more data- PULP98 and AVGAS and det and vapour lock

[facthunter]

Lead gave a lot of scope for higher power to be safely produced after the late 20's. The new fuel replacements are hardly likely to equal the Lead 130/145 engines EVER. Pre ignition and detonation ruins motors. Piston engine reliability is way behind the Turbine equivalents by about a factor of 10 x. Engines need direct cylinder injection for safety.  (or run lower powered ).    Nev

[skippydiesel]

1 hour ago, kgwilson said:

A lot of them don't have to use Avgas. During the debate in the US there was a study done & they found over 80% of the US fleet of piston powered aircraft could run on unleaded fuel. Most don't because of ignorance or availability. Now with the Gami approval hopefully that will change. It needs to here as well

Read my earlier story (no facts provided) of the RR (Continental) owner who went through 2 engine recons, he feels solely due to using ULP and has reverted (happily) to AvGas.

 

Will any unleaded  aviation fuel even come close  to the cost of  ULP? - I doubt it. Even if it did, my observation above stands - why tool around in a gas guzzler when there are viable & fuel efficient alternatives?

 

 

[old man emu]

14 hours ago, skippydiesel said:

the RR (Continental) owner who went through 2 engine recons

That is most likely explained by the fact that Continental has only begun fitting hardened valve seats in recent years. Pre-2019 engines would not have them. What information do we have about ULP in Lycomings? But then again, when did Lycoming start fitting hardened valve seats? 

 

This Mogas/Avgas question has two prongs - the effect of removing TEL on exhaust valves and valve seats, and the effects of surface tension on evaporation of the liquid.

 

The effect of removing TEL has long since been solved. Just look out at the traffic passing by. Almost all the petrol-powered light vehicles you see are using unleaded fuel. When I had the engine of my 80-year-old motorcycle reconditioned, I had hardened valve seats fitted and run it on 91 non-ethanol fuel.

 

For aviation, the problem is the difference in surface tension between the two types of fuel. Surface tension determines how readily a molecule in a liquid will cross the boundary between the surface of the liquid and the atmosphere above. In general terms, a less dense liquid has a lower surface tension that a denser one. Mogas is less dense that Avgas, so it has a lower surface tension and will evaporate more readily when subjected to the same conditions of temperature and  atmospheric pressure.

[RFguy]

I'm in the process of buying an Archer. The 8.5:1 Lyco has a MOGAS STC, which sort of surprises me because I would have thought that only 7:1 Lycos  would tolerate the ULP quality issues.  So they must be tough......and 8.5:1 isnt all that high.

The engine is originally factory specified for 91/96 MOGAS (~ 91AKI)  which is something like (AUstralia) 94RON from memory (will check) 

 

but the heads do get hot.  enemy #2 of course is the higher vapour pressure. but clearly, with STC issued,  not seen as too much of a Vapor lock problem , as least evidently... low wing, aux fuel pumps . maybe in warmer weather if you do not use the fuel pumps on takeoff there is a low pressure in the lines == vapour bubble issue which could cause trouble at the wrong moment just after takeoff...  Potential for trouble also at high DA.....It might be something I only use in winter..... .

 

See my earlier posts of symptoms of vapour in the fuel lines- cycling fuel pressure over 20-200 seconds

 

I'll dig up the STC and take a read to what was done. and if there is any specific placarding. And remember MOGAS does NOT mean 'automotive bowser dispensed'.....

Edited March 6, 2023 by RFguy

[skippydiesel]

With no professional knowledge/scientific evidence -

"

For those of us (I suspect the majority in Australia) operating below 10,000ft the issue of lower vapour pressure in ULP can be  managed  ie its a mountain out of a molehill".

 

As for winter/summer fuel, surely this is a potential problem for those operating out of a small area in the south east coast hinterland (Snows/Canberra/ etc), possibly a few high spots in Vic and of course the frozen Tasmanians. I have very little Canadian flying experience, bit more with road vehicles however the use of winter/summer fuels (& oils) is just part of the culture - nothing to get worked up about.

 

Fuel vaporisation is principally a hot day phenomena of aircraft on the ground - not in flight. Yes it can impact the engines power delivery on initial TO BUT if the pilot is aware of the possibility , he/she can have strategies a to A minimise the chances and B what to do if all efforts to mitigate fail and the engine looses power.

 

Summer/Winter fuel - knowing what area /season you are in, will give you a clue as to what sort of fuel may be in the bowser - act accordingly.

 

This is not unlike the awareness/management we bring to the possibility off carburettor ice

[RFguy]

Dont quite agree, but anyway that's fine.

 by the way,   PULP has a higher vapour pressure. ... not lower,  than 100LL, but I think that's what you meant. 

I have thought a bit more about my (wrong) use of the phrase "sort of surprises me because I would have thought that only 7:1 Lycos  would tolerate the ULP quality issues. " ( with reference to suitability for 8.5:1 compression also for the MOGAS STC) 

 

But the STC relates to fuel of a particular standard.  Then in practical terms, this means probably buying PULP in a drum where  
 there are no quality issues compared to  the variability of running automotive bowser ULP. IE if the PULP you are buying meets the STC standard, then its fine. Buy automotive ULP, and your mileage (and altitude! ) may vary. 

