BAK Questions Thread

[Romeo Juliet Whiskey]

Hi guys,

 

Started learning my BAK theory last week. I have the Aviation Theory Centre and Bob Tait books which i am working through with a friend. Im sure its going to raise a lot of unanswered questions so i thought Id start posting them here for some help/clarification.

 

Anyway, first couple of questions:

 

1) Can moving the prop with the ignition turned off start the engine? I presume no, unless there is faulty wiring leading to the magnetos sparking.

 

2) Taxing - approaching head on both aircraft pass each other to the right. What happens if you are both on a narrow taxiway and say the grass to the side is very wet?

 

Any help appreciated, Rich :)

 

 

[facthunter]

Any piston motor that has just been shut down may fire up due an incandescant carbon flake or hot valve.

 

Many aircraft can not be taxiied on grass due their weight. If you are head onto another plane on a taxyway in that circumstance, you have a big problem. Nev

 

 

[P4D]

1) Never risk turning prop before checking the electrics are off. Don't ask someone, check yourself, its your arm that's gonna get chopped off.

 

2)Use your radio to communicate when manouvering. Always state your intentions prior to commencing a taxi. (check out compulsory radio calls) Listen out for others doing the same so you can avoid them. Common courtesy would see one pilot "HOLD POSITION " for the other to make clearance on taxiways. (size matters)

 

That way not two aircraft should ever be on the same trajectory. On the ground or in the air.

 

 

[Pearo]

1) Never risk turning prop before checking the electrics are off. Don't ask someone, check yourself, its your arm that's gonna get chopped off.

May I add to that, never turn a prop unless you have been taught proper technique. Even if the electrics are turned off, it will still fire. And even thought the mags grounded, a faulty ground is possible. Never become complacent.

 

 

[Romeo Juliet Whiskey]

Thanks for the answers guys. Dont quite understand though why is it important to have electrics OFF? Doesn't it just provide power to the starter motor? The engine runs without electrics anyway. I would have thought Ignitions OFF is the most crucial step to avoid the prop and engine inadvertently starting up via the magnetos.

 

Rich

 

 

[mnewbery]

When taxiing, the aircraft landing and leaving the runway has right of way over the aircraft travelling towards the runway. Doesn't matter which runway if the airfield is uncontrolled. No idea what the rule reference is but I will find it. Came out of the Berlin air lift I imagine

 

 

[kaz3g]

Treat every prop as live.

 

In normal circumstances you shouldn't find yourself taxiing in the direction opposite another aircraft because you should both be using the same runway. If you do, keep to the right and turn 90 degrees and stop if necessary to ensure the wings are clear of the other.

 

Kaz

 

 

[dutchroll]

Thanks for the answers guys. Dont quite understand though why is it important to have electrics OFF? Doesn't it just provide power to the starter motor? The engine runs without electrics anyway. I would have thought Ignitions OFF is the most crucial step to avoid the prop and engine inadvertently starting up via the magnetos.Rich

This kind of crosses back & forth between theory and practical safety.

Theory: the engine won't fire if it's turned with the ignition switches off (true).

 

Practice: a number of fault scenarios can negate this theory, and it has happened many times in real life. Therefore be very careful.

 

On my aircraft the prop must be hand turned through 9 blades on the first flight of the day to check for hydraulic lock. The engine has never fired, but I double check the switches are off, and turn it as if it will suddenly start (carefully!).

 

Electrics? Well no it shouldn't make a difference as far as whether the engine will fire on magnetos, but some planes have a number of electrically operated systems which, if inadvertently operated on the ground, could hurt someone. Therefore, electrics off when you're not in it (unless you're testing something).

 

 

[spacesailor]

Kaz3g

 

Surely

 

On rnw 36 with a southerly wind scenario.

 

The taxying plane halfway along said rnw , plane heading N & A fast commuter not having to due circuits would be landing head on, being too faraway to hear taxi call from taxi way

 

(I don't seem to be able get this into good English (slow taxying plane and long runway))

 

spacesailor

 

 

[kaz3g]

Hi SS

 

I guess if there is a southerly wind both the commuter and the lightie should use 18.

