There's low cloud in the morning, then rain, then snow. And of course that's the point at which the client needs me to run the airplane for another computer upgrade. We go out to the airplane. The engines were run for about ten hours yesterday (yes, my co-worker worked his tail off), so after I pull off the engine tents I check the oil. And indeed it's down a quart each side. I grab a couple of bottles and a funnel out of the nose compartment. The wind is making it really cold out here. And it's ironic that two days ago in 25 degree weather I was running less viscous 15W50 oil, but now that it's minus five or so, before the wind chill, I'm trying to get W100 to run out of the little bottle into the crankcase. As I hold the bottle and wish the oil would hurry up, the wind is driving snow into my face.
After I've added a litre to each engine and removed the engine plugs, there is snow and ice caked on my toque and gloves. I pull them off after I climb on board to start up. I can't run the combustion heater on the ground for extended periods, so I'm running an electric heater plugged into the aircraft AC. It's a perfectly normal socket, like the ones in your wall if you're in the US or Canada, but it only works when the airplane is on the ground plugged into an extension cord. It is, but after forty-five minutes or so (yeah, this upgrade isn't going well) that plug comes out and it starts to cool off in here. Plus after another half hour goes by (did I mention that the upgrade is not going well) I run into another problem: I'm running out of fuel.
My co-worker landed last night with minimum legal fuel, and then ran the aircraft on the ground for an hour, and now I've run it for more than another hour. Fuel consumption is less on the ground than at cruise, but it's not none. And I have to run it higher than idle to meet the power needs. They aren't finished yet, but I have to shut down and refuel. There's another reason why I want to refuel sooner rather than later, and that's that the fuel tanks are due to be refuelled today, and we won't be able to buy fuel during that transfer. The FBO manager is here, so he fuels. I don't really have to, but I stand out in the snow with him as a gesture of solidarity. I also want to be here to see how much goes in each tank. I confirm that they were all almost dry after running that long.
He pushes the plane back into its space and I reconnect the heater for another marathon session of wrestling with the computer. There's a bad smell from the heater, though, so we disconnect it. While we're doing this, a tanker truck arrives to refill the avgas tank. We got ours just in time. It finishes and moves on to the Jet A tank and finally I'm cleared to shut down.
As we're on our way back through the FBO to the parking, the tanker truck driver is billing the FBO. I ask how much fuel went into the avgas tank and it's about a week's worth for us. The manager knows this, so it isn't very difficult to get free hangarage for a couple of days. That saves us from having to worry about the computers freezing.
You've mentioned in a couple of posts that the client has to upgrade the S/W on the gear. So, that implies it's their gear.
More or less knowing the kind of work you're doing, I'm surprised that different customers can swap out gear and it will still work in the plane. The planes I've seen seem rather specialized for the mission at hand.
It could be that the customers are all doing the same thing - each with their own gear. But, I would have expected that different customers would use you for different missions types. Similar profiles maybe, but different outcomes.
(Hopefully that makes sense. Trying to be vague and yet specific at the same time is difficult.)
I don't know about planes, but a fourstroke car or motorcycle that would burn so much oil in a day would be broken, not to speak of the fouling caused in the cylinders and cake on the piston/sparkplug.
Are aircraft engines designed that way or is it old age?
You wear a toque? That is so cool. Julien.
They have mixed fuel tanker loads ? In UK that is seriously "verboten" . As a matter of interest how many storage tanks does this FBO have ? Again UK practice is for 24hrs "settlement" after every delivery - so a single storage tank would entail a 24hr out of service period - yet your post seems to indicate there is only one tank at least for the jet A1 - is this normal practice ?
I'm curious why the engines must be run to test the computer equipment in back. Apparently the ground power bus can't be used to do this...? Seems like it would be a useful modification.
Curious minds want to know... and nosy ones too.
GPS_direct: We run two different types of system, which can be changed out, or removed altogether so the airplane can "pass" as a normal one. There are cables all over the interior of the airplane. It's not all built-in.
Anonymous: A litre per engine in twelve to fourteen hours is fairly normal. Twice that is still within the manufacturer's tolerance.
Julien: I even took a picture of the snow-encrusted toque. I'll post it sometime.
Dafydd: I assume that one of the tanks you see there was avgas and the other Jet-A. I've never seen an operator observe a settlement period. The fuel tanks are unavailable during the transfer and then when the truck pulls away the airplanes pull up.
gms: You snuck your question in while I was replying. The aircraft battery is nowhere near large enough capacity to run all the equipment. It's not just a couple of laptops. The "why didn't you use a GPU?" question will be answered in an already-queued blog entry.
Anonymous -- The operational profile of an aircraft engine is different enough from a car engine that you get some interesting behavior. The thermal and barometric environments are different, as well as the operational profiles. Some engines are (relatively) low compression and "leaky" compared to automotive norms. And some operate for extended periods of time at speed and lose oil through ordinary consumption.
It's a complex issue to address fully in a blog comment, but here's an interesting modality of loss: aircraft operate in an environment of lower air pressure than your car (typically). Thus, the pressure difference between the crankcase and the outside world is higher at altitude. Thus, the breather tends to eject more oil vapor in a plane than your PCV would in a car.