If 95RON PULP  (just ) gets you over the line (min = 94 RON equiv) , then if using automotive bowser PULP, you'd be wise to give yourself some headroom I suspect by using only 98 PULP.  Putting aside potential of adulteration of the fuel....

 

 

Edited March 7, 2023 by RFguy

[old man emu]

One thing I just remembered. Australian petrol is the worst in the world. It is of such poor quality that the European manufacturers of cars don't bother to wage major campaigns her to see their cars.

[skippydiesel]

I have always used 98 RON, when every available , which is most of the time (for the very reasons you suggest) however needs must & I have been known to use no name 95 RON  (despite being a shandy , there was real/imagined power loss) and AvGas (no apparent performance improvement).

 

Yeh! I juxtaposed my vapour pressures - bad habit, in more than one instance. Thanks for the head up.

Edited March 7, 2023 by skippydiesel

[RFguy]

On MOGAS / ULP and flying at high altitude. I was thinking about this with my flying at FL115 with ULP for cruise.

The big issue is the RVP, (Reid vapour pressure)  and the VP.   (RVP is at 40 deg C)

The RVP for AVGAS varies between 38 to 49 kPa. For Australian BP Premium 98, it is listed as 30 to 100 kPa . Many states mandate maximum average RVP of 67 kPa and some lower- 55 kPa  in summer months ( don't store fuel across seasons) .

The air pressure at 3000m is 70kPa (stp)  and ~62kPa at 4000m.  So we are getting into trouble territory for some MOGAS deliveries / tolerances at higher temperatures or high altitudes .. 

Take the temperature down and things look much better.

There are two regions to think about, tank temperatures, which could be high if the aircraft is sitting on the ground all day in the summer, and engine bay temperatures.

In the engine bay, temps are high and the VP may be exceeded just because it is hot, requiring that region to be pressurized with the aux fuel pump. - pressurizing to 5psi (~ 71kPa) using the aux fuel pump will in most cases push the pressure above the vapor pressure if the fuel and prevent vapor bubbles forming between the firewall and the engine fuel pump. Beyond the engine fuel pump, that's deemed 5psi (PA28) , also (is it at all flow rates for your aircraft ?) .   Which brings me to :
To ensure the fuel between the firewall and engine fuel pump stays a liquid. :

a) aux fuel pump may be required at altitude  where DA > VP . 

b) aux fuel pump may be required with hot fuel from the wings at any altitude.

c) Use of a low RVP fuel (AVGAS or summer MOGAS)  may be necessary any time the fuel between the fuel pump  and the carb is > 40 deg C.
 

It's not all bad : The VP does reduce substantially  as the temperature falls . (see graph below) 
But- If the ULP is 'winter fuel' the RVP could be up to 100 kPa. Certainly in the USA. Not sure in Australia, but the data sheet does say 55-100kPa in the Australian datasheet.

For the winter fuel,  the VP at 21deg C is about 71kPa- about fuel pump/ fuel system pressure. Trouble region.

At 10 deg C, its down to around 50 kPa. So there lies an issue - a hot engine bay AND winter ULP - the combination is problematic. I would like to have fuel temperature as well as fuel pressure. 

For low wing aircraft, or  high wing with low mounted collector tank  it needs to be drawn through long tube, reducing the pressure as the system in that region is in tension. Fortunately it is not always hot in these regions of the airframe.   That is UNLIKELY to be an issue unless you are taking off from a high altitude airstrip (or in high DA scenario)  and  have hot fuel in the wings.

If the fuel in the wings is at 40 deg C,  trouble between the fuel draw and the firewall pump is unlikely to occur at DA of below 3000' . 
Fuel suction tension in 2m of 1/4" tube at 55 gph is ~ 13kPa. at 30 gph, 4kPa.  For 7/16ID @ 55 gph 7kPa... so that will increase the  effective DA with the suction component for a low wing. 

 

Conclusion- TO, climb  and land on AVGAS or other low RVP fuel (summer MOGAS)    . Footnote- 100% Ethanol is quite good.....  

 

more useful info
page 40 onwards
https://www.chevron.com/-/media/chevron/operations/documents/aviation-tech-review.pdf

 

Edited July 13, 2023 by RFguy

[Blueadventures]

RF what would the Fuel suction tension in 2m of 5/16" tube at 5 gph, as usual for Rotax installs, be?  

[RFguy]

13 minutes ago, Blueadventures said:

RF what would the Fuel suction tension in 2m of 5/16" tube at 5 gph, as usual for Rotax installs, be?  

bugger all.  0.064kPa. at 9 gph only 0.1kPa
dont forget fuel filter pressure drop, also.   bugger all again at those flow rates.

[RFguy]

Oh and I did numbers for huge gph before
try this instead- I meant litres per hour ....

