Jab engines

[coinz]

Coinz, 245F is too cold I agree. Was this the max on climbout? How was it measured? I have never heard of such a cold running Jabiru (or Lycoming) engine.

While I can't argue with the results, I can't see how any air which doesn't come into contact with the hot metal removing any heat. I imagine hot engine molecules vibrating strongly causing adjacent air molecules to be shot away, taking energy from the engine with them.

Please don't be offended by my questions, I am quite capable of being wrong. Gosh, it has taken me 20 years to get the 4 temperatures fairly equal in my old 2.2 engine.

Cruise temp,is now 255F.Don't forget air entering Ram ducts is travelling horizontally before being forced into a vertical path,you are assuming air is simply passing from one end and straight out the other.My assumption when initially looking into Duct,was if ambient temp is 15C and i'm travelling at 200 kph i want air travelling through the duct at 200 kph and at 15C,i don't want to slow it down and superheat it,by restricting the flow,i would only end up the same as these m/cycles with hot running rear cylinders.Of course this is only talk,i know that it is only theory but it helped.Exit area is ample in my Jab.

 

I believe that the plugs will always be black/brown running unleaded. Only grey if running leaded..

The colour of my chinese 4 stroke mower plugs is textbook perfect light tan,using the same fuel as the Jab.

[Bruce Tuncks]

Thanks coinz. I agree that the most effective thing I did was making the lower cowl skirts extend out a bit so that the exit area was increased.

What I still don't understand is how removing the tape which blocked air from the ducts to the engine (hole at the front of the ducts) made such a big difference. Black magic, I reckon.

There is a limbach website which agrees with your idea to keep un-needed restrictions from the cooling air. Congratulations on a good job.

[Yenn]

One of the aims of the cooling gurus is to get the airflow speed down. They do that by increasing the cross section area of the ducting. Lower speed means higher pressure, it also allows more time for the air to absorb heat.

There can only ever be a small amount or air in actual contact with the metal of the engine, so heat is going to have to flow through the adjacent air away from the engine. It may sound too difficult but it seems to work in most cases,

Having said that one way to improve cooling is to increase speed. That works by increasing the volume of air passing the engine.

[tillmanr]

Yen, did you mean to say lower speed and pressure?

[Blueadventures]

Also need to lessen the eddy still air area on the lee of the profile / shape. Need to disturb it to have the movement happening. Air flow similar to fluid flow.

[Bruce Tuncks]

I reckon that common sense is a poor guide and not nearly as good as tufting and seeing the actual airflows. I think Yenn did this.

If so, I would like to hear more.

[Yenn]

I meant lower speed and higher pressure. That is what the experts say happens. Their reasoning is that the air has a total pressure, which is the total of static and dynamic pressures. Therefore if the dynamic or moving pressure is greater, then the static pressure must be lower. I know it seems silly because when you ride a motor bike the pressure seems higher on your face, but in reality it is lower.

Look on the front of your car and you will see inlets for ventilation beneath the windscreen.. That is a low speed, high pressure area.

[Bruce Tuncks]

In the Jabiru, air exits at the door gaps and enters at the tail. This is counter-intuitive but what Yenn says really happens.

Carbon monoxide from the exhaust can enter the cabin this way.

[jetjr]

I get plenty of air entering at door seals

[turboplanner]

I get plenty of air entering at door seals

I've had rain in my face from the top front corner of a J170 door, and cold air, but it's still possible that air is exiting further back due to the Bernouli effect. Some wool tufts stuck around the window area would tell you.

 

The Bernoulli effect on a rounded cabin area is very strong. I didn't latch a Cherokee hatch properly once and the door let go as soon as I reached flying speed with an explosive bang followed by a roar of wind. The low outside pressure held it open and I tried leaning over and pulling it shut but couldn't get enough leverage.

[Guest Machtuk]

I had a C310 door pop open just after t/off once, frieghtened the crap out of the pax next to me and myself! Luckily doors don't open more than an inch or two but sure did get everyone's attention!

