Jab engines

[facthunter]

 Older Motorcycles show the same symptoms with the modern mogas. You have to "tickle" the float or they won't even fire when warm sometimes. . Some motors have hand priming with a plunger pump on the dash. Puts you back in charge (of the charge). Nev

[Mhalc]

I thought I would post some updates to my supercharger project.  I have changed the drive section from a 2 x 25mm pulley/belt system to a single 50mm pulley/belt system.  Much easier assembly and maintenance, so far much more reliable.  The test flights have been at altitudes between 8000’-10000’ (DA) at 2900-3000 RPM.  With the boost controller set to provide 32 - 36 inHg MAP.  

 

In this range my Lightning is cruising at 178 mph (up from 147).  Increasing the boost above 36 inHg does produce more (HP) and speed but the speed increment is smaller for each increase above 36 inHg. (Still noodling on that one).  

 

BTW the CHT/Oil temps have increased slightly on my gen4, but well within the green.

 

If interested more details can be viewed at: <N530mh.tumblr.com>

 

[skippydiesel]

On 28/05/2021 at 4:50 PM, Bruce Tuncks said:

Yesterday I tried, from a cold start, opening the throttle a few seconds after the engine started with choke, and sure enough it stopped. 

In nearly 20 years of avgas, I had fallen into the habit of opening the throttle early on to get the revs over 1000 when the engine runs much smoother than with the 600 rpm idle I have it set to. Not once did it cause the engine to stop, so this is the only difference between mogas and avgas I have noticed so far.

The slow idle is in order to shorten the ground run after landing, and yes it is marginal. But on a warmed up engine, there is no more tendancy for stoppage than before the change to mogas.

So thanks again guys for the help.

All engines should be warmed prior to loading (flying/driving/mowing the lawn/ plowing the paddock/ etc)

 

Petrol, in particular, need to be warmed before a smooth running/power delivery can be expected.

 

Recent computer management/fuel injected systems may not appear to need the warm up period but I suggest this is the computer masking the symptoms of a cold stat rather than actually preventing them.

 

Two strokes seem to get over the warm up chugs quicker than 4/

 

Diesel engines appear to not have the problem at all however good engine management still calls for a warm period.

 

So the type of fuel (even the grade/RON of petrol) may impact on the time taken to warm up - should not be an issue for any pilot, unless expecting to conduct an emergency take off due to attacking enemy🤣

[Flightrite]

I rarely warm an engine to normal in flight operating temp, life’s too short as it is👍My ride on mower goes from stone cold to flat out as does all my other garden implements of destruction. Lyc says as long as it doesn’t cough upon hitting the gas pedal it’s good to go👍 My Jab donks I do the same, once they have reliable power I hit the gas pedal👍Some lose sleep over old wives tales😂

Edited November 4, 2021 by Flightrite

[facthunter]

I wouldn't recommend it with 2 stroke aero engines. Most cars say move off fairly soon after start but don't do high speeds and loads till the normal temps are reached..  The thick oils in aero engines are a concern when the Ambient is below the recommended lube oil type is used You can get this if you visit an alpine area when a cool change goes through overnight.. Nev

[turboplanner]

14 hours ago, skippydiesel said:

All engines should be warmed prior to loading (flying/driving/mowing the lawn/ plowing the paddock/ etc)

 

Petrol, in particular, need to be warmed before a smooth running/power delivery can be expected.

 

Recent computer management/fuel injected systems may not appear to need the warm up period but I suggest this is the computer masking the symptoms of a cold stat rather than actually preventing them.

 

Two strokes seem to get over the warm up chugs quicker than 4/

 

Diesel engines appear to not have the problem at all however good engine management still calls for a warm period.

 

So the type of fuel (even the grade/RON of petrol) may impact on the time taken to warm up - should not be an issue for any pilot, unless expecting to conduct an emergency take off due to attacking enemy🤣

You're covering a lot of territory there with a lot of different reasons but it does show an understanding of how to increase reliability and engine life.

 

Another factor is whether the engine is desined for intermittent power or constant power at a selected operating rpm.

 

Piston aircraft engines fit into the constant power class, so when designed as aircraft engines, the designer will be looking to optimise engine life at that rpm.

 

When you're setting tolerances life isn't always easy; sometimes you might be lucky and only have to contend with a single expansion load, other times you may have several disparate metals that produce one or two optimums so you have to compromies, and the product will be tighter and wear more at one rpm than another.

 

With a constant power engine the decision is easier, you set the tolerances to give minimum wear at operating temperature at the constant speed (cruise) setting.

 

It follows that at lower temperatures there will be more wear and the less rpm the less the wear, so usually a constant power engine should be warmed up before use.

 

A pilot doing less than 5 hours a year isn't even going to have this in their head, but an owner might.

 

In heavy trucks it's a financial consideration. In line haul operations where oil changes and tyre changes are done over the pit at the same time and the engines never cool down, the time to in-frame rebuild can be $40,000.00  less than a short haul engine.

 

 

 

[skippydiesel]

Turbs - I was specifically addressing engine cold start & run - I agree with your tangential statements.

[turboplanner]

On 28/05/2021 at 4:50 PM, Bruce Tuncks said:

Yesterday I tried, from a cold start, opening the throttle a few seconds after the engine started with choke, and sure enough it stopped. 

In nearly 20 years of avgas, I had fallen into the habit of opening the throttle early on to get the revs over 1000 when the engine runs much smoother than with the 600 rpm idle I have it set to. Not once did it cause the engine to stop, so this is the only difference between mogas and avgas I have noticed so far.

The slow idle is in order to shorten the ground run after landing, and yes it is marginal. But on a warmed up engine, there is no more tendancy for stoppage than before the change to mogas.

So thanks again guys for the help.

 

Having talked about warmup, there's another trail you can follow.

 

Mogas aint mogas

Mogas is slang for US motor gasoline and their standards of fuels are hugely different to ours which some people would say are some of the cheapest and dirtiest in the world.

Just talking about petrol.

First you have to get away from suppliers who from time to time adulterate their tanks with thinners or other cheap byproducts.

Next, unless you use the engine every day you have to get away from cheap alternatives like ethanol which can block  the non-serviceable/reachable parts of carbys.

Next, again unless you use the engine every day you have to get away from petrol types which specify ethanol percentages or are likely to pad out their product with cheaper ethanol.

That leaves you, depending on the Brand with one or two options.

If you pick the top option, you don't get any of the problems with the type mentioned above, but it contains aromatics which evaporate off in the tank over time, so after a couple of weeks idle you may not be able to start the engine. This is easily fixed by pouring in a litre or two of fresh fuel and this seems to catalyse the whole tank.

 

From your description, you're not having any aromatic problem.

 

 

However, I wonder if instead of your fond memory of what Avgas used to do, the carby may have got a dose of ethanol residue in the idle to 1/4 segment of the carby?

 

[facthunter]

If you run an (older) bike on Avgas it needs less choke than with the current Mogas varieties. Unless you have only just stopped the engine it starts best with a little tickle even when still warm.

   . The choke on the CV Bing REQUIRES the throttle to be closed to work as it's a separate bypass mixing chamber. IF you crack the throttle a bit too soon on a cold morning it may just die if you open it too far  if it hasn't warmed a bit. Nev

[RFguy]

And, Jabiru engines rely on the bores and head and crankcase all up to temperature  (expanded) to get the Thru-Bolt preload up to what is necessary for a full smoke takeoff run....

[lee-wave]

14 hours ago, RFguy said:

And, Jabiru engines rely on the bores and head and crankcase all up to temperature  (expanded) to get the Thru-Bolt preload up to what is necessary for a full smoke takeoff run....

With all due respect RF this is the most ridiculous statement I have ever heard about a Jabiru motor and the thru bolts, even if it has been written in the Jabiru manual.  First of all what is the temperature that the bores, head and crankcase need to be at before applying full power ?  Secondly how would you determine those temperatures. The only temperature gauges available are CHT, oil temp and EGT. 

