Fuel Pumps

[skippydiesel]

1 hour ago, Thruster88 said:

Good info Glen. 

Skippy the concern with your low fuel pressure is the cause. If it is due to some restriction in the supply to engine pump then you will be at increased risk of vapour lock at altitude. In Glens case the PA-28 has large fuel lines and would have been burning only 30 lph, not much difference to the 27lph for a 912 @100% power.

I take your point about fuel line losses due to constriction & friction. To a large extent this has been addressed by enabling the Boost pump to draw from the Header tanks. In practice this will mean using the Header (rather than Wing tanks) for TO/CO. The Header is right behind  & slightly higher than the engine, so has the combined benefit of a shorter delivery line and a bit of gravity, to assist in fuel flow.

 

I have never seen any where near 27L/hr on my two Rotax 912ULS engines. Yes that's what Rotax specifications say for max power ,however I think a real world figure might be more like 24 L/Hr

[skippydiesel]

11 minutes ago, onetrack said:

Don't forget that unions and elbows in fuel lines provide increased flow restriction. 90° drilled elbows are notorious for flow disruptions, swirls and cavitation.

Thanks for that OT.

 

I have gone to considerable trouble & expense to try and make all my unions/bends high flow.

 

Most of my fuel line fittings have come from Aeroflow Performance   . https://aeroflowperformance.com/pub/media/external/downloads/cataloguev13.pdf

[facthunter]

Glen, you really should not be trying to run on MOGAS at FL120. IF you were cold soaked you might do a bit better but that takes time at height. .    Skip, there will be lower pressures on the inside of small radius bends no matter how smooth they are. Nev.

[BrendAn]

On 22/09/2023 at 7:33 AM, Thruster88 said:

These pumps can produce about 4 bar or 60psi. If the receiving fuel tank became full or there was a blockage in the vent system the tank would most likely burst. Not good.

Why would you be flying with blocked vents. Even 6 or 7 psi could problems then.  

[skippydiesel]

57 minutes ago, facthunter said:

Glen, you really should not be trying to run on MOGAS at FL120. IF you were cold soaked you might do a bit better but that takes time at height. .    Skip, there will be lower pressures on the inside of small radius bends no matter how smooth they are. Nev.

 True! But its all about doing the best that you can with resources available eg two 90 degree fittings one high flow, one not.

 

[Thruster88]

45 minutes ago, BrendAn said:

Why would you be flying with blocked vents. Even 6 or 7 psi could problems then.  

If you check your vents before every flight that is great, probably not everyone does. We have insects in this area that can block holes 2-10mm very quickly with mud. 

[RFguy]

2 hours ago, facthunter said:

Glen, you really should not be trying to run on MOGAS at FL120. IF you were cold soaked you might do a bit better but that takes time at height. .    Skip, there will be lower pressures on the inside of small radius bends no matter how smooth they are. Nev.

Hi Nev

and I have learned  this.... I knew it might be a problem, ffrom calcs - and so it was.... and it was a warm day.... The math said it would be a problem somewhere over 11,500' PA, and it was  when >  FL120....  
at a PA of 12,000 feet, the air pressure is 65 kPa, WELL within the MOGAS  RVP  seasonal range of 55 to 80 kPa...... (avg approx 65kPa at 35degC)
AVGAS is 40-50.
so, if the air pressure was the same as the 35degC RVP, it would not take much suction to get vapour. (noting that the RVP reduces substantially at lower temperatures lessening the issue as you pointed out Nev with cold soaked tanks) .   Not seen any issue at all at FL115 so far.
Note that some manufacturers have wider ranges of RVP  of their unleaded petrol than others, for whatever reason. BP says 30 to 100  (20 deg C),  Shell PULP98 55-80 (37.8C), United98 27-80 (20 deg C).
here are a collection of datasheets. Probably a good reason to avoid leaving MOGAS lying around, also, since the suppliers increase the vapour pressure for winter. (dont use it in summer)

