C/S prop installation on Jabiru 2200 &fuel injection

[Old Koreelah]

Just re-checked my post: 

A well-respected LAME I know always advised overproping (and having a little carb heat all the time).

Lots of Jab owners are happy with the results.

 

What I meant to say was he advised against too high a pitch- in other words, let the engine rev rather than lug.

(I presume a lugging engine is more likely to suffer detonation).

[RFguy]

Ken, I operate my Jab at 6 to 7 minutes at WOT for roll and climb. but never WOT > 3000 RPM.

if the RPM comes up during the climb (speed increasing) , I'll climb a bit steeper and slow it down back to 2800-2900.. 

[skippydiesel]

2 hours ago, RFguy said:

Ken, I operate my Jab at 6 to 7 minutes at WOT for roll and climb. but never WOT > 3000 RPM.

if the RPM comes up during the climb (speed increasing) , I'll climb a bit steeper and slow it down back to 2800-2900.. 

Basic airmanship

[kgwilson]

Maximum continuous operating speed for the Jabiru 3300A engine is 3300rpm so unless your temperatures get close to or above the maximums specified you can run it all day at this speed.

 

 

[facthunter]

There seems to be some confusion here. Slowing up and causing the revs to drop is loading the motor. Anytime temps rise increase speed for more cooling and do it AS the temp starts to rise not when it has already gone too high. AS you climb, full throttle gives you a lower MP  and unloads the motor. Nev

[RFguy]

yes, if temps rise beyond continous ratings, certainly get more airspeed or back off the throttle appreciably

- as the Jabs  (Bing) run full rich at WOT, which is a fairly safe region for the exhaust valves , but once you are out of the main jet, the engine leans considerably  and EGTs will rise considerably

 

I find that I fly either WOT ~ 36 lph -  or somewhere below 28 lph - KG is that your feeling ?

 

Flying in the 28-34 lph region > 2800 RPM is a region I want to avoid.   I find EGTs rise to their high end (IE engine working hard , leaned off a bit) , unless CHTs are cool as a cucumber (high airspeed, cool OAT) . 

 

[facthunter]

The position of the dashpot (and attached needle) determine the mixture.  At sea Level you should get full open if the engine is in good shape, and the carburettor the correct size for the engine. At higher density altitudes the dashpot will not rise fully. This is the case for ALL CV carburettors.  Nev

[kgwilson]

WOT for me is 3300rpm S&L. Static WOT is 2850-2900. Takeoff WOT is 3000 to 3100 rpm. I have set these values with adjustment of the prop pitch. The limitations are related to CHT temps and Oil temps. There are also EGT temperature maximums recommended if you have EGT monitoring. In the climb Max CHT should not be between 180 & 200 deg Celsius for more than 5 minutes. Normal operations max is 180 deg C. My best climb is around 1500 fpm at 80 knots 1 up. I never get near the maximums even on a hot 30 deg+ day with plenty of fuel and airflow keeping temps in the good zone.

 

I only have a single CHT but have moved it when testing, around all 6 cylinders & found very little difference. The hottest was not No 6 as I thought it would be, but No 4 ( centre left bank) so that's where I left it. The original under the plug sensor ring terminal was modifed as per the Jabiru AVDALSR085-1  to a small 4mm sensor ring screwed in to a tapped thread between plugs. The engine did not come with tapped threads so you have to tap them yourself. I don't monitor EGTs. Originally I fitted a dual EGT on Cylinders 5 & 6 & found the differences relatively minor. Eventually the sensors played up before crapping out altogether & I have never bothered to replace them.

 

I don't have a fuel flow gauge so don't know my WOT climb burn. When cruising at low altitude at around 2800 rpm the consumption from dipstick to dipstick reading is 18-20 LPH. Above 5000 feet at 2850-2900 rpm consumption is about 24-25 LPH. I recently took a friend up to Boonah to pick up his aircraft. Altitude between 4000 & 6000 so 2 up going there & 1 up returning. Total tacho time 2.3 hours & consumption 21.4 LPH.

 

According to the Jabiru manual takeoff max fuel consumption is 38-40 LPH, normal cruise 23-26 LPH.

[Old Koreelah]

1 hour ago, kgwilson said:

WOT for me is 3300rpm S&L. Static WOT is 2850-2900. Takeoff WOT is 3000 to 3100 rpm.

Kevin it seems your prop is pitched at the safest angle. Not loaded too much.

Testing mine while tethered to a post gives a max of 2700. That may not be due to prop pitch alone (standard wooden Jab 60x42) but perhaps power being limited by my hydraulic tappet not opening as wide as solid lifters.

Takeoff WOT is 3000, showing 21 l/h on the Mizer.

The only time I’ve been game to use WOT in level flight (coming home late in the day in silky smooth air) I saw about 3200. 

 

 

Quote

I recently took a friend up to Boonah to pick up his aircraft. Altitude between 4000 & 6000..

That took you right over my home district, which I’m yet to fly over. Lots of yowie country, few open paddocks, almost no landing strips. I hope to fly in to visit family one day, after I’ve improved my skills and my plane.

[RFguy]

good info. and I am talking about the Jab.

 

When I am flying the Brumby (R912ULS) , I do back off the throttle a little from WOT for a long climb if oil temps  are getting a bit hot , the EGT rises, but is well within the rotax limits.  In the jab, with slightly backed off throttle in that 28-34 lph (6 cylinder) region, the EGTs rise into the hot zone.  I've heard of a few Jabs going bang at sustained WOT S&L > 3100 RPM, so I never go there intentionally.

 

flew monday evening. regular flying (2 weeks max) is oh so important for skills sharpness, even if it is just a couple of circuits. 

