more data- PULP98 and AVGAS and det and vapour lock

[RFguy]

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

 

takeaways  if you dont get time to read the 59 pages comparing central US winter PULP and AVGAS 100LL, and then spend time examining Australian fuel data sheets ---

My takeaway-

use AVGAS 100LL in summer over PULP if tank temps are over 30 deg C  and below 45C.

add some Decalin Runup additive if you dont want lead buildup in low temperature (Jabiru, Rotax) engines.

 

0) Vapour lock and detonation was not detected using AVGAS 100LL.

0b) Winter PULP with higher vapour pressure is a significant issue  for vapour lock, especially if it is purchased in winter  and used in summer..... and due to altitude effects, may be problematic without fuel lines under pressure.

1) vapour lock in the fuel lines generally shows up as cyclic fuel pressure indication over the course of 20 sec to 120 secs as fuel percolates in the lines and is removed.

2) vapour lock is most likely just below and at the minimum boiling point of the fuel. High fuel tank temperatures 10deg C above the boiling point  are less trouble that just below because the volatile compunds have been evaporated off and the vapour pressure drops (desirable) .

3) operation of fuels around their boiling point is unwanted. Airplane with PULP sitting out in the hot sun all day = bad. Probably worst case scenario fpr PULP since high Australian  ambient temps are similar to the boiling point.

4)  vented storage 'stale'   PULP reduced tendency to vapour lock, even though the RVP wasnt substantially affected. Octane increased slightly with vented / stale PULP.

5) changing throttle settings when vapour lock is encountered doesnt help much- the problem is a fuel delivery issue.

6) For PULP, Detonation is more severe with low humidity and high engine temps. 

FYI - recommended max RVP for aircraft (source : aircraft mfr : 49 kPa)

AVGAS 100LL : (Australia) RVP 45kPa (39-49 max range) , 10% distilled at 75 deg C, IBP(initial boiling point) : >42C.

PULP98 : large range RVP 45 -100 kPa  (typical : 60-80 depends summer/winter) ,

Typical Australian fuel  : 10 % distilled at 49 deg C. IBP ~ 32 deg C

 

 

Edited February 4, 2023 by RFguy

[kgwilson]

No issue if you push fuel to the engine rather than trying to suck it through. It was 38 deg on the ground on Friday. Started the 3300A without choke  after 10 second electric pump. Pump off & no problems during the flight. Then again fuel from my main tank is gravity fed to the engine. Used the electric pump for TO & landing only. Altitude is the issue if you suck fuel through.

[RFguy]

agreed.  I am going to buy a Piper, selling the Jab. many reasons . Piper sucks fuel of course . I was reading up on the Piper MOGAS STC. which seems good for the 7:1 compression engines. 

Edited February 5, 2023 by RFguy

[Kiwi]

[kgwilson]

The 140 was underpowered for sure. Even the 160HP Warrior is marginal in my opinion. The Cherokee Archer 2 (PA28-181) 180HP I flew for 20 years was about right & I could get in & out of fairly short grass fields easily though not with 3 Pax, baggage  & full tanks. The Dakota though with its O-540 235HP engine & CS prop was the best for sure but sucked about 48-52 lph of fuel

Edited February 5, 2023 by kgwilson

[RFguy]

depends how many you have in it. I'm looking at ARcher1 / challenger, but also 140s which are fine for two place airplanes..  not looking for a short field plane... I'll get a savannah / Cygnet / for that. A 19- build anyway....

[kgwilson]

47 minutes ago, RFguy said:

agreed.  I am going to buy a Piper, selling the Jab. many reasons . Piper sucks fuel of course . I was reading up on the Piper MOGAS STC. which seems good for the 7:1 compression engines. 

A survey done a year or so back regarding the then imminent release of GAMI Unleaded Avgas found that 86% (from memory) of all GA aircraft in the US could already run on unleaded fuel & it was just certification issues that were holding things up.

[RFguy]

I'll be tripping over my beard by the time we get unleaded AVGAS...... I'll finished refurbing this late  Gen3 engine (300 hours)  . clean & dye pen check  the pistons,  new rings, hone bores, clean/shim heads from recession, clean out the valve guides. done.  unless someone wants the rotax conversion or the LCH. plane is probably worth most in 24- condition but getting best prrice is not really an objective. 

