? Rotax 912 minimum things that need to be done for specific hours up.????

[Thruster88]

1 hour ago, facthunter said:

The oil does get hotter in some parts of the engine than the gauge shows. My 85C is I believe the desired minimum. With synthetic oil the higher temps are coped with better. All the vented blow-by goes to the remote oil tank and then over board. That's how the oil is returned. It's the only engine that does it this way that I am  aware of. Nev

I think the Rotax 9 series oil system is pure genius. The dry sump allows for a compact engine, many aircraft have the nose leg in the space where the sump would normally be. There is no scavenging pump to fail. The oil tank can be placed anywhere. The tank can be opened and checked for contamination if a problem is suspected.  

[Kyle Communications]

Well the oil tank just cant be placed anywhere there is a dimensional area it is supposed to sit in behind or at the side of the engine. its height dimension

[skippydiesel]

Hight relative to crank case - there is some "lea way" - I have seen quit a few different heights on different aircraft

[facthunter]

I disagree. It's weird and pressurises the engine to work and you get more contamination and if a seal fails you get problems. In turbulence the tank will vent  oil as there's pressure/ air flow,  all the time to do it. Conventional scavenge systems are reliable and easily designed. Really thin oil is subject to letting the oil flow back unless the pipe section is restricted.. A positive displacement set up is the most reliable way. (or gravity in a sump). The 0-200  sump can be removed cleaned and replaced in no time  Compare that with the effort with the 9 series..Nev

Edited June 13, 2021 by facthunter

[RFguy]

WRT keeping the 6 cyl engine, We'll see how I go with holding the temperatures down. 
 

- Abs Max temp 165C measured on top (185+ under)   (keep the head hardware cool ++, and improve bore cooling)
- WOT at not  greater than  3000 RPM (piston thermal load)  (essentially, derating) 

 

if I can get it to do that, then will likely be fairly reliable. There are a whole load of thermally sensitive items (I can list them) that will be fine if kept cool.

The 6 is hard with  the jab cooling arrangement . leaks around the rear are terrible and those baffles in side the back are nonsense. . Take care of the leaks and its probably OK to keep < 180C at 30 ambient.
I'm sure also the 6 would maintain altitude if lost one pot's spark  . (would it end up igniting in the exhaust muffler can ??)

[skippydiesel]

Ref; Rotax engine oil circulation

 

I think most of us have had this debate many times befor - we usually end up in the two apposing camps, unreconciled.

 

For me that fact that Rotax 91 series engines, in their many thousands, are operating all over the world, in a host of different aircraft applications with most exceeding their TBO (without costly life extending interventions) is testament enough to their engineering excellence.

[facthunter]

It's got 2 plugs. IF the pot's out for some other reason the effect varies. When the LIFTER failed on the 0-300 the C 172 (early one) would not climb out. I do not know whether it was an intake or exhaust. I suspect the effect would be worse with an exhaust. Nev

[RFguy]

Nev, what's you experience with a pot out on a 6 cyl ?  Hold S&L ?

 

IF there is an inlet valve stuck open, that is going to mess things up for every cylinder (if common plenum) 

If there is an exhaust valve stuck open, inlet fuel/air charge might flow through and out the exhaust and ignite in the muffler .

 

 

I was reading today about a inlet pipe falling off a Airvan engine. 

It was the fuel injection system that got confused, reducing fuel charge to everything else.

Edited June 13, 2021 by RFguy

[facthunter]

THAT is ducking the issue skippy. Are you aware they can vent oil in turbulence? NO motor is perfect. They are also not easy to do a GOOD oil change. Get ALL the oil out.

  I would not know Glen. but I would think there's a chance. In that airvan case you would be better off if it was supercharged and you an set up MP equal to ambient if a manifold leak .  I'd have to know more about the system in that particular motor.  In the earlier injection systems I would have thought they would still function at higher settings. It's not going to throttle well at lower ones is it, with one bit opened to atmosphere. Nev

Edited June 13, 2021 by facthunter

[skippydiesel]

13 minutes ago, facthunter said:

THAT is ducking the issue skippy. Are you aware they can vent oil in turbulence? NO motor is perfect..Nev

No to the venting - have been in hart stopping turbulence a few times (Katoomba area) - never saw any oil being vented (during or after). Oil venting is a common problem in many aircraft engines and usually relates to overfilling or "aerobatic/turbulent?" manoeuvres that the engine is not designed for.

 

No motor is perfect - agreed without reservation, however some of us perceive that some motors are closer to perfection than others.