 

The recommended way to warm the 2200 motor is to start it and idle at around 1500 rpm for a few minutes.   Then taxi at a fast pace to the pre take off checks holding point.  Oil temperature needs to be at least off the lower stop (around 50C). Carry out the checks line up and takeoff.   By design the best cooling of the motor takes place in flight with the airstream moving through the motor.    Idle too long on the ground in an attempt to warm the motor up is the shortest path to its destruction... 

 

On the subject of fuel in other postings...I use Esso Synergy 97+ mogas.  With absolute certainty there is zero alcohol added,  at least here in the UK.   If uncertain about the alcohol content in petrol adding water to a sample will draw out the alcohol content. 

 

Pour 10 ml  of the fuel in a  50 ml graduated cylinder... then 2 mls of water ...shake for 15 minutes.   If there is no alcohol present then the separation line will be at the 2 ml mark. If the separation line is above the 2 ml mark then there is alcohol present.  I did a test on the latest crap E10 fuels been supplied on forecourts.   It showed around 9 % of alcohol added.  Not good for combustion motors, fuel lines carburettor, seals etc.....

[RFguy]

ROFL. yeah rightio mate. everyone is entitled to their opinion. Have you done the numbers on the materials, measured the bolt stretch versus applied torque, tried different thru bolt thread lubes, and then verified the compressibility of the various interfaces and intermediate metals  to plug into the total tension numbers ? It isnt written in the Jab manual.

[facthunter]

Engines are designed with CLEARANCES that are correct at running temperatures. NOT when they are cold. 

 An aero engine has a bit of a hard time as it's expected to do a full throttle critical operation at the beginning of each trip. It's not ideal in may ways.  Oil is thick, some parts of the engine are still quite cold. The engine acts as a heat sink for the hotter parts and gradually attains a stable range of temps throughout it's structure that stay pretty constant after probably 40 minutes.. 

   With a road vehicle you are told to get moving once the oil has had time to get to all parts of the engine and take it easy with revs and load till normal temps are reached.

 

[spacesailor]

Motor oil  15- 40. Syn. ( we are told  ), IS thinner when cold and gets thicker when hot.

BUT

Even my old VW, recommends straight 30 grade.

Thick wnen cold, getting thinner when it needs that thicker oil at high loads & tempreture.

So, how about an ' oil heater ', at startup.  Like we used in those Cold European winters, that saved many from a cracked block !.

spaceailor

 

[Old Koreelah]

Ideally, a pre-warmer and pump to get that oil circulating before we crank the engine. It could be plugged into any external oil line. 

 

During WWII winters, the Swedish Air Force kept oil hot and added it their fighter engines just before they were scrambled.

[RFguy]

the argument depends a bit whether you are at Jindabyne in winter or Darwin in summer.

 

[facthunter]

IT doesn't get thicker when hot.  THEY use two "measures of temperature" for viscosity figures and  a straight oil. One without viscosity stabilisers (which are NOT OIL, do not lubricate and wear out in use) as a comparo.  which can be thinner when cold (than the straight oil) and thicker when hot (Than  the straight oil). because of the added Polymers.  The straight oil will stay the same whereas the one with Polymers will deteriorate. with use.  Both can absorb impurities water being the most serious, as when the thermostat fails engine wear increases markedly. Nev

Edited November 8, 2021 by facthunter

[Flightrite]

I don’t think I’ll ever fly my planes again, it’s just too risky😉

[turboplanner]

47 minutes ago, Old Koreelah said:

Ideally, a pre-warmer and pump to get that oil circulating before we crank the engine. It could be plugged into any external oil line. 

 

During WWII winters, the Swedish Air Force kept oil hot and added it their fighter engines just before they were scrambled.

The issue is not with the oil, which lubricates hot or cold. 

As Facthunter explained, the tolerances are set for minimum wear at operating speed (cruise speed), which I think I explained in a thread a couple of days ago. Just pumping hot oil isn't going to do an awful lot because the engine itself with dozens of different interactions and dissimilar components warms the components up itself to its operating temperature for that component.

 

Sythetic oil lubricates under mor extreme pressure and heat - reduces were at the top stress/temperature end, like through turbos.