Bing carby altitude compensation

Do you find the built in altitude / density compensation on the Bing carby works OK?

I run a Jab 2200 and don't find it that good at adjusting for winter/summer conditions or even altitude. Looks as though a seasonal change of carb setup may be required. Any hints or tips appreciated.

Nick

I can put you onto an expert about this who firmly believes that it doesn't work at all. Moreseo it's set at a figure somewhere roughly in the middle where 'most' people fly at. Same guy flew from Perth to Melbourne at 500 ft and burnt out all his valves because it's set for a higher altitude. Might sound a bit far fetched, however there's a lot of science behind that comment.

The expert can believe what he likes, dosn't mean it's a fact. I was climbing out of Gympie-Bundy today. At 1000' readings at 100kn 2800rpm. F/F 25lt/hr Manifold Pressure 27" By 5000' at 100kn 2800rpm F/F 18.5lt/hr MP 24". (EGTs 700) Somethings happening, looks like it's leanig as the MP drops to me. Try this on a Lycoming without manual leaning it just doesn't happen. Ran the idea passed the Jab engine guys at Bundy they compared the idea with the brown stuff you find in cattle paddocks. Wouldn't comment on how well the Bing does it though!

Modestpilot, I'm sorry but your numbers don't add up to me and my understanding of the physics and technology behind this.

2,800rpm at 1,000ft and 100 knots does not correlate to 2,800rpm at 5,000ft because you won't do 100 knots indicated, at 5,000ft on 2,800rpm as your engine is developing less power and the air is less dense.

As an example, at 6,500ft you'll only develop around 75-78% power.

In the GA world with mixture control you would increase throttle to full throttle as you increased your altitude, whilst leaning off the mixture. In your example the numbers could only be correct if your airspeed was less than 100 knots, more like 94-95 and based on that the engine is using less fuel because it's developing less power.

The true test would be to leave the throttle wide open from 0ft to 10,000ft, but even then it would be hard to tell if it was leaning as you would be losing power all the way up, so you'd have to use the EGT to compare, but even then that can be confusing as it will be cooler up top which will affect readings.

What is your 1,000ft EGT temperature?

Try this for size: The reason we have less power at altitude is that we have less oxygen per unit volume to burn.

"Richness" is a measure of the proportion of fuel per unit air.

In order to maintain the same richness as the aircraft climbs we either have to manually lean the mixture, or the carburetor needs to compensate for the decrease O2 per unit volume.

So if we left the same throttle setting as we climbed - say full throttle - and we neither leaned the mixture nor did the carburetor compensate for altitude then the mixture would simply become progressively richer.

Of course it doesn't - in fact fuel flow falls - so in the case of engines using the Bing carbies the carbie must be compensating.

Of course you are quite right, I was trying to relate to what a pilot operating

normally see's and does; it would take 100's of pages to go thru the physics involved, (including interesting data from Orbital Engines test cell results) the point is that the Bing compensates, the only real argument is how well, considering the price I figure it's not to bad. My EGT's are usually below 700 or less; on a hot day they can go higher (740) after T/O on first power reduction if I don't go straight to 25-26lt/hr. As Jabs Don says you can't have everything. The F/F may seem low but I'm running a Sensenich 62"x56" prop and Hoerner 3.7:1 teardrop type wheel spats, the extra 7-8kn deems to unload the engine considerably, bit like when you do a power on high speed descent. I’ll post more on the spats later still a bit of tweaking to do, but looks like maybe 125kn at 2800RPM and 19lt/hr at 550KG.

the point is that the Bing compensates, the only real argument is how well

Not unusual for a Jab to burn valves at altitude, they do that regulary at any altitude. Can't believe that the jab guys haven't actually got the carbs set up for their engines yet, after all this time. Have they got any idea ?. It's obvious they don't make a habit of talking to Wal at Bert Floods.

The Bing is one of the simplest, and reliable carb you could use. Of course the altitude compensation works, I have had 912s up to 9 grand without any problems, and remember no mixture control. Don't attempt to put shxx on a great carb, just because you go and put it on a shxx engine..........The Diaphragm in the Bing carb is included in the 5 year recommended rubber replacement on 912 engines, they should be renewed then to maintain their reliability.........................

The Maj. makes a good point, I fly from a strip where there are 912 engines. It looks as though I will have to change the jetting summer/winter to keep within the Jab set-up specs, and it doesn't compensate much for altitude. The Rotax doesn't seem to have any problems with mixture due to altitude or seasonal changes, so the Bing must work to some degree as advertised. Why so much grief when it is fitted to the Jabiru engine? Is it the inlet plumbing, lack of variable ignition timing or what?

xair1159, you'r obviosly a fair and understanding person....................

On the Jabiru engine that I have, the small bore clear plastic tube from the Bing carburettor to the air cleaner is very soft and pliable.