 

If there is an aircraft already taxiing on 18 that sort of gives the commuter a bit of a clue that it's going to create a problem if he continues with a straight in to the north.

 

If the lightie is taxiing along 36, it already occupies the runway and it isn't safe for the commuter to land.

 

Kaz

 

 

[djpacro]

Hi SSI guess if there is a southerly wind both the commuter and the lightie should use 18.

 

If there is an aircraft already taxiing on 18 .../QUOTE]There are rules wrt this situation.

[Pearo]

Going to change my aforementioned statement,

 

Dont touch the prop until you understand the aircraft systems.

 

 

[Roundsounds]

Hi guys,Started learning my BAK theory last week. I have the Aviation Theory Centre and Bob Tait books which i am working through with a friend. Im sure its going to raise a lot of unanswered questions so i thought Id start posting them here for some help/clarification.

 

Anyway, first couple of questions:

 

1) Can moving the prop with the ignition turned off start the engine? I presume no, unless there is faulty wiring leading to the magnetos sparking.

 

2) Taxing - approaching head on both aircraft pass each other to the right. What happens if you are both on a narrow taxiway and say the grass to the side is very wet?

 

Any help appreciated, Rich :)

Hi RJW, have you started taking lessons as yet? If so your instructor should be able to assist in answering these questions.

 

 

[Romeo Juliet Whiskey]

Haven't started any lessons yet. Waiting to talk to the new CFI at nswair before making a decision whether to go the GA or RRA route.

 

The benefit of forums is that you can get a more in depth discussion and a range of opinions which I really value as opposed to just one person's opinion. Thanks for all the replies. Been really helpful.

 

Other than deconflicting with other traffic taxing and landing, is there any other purpose of the taxi call at class g aerodromes?

 

 

[biggles]

Confirmation that you are, in fact, transmitting and on the correct frequency ... Bob

 

 

[facthunter]

Incoming traffic are then aware of you being in the circuit, and what your intentions are including which runway will be used. Nev

 

 

[rhysmcc]

Also helps the airport know who to charge

 

 

[Yenn]

Plus if you do broadcast you are complying with the regulations. It is always good to comply as it makes it less likely that CASA will come down on you.

 

Having said that I seldom broadcast at my local field because the regulations say I should broadcast on area frequency. Others insist on using 126.7 and the nearest major airport is on 118.8. I listen to area frequency, then change as necessary when airborne. I would feel less comfortable if I didn't have 180 degree visibility above.

 

 

[dutchroll]

I meant to say on earlier here that it's not 100% (maybe 99%) a careless switch selection or wiring fault which can cause the thing to fire. It is possible for a hot engine to "diesel" if you swing a prop with enough compression and a bit of fuel vapour left in the cylinders, even without a live mag. I know someone who has had it happen.

 

 

[P4D]

Make sure your insurance is valid by complying with the law.

 

 

[Romeo Juliet Whiskey]

Another couple of questions i hope someone can help me with:

 

1) Why does my car engine red line at 6500 rpm whereas my Jabiru 170 redlines at less than half that?

 

2) Why do we have to earth the plane and refuelling equipment during refuelling of an aereoplane, but not that of an automobile at a petrol station? I presume it has something to do with the type of fuel, but even some aircraft can run off petrol.

 

Rich

 

 

[mnewbery]

Not BAK questions but here goes anyway.

 

Answer 1:

 

Car engines aren't aero engines, is the short answer. The aero engine redline is for the combination of the engine AND propellor. At redline, it is expected that the correct propellor will be transonic at the tip and therefore not as effective. Also this is 1950's technology so aero engines fitted with vacuum pumps for gyros and other vacuum instruments will overheat their vacuum pumps, killing the pumps sooner than expected. Acro pilots with acro planes regularly get well over their manufacturer redline but the TBO time is much lower, about 10% of the original in some cases. The prop is a big gyroscope at the end of the crank so imagine the forces transmitted through a crankshaft to everything attached as the prop bends it.

 

Also a plane engine going 100 knots for 100 hours covers over 18,000 kms. Try driving that fast in your car and see how long the engine lasts. Better still, don't. It will be better for everyