Prop stopped.

[IBob]

Nev, I don't think anyone is trying to argue that having high mounted carbs is a good idea.

The title of this thread is Prop Stopped, and I thought the discussion was around practical means for avoiding that.

That said, I'm (also) not trying to argue that the Rotax fuel return answers all our fuel delivery prayers.
But what I would suggest is that with the 912, it does a good job of reducing the possibility of vapour lock in a heat soaked engine bay.
To dismiss that by saying the carbs shouldn't be high and that an orifice won't pass much liquid adds nothing useful in a practical sense to the conversation.

 

Here is a heat soaked event......the EFATO is at the start, but the analysis (if you can call it that) is at the end. And to my mind the guy displays little understanding with the 'return' he has now piped in (that is not a return at all):
https://mail.google.com/mail/u/0/#inbox/FMfcgzGpGTHLQrlpggWzXQjxQlPfnzsr?projector=1

[Garfly]

There was a good discussion on the topic of fuel return lines a few years back in this thread:

 

 

[IBob]

Ops, that should have been:

 

But it's not well presented: what he doesn't show is that he landed and turned off his engine before restarting and attempting to take off. You see a bit of that here:

 

But at the end of Part2 he focuses on his fuel pump replacement and his (in my opinion inadequate) attempt at a fuel return, with only a fleeting mention of grounding running to cool the engine bay: which would probably have saved him the cost of a propeller etc.

[RFguy]

Hi Bob

agreed that the insulation wont fix a heat soak.

6 cyl jab has float bowl at bottom of cowling. but fuel pump location is a hottie (and has exhaust shield).

 

heat soak used to happen on my 260Z. Drive on hot day  from sydney up the hill to Mittagong (600m) , stop to get fuel for 10 min , the start and 1 minute down the road, die.....wait about an hour . it was OK.

I always run the fuel pump in the club rotax in similar sit. 

 

I still favour the fuel loop. Then really the remainign problem is hot fuel bowl I guess. brushless fan for cowling ventilation to run once cowling temp > x ????

  I'll need to do some reading on the vapour pressure of the various agents in gasoline. Gather they come out one at a time. 

 

 

 

[RFguy]

after reading some vapour pressures of various gasoline compunds....

 

Bob :  In the case that bubble are present at the fuel pump  (putting aside the other options) , the fuel pump when the engine fuel pump is sucking, this is creating a lower pressure in the fuel lines preceding it. Surely if an aux pump back at the tank keeps this hot line in the cowling to the fuel pump nice and pressurized, then the low pressure scenario wont occur THERE. (of course low prez is now elsewhere but hopefully cooler).

 

??

 

[RFguy]

good reading : tech report 

 

"A review of vapour lock issues during motor gasoline or automotive gasoline usage in piston engine aircraft"

https://iopscience.iop.org/article/10.1088/1757-899X/370/1/012008/pdf

 

fig21, 39 are interesting

http://www.tc.faa.gov/its/worldpac/techrpt/ct84-12.pdf

 

more good reading

https://www.jstage.jst.go.jp/article/jpi1959/9/0/9_0_58/_pdf

 

 

[IBob]

That certainly seems like a reasonable suggestion, RFGuy.

 

In conversations like this I think we have to be careful that we are not chasing ghosts or tilting at windmills. For instance, Facthunter's assertion that a high mounted carburettor is not ideal placement (for at least two good reasons) is absolutely correct. However, we also know that many thousands of aviators have top mounted carburettors, which they cannot alter, but which fortunately do not seem to have resulted in a history of problems.

I would be starting, if possible, by asking what observed problem are we working to overcome here? Or in the plant automation world where I used to work: what have been the practical experiences of others that I can benefit from? That does not mean we cannot use our own imagination and ideas, but it helps keep us grounded in the current realities.

[RFguy]

take away from one of those posted links https://iopscience.iop.org/article/10.1088/1757-899X/370/1/012008/pdf

 

was that lots of flow and skinny lines can exacerbate VL issues because the pressure is lowered in that configuration. 

 

Interesting also about the tolerance of various carburettors Liquid to Vapour ratio...

 

in hot regions., seems that the RVP of PULP 95 is around 65kPa

LL100 has a max RVP of 47kPa approx but has a different curve to MOGAS

 

Edited June 15, 2022 by RFguy

[RFguy]

More gold for you vapourlock freaks (like me)

 

https://www.fire.tc.faa.gov/pdf/ct86-21.pdf

 

reading some MDAS : MOGAS can vary quite alot-  from RVP of 100kPa  in cool regions  to 60 kPa for hot reigons.

 

as i read that : 

If you put winter MOGAS in some sealed jerry cans, and use it in summer- TROUBLE ??? opinions ?

Edited June 15, 2022 by RFguy

[onetrack]

Glen, you have to stop reading this American stuff that talks about Winter and Summer Gasoline and Mogas. We live in Australia, we call it petrol, and we don't have Winter and Summer blends of petrol - unlike America, where the ambient local ground conditions can vary from -40°C to +50°C, and ground level elevations can reach 10,000 feet.

 

What we do have, is petrol supplied to end users, refined to meet the following Standards;

 

Fuel Standard (Petrol) Determination 2019

New South Wales Protection of the Environment Operations (Clean Air) Regulation 2010

Queensland Environmental Protection Regulation 2019

Victoria Environment Protection (Vehicle Emissions) Regulations 2003

Environmental Protection (Petrol) Regulations 1999 (WA)

 

https://jade.io/j/?a=outline&id=785918

 

The first Standard governs the quality, the octane rating, the various ingredient parameters allowed, as well as a range of other measurements, which are all carried out via testing to various ASTM Standards.

Note that the other four Standards above are largely related to environmental pollution via emissions - either before or after combustion of said fuel.

 

Our petrol is refined then blended to meet a specific Reid Vapour Pressure according to the climatic season and ambient temperatures. In essence, it's illegal for the oil companies to supply petrol in the warmer months that has too many volatile ingredients, which add to environmental pollution via VOC's (Volatile Organic Compounds).

Every time you refuel, you release a certain amount of VOC's into the atmosphere, the environmental laws are designed to minimise that pollution, specifically in densely-populated areas.

These VOC's were recognised as a major pollution problem in the late 1960's, and it's the reason all our new road vehicles from about 1971 have had charcoal canisters fitted - to catch those VOC's.

 

The local oil companies are obliged to meet set RVP levels with every fuel batch in the hotter months and hotter regions, so they blend the ingredients accordingly to reduce the RVP in hot weather, and then allow it to creep up in cold weather, to ensure good starting.

I can't speak for other States, they all have different legislation, but the link below gives advice to fuel suppliers in Perth as to the levels of "monthly volumetric average levels" of RVP they must meet during the hotter months of the year in Perth (Oct 15th to Apr 15th).

 

https://www.der.wa.gov.au/component/k2/item/4152-calculating-reid-vapour-pressure

 

 

 

 

 

Edited June 15, 2022 by onetrack

[kgwilson]

Jabiru engines do not need a fuel return. The carb is at the bottom of the engine and there is a heat shield protecting the whole induction system from the exhaust system. The air that passes the carb is warm as it is heated from the heat transfer from the heads and cylinders. The mechanical pump obviously has to be part of the engine as that is how it is driven but it does not get specifically very hot. A high wing aircraft like the jabiru has the fuel gravity fed from the wing tanks into a header & then to the engine so the engine is not sucking fuel and vapour lock is highly unlikely unless after the aircraft has been sitting on the ground and fuel in the lines overheats. All fuel lines under the canopy are shielded and insulated.

 

The standard Jabiru engine start up procedure is to use the electric fuel pump for 10 seconds to push fresh fuel in to the float bowl both in a cold and hot start situation. Gravity fed fuel and an electric boost pump in the fuselage virtually eliminates the possibility of vapour lock in flight.

 

I have 2 wing tanks and a main fuselage tank. All the fuel to the engine flows from the fuselage tank which is higher than the engine fuel pump & obviously the carb at the bottom & I have an electric boost pump in the fuselage. I have an auxiliary higher pressure fuel pump and a L/R tank selector to pump wing tank fuel in to the main fuselage tank. I know exactly how long it takes to pump the 35 litres in each tank into the main tank & usually change it 4 times to empty. This takes the fuel gauge (main tank only) from 1/4 to full once I have emptied both wing tanks. My total fuel capacity is 170 litres.

 

The problem is only a Rotax one with the carbs sitting at the rear on top of a hot engine.

[RFguy]

Agreed KG, there are very few problems with Jabiru fuel systems when proceedures are followed.

My takeaways , in different combinations of weights:

 

0) A low pressure region in the fuel lines, perhaps a constriction back in the system  on the source side of the fuel pump likely will cause  a low pressure region and potential for vapour.

1) dont let your Australian std MOGAS get hotter than 35-40 deg C in a suction at the engine only system.

2) LL100 almost eliminates likelihood, but not completely- again low pressure regions on source side of pump is a vulnerability for any fuel.

3) boost pumps located near the tanks are a useful mitigation strategy. 

4) fuel return is useful for both run and soak problems if all the gotchas are taken care of.

5) watch out for fuel line constrictions.