Fuel suction tension in 2m of 1/4" tube at 55 lph is ~ 1.1 kPa. at 30 lph, 0.25 kPa.  For 7/16ID @ 55 lph 0.05 kPa... 
velocity is only 0.5 m/s at 55 lph at 1/4" ID.

so, bugger all. 
and each 50mm radius 90 deg bend (constant ID) at 55 lph  in 1/4" ID costs about  0.1 kPa.. If the ID in the bend is 4.5mm instead of 6.35mm, drop rises to 0.3kPa / 90 deg bend.   There is probably 4 bends in my system .
 

 

Edited July 13, 2023 by RFguy

[RFguy]

The high vapour pressure numbers of  auto ULP are not all bad though.  You get more vaporization  at  the carburettor, and less fuel runs into the engine as large droplets , so likely better fuel burning- economy and power----  and this is said to reduce engine wear because droplets of fuel don't end up on the walls of the cylinder (killing the oil film)  . On the other hand, more vapourization at the carb leads to higher icing potential . My Lycoming carb is heated/ heatsunk by the oil sump / inlet plenum, so icing is probably more likely initially  before everything heat soaks after 10-15 min airborne.  If doing circuits, that's probably the first couple of circuits.   

[facthunter]

Warm it up properly.  My 7ECA never showed any carb icing. Un vapourised fuel is why you need a richer mixture when cold .It doesn't take long for the cylinders to get quite hot, but about 40 minutes of flight to reach equilibrium temp  for the whole engine. Those engine intake pipes going through the sump causes some sludge build up inside the motor. and lycoming camshafts are at the top where condensation often occurs if the motor doesn't get  hot enough.  Nev

[spacesailor]

Only have " icing " when there's " moisture ' in the sky .

SO SAID my test paper ! .

spacesailor

[facthunter]

Pressure in the Carb bowl has to be considered as any bubbles there can make the float(S) sink and the carby flood. You get bubbles just like when you pop a champagne cork. That lowers the density of the liquid the floats displace.  Injection anyone??  Nev

[Methusala]

Yes me!🤣

[spacesailor]

IS, There such a thing as fully " electrical "  injection , for a two cylinder motor .

spacesailor

[facthunter]

These days Single cylinder 2  stroke motorcycles have it.   Nev

[Thruster88]

4 hours ago, facthunter said:

Pressure in the Carb bowl has to be considered as any bubbles there can make the float(S) sink and the carby flood. You get bubbles just like when you pop a champagne cork. That lowers the density of the liquid the floats displace.  Injection anyone??  Nev

I am guessing slightly more than half the light aircraft fleet powered by lycoming and Continental engines have carburetors.  Cessna 150 to 182, Piper Cubs, PA-28 fixed gear plus lots of others. They fly alot of hours every day out of capital city airports, carburetor faults showing up in ATSB investigation?  Not happening.  

[facthunter]

Because the fuel systems are simple and don't have fuel lines all through the cowl and the carb heating systems work. There's still the odd one or two who get it wrong.  Catches people who don't see it as important. I've NEVER had carb icing problems in any of those planes you mention but I've always used carb heat when there's any likelihood of it being an issue. That's HOW I was taught. Nev

[skippydiesel]

I have about 2 hrs ,C172, flying time in The Okanagan Valley (Rocky's), BC Canada. They were going to let me go up, with two little sons, without an instructor but I insisted on having one (foreign langrage/customs/unfamiliar geography, etc) . Glade I did, I not only had a far more relaxing/enjoyable flight with tour commentary from the instructor, he also taught me two things:

• Carb heat on, just before reducing power EVEY TIME 
• Its good piloting manors, to expedite your exit from the active runway, particularly on a RPT air field - Fly down  the  runway in ground effect, cut power just before exit.

[facthunter]

Pilot's should KNOW which taxiway they will require. IF you slow down but can't quite make it you've heated brakes and wasted a lot of time on the runway. Your comment Skip makes me recall the first trip I did to mascot from Bankstown in an Auster J1/n with an Instructor Keith Robey. The tower slotted me in on 16, but the DC-6B on my tail was too close and my max cruise speed was about that of the Douglass approach speed. It was hard to avoid sending him  around. Nev

[Old Koreelah]

On 17/7/2023 at 6:05 PM, skippydiesel said:

Its good piloting manors, to expedite your exit from the active runway, particularly on a RPT air field - Fly down  the  runway in ground effect, cut power just before exit.

Good point for those of us accustomed to having a quiet runway to ourselves.

I once landed at the start of Gunnedah’s long main strip, then realised I’d have to taxi a kilometer to the exit!
I’d made the normal calls, but noticed a big twin moving out onto the blacktop. Another call and the pilot finally noticed me, with a “gee you’re little!”.

[kgwilson]

They get up to 10,000 aircraft in at Oshkosh over a weekend (this weekend 2023) and the runways have a series of coloured dots on them. You are told which runway and which dot to land on and then get off at the next exit. It is by far the busiest airport in the world for 1 week a year. The rapid fire instructions from the controllers is amazing. Check it out below.