[pmccarthy]

I bought PULP 98 yesterday from my local BP. Calibrated plastic jerry cans. Bowser said 10 litres, jerry can said 9.6, it was a cold day. Experiment repeated for a total of 90 litres in the ten and four 20 litre jerry cans, I paid for 94 litres.

[kgwilson]

My 20 litre Jerrycans hold 24 litres. I doubt whether the 9.6 litre mark is very accurate on a plastic Jerrycan. If you leave one with some fuel in it & plenty of air with the caps tightly sealed it will blow up like a balloon in the Summer heat. It will eventually return to more or less its original shape but it will still hold a bit more.

[pmccarthy]

This was my brand new 10 litre tuff jug, which is well calibrated. The other 20 litre plastic ones have a 20 litre mark, they have never blown up. I think the servo calibration is wrong in their advantage.

[old man emu]

4 hours ago, pmccarthy said:

I think the servo calibration is wrong in their advantage.

I don't think that you are very wrong in your thinking. Fiddling with the display on pumps has been going on since the replacement of the manual pump with at least the computing pump in 1935.

It is amazing that the State government bodies responsible for weights and measures in commerce don't get about the place testing pump meters. So here comes the conspiracy theory: If a servo charges for more fuel than it actually purchases from the supplier, it collects more money. From the money paid for the difference (Litres on the meter - litres actually delivered), the servo pays 10% to the Federal government as GST, and keeps 90% for itself. The Federal government returns a portion of that GST to the State. Therefore the State profits from the deception.  Approximately 646.1 megalitres of fuel oil were sold in Australia in the financial year 2021. That's 646,100,000 litres. At one cent for every litre charged for, but not delivered, that's $646.1 million dollars. Imagine what the servos are making.

 

If you want to get a rough check of the accuracy of the servo's pump, take note of the machine's true delivery metre before and after you get fuel. The meter is like a little HObbs meter and should be visible through a glass-covers slit on the  face of the pump

 

For added trivia, here's a link to the history of the bowser fuel pump  https://aoghs.org/transportation/first-gas-pump-and-service-stations/

[kgwilson]

Servo fuel pumps are supposed to be calibrated and checked regularly so if you suspect one is crook you should make a complaint to 1, the Srvo and 2,the government agency who carries out calibration and compliance checks. First check the jerrycan to make sure it is correct. 1 litre is 1 cubic decimetre. 1 litre of water weighs 1 kilogram at 4 degrees celsius.

[RFguy]

expansion when sealed could permanently  add quite a few cubic centimeters to the volume.   I wonder what type of plastic is used.
I would expect all servo meters to be within 2%, surely ???!!

[Carbon Canary]

Plastic jerry cans are usually constructed from HDPE which has a relatively high thermal expansion coefficient.

[Bosi72]

it also depends on time of the day. Early morning refuelling when the temperatures are lower should be more accurate than late afternoon when the tanks/pumps are warmer.

[RFguy]

OK, so HDPE has an expansion coefficient of around 12 ppm/K. varies a bit depending on constitution.

volume change will be the cube of that 1728ppm/K...... (IE about 1.7% per 10 deg C) ..... gasoline volume about 950 ppm/K. if the gasoline is experiencing vaporization at elevated temps,  I guess there will be additional gas pressure 

Glass temperatute is around 75 deg C.

[skippydiesel]

Great topic - to carry it a little further -. I did the initial fuel tank calibrations, on my Sonex, during our winter months (day temps max 15C). Recently rechecked - now summer temps (25-27C) - no way I could get the same volume of fuel into the tank. I always knew this but was still surprised at the change. I actually changed the metering to reflect the (lesser) summer volume, as this will be a more conservative fuel quantity than the reverse.

[Carbon Canary]

1 hour ago, old man emu said:

I don't think that you are very wrong in your thinking. Fiddling with the display on pumps has been going on since the replacement of the manual pump with at least the computing pump in 1935.

It is amazing that the State government bodies responsible for weights and measures in commerce don't get about the place testing pump meters. So here comes the conspiracy theory: If a servo charges for more fuel than it actually purchases from the supplier, it collects more money. From the money paid for the difference (Litres on the meter - litres actually delivered), the servo pays 10% to the Federal government as GST, and keeps 90% for itself. The Federal government returns a portion of that GST to the State. Therefore the State profits from the deception.  Approximately 646.1 megalitres of fuel oil were sold in Australia in the financial year 2021. That's 646,100,000 litres. At one cent for every litre charged for, but not delivered, that's $646.1 million dollars. Imagine what the servos are making.