6) heat shield fuel containing line and apparatus from radiated /convective heat sources

 

 

 

[facthunter]

The 912 doesn't like 100 LL. We all know that. Mogas can vary and does. Fuel tank pump can give more confidence. Once the fuel is in the  Carbutretter Bowl it as at ambient pressure. IF bubbles form there the float may sink as the fuel density drops  IF that happens the carb. floods  Your fuel consumption is 13-16 and a bit more on the  100 hp. 1/5th of that rate of flow is not much cool fuel and if the plane has been sitting in the sun on a hot day ,it's not that cool either. When the engine is shut down it will stay hot for a fair while unless the Plane is parked into a fair breeze. Injection would cover these problems and has been available back to the early 60's with a mechanical system that eliminated this problem and icing as well..

 The engine mounted fuel pump usually has an insulating thick gasket (or should have..   Nev

[RFguy]

and the carb floods and spills the fuel overboard ? causing a fire. maybe.

Being at Jindabyne in the summer (DA ~ 5000') might exacerbate MOGAS VL problems...

 

anyway, was a good discussion. IO-360 compared to an O360 seems a no brainer for new installs and MOGAS

 

 

[kgwilson]

I have only ever used Avgas in my Jab 3300 engine when I couldn't get automotive petrol. I noted from another thread that 83% of all piston engined aircraft in the US do not need Avgas. There may be a lower %age in Australia as the GA fleet could be older, I don't know. Quality is not an issue except maybe at outback servos where the usage is low & storage tanks are old. Anyone using Avgas when they don't have to is nuts IMO.

[Mike Gearon]

8 hours ago, RFguy said:

More gold for you vapourlock freaks (like me)

 

https://www.fire.tc.faa.gov/pdf/ct86-21.pdf

 

reading some MDAS : MOGAS can vary quite alot-  from RVP of 100kPa  in cool regions  to 60 kPa for hot reigons.

 

as i read that : 

If you put winter MOGAS in some sealed jerry cans, and use it in summer- TROUBLE ??? opinions ?

I think more than a few of us aviator types will chase a problem hard to conclusion. Working out what’s actually a problem is as Ibob mentions the key point. I dare say we also,have to know when to put the problem away and just get in with it. So much going on as airmen.. airpeople? I’m doing IFR at the moment and hold entry is driving me nuts let alone all the rest of IFR and just plain flying the aircraft 
 

Here is a Rotax thread where 2 guys have engine problems solved by fuel pump being turned on (pressure fixed) and in at least one case no return line. https://www.rotax-owner.com/en/912-914-technical-questions/4950-engine-missing-low-fuel-p-must-be-vapor-lock
 

100% need the return line. Don’t return to tank feed line by T or to header. Bad idea. Return to fuel tank.  Ideal world it’s split into say 20 litres per hour going equally to your multiple tanks. We don’t have that so just pay attention and don’t throw your reserve fuel out the return tank breather port. I threw near an hours flying time out.  I’m 100% certain I’ll never do this again! I’d rather not learn through experience. I screwed up a few ways on the New Mexico trip. 1. Flew over desolate ground and 2 I had a late departure to my destination and didn’t contact Robert. He emailed if I was coming and I’d missed it. I’d have got the plane down just fine. 99% landed it and worst case pulled the chute. Problem as Robert mentioned was I’d end up with no coverage at an abandoned farm house in the desert heat. Oh yeah…3rd problem. I didn’t have Center on radio and was so bumped around I couldn’t hold the iPad still enough to sort. I was very aware I didn’t have emergency frequency set up…. Again… never again. 
 

Paying it forward… COVID in Taiwan and I was stuck for 9 months. I knew this site was struggling as I was and gave it 1k. Yes, I was the crazy bastard did that! I’m happy with the advice on this thread and not sticking my (to be manufactured header tank) with included return line t. 1k of advice. Done!

 

I was a little annoyed my glider airport recently had a miscellaneous charge of $350 from 2021…It was storage of a few boxes of crap and a few weeks  my motor glider was there. I told the manager I’d happily pay just for the advice. 2021 he watched me taxi over some rough ground and advised I was lucky not to get a prop strike. …. New tail wheel pilot and I’d not thought of it. Tundra tyres coming btw will fix this.. Advice…..350 dollars well spent.

 

 

 

 

Edited June 15, 2022 by Mike Gearon

[Bosi72]

Maybe installing a large top cowling door would be a simple solution? Then open it every time after landing.

From memory to check oil on Foxbat I had to remove whole top cover, then finicky process to put it back 

Installing a door would help with oil checks, and also cool engine bay much faster.

Installing a couple of temperature sensors would help too.

Only suggesting ideas.

[IBob]

Mike Gearon, I don't know what the stats say now, but it used to be that a significant proportion of forced landings were due to pilot error in not understanding or correctly operating the fuel system of the aircraft they were in.

