Jab engines

[Markdun]

1 hour ago, Old Koreelah said:

Too plurry right!

The claim that the Bing CV carb is ‘altitude adjusting’ is just marketing BS. It’s a constant velocity carb. It’s not as bad as a plain slide carb but not hugely different in terms of getting richer with increase in altitude.  It is much better than a plain slide carb in terms of ‘pick up’ and generally doesn’t need an accelerator pump.  Size for size theCV also needs to be a bit bigger than plain sliders and for any given engine the plain sliders are argued by the motor bike racers to deliver a slight increase in power.  In my experience the cv carbs are slightly more difficult to tune and much more sensitive to inlet runner lengths....you can get harmonic pulsing of the piston/diaphragm.

like koalas and wombats, carburettors are doomed to extinction.  Everything is going EFI....more reliable and cheaper. How many people now have glass panels for primary flight instruments?  I’ve heard of one in flight EFI failure and that was due to fatigue cracking of a 10cent 10A glass fuse that powered the EFI computer.  It should have been an automotive fuse designed for a vibrating environment. EFI is also doomed and will be replaced by E.

[RFguy]

Hey Turbs !  that's a bit mean.  as the student pilot, I take alot for care and interest and hands on in looking after the airplane  than most student pilots.  All other student pilots I see just get in the aircraft and off they go . My preflight is thorough. 

 

There are those around me that have known this plane for over 1500 hours.  If I bring up that its not making static RPM by a small value  and they're unfussed, then I am satisfied. I did check the carb linkages myself.

 

They were not too worried about the drift down in static RPM, most usually drifting carb balance, carb heat cable not going to "zero heat", and throttle linkages/cables (which I checked myself) 

 

The static RPM on that aircraft when I started flying was ~5150 rpm.  It had fallen to 4900 rpm in 30 hours ish of its flying since I started flying it.  The day before it I decided it was no good, was 4870

 

But since I got a bit more involved with looking after that aircraft.  and reading all the books,  the spec was 5500 or better. It was a long way down, but flew OK, no obvious vibration 

 

The take off roll was clearly longer at 4870. 

 

 

Edited September 24, 2020 by RFguy

[RFguy]

Mark, thanks for the Bing writeup. My background is SU carbs as a kid building rally cars.... But for whatever reason, I cannot recall, I had a leaning issue with my side draught SUs at 3000 feet ish.  dunno. 33 years ago. 

 

As for glass fuses. they're garbage in that type of service, and the screw-in fuse  holders with springs for compression ends ?!

 

The fuses run HOT and the spring gets heat treated and loses its spring. crap.

[turboplanner]

46 minutes ago, RFguy said:

1. Hey Turbs !  that's a bit mean.

 

2. The static RPM on that aircraft when I started flying was ~5150 rpm.  It had fallen to 4900 rpm in 30 hours ish of its flying since I started flying it.  The day before it I decided it was no good, was 4870

 

The spec was 5500 or better. 

 

1. No, just trying to save you from an EFATO, which could cost you  your life

 

2. If in your pre-takeoff checks out at the runway when the engine has warmed up, your runup check is 5500 rpm or better,

    if it doesn't make 5500 you turn around and take it back to the workshop; every time.

    

    It might be nothing more than an oiled up plug, or it might be more serious and could starve you of power or cut the engine        anywhere in the circuit and kill you if you couldn't make it to a forced landing. You can't roll to the side of the road in an aircraft.

 

  Floats and sink in any carburettor engine, usually because they have been installed incorrrectly and have been rubbing for hundreds of hours. In the two other engines the exact same thing could happen for the eact same reason.

 

      

 

    

 

[Kenlsa]

The Jab and Bing were developed in the days that we were limited to 5k feet, so it all worked out nicely, thanks very much.  Now we have 10k feet and where you lean a LyCon carb  above 5k,  we never ventured there until lately.  It is understandable that our little planes need leaning. The few times we fly up there the Bing is OK.

BUT, we must ask ourselves "how often are we near 8 to 10K?".  Not often I bet.  The80/20 rule still applies.

I have got to say that I get a nose bleed if above 2k as I like to get some sensation of speed and look around at the ground features. This is what Rec flying is all about.

If you want to play up there often, you will have to have some capability to monitor and adjust. So a an analog or electronic indicator of 23-24 inches with associated cables/handles, and panel space to fit it all.  This adds complexity and weight. Or you could go full EFI with more complexity and even more weight.

You will do most of your flying under 5k- So keep it simple, keep it light, look outside and enjoy the ride.

Ken

[RFguy]

Hi Turbs

Understood. yeah. OK.  This engine was a long way down. And I could notice the difference between 5150 (where i first started flying it) and 4900. Remember I started flying it at 5150, so I dunno how long it had been below 5500. anyway...   So I have not flown for a 13 days now, due to U/S plane and  bad weather , so when I get there on Sunday, I will be interested to how the freshly serviced airplane performs. 

 

That 912ULS is a (relatively) new engine for it, and has  400 hours on it now. The previous engine was sold off at 1500h. 

 

cheers- glen.