[rendrag]

We have had a load of waffle about Jab engines and the thread drift is going on all the time. Here is your chance to say what you "know" about Jab engines.

I have a 2200 Jab in a Corby Starlet, it runs well although I got poor mogas and busted a piston with detonation. Avgas is the go for me. I would like to try a different carburettor from the Bing, although the Bing runs fairly well.

Don't bother talking about the engine if you don't run one or regularly fly one.

Someone in Australia is marketing fuel injection for the Jabiru enginrs

[John M]

We have had a load of waffle about Jab engines and the thread drift is going on all the time. Here is your chance to say what you "know" about Jab engines.

I have a 2200 Jab in a Corby Starlet, it runs well although I got poor mogas and busted a piston with detonation. Avgas is the go for me. I would like to try a different carburettor from the Bing, although the Bing runs fairly well.

Don't bother talking about the engine if you don't run one or regularly fly one.

I am flying my 3rd Jab 2200. I have over 3,000 hours with the engine.

The TBO for the top is 1,000 hours. On my 1st Jab I tried to see how far over I could go. At 1195 hours the valve seat on number 4 dislodged causing the piston to hit the valve with same damage.

I sent the engine in to Jab in Tennessee and Ben rebuilt the damaged area. The newer Jabs now have a recess in the top of the piston to prevent the stuck valve from being hit by the piston.

 

On #2 engine it started running rough at about 900 hours. I found that the hyd lifter on #1 was sticking. The bottom of the lifter was mushroomed which made it hard to remove. The cam lobe was worn by this event, but I replaced the lifter and the engine ran well. I sold it to someone in Canada with the caveat that the cam lobe was worn.

 

I bought a new Jab 2200 Gen 4 to take me to the end of my flying days. I'm 82, so time is short.

 

This engine has a completely redesigned top end which was the weak point on earlier engines. Head and jug are one unit and all cast aluminum so tolerances can be held tighter since we don't have to contend with different expansion from Aluminum head to steel cylinder.

 

The lubrication of the rocker box parts is much better with oil up through the push rods instead of from an outside pipe.

 

Roller lifters make it possible for extremely low idle...500 RPM when warm. The idle is very smooth.

 

Leak down test at 95 hours was 72/80 lowest and 75/80 highest. This was done on the cold engine so a hot leak down would be much better.

 

My aircraft is an Avid Flyer MK4 with fiberglass tanks that can't take ethanol laced motor fuel. This has always bothered me because I know that running avgas just loads the piston tops and other parts with lead accumulation.

 

Do I had a brain fart. I bought a marine plastic 6 gallon tank which sits on my right seat. I know...fuel in the cockpit? I flew a Piper Cub for many hours with the tank suspended above my legs and my header tank is behind my seat.

 

Jabiru requires octane of 95 RON. I use 91 AKI ARCO gas. AKI is RON-MON/2 so to get 92 octane AKI RON has to be 95.

 

I have taken a before borescope shot of the #1 cylinder showing the lead accumulation on the top of the piston and the head. After flying off several tanks of mogas I will take an after shot to see the difference.

 

In summary: I like the simplicity and low weight of the Jab 2200. My friends all have Rotax 912s and while the engine is robust, the ancillary parts...gearbox, sprague clutch, water pipes, etc are not so robust.

 

The Jab is turning a 66" Whirlwind 2 blade prop which allows me to climb 1000-1200 FPM and cruise at 100+ MPH on 2.8 GPH.

 

The fuel tank I mentioned allows me to fly about 80 miles round trip on $1.00 less per gallon than avgas.

 

For more info on the Jab engine there is the JabCamit forum.'

 

Fly safe.

 

John M

[Mike Borgelt]

In the Jabiru, air exits at the door gaps and enters at the tail. This is counter-intuitive but what Yenn says really happens.

Carbon monoxide from the exhaust can enter the cabin this way.