Edited June 13, 2021 by skippydiesel

[facthunter]

Yes I thought that P&W engines are near perfect too. (at one time). I'm talking about pistons, not the Kero burners.  Nev

[RFguy]

1 pot out in a 6 :

 

valve stuck open- at least the remaining engine wont have to fight any compression

 

IF there is an inlet valve stuck open, that is going to mess things up for every cylinder (if common plenum) oh boy. BANG and the combust gas ends up in the inlet plenum also ? that sounds bad ! (BUT would the cylinder ignite with no compression ????

 

If there is an exhaust valve stuck open, inlet fuel/air charge might flow through and out the exhaust and ignite in the muffler . bad. again, might not ignit ewith no compression ? or definitely will ????

 

insufficient lift due to lifter failure - well, somewhere in between not much output and problem causing for the others

 

valve spring failure - piston contact with valve most likely. That will make quite a mess .

 

Inlet pipe seal failure - cylinder will run lean, possibly HIGH EGT leading to valve stem failure ?

 

Inlet pipe  seal failure- in extreme, other cylinders will suck air from the gaping hole, so similar to very low throttle setting as little will be pulled through the carby. (try primer to push some drops in ?) 

 

No spark on both. fuel-air charge may ignite in the muffler ?

 

what else ?

Edited June 13, 2021 by RFguy

[facthunter]

Cylinders WILL fire without compression but not evenly. On deadspark engines this is common when starting . Mixture from a dead cylinder will often be ignited in the manifold or muffler. This may just be an irregular moderate bang. Cut the ignition in flight and turn it back on and a much larger bang may occur the muffler could easily split. Backfiring in an inlet manifold can do BIG damage to a motor. the significant amount of combustible mixture can supercharge one or more cylinders at the time to many multiples of the normal figure. This may be happening more often than we think, particularly with lean mixtures and carburetters fitted. It would be much less likely with individual port injection. Nev

[facthunter]

Funny thing about valve lifters the ones you use on older engines to make them easier to kickstart Running downhill with the exhaust valve lifter will retard the vehicle more that leaving the compression normal with good sealing it's just an airspring and gives back most of the effort. WE save the brakes on long downhills all the time by this method. Nev

[RFguy]

Alright, who knows about motorcycle engines ? Rotax is 100HP in 1352cc. Can we at 2x RPM in half the displacement and get same 100HP (for a generator) 

 

 4 stoke 500cc motorcyle racing ?

?

 

Edited June 14, 2021 by RFguy

[Thruster88]

There was a time when I contemplated obtaining a honda cbr600rr. 120hp@13,000. Red line about 16k, stroke is 42mm.

[facthunter]

What makes you think that's the pathway?. That kind of engine needs a good redrive and any high power thing will be liquid cooled and will be superseded each 4 years.. Who wants to be near something doing 8 thousand revs or more anyhow. Nev

[RFguy]

high speed piston engines are a fairly well developed pathway. 500cc tops maybe twin or triple ? sure it will scream like a PT6,  but.... 

 

Drive to electric generator might be direct.  or MHD.

 

What is a redrive ?

[facthunter]

Re(reduction) drive..  Yeah they are developed for motorcycles that never have maximum power for more than a few minutes at a time. Nev

[RFguy]

If a 500cc engine can do 14k RPM, 160 HP.... liquid cooled, MAYBE it can do half that reliably.  I have no idea. but someone in the know, will know.

Edited June 14, 2021 by RFguy

[facthunter]

I believe an aero engine should be purpose built for an aeroplane. Like any engine is for anything these days. Most bike engines have the clutch and gearbox integral. How do you get rid of those bits and mount the thing ?. (just for starters) then you need a Re drive set up that will take the power constantly. Earlier bike engines were an engine only and a lot more suitable for a small plane or a GYRO. Flat twins Vee twins or vertical twins. OR a Henderson 4.. NEV

[RFguy]

points taken

 

direct drive to generator/starter..... no need for reduction.

 

(rememberthis is a hybrid system- has battery).

[onetrack]

Quote

Who wants to be near something doing 8 thousand revs or more anyhow. Nev

Plenty of motorcyclists do that on a regular basis - with the engine doing 8000RPM or more - between their knees.

[spacesailor]

Only half the revs of a Sainty drag car motor,

Unbelievable redline on their tacho.

spacesailor

[Kyle Communications]

Why not one of these as the generator driver. I am sure further development could solve a lot of the issues