And then there's turbocharging ...
@Anon / @dpierce;
And then there is the different usage profile
- a/c engines are built to drone along at 65% power (or higher) for hours, where an auto engine on the freeway is working at slightly more than an idle,
- a/c engines are air-cooled, resulting in a very wide range of temperatures during operation. Auto engines are liquid-cooled, and run at a very even temperature during all phases of operation (except winter morning startup). A/C engines are, as a result, "looser" and will tend to burn more oil as a result,
- a/c engines are inspected constantly, including oil-level checks before every flight. Auto engines have to use virtually no oil - aside from the marketing reasons so important to the shint sheet-metal companies, if an auto engine burned oil like an a/c engine then there would be oil lights on all over the world - since virtually nobody (including self) ever checks the oil level in their car. I change it every 5,000km (the book says 8,000km), and ignore it inbetween.
My chief pilot once took on a load of avgas that was contaminated by Jet-A. Fortunately it had been a partial fill and there were uncontaminated tanks on which to make a safe return to the airport.
The company, BP, did not acknowledge any responsibility, so we don't buy fuel from them anymore. I imagine there are a lot of people making that decision these days.
Jet-A + 100LL : I thought of this, seeing the picture of the dual tank truck. One for 100LL and one for Jet-A, I presume.
What I fly could not possibly be confused with a kerosene-burner, so even though I like to to be present for refueling that's not the worry. Its the contamination issue. Maybe I should start smelling the sump drains .. and/or doing the "paper towel drop evaporation test" once in a while. I'm not confident I could smell or feel an oily presence.
Effects can be subtle, so I'm curious - what were the symptoms for your Chief Pilot on that flight?
You and the others are correct about oil consumption. For the Lycoming big sixes the max consumption listed in the operators manual is between .7 to .87 quarts per hour (economy or best power respectively). Never flown one that drank that much thankfully. They tend to grenade long before those levels are reached lol. The big Contis should be about the same FWIW.
Aviatrix may correct me on this but based on what I know a slight amount of Jet A with your gas will cause the cylinder head temps to skyrocket out of control as the engine detonates. This has to do with the different flashpoint and burn temperature of Jet A. Anything more than 20% kerosene the engine will just stop. The worst part is the plane will run at low power 'fine' but once it goes to high power it is game over for the engine.
I'm betting Aviatrix's CP felt something wasn't right, saw the temps going through the roof and returned to the airport ASAP...
Yes, high temps and rough running engines were the indication.
The contamination, if I remember correctly was somewhere between one and three per cent. I don't know how that happens.
It happens because of poor practice - mixed loads is one indicator . The chief problem however is usually water droplets in suspension ( there are always water droplets present ) - this can be combated by the settlement period ) Mostly things run just fine , but when they don't !
I was taught to always pour a few drops of fuel on my fingers when checking fuel drains and then rub my fingers together to detect any oily residues indicative of jet fuel in AVGAS.
The same can be done by putting a few drops of fuel onto a sheet of paper and look for an oily patch once the AVGAS has evaporated.
The theory being that one can detect jet fuel this way long before it modifies the colour of AVGAS in the fuel tester.
Has anyone heard of fuel contamination being successfully detected this way?
How could water droplets cause Jet A contamination? And why are you calling it a mixed fuel load? Do you not see that there are two separate tanks on that truck? This isn't the fuel truck that delivers the fuel to the airplanes, it's the one putting the fuel in the tank that the airplanes are fuelled out of.
Where you are from, would two completely separate trucks make the trip to the FBO, each pulling a different grade? Do they not put the same grade on the same train or boat either?
Where I work, we definitely allow a settling period in the storage tanks after bulk truck deliveries. I suspect this is one of the reasons most tank farms usually have two or more tanks, instead of One Big Tank, to allow settling out and use in rotation.
We also test Jet-A ( and AvGas )numerous times, specifically for both solids and water contamination. In fact, fuel would never make it into an aircraft without being tested at least four times from the point of delivery to our tank farm, to aircraft delivery.
Water tests consist of testing for both "solid" water contamination, as well as suspended water.
I suspect the Jet-A tanks at a lot of smaller airports have had their fuel "settled" at a larger tank farm prior to being delivered to them.
On mixed loads, I know we allow trucks in Canada that have two or more seperate tanks mounted on the same truck chassis, carrying different products.
I'm almost positive that using one tank for Jet-A one day and AvGas the next would be impossible.
The plumbing on into-plane delivery vehicles are permanently marked with grade markings and the filling adapters ( as well as the delivery nozzles ) are non-compatible and grade-specific as well.
Water does not contaminate the fuel per se but does fall out of suspension and can pool to provide an environment suitable for the inadvertant culture of Cladisporium Resinae -the "fuel bug" . In bulk storage this water can be drawn off before issue to tankers or aircraft . It's a complex area and there are fixes but best practice is prevention .
Interestingly these drawn off "water bottoms" have a commercial value - alongside washed off fuel from airfield surfaces captured in traps in the drainage system . Periodically contractors bid to carry away both sources whereafter they are reprocessed mainly as heating oil .
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