Fuels, Safety Data Sheets, Suppliers - Dry Lakes Racers Australia

WWW.DLRA.ORG.AU

---

The official home page of the Dry Lakes Racers Australia

 

Edited September 23, 2023 by RFguy

[facthunter]

ALL  correct. The only engine you SHOULD run mogas in is the Rotax  9xx because  the valve seats run too cool for the lubricating action of the tetraethyl Lead to work normally and it can build up and fall off  parts of the seat and you lose compression and MAY cause seat and/or valve  damage. . . There's also the equivalent OCTANE figures. The AVGAS one is higher and has a lean and rich figure. Like the now unavailable 130/145 that was used on the Larger motors universally. . Leaning lowers octane. and Mogas can vary a lot and is not certified when straight from the usual pumps. You really are not certain of what you are getting. Your OAT standard lapse rate is close enough the 2 degrees C /1,000 ft where water could freeze in the fuel at your higher levels, and you could also be exposed to hypoxia and COLD your self.  A cold soaked airframe can accumulate ice from  descending  with the skin temp putting the water vapour to below it's dew point AND below freezing temp.   Nev

[RFguy]

It is a good point about water freezing in the fuel lines, Nev. Fortunately, the Piper has good fuel sumps and I've never seen any water in them ever. (never say never ) .   It's certainly always below 0  up there. 

Good point also about wing skins being cold. If I descended through a humid region, or cloud, that's something to consider. 

 

I still affirm for long pt to pt flying , flying low is TAS on the table. (FL125 is 123 kts TAS for 100 knots indicated which I can do)
Interesting though what happens with the east west winds up there, going west, almost always better being down at say 8500 or 6500 with the headwinds. 8500 is a reasonable compromise. up high, bumps are less, radio coverage is better and options are better for engine trouble (unless u have a fire...)  glen (PS:  left tank always AVGAS and used for TO and landings, right tank ULP98 when available outbound) 
 

Edited September 24, 2023 by RFguy

[Old Koreelah]

Glen that’s very similar to my practice, but to remember which tank, I use:

RH (Right Wing Conservative) tank for AvGas and LH (Left Wing anti-Lead pollution Greenie) tank for Shell 98.

[skippydiesel]

53 minutes ago, RFguy said:

PS:  left tank always AVGAS and used for TO and landings, right tank ULP98 when available outbound) 
 

Hi Glen,

 

I have zero experience with ULP in what would normally be an AvGas engine however I pass on the following;

 

I have a  friend who flies a 100 hp RR (Continental?). He switched over to ULP (STC). Engine ran fine until it got valve problems (not sure what - stems / seats?). Got it all fixed up - same story repeated $$$$$$. He has gone back to 100% AvGas and not a problem since.

[RFguy]

some engines are good for no-lead, some are not. 

many have had no-lead suitable seats and guides fitted during overhauls in their 50 year life span.....

 

[facthunter]

Lead only affects the seats. If your guides are gumming up it's most likely an oil additive. The guide and valve stem metal  should be compatible or they will Gall and wear out in no time. Nev

[BrendAn]

i was speaking to a bloke about his avro biplane and he told me he uses unleaded because his radial was made before lead additives were introduced. and if he runs avgas it builds up lead depsoits in the bottom cylinders.

[facthunter]

Lead came out in the Late 20's,  If it's the Avro I think it is the engines, Armstrong Sidderley, overheat here and often run on a few minutes after shutdown from glowing deposits. I've seen them do it at least 5 minutes after shutdown. No one in the plane.   Nev

[facthunter]

The Gypsy Major 1-c had bronze cylinder heads and couldn't use TEL as the seats would part weld to the valve seat and attempts on those days to Insert them were not reliable. The bigger version 10 Mk 2 DeHavilland had alloy heads with inserts and 145 HP.  Now you can Insert the Bronze heads successfully with high nickel seats and liquid nitrogen to shrink them.   Nev