mixing av gas with jet fuel?

[ARGPILOT]

does anyone knows what are the drawbacks of using a mix of jet fuel with avgas?

[morning mungrel]

If you are going to use it in a piston engine then catastrophic damage will probably occur. OTOH, many turbine engines are certified for a mix or even straight avgas in an emergency, usually with some flight limitations and overhaul times. Of course, if all you want to do is burn something down, then any mix will do.....

[411A]

A friend of mine years ago departed KBUR in his Navajo with jet fuel in the tanks mixed with avgas...engines failed and he crashed into the dome of the building in the middle of the Burbank cemetary...no need for a funeral...already buried in the rubble. :uhoh:

[enicalyth]

I can't believe I am reading this. The whole essence of piston engines and jet engines is that they work on different power cycles.

The piston engine is Otto cycle? Recall that at combustion pressure rises immensely for little change in volume. Combustion occurring more or less at top dead centre. Such is the pressure rise that the cyclinder walls are rather thick are they not? Try knocking a hole through with a Coles screwdriver and a hammer. No go.

The jet engine is Brayton cycle? Recall that at combustion the pressure across the burner does not change but something does namely volume. And you can knock a hole through the engine walls quite easily.

Thus you can draw the P-V diagrams for each cycle using this mental picture and it explains why a Brayton cycle can burn anything from cheap naphtha to kerosine so that if it can turn the compressor you get thrust. It is also the reason why Otto and Diesel cycles that produce high near instantaneous pressures on combustion like to have the correct fuel in the tanks.

Whoooweeee. Fill 'er up and let's go.

[No Country Members]

Pedantic I know but Thielert (http://www.thielert.com/) would disagree with you re fueling the otto cycle engine. Just don't put petrol in it!

[barit1]

What's the first thing you think of when you read this? (http://www.ntsb.gov/ntsb/brief.asp?ev_id=20070730X01039&key=1)

:ugh:

[Capot]

OK, possibly fuel, but thereafter, in no special order, water in fuel, mags, X-feed screwed up, mixture settings all wrong, pressure insufficient, there's plenty more, and ah yes, put in some Jet A1 on top of the AVGAS that was in there, silly me, I thought the nozzle was a bit big, and the huge letters on the tanker should have been a clue...

Was the last fill just before that flight? The report doesn't say.

Sorry, I'm not trying to be dismissive, but even with that report I'd be surprised if it's a fuel type mix-up, not because it's not consistent with the report, as far as the brief report goes, but because so are lots of other things and in my book it's quite difficult to put the wrong stuff in an airplane (and not to realise in time if you do) unlike how easy it is with a car.

How many aviation fuel sellers have low pressure Jet-A1 "drop in" nozzles? (Sorry I can't remember the proper name; I mean the same nozzles as used for low-pressure AVGAS hand-filling, or in motor service stations for diesel and petrol/gas.)

[Island Jockey]

As an aside DHC Twin Otter PT6-27 Turbine aircraft have a limitation in the manual that if Avaga is used a Hot Section Inspection is requred within 100hrs.
A Get out of Jungle option!!!

[Dan Winterland]

A lot of jet engines will run on many fuels. Avgas engines won't. Some jet emgines have been clared to run on a variety of fuels - such as the aforementioned PT6. The engine fiteed to the British Army Wasp helicopter could run on may fuels, including Avgas, Diesel and Civgas. The Russian SU25 is cleared to fly on Diesel.

[ahramin]

While it is true that a jet engine can burn just about anything, the fuel system is not designed for avgas. Most jet engines have procedures for burning avgas which limits the amount of avgas burned between overhauls. The limiting factor is often the fuel pumps as they need the lubrication provided by the heavier jet fuel.

The history behind the ability to run avgas in jet engines comes from the US military which required engine manufacturers to include this capability and the procedures for it in case a aircraft ended up at a base without jet fuel.

Kind of an anachronism these days though.

[604guy]

Unless there is something very peculiar with the -27, I think you will find that the limitation is that you are limited to 100 hrs use of avgas through the life of the TBO, not that you have to do a HSI within 100hrs. That 100 hrs is also assuming 100% avgas use, not a mixture. There is a pro-rated formula to adjust the 100 hrs of use according to the mixture percentages but most operators that have to use avgas for any reason don't bother with the formula and just assume 100% avgas in the tanks. Makes for much easier record keeping and errs well on the conservative side.

As well, all other limitations for avgas use (max alt etc) apply.

[Dan Winterland]

The Shackleton Mk3 had two RR Vipers in the outer nacelles to help it get airborne. They burned Avgas.

[henry crun]

The AJ-2P Savage had a single jet engine for added thrust on takeoff, which used the same fuel as the piston engines.

The ones that I saw operating always insisted on having a couple of fire engines close by before starting the jet.

[rigpiggy]

E. Emergency Fuels
(1) The fuels listed in Table 13 are considered by P&WC to be satisfactory for
emergency use only.
NOTE: Unless otherwise stated, the latest revision of the fuel specifications will
apply in Table 13.
CAUTION: ADDITIVES SUCH AS TETRAETHYL LEAD AND PHOSPHORUS
COMPOUNDS, USUALLY COMMON TO GASOLINE FUELS ARE
DELETERIOUS TO HOT SECTION PARTS FROM A CORROSION,
SULPHIDATION AND METALLURGICAL STRENGTH STANDPOINT.
(2) The use of aviation gasoline (avgas) must be restricted to emergency purposes
only. Avgas shall not be used for more than 150 hours during any period between
engine overhauls.
CAUTION: ALTHOUGH DIESEL AND HEATING FUELS ARE CHEMICALLY SIMILAR
TO JET FUELS, THEIR COLD FLOW, VISCOSITY AND FREEZING POINT
CHARACTERISTICS ARE SPECIFICALLY CONTROLLED DURING
REFINING TO A LEVEL GENERALLY NOT SUITABLE FOR USE IN
AIRCRAFT.
(3) The operation of P&WC commercial engines covered by this Service Bulletin on
fuels other than the approved Jet fuels is not permitted without the express
permission of P&WC. Specifically excluded, as possible alternate of emergency
fuels, are such products as automotive gasoline, diesel fuel, heating fuel or any
combination of these products with Jet fuels.
PRATT & WHITNEY CANADA
SERVICE BULLETIN
P&WC S.B. No. 1244R18
Jul 24/75 PT6A-72-1244
Revision No. 18: Feb 14/2000 Page 15 of 16