If it is tied to one of the engine mount tubes with cable ties it may not provide any functional air pressure connection between the carburettor and the air cleaner.

The tube obviously needs to be tested for a clear passage of air.

Regards

Do you find the built in altitude / density compensation on the Bing carby works OK?I run a Jab 2200 and don't find it that good at adjusting for winter/summer conditions or even altitude. Looks as though a seasonal change of carb setup may be required. Any hints or tips appreciated. Nick

I've only been in this game for a few years and only been flying my 230 with a 3300 for a little over a year, but apart from an unexplained difference in EGT on cylinder 2 between summer & winter I find that my Bing works just fine.

And it is a generalisation I know, but my observation is that those that dick around with their 2200 & 3300 engines are most often the ones that have the trouble (and many then blame the manufacturer).

Enthusiastic amateurs who think they know more than the combined experience of the manufacturer's owner feedback, dyno work and their own product testing can get themselves into real trouble in this flying caper.

My view is that J have got the latest carby tuning, and their tome about EGT and CHT settings and limits, about right (and I think that Maj's comments about "burning valves at any altitude" is unfair, out of date, slanted, & reflects his personal one-eyed love affair with 912's).

(But I did install a more robust piece of tube between the carby and the airbox, as per Ross's post, when I built mine).

Hope this helps

Geoff

[snip]

My view is that J have got the latest carby tuning, and their tome about EGT and CHT settings and limits, about right (and I think that Maj's comments about "burning valves at any altitude" is unfair, out of date, slanted, & reflects his personal one-eyed love affair with 912's).

 

[snip

 

Geoff

I have to agree with Mike. You can do better than that Geoff.

I've had a couple of Bings on my BMW for 32 years. It roars just as well up in the Snowy's as it does down the coast. The constant velocity carburettor's altitude compensation works if the air line is clear and there are no holes in the diaphragm.

Works really well on my plane too.

Awww C'mon Captain...here's me waiting for this thread to fire up and all you can muster is that pussy cat response to someone who's had a go at Jabs!! Do a proper job on him....please:cool:

That pussy-cat response is called "reasoned and informed debate".

I thought I would get a medal for my restraint and professionalism.

Also thought this might qualify me for a deputy assistant Administratotor's honourarium.

I must be getting soft, eh?

Regards Geoff

Before the pussy-cat bares his fangs, perhaps I'd better say I prefer the simplicity of the Jab to the plumbers dream complication of the 912. The Jab also sounds like a real engine rather than a girly sewing machine (is that provocative enough?)

My previous experience has been 350 hrs behind a 4 stroke engine with a gearbox which was a lot less sensitive to prop load than the direct drive Jab. Getting the best prop match looks to be a major factor in sorting the mixture, so rather than collect a box of fixed pitch wood props that are nearly right, I'm waiting on a ground adjustable from your part of the world, but delivery is slow.

There is a fair difference in conditions between Bundaberg and the west of Ireland, so some rejetting might be expected, but once running OK I would rather fly the thing than mess with it.

The carby inlet is very close to the firewall and uses a glassfibre Cobrahead with the inlet vertical. I imagine any turbulence in this would have a short term effect rather than a long term seasonal change. The breather tube is vented into the filter as prescribed and should be clear, but I will check this.

There is a fair difference in conditions between Bundaberg and the west of Ireland, so some rejetting might be expected, but once running OK I would rather fly the thing than mess with it.

Sea level is about the same in both places and there are plenty of J's 2200 & 3300 engines that are operating successfully in cold areas here and elsewhere here with crappy weather at times that might approximate your own.

Slarti is one who operated his 2200 out of Adaminaby and Cooma for a while which are both up near our Snowy mountains (hills to everyone else) from strips up at about 3000 ft amsl or so and occasional snowy type conditions/temps.

Based on my experience flying behind both the 2200 & 3300, if you have a genuine issue I would check that tube as previously discussed and make sure it will not crush under any circumstances, also have the diaphragm checked and if they are both OK + you have no induction air leaks and the latest jet/needle kit where your EGT's and CHT's comply with J's latest advice on their website, you should have a good result.

If that still doesn't do it for you, check all aspects of your particular carby & installation.

You are the 1st I have heard of anyone contemplating changing jets between summer & winter and my tip to you is that isn't right or necessary.

All of this, of course, assumes that you have the right prop and if you have the engine in a non J aircraft there may be issues to be addressed there, but I'd be surprised if J weren't very helpful to you in getting that about right, as you wouldn't be the 1st.

Best regards Geoff

Capt, he has a Revolution Carbon Fibre on the way from OZ so hopefully everything might be solved once that baby is fitted.

