's ..... Bob

 

 

[Paul davenport]

Yes , ambient temp. does have an effect on CHT's ..... Bob

So those numbers are your best on a cold day or normal summer time temps ?

[Bruce Tuncks]

The temp sure does vary day to day. For the same cooling, you need the same difference between ambient and cht.

 

If you want to be pedantic, slightly more as the air gets hotter and therefore thinner.

 

On my original setup, the indication was based on the "cold" thermostat junction which was at ambient, so the cht was the same summer and winter, but this was false info.

 

 

[biggles]

So those numbers are your best on a cold day or normal summer time temps ?

I can't recall, but doubt that it would have been less than 20oC or more than 25oC ... Bob

 

 

[Paul davenport]

Just back from a 1hr flight ,ground ambient temp 28c engine temp at 6000 ft 122c at 2700 rpm. That was the hotest cyl all the others ranged from 100c up to 122. Temps went up at 2800 rpm but only to 127. On climb temps all under 150. Not bad for a 6 cylinder j230

 

 

[N237F]

Guys, I've been following this thread as I've just installed a Jab2200 rollercam in my Cygnet which previously had an 1835VW, and I've had the usual issues sorting out cooling. I've now got about 23 hours with the Jab motor.My CHT temps at cruise with 25C OAT and at 90kts are 140, 122, 135, 120 & EGTs at around 15.5lph are 695, 650, 690, 645 at between 4000asl and 5000asl. Rpm 2900. They max if I throttle back to 14lph and 80kt and 2750rpm at 720, 660, 720, 645. No matter what I do I can't get the stb cylinders cooler. No 1 & 2 were my hottest cht wise, but baffles in the pressure ducts were adjusted to get rear cylinders chts as close as possible to the front.

I originally had over 120C egt spread and that was mostly fixed by putting a fence of about 2cm high in front of the air inlet (which is simply a hole in the side of the cowl). This makes sure there is no ram air. Drawing cowl air made no difference. I also have flow straighteners in the airbox outlet and carb inlet. I do not have a simple cross because, if placed in the nsew orientation, the bottom interferes with the emulsion tube air inlet on the Bing and minute changes produce crazy results. When I installed the fence on my air intake my egt spread dropped and the average egts dropped so I've gone one size smaller on main and needle jets (230 & 2.8 if my memory is ok).

 

I was getting over 140C CHT on no.1 in cruise and oil temps over 90C so I ditched the 50mm lip on the cowl outlet and replaced it with a ramp for more suction. Result was a 5-10C drop on all CHTs and oil temps now mid 70s...so my next step is to put in a plate to exhaust the oil cooler air separately from the cylinders and adjust for mid 80C OT.....I'm worried about winter. Downside is higher Chts on 3&4 when taxiing (+135C).

 

My problem is on climb. When I go WOT, no.4 goes lean and the egt will, if allowed, runaway over 720C. So I throttle back to 3050 rpm where my egts are 650, 670, 645, 690 (Fuel flow somewhere around 25lph). CHTs on climb at 70-75kts don't go above 150C so far. If I rotate the carb to even mixture on cruise, it makes it much worse on WOT. And yes, the butterfly throttle is limited to 80 degrees open. By throttling back I lose about 50 to 100 revs on climb.

 

So now I'm reasonably happy and thinking there is just some tweaking on the cowl outlet with perhaps a bit of exhaust augmentation. I'm thinking my right bank is running hotter because that side is leaner and that may be because the inlet plenum diffuser is not exactly centre, or because of the orientation of the 4 horizontal holes in the emulsion tube/ atomizer which the needle jet sits in, or how the needle lays in the needle jet, eg it might lie against the stb side causing the fuel spray/plume to favour the port side?

 

I get a small drop of oil at the front crankshaft oil seal. Is this normal? Motor runs very smooth.

The JAB2200 looks like a good fit for the Cygnet. The original Sisler Prototype was fitted with one before it returned to the Taylor family Pat and Robin at Viking Aircraft World Headquarters in Burlington WI.

Cygnet Sport Airplane Light Engine Choices | Viking Aircraft

 

They paid a visit when Zig Berzins Award Winning Cygnet now sporting a US N-number arrived in Wisconsin flown by it's 4th owner & Cygnet Builder Jerry Folkerts. (See two in the barn) Mine ignores the direction to limit your VW to 1835 sitting at 2276cc. The build is super clean external fasteners were streamlined. Performance: 105 mph on 50 percent power (19.5” MP) I am told on 3 us gallons per hour TBC.

 

All Cygnets possess great Visibility ground and Air = No S-turns except to avoid potholes or trash on the ground you can see 5 feet in front of the prop!

 

http://www.youtube.com/watch?v=ilK3Uj4Dxfk

 

For the record! Ok obvious now I like the design.

 

We only have about 20 in the US and 100+ world wide I am under the impression the Australia has quite a stash of Cygnets. I think the UK is close behind for second place.

 

The Deisign is 45 years old this year.. Give me the privelage of a tail number NX237F in lieu of the big word EXPERIMENTAL embossed in large friendly letters on the side. I would like to organize a gaggle of cygnet before after or during Oshkosh. The Austrailian airline used to haul a boat load of people to oshkosh if you fellow would pull the wings we could make it a real big bash. Target 40!

 

Best

 

Matt

 

 

 

 

 

[Bruce Tuncks]

N237F, thanks for the pics.

 

I see a plastic tube coming up the windscreen center-beam. Is this the fuel indicator? I have been wondering about something like this for my Jabiru as the last bit of the tank is hard to see.

 

I sure agree with your decision to use a Jabiru engine instead of a VW conversion. Happy flying...

 

Bruce

 

 

[Markdun]

N237F, thanks for the pics.I see a plastic tube coming up the windscreen center-beam. Is this the fuel indicator? I have been wondering about something like this for my Jabiru as the last bit of the tank is hard to see.

 

I sure agree with your decision to use a Jabiru engine instead of a VW conversion. Happy flying...

 

Bruce

It's  actually a vapour return line from a header tank (about 2l) mounted on the aft side of the firewall... the VW installation was gravity fuel flow.   But the line can be used as a fuel level check. ...my plane also has a translucent epoxy/glass window in the fuel tank and a sight tube on the tank....and a calibrated fuel flow meter for a computed fuel remaining. You can never be too sure on fuel reserves. Mark

 

 

[N237F]

Yep....fantastic visibility. It's the third plane I've built and when I was deciding it was going to be the Jodel sovereign or the Cygnet. The low wing on the Jodel and my experience with a low wing Minimax swung me to the Cygnet. A few people are put off by the Cygent's geodesic wooden wing structure but it was really easy to build....definitely easier than the Minimax, Karatoo or the Carbon Dragon wings I've built. The plane still puts a smile on my face after 17 years of operation. The Jab engine had put 15-20kts increased cruise speed and 400fpm extra climb rate compared to the old 1835VW engine.

 

Cygnets are Smile makers. They gather questions at every fuel pump from young and old.

 

I think of NX237F as a room with a view in the sky. https://www.youtube.com/results?search_query=NX237F