 

[Yenn]

EGTs rising to high end does not equate to engine running hard. It is showing that there is higher temperature exhaust gas late in the combustion cycle. CHT is what shows how hard the engine is working. Late ignition will cause high EGT and EGTs can be high at either rich or lean running. At rich mixtures it is because there is enough fuel to still burn in the exhaust and at lean mixtures it is because the burn is slow.

[RFguy]

With the Bing, backing off from WOT , my understanding is that  it's just coming away from full rich, where there is some cooling benefit due to unburned fuel being left over by the time the exhaust phase begins. 

 

Now, Yenn that is an interesting point you discuss - about high EGT can also be  rich running, (lots to burn) well worth pointing out.  I would think by the time that is occuring that performance has dropped significantly and you'd never get the engine there under any designed conditions. I'd be surprised if it burned hot enough to push EGTs high, or are you taking another peak ?

I dont have the practical experience to comment .

 

 

 

[facthunter]

The tapered needle is not directly hooked to the throttle in any way. Above 5000' you would only get about 75% power regardless of the throttle being wide open. Your volumetric efficiency gets worse at higher DA's. Rich mixtures will burn slower. Retarded ignition will give a hotter EGT. and CHT other things being equal.. Nev

[RFguy]

It's why I fly on FUEL FLOW - IE throttle setting for me is fuel flow, not  RPM....  if WOT is only 27 lph due to DA, well then I use WOT

 

I should have prefixed my previous discussions as "SEA LEVEL WOT and standard atmosphere" 

[Yenn]

I slipped up with the rich mix being hotter EGT. Brain fade. Highest EGT is only very slightly higher than stoichiometric mix.

Throttle opening does not equate to mixture in a petrol engine. It controls air flow and the mixture is controlled by jets and settings. In a compression ignition engine ie diesel, throttle does exactly control fuel flow, but then a diesel does not have a throttle.

[facthunter]

GLEN.. If we are considering LOADING the engine the RPM is akin to using the gears. The engine is also a pump and the MASS airflow through it will be proportional to POWER if it's all processed properly. More RPM allows more mass airflow but it may NOT be a direct relationship as volumetric efficiency will drop off at higher RPM and due to Density Altitude Factors (Manifold Pressure) also. Nev

[RFguy]

yes, all true. especially when talking CS prop. (the original discussion) 

 

 

 

 

[facthunter]

Anyhow Variable in flight pitch will obviously have efficiency advantages at each end of the speed envelope. Cost ,weight and complexity (safety) come into it. A lot of our plane s are limited by the allowable AUW (structural). and every bit of weight added, counts The "TWIST"of an "adjustable" blade is "fixed" though so it would be designed for an optimum angle, which with your engine chosen RPM translates to a speed it's best at.  Nev

[RFguy]

That's what I looked at when I did the calcs for a 912 ULS 100HP rotax and how it would affect the performance of the J230. I crunched all the numbers for efficiencies at various airspeeds, DAs etc -  A CS prop was required to bring it up to similar TO performance. J230 cruise speed (115-120 INDICATED) is just over the performance  edge where a CS prop is useful (IMO)

[facthunter]

I guess I would have to be biased as MOST of my "Pistons" experience had C/S props, but I'm advocating to keep the "practical" aspects of this in mind and use the arbitrary 110 Knots cruise as a guide in a rough sense. Some of the "better" modern composites will reduce the advantage/ need for C/S further, I would think. Whatever you do must be "matched" to the plane you have. Nev

[RFguy]

yeah on TO roll, for fixed prop roughly same equiv pitch, 6 cyl Jabiru makes about 17% more thrust than the 912ULS can make.

I have not done much 120 KIAS flying in the Jab since the turbulent weather started. back at 90-100 ktsIAS.... otherwise awfully uncomfortable. could go higher on long trip I guess. 

 

footnote :  that's for the ULS set for 5350 ish static, so you dont overspeed as soon as the airspeed builds and are sea level WOT.  If the rotax was pitched for soemthing like 5700-5800 RPM on rotation, the deficit  to the 6 cylinder is more like only 12% , but then you got to be red hot on the throttle to prevent overspeed once speed builds (immediately !) (or have some overspeed controller) . 

Edited January 27, 2022 by RFguy

[facthunter]

You are just going to get "belted around" a bit more and use a bit more fuel. A plane that will stall at 50 K clean has a lot of extra lift potentially at 120 knots.. Nev

[RossK]

On 22/01/2022 at 4:09 AM, Thruster88 said:

I see that Trent Palmer has removed the constant speed propeller from his freedom fox bush plane and gone back to a simple ground adjustable. The downside must have been greater that the benefit in his case.

Yes, his comment was that for the sort of flying he does, the weight penalty wasn't worth it (had to add weight to the tail to balance the prop)

He can get the same take off performance from the ground adjustable with a little less top end, but the guys he flys with are all cruising at 90-100 anyway, so top end isn't his priority, and he thinks the plane handles better by taking the weight out of the ends.

Saved +15kg from memory

[facthunter]

Weight well away from the centre of gravity is something to be avoided if you  can manage it. Nev

[bushcaddy105]

5 hours ago, Yenn said:

but then a diesel does not have a throttle.

Only old-style mechanical injection diesels, and even then not always. For example, I still drive an RA Rodeo (2004) with a mechanically injected 3 litre diesel. It has a throttle with a throttle position sensor and also an air mass sensor, just like petrol injection. The mechanical injection pump has the rack controlled by an ECU and servomotor. Shortly after Isuzu went to common rail electronic injection so a completely different setup.