You can check mine out on Saturday and come for a spin if you want. (the prop that is)

Aw you guys, I have to agree with the Captain that my comments were probabily 'one eyed' and 'biased', and I did feel just a little bad after posting them. Any plane with any engine that returns it's occupants safely back to the ground (on fire or not), is fine in my books. I must say though that like some fish species up here lately, the Jabbies just aren't biteing like they used to!.. It is of course nothing more than an 'informed debate', and that's what this forum is about anyway.

I must agree with Captain and his comment about some Jabbies owners apparently having a bad case of 'tinkeritis', and some of them remind me unfortunatly of those in past years, who insisted in perservering with some VW derivities, myself included I must admit. There are those who just have a bad case of "tinkeritis" with any engine, and are often the type of people who shouldn't be let within 10 yards of an engine anyway.

The incoming airflow pressure on the rubber diaphragm in the Bing is what solely determines the fuel metered to the engine. Downstream of that, it's just the fixed jets and particulary the main jet and needle that determine amount of fuel into the incoming airstream. Obviosly the diaphragm has to be in good shape, and they should be renewed if they are not per Rotaxs recommendations. It bugs me geatly when I here people take about adjusing the float level in Bings, as it is totally unnecessary and could even be dangerous, causing fuel to be ejected overboard via the float chamber vent tube, which doubles as a fuel drain. This tube is also very important in providing ambient (atmospheric) pressure onto the top of the fuel, in the fuel bowl. Changing or re-routing this tube can have instant effects like enriching your mixture, or causing rough running above 5000 rpm, amoungst others. Just leave it where it is, tucked under the carb bowl retainer clip.

Set your carb/carbs up with the recommended jets for your engine, see that it has a stable and adequet incoming airflow, so the diaphragm can do it's thing, and go fly. It's that simple. If you know somebody who continiously messes with a Bing, please kick him/her in the arxx, as they are trying to give a really good carb, an underserved bad name. That's it, I'm going fishing for Jabbies now..................................

Aw you guys, I have to agree with the Captain that my comments were probabily 'one eyed' and 'biased', and I did feel just a little bad after posting them. Any plane with any engine that returns it's occupants safely back to the ground (on fire or not)is fine in my books. I must say though that like some fish species up here lately, the Jabbies just aren't biteing like they used to!.. It is of course nothing more than an 'informed debate', and that's what this forum is about anyway.I must agree with Captain and his comment about some Jabbies owners apparently having a bad case of 'tinkeritis', and some of them remind me unfortunatly of those in past years, who insisted in perservering with some VW derivities, myself included I must admit. There are those who just have a bad case of "tinkeritis" with any engine, and are often the type of people who shouldn't be let within 10 yards of an engine anyway.

See Mike/Ross.

We are all mates here (at least until next time).

Self-moderation rocks.

Regards Geoff

And, Maj, get yourself a Jabbie net and you'll be fine.

full throtle at 10000 feet??

can any one confirm fuel burn at altitude & high revs if it is significantly above low level normal cruise 2800 rpm (75% pwr) the bing carb obviously does not compensate properly for aircraft aplications ?? coments please ,,in lycoming or continental operating at altitude the hanbook recomends leaning ,and in many probaly millions of hours world wide fuel consumptin at a constant percentage power (even if rpms increase as in fixed pitch props ) only rises a little.

I would go as far as saying the bing carb does not lean enough with altitude<<<<<<

Basic principles.

The bing is a CV carb. The slide/dashpot will rise IF the throttle is opened, the ambient air pressure adequate and the engine sucking air. The more of these three the higher the slide and the higher the needle moves allowing fuel to flow more.

If you reduce any of the three elements then the slide will settle to a position somewhere between the idle position and the full open position. It compensates by varying the area of what might be considered the venturi to relate to the flow of air, and the tapered needle takes care of the adjusting of the fuel flow to suit. If the figures are wrong you go back to the needle shape and adjust its diameter. (by remaking it).

If the mixture didn't have a reduced fuel flow at altitude to match the reduced airflow caused by altitude effect (lower air pressure), it wouldn't have the right mixture at part-throttle either, so it must correct itself.

The engine revs have an effect on the engines ability to pump air so the prop has to be considered as a factor.

The Schebler carbs fitted to Lycomong/Continental engines have a fixed venturi and due to the behaviour of gases and liquids flow characteristics will always run a richer mixture as altitude increases. Nev.

full throtle hight

so are you saying as long as you do not use full throthle at say 10000 feet it will lean it out ok? how near to full throtle could you run it?, as it would be well below 75% pwr?

Full throttle height.

There is no problem at height as the engine power is well below max, due to the drop in atmospheric pressure, and the mixture looks after itself .the airflow through the carb is sensed by the diaphragm with a pressure variation and the slide compensates by moving to a new position.in response to the airflow. There is no direct connection between the throttle and the slide. Nev..