Some years ago I was at a BBQ in Napier when, to our astonishment, a Spitfire came through fast, low and banked. About 10 minutes later, the same aircraft was down in a plowed field: it transpires that Spitfire fuel must be pumped between tanks, and the pump is engine operated: the engine stops, you've got no way of transferring fuel. Unlikely that he'd have had time anyway, but the reason for the crash was fuel exhaustion with fuel still onboard.

And somewhere in outback Australia there is a twin whose pilot lost an engine, then lost the other perfectly good one because he hadn't read the fine print saying not to put on multiple fuel pumps.

 

So, those and other events, I've taken a special interest in the detail of my own fuel system, which is exactly as spelled out in the Rotax link within your link above:
http://forums.matronics.com/files/912_fuel_fig_54_941.jpg

but with the addition of a receiver tank taking fuel from the wing tanks, as mentioned previously.

 

Regarding the conversation in your link, I think if I experienced heat related fuel pressure problems in normal flight (and that could not be fixed by changing pump and filters) I would be looking very hard at ways to reduce the heat on the fuel system. And while I would be adding a fuel return if that was not fitted, I would not be relying on that to fix the problem.

 

Regarding my Plane Crash YouTube links above, the pilot has not thought it through. The reason his fuel has gassed in the pipes is the elevated temperature in the engine compartment. Ideally, his fuel system should have a return that moves that gas, and the heat it contains, out of the engine compartment (as per Rotax recommendations), replacing it with cooler fuel. But what he has put in is a short loop that simply recirculates gas and heat under the hood, because somebody has told him this will fix the problem. That's what's called magical thinking.

 

Finally, since I wrote 'detail': note the fine fuel filter before pump and return etc in the Rotax recommended fuel system. This prevents not only carburettor jet blockage, it also prevents blockage of the orifice in the fuel return, and ensures the pressure relief bypass in the electric pump seats properly.

Edited June 15, 2022 by IBob

[Garfly]

 

2 hours ago, Bosi72 said:

Maybe installing a large top cowling door would be a simple solution? Then open it every time after landing.

From memory to check oil on Foxbat I had to remove whole top cover, then finicky process to put it back 

Installing a door would help with oil checks, and also cool engine bay much faster.

Installing a couple of temperature sensors would help too.

Only suggesting ideas.

 

The French flyer Frédéric Peuzin who writes a blog and has a YouTube channel about his Jodel (SpeedJOJO) adventures, came up with an automatic tilting door for the top of his cowl:

 

 

He describes it here:

 

https://speedjojo-blogspot-com.translate.goog/search?updated-max=2019-02-01T18:21:00%2B01:00&max-results=2&start=27&by-date=false&_x_tr_sl=fr&_x_tr_tl=en&_x_tr_hl=en&_x_tr_sch=http

 

 

And it can be seen in action here:

 

 

Edited June 15, 2022 by Garfly

[kgwilson]

The real problem is that the design of the Rotax has put 2 carburettors in virtually the hottest place they could have chosen.

[IBob]

17 minutes ago, kgwilson said:

The real problem is that the design of the Rotax has put 2 carburettors in virtually the hottest place they could have chosen.

Yes, you keep saying that, kgwilson, and nobody is disagreeing with you.

 

We are talking now about the solution......which for many thousands of happy users does not involve buying a different engine........)

[IBob]

1 hour ago, Garfly said:

 

 

The French flyer Frédéric Peuzin who writes a blog and has a YouTube channel about his Jodel (SpeedJOJO) adventures, came up with an automatic tilting door for the top of his cowl:

 

 

He describes it here:

 

https://speedjojo-blogspot-com.translate.goog/search?updated-max=2019-02-01T18:21:00%2B01:00&max-results=2&start=27&by-date=false&_x_tr_sl=fr&_x_tr_tl=en&_x_tr_hl=en&_x_tr_sch=http

 

 

And it can be seen in action here:

 

 

 

Garfly, that's a really nice innovation!

 

Also sort of mesmerising footage: they're certainly flying through the hills, not over them!

 

I know another user here who always pops his oil filler hatch after landing. In his case he is concerned about the possible effects of heat on the ignition modules (as the earlier ones had a history of failing over time).

[Garfly]

1 hour ago, IBob said:

 

Garfly, that's a really nice innovation!

 

Also sort of mesmerising footage: they're certainly flying through the hills, not over them!

 

 

Yes, he loves his mountain strips in the SW of France.  You can clearly see his little trap-door operating in this one posted just a few months back:

 

 

 

 

Then there's this classic from a few years back at La Salette (posted here before). 

The Skyranger is owned by Fred's uncle.  All three generations of his family are totally into flying.

It's his son doing the amazing drone cinematography for this one.

 

 

 

 

[Old Koreelah]

Beautiful countryside. Pilots obviously have great faith in their engines.

[IBob]

Really enjoy that footage.

And that's really cleaned up and fast for a Jodel. Very small air intakes......