 

If you want to get a rough check of the accuracy of the servo's pump, take note of the machine's true delivery metre before and after you get fuel. The meter is like a little HObbs meter and should be visible through a glass-covers slit on the  face of the pump

 

For added trivia, here's a link to the history of the bowser fuel pump  https://aoghs.org/transportation/first-gas-pump-and-service-stations/

I didn't want to feed the conspiracy theory, but servo pumps can be out, but usually not many, and not by much.

 

Are your Pumps accurate? NMI inspectors visiting sites in the wake of increase in pump inaccuracy – ACAPMAg

[facthunter]

RFGuy the Cherokees do have some corrosion issues. They are nowhere near as good in the proofing as the Comanche's were. The rear inner spar just forward of the flaps is where to look HARD. You really have got to get in there to do it right. Had a look at a Decathlon? Nev

[RFguy]

Hi Nev. Decathlon no. But now I've read about 150 pages all up of Piper maintenance logs from from a dozen airplanes the past month, now taking a closer eye. 

 

I am getting so know what goes on. There are planes that are 'let go' then need ALOT of work in bursts , there are planes that continuously get fixed up as they need , and there are planes that just seem to be unlucky. Most of these 50 yo airplanes have lived  in various places by now, both  inland and by the sea.  Theer was an AD a few years ago which required an inspection cover be put in to get a good look at the wing spar  etc.  Leaking baggage doors seems to be common (on those with the baggage door) . and I now understand all the different models..... The newer instrument panel layout came in in 1969, for example.

 

 

[kgwilson]

I am sure that there was an AD on certain Pipers regarding corrosion somewhere in the main spar. It required a full strip and inspection. I am fairly sure but not certain that this did not affect any of the PA28 models.

[onetrack]

Fuel delivery measurement from bowsers is supposed to be measured and calculated at 15°C. In Europe, some countries have instigated STA - standard temperature accounting, for fuel delivery.

STA introduces a temperature correction into fuel delivery to correct it to 15°C, which means much more accurate fuel delivery to the customer. But the Govt and oil companies here in Australia do not use STA - for obvious reasons.

 

The Govt relies on occasional and random flow checks on bowsers to ensure fuel users are getting what they paid for. The authorities rely on service stations and oil companies to check their own fuel metering accuracy.

But in the limited number of random checks carried out, nearly 5% of servos are cheating fuel users on the amount of fuel they're getting - i.e., shortchanging them.

 

Naturally, if you buy fuel on a hot day with a stinking hot forecourt and hot bowsers, you're not going to get the amount of fuel you think you're getting. Conversely, buying your fuel when there's ice everywhere, means you will gain a small advantage in the quantity of fuel delivered. The fuel is normally delivered from underground tanks that are at a pretty constant 15°C, but the lines and pumps heat up in very hot weather and expand the fuel.

 

U.K. advice re STA - https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/283253/laymans-guide-on-sta-measurement-v2-march_2011.pdf

 

Australian fuel retailers fined for inaccurate fuel delivery - https://www.industry.gov.au/news/fuel-retailers-fined-after-being-caught-short-bowser

[RFguy]

it's a tough problem. . I cant imagine that heated up fuel lines on the surface would stay warm for long with 15deg C fuel flowing , though.

 

so we should buy fuel on weight ? that's problematic also !  We need real time analysers in our cars so we can pay based on octane and energy density ,....

 

ONETRACK- I read the limit is 0.3%..... I would like to have seen a histogram of the problem. (IE std dev, outliers etc) 

 

Most Piper ADs are well sorted, there are the continuing ones of course. No more 24- LSAs for me.... 19- and VH &  VH-exp.

Edited February 6, 2023 by RFguy

[Jabiru7252]

36 minutes ago, kgwilson said:

I am sure that there was an AD on certain Pipers regarding corrosion somewhere in the main spar. It required a full strip and inspection. I am fairly sure but not certain that this did not affect any of the PA28 models.

Back in the early 90's I flew VH-ASV a Piper PA28. One day a storm cam through and flipped it over. I said to one of the instructors that I really enjoyed flying that plane. His reply was "Well, the main spar was corroded so it's no great loss". I was a little freaked out that I was flying a plane with a rotten main spar!!!