Edited September 24, 2020 by RFguy

[RFguy]

At least having a single carb in the Jab it cannot go out of balance ....

 

Are the two Bing carbs in the 912 smaller throats than the Jab carb ?

[turboplanner]

2 minutes ago, RFguy said:

Hi Turbs

Understood. yeah. OK.  This engine was a long way down. And I could notice the difference between 5150 (where i first started flying it) and 4900. Remember I started flying it at 5150, so I dunno how long it had been below 5500. I did check the linkages and cable  for loose anything .   So I have not flown for a 13 days now, due to U/S plane and  bad weather , so when I get there on Sunday, I will be interested to how the freshly serviced airplane performs. 

 

That 912ULS is a 9relatively) new engine for it, and has  400 hours on it now. The previous engine was sold off at 1500h. 

 

cheers- glen.

There's something not right here; you were telling us you were a new student. Are you saying you weren't given a set of pre-flight and pre-takeoff checks for the aircraft? They have all the RPMs speeds etc for the aircraft. You're not expected to go hunting for data becaise you cold easily pick up a spec that didn't appply to your aircraft.

 

[Kenlsa]

How does the Brumby 610 high wing, go with the jab 6.  I see that there is at least one flying.  I am always keen to support OZ.

Ken

[RFguy]

Static RPM is not in the checklist, and  Static RPM check is not in the POH.

 

There is mention of 'maximum RPM' in the POH .

Other checks for idle, magneto ,carb heat etc checks are all in there.

When  I mention static RPM, that is the RPM in the first 5 seconds of the roll after maximum power is requested.  RPM climbs a bit up to maybe 5200 by about 500'.

 

When I read the 5500 in the book, and asked, the maintenance crew went looking for problems  for an hour but didnt find any. linkages, cables , stops checked.  I dont know how much of the low static was due to say imbalance. When the vibration  appeared that morning , the oil that morning (50h old) had blackened quite a bit from the previous day- a delta change. I was advised that the oil would tend to darken up a bit at the end of the maintenance  cycle due to richness likely with growing imbalance. But clearly on the day I returned it back to the hanger, something had happened overnight- there had been a step change to go from no vibration and smooth running to shaking all over at mid RPM.

 

[RFguy]

Ken : Well, my instructor, Rob says it is a great, tough trainer and more like  GA with all its rods instead of teleflex cables. It is very precise in controls. I can fly the aircraft totally with two fingers on the stick (not a yoke) .

 

He likes it. I think the only thing he doesnt really like is that it almost refuses to wing drop in a stall ! it mushes. with a flap and bit a roll it will just try a bit of wing drop.  not much..For a trainer, for the purposes of demonstration and learning,  He'd like to see a more obvious and definite stall effect. Of course the designers pride themselves on an aircraft that has such a docile stall , which is fair enough .

 

Secondary effects of prop power on yaw turning takeoff  are obvious but easily correctly (by me) .  that's abotu all I can say . Would I buy one ? yeah.  there are a few owners I have talked to and they love the two finger flying- IE that there is NO slop in the controls. 

As for does it run out of rudder in a high Xwind? Dunno yet.

 

I am long legged and with the pedals where they are the seat all the way back, I am a little far for comfort from the panel, and Brumby say yeah it is set for the middle of the road and that  the pedals fore or aft if you want without too much work. 

With my seat all the way back and my instructor's seat forward, I find it hard to look out of the right of the plane without a big lean.  (because his head is in the way) . harness is single strap anchor  behind  to a Y and a strap over each shoulder.

 

 

 

Edited September 24, 2020 by RFguy

[Jim McDowall]

Wasn't there a service bulletin out on Rotax motors a few years ago about Bing carby floats sinking?

[RFguy]

yeah but it is known to and continues to happen. I did look at it and from memory it deals with how to identify the problem and how to check for float height , health etc. There might have been a bad batch but everything I read suggests it is part of life.

Edited September 24, 2020 by RFguy

[RFguy]

And Turbs :  The Brumby I fly - 

It's not a school- it is the club's plane I hire. 

day by day, I take more  and more responsibility for its condition. 

 

I 'tolerate' others flying it, I don't like it.  I don't mind other students flying it- ones I have met and got to know - that's OK.  But  don't like seeing that its been gone for 4 hours cross country with someone I dont know... ! and not washed when brought back !!!! grrrr. still that's fine-  if I wash the plane I get to look over every square inch for damage.   I check play in controls and control surfaces and linkages that I can access like a hawk. I check the bolts and Nylocs etc on control surfaces every flight, even the ones at the top of the rudder. I check for brake surface contamination on the disks, I pull and push the aircraft by its struts inbound and look for any different mechanical relaxation behaviour of the struts /fuselage , as goes for the mains and the nosewheel . I remove grease that gets 'blown' out of joints onto the welds so I can check for cracks in welds around the nose wheel and joints, and also this way i can track if oil or grease loss has accelerated.  I test the fuel like I have to drink it.  The list goes on. How many students do that eh ?

 

 

Edited September 24, 2020 by RFguy

[turboplanner]

None that I've ever flown with.