FW190 had a fabric seal aft of the cockpit to stop this. See Youtube Greg's automobiles and airplanes for a very recent two part on the FW190.

[Mike Borgelt]

An aft facing opening is NOT a low pressure area, as found by at least one sailplane manufacturer. You can't aid cockpit ventilation that way as the pressure is higher than static pressure. Nowadays they use an aft facing vent mounted either below the cockpit or above and aft on the fattest part of the fuselage.

I've seen why people have trouble cooling Jab cylinders. They have a front mounted oil cooler under the spinner. Leakage around that will increase pressure UNDER the cylinders and thwart attempts to increase airflow down through the cylinders. Seal around that and run the outlet in a sealed duct right back to the firewall before going down and out.

[Guest Machtuk]

I am flying my 3rd Jab 2200. I have over 3,000 hours with the engine.

The TBO for the top is 1,000 hours. On my 1st Jab I tried to see how far over I could go. At 1195 hours the valve seat on number 4 dislodged causing the piston to hit the valve with same damage.

I sent the engine in to Jab in Tennessee and Ben rebuilt the damaged area. The newer Jabs now have a recess in the top of the piston to prevent the stuck valve from being hit by the piston.

 

On #2 engine it started running rough at about 900 hours. I found that the hyd lifter on #1 was sticking. The bottom of the lifter was mushroomed which made it hard to remove. The cam lobe was worn by this event, but I replaced the lifter and the engine ran well. I sold it to someone in Canada with the caveat that the cam lobe was worn.

 

I bought a new Jab 2200 Gen 4 to take me to the end of my flying days. I'm 82, so time is short.

 

This engine has a completely redesigned top end which was the weak point on earlier engines. Head and jug are one unit and all cast aluminum so tolerances can be held tighter since we don't have to contend with different expansion from Aluminum head to steel cylinder.

 

The lubrication of the rocker box parts is much better with oil up through the push rods instead of from an outside pipe.

 

Roller lifters make it possible for extremely low idle...500 RPM when warm. The idle is very smooth.

 

Leak down test at 95 hours was 72/80 lowest and 75/80 highest. This was done on the cold engine so a hot leak down would be much better.

 

My aircraft is an Avid Flyer MK4 with fiberglass tanks that can't take ethanol laced motor fuel. This has always bothered me because I know that running avgas just loads the piston tops and other parts with lead accumulation.

 

Do I had a brain fart. I bought a marine plastic 6 gallon tank which sits on my right seat. I know...fuel in the cockpit? I flew a Piper Cub for many hours with the tank suspended above my legs and my header tank is behind my seat.

 

Jabiru requires octane of 95 RON. I use 91 AKI ARCO gas. AKI is RON-MON/2 so to get 92 octane AKI RON has to be 95.

 

I have taken a before borescope shot of the #1 cylinder showing the lead accumulation on the top of the piston and the head. After flying off several tanks of mogas I will take an after shot to see the difference.

 

In summary: I like the simplicity and low weight of the Jab 2200. My friends all have Rotax 912s and while the engine is robust, the ancillary parts...gearbox, sprague clutch, water pipes, etc are not so robust.

 

The Jab is turning a 66" Whirlwind 2 blade prop which allows me to climb 1000-1200 FPM and cruise at 100+ MPH on 2.8 GPH.

 

The fuel tank I mentioned allows me to fly about 80 miles round trip on $1.00 less per gallon than avgas.

 

For more info on the Jab engine there is the JabCamit forum.'

 

Fly safe.

 

John M

 

Most informative, thanks a lot?

[440032]

Informative, and from someone who actually has one too.

I've said it before, I'll say it again, whenever someone poo-poo's Jabiru to me, I just say:

Oh, you own one? (no)

Oh, you fly one? (no)

Oh, you maintain one? (no)

[Bruce Tuncks]

Well I still liked Mike Borgelt's comments. One of the early mods I did was to partially block off that big hole under the spinner and direct all the air from the remaining open bit to the oil cooler. Surplus air in here only goes to raising the lower-cowl pressure.

A manometer ( fancy word for a U tube) from the ducts to the lower cowl will tell the story.

I didn't think of isolating the airflow out of the oil cooler, maybe if I did this it wouldn't have been necessary to make the small skirt on the lower cowl exit.

And I was interested that the FW 190 had a fix for the problem of reverse flow containing exhaust gas up the fuse.

Edited March 8, 2020 by Bruce Tuncks

[kgwilson]

Having a separate NACA duct sealed from the rest of the engine to my oil cooler on the lower firewall has kept my oil temps at the lower end of the scale even on stinking hot summer days. In the Winter I put some gaffer tape over half of the cooler or the oil gets too cool. The lip on the bottom of the cowl is a metre wide & helps suck the air through.

 

[Old Koreelah]

Having a separate NACA duct sealed from the rest of the engine to my oil cooler on the lower firewall has kept my oil temps at the lower end of the scale even on stinking hot summer days...

 

Nice. I tried a separate NACA inlet and outlet for my oil cooler to avoid, as Mike Borgelt said, dumping extra air into the lower engine bay and reducing the cooling effectiveness of that system.

The other reason was to create a source of clean (no chance of exhaust gases) warmed air for heating the cabin in winter. That part worked, but my NACA duct was too far aft to be effective, so I scrapped the whole thing and went back to the previous setup.

 

However, I'd still like to separate the two cooling systems. It may be possible to dump oil cooler air out the bottom of my cowl belly.

[turboplanner]

However, I'd still like to separate the two cooling systems. It may be possible to dump oil cooler air out the bottom of my cowl belly.

What is the oil temp range in flight.

[Old Koreelah]

Oil temp from 85 to 100C, depending on how much of the oil cooler I mask off with tape.

CHTs kept below 130C even on the hottest days if I open the cowl flaps enough. So cooling is okey, but I’d still like to separate the oil cooling airflow from the engine cooling airflow.

[brinykraut]

Okay, so I've been running my preowned S/N 37** 2200Jab in an Avid Flyer for ~110 hrs since installed in 2015 (shorter flying season up here in the Yank hemisphere near the Pacific coast) Hydraulic tappets, Does all that make it a Gen 3? Sorta fuzzy on the distinction.

 

Leakdowns have stayed at 80/70, CHTs around 300-350 dependent on OAT's, EGT's 1350-1400, all fairly consistent with one another. Using 100LL with TCP to scavenge lead, Camguard, Phillips X/C 20w50 changed @25hrs/6mos. Have to tape over the oil cooler and block the inlet until summer to get 180F, so she definitely runs cool.

 

We have a several Jabs and two Camits here in our small EAA chapter, all running for more years than mine with no major issues. As others have pointed out, they are 'economical' alternative powerplants, reliability seems tied to operation and maintenance as much as most other engines.

 

Full disclosure: this airframe went through 2 VW's and an early Jab with valve spring failure before I got it, so I'm aware Jab has had it's teething problems.

 

I appreciate the knowledge/experience base here, even if it is 'upside down'!

 

Cheers,

G

[turboplanner]

Oil temp from 85 to 100C, depending on how much of the oil cooler I mask off with tape.

CHTs kept below 130C even on the hottest days if I open the cowl flaps enough. So cooling is okey, but I’d still like to separate the oil cooling airflow from the engine cooling airflow.

Sounds good.

Below 85, water may not evaporate fast enough.

Normal Chev 350 oil operating temp is 115

Normal Harley operating temp is 104<105

[Old Koreelah]

One issue with these older Jab engines is corrosion of the steel barrels if left idle too long.

It hasn't been a problem in our normally dry inland climate, but I put a few ml of Moreys into the fuel just in case. If planning a long period of inactivity, I run it hard and inject some 2 stroke oil downstream of the carbie.