 

[RFguy]

but I take your point you were trying to make above. good advice. anything out of spec/regular has to be investigated and taken notice of. From little brooks run big rivers...

[Downunder]

With the sds fuel injection, you can get dual ecu's and dual fuel pumps......

That, combined with modern automotive injection components makes it reliable as it can be.

You just need the electrical "juice" to keep it going.

Those questioning the reliability also need to remember you are eliminating 100% of the carby faults at the same time, and getting better fuel economy (therefore greater range) and better tuning with even egt's to all altitudes.

 

 

[skippydiesel]

Hmmmmmm - bit odd !!! Rotax recommend a "static"  (tied to the fence) minimum of 5200 rpm and the same for climb (for 912ULS).

 

f your static is 5500 rpm I would expect reduced cruise performance, poor fuel consumption and high WOT - perhaps your aircraft has a high empty weight? This might explain the need for such high static rpm.

 

If you have a CS prop, I guess you might expect something else again.

 

When I do my "run ups" its at 4000 rpm - much more on grass/dirt and I will be moving forward.

 

My take on your run up rpm fluctuations - suggest checking:

Wind velocity & direction 

Prop pitch adjustment

Carburettor synchronisation

Carburettor linkage slip

Carburettor malfunction

Change in fuel quality (unlikely) 

[RFguy]

Hi Sean

I agree all round .  As you saw, I got 5150 static-ish about 30 hours back in the history.  The POH only refers to maximum RPM as an engine spec (5500/5800). POH runups are at 3500 , and I did note it was 4000 after reading the operators and maintenance manuals on the 912ULS a few weeks ago.  I do them at 3500, 4000 is a bit of a stretch on grass, and adjust the permitted variations and spread of magneto check accordingly. (3500/4000)

 

This thread is polluted like the Tower of London moat, so I will continue to digress: 

With LONG warmups I was wondering if the thermostat was bad it it- but it appears they dont have one ?!!??. A few aircraft mfrs have resorted to a pullable vane arrangement over the radiator to improve this. Otherwise warmup from 6 deg C is long.... Warmups are faster at 2000 v 2500 idle I find and I put that down to lower airspeed through the radiator.

 

-glen

Edited September 24, 2020 by RFguy

[skippydiesel]

Some Rotax 912 installation's are fitted with oil and or coolant thermostats.  Mine doesnt have either.

 

I know of one person with an oil thermostat fitted , he swears that he gets a significantly faster "warm up" - makes sense.

 

I have often contemplated fitting one or both  - have yet to do so. Unlikely to make any difference to cruise/climb out temps and  the added complexity (potential failure point) worries me.

 

Probably more popular in the colder reaches of the northern hemisphere (or Canberra ha!)

 

Its common, in the colder months, for operators to partially block a coolant/oil radiator. The risk of course is then overheating but I guess that down to pilot attention.

[Bruce Tuncks]

Jab plenum...

I just saw the latest kitplanes email and they featured a carbon "tunable" plenum.  There is some sort of adjustment thing in the very middle of a x shaped plenum with 4 exit pipes.

This got me to realize that the standard Jab plenum could be much improved by making the exits radial.

If you could do this, then every cylinder would get the same fuel/air by symmetry.

 

[Markdun]

Skippy, a friend with a Rotax is ‘gunna’ put a TOCA on his to decrease warm-up time and reduce the workload involved in the manual TOCA here in Canberra.....gaffa tape on the oil cooler, which is what I use in winter on the Jabs to assist getting oil temps above 65C.  I’ve just taken them off for the summer.

 

Bruce, I machined up an alloy adapter fitting that goes between the Jab plenum and the Bing with an ‘airfoil’ shaped brass bar which can be turned with a screw driver and locked in a position with a lock nut. Mine just is vertical, but you could have one horizontal too.  I haven’t bothered fitting it as my cruise egt spread is ok....it’s just on climb where it goes all over the place depending on the day and what constellation the moon is in.  

[RFguy]

On 06/06/2020 at 12:40 PM, onetrack said:

You need to figure out a soft-start arrangement for the starter. Leece-Neville are producing new 12V and 24V starters for truck and industrial diesels that contain an inbuilt soft-starter.

There must be some smart electronics whizz who can design up an electronic "black box" that feeds in the electric current on a "current ramp-up" basis, to prevent the bang you get now, with full current supply upon starter initiation.

OK I will do it.

it probably needs a pulse just long enough to engage and then needs to back off a bit to reduce the peak torque load for a short time. It will be interesting to  measure  how much is required to get a solid engage. It will be pretty obvious to the sensing circuit when the engagement has happened.

[skippydiesel]

1 hour ago, RFguy said:

OK I will do it.

it probably needs a pulse just long enough to engage and then needs to back off a bit to reduce the peak torque load for a short time. It will be interesting to  measure  how much is required to get a solid engage. It will be pretty obvious to the sensing circuit when the engagement has happened.

 Good -on -yah! Jabs, so fitted, may start to catch up with Rotax 912/914 range that have had soft -start for quite a few years now.

[Steve L]

My 912 has soft start on it. I believe it retards the timing until a few seconds after start. Surely it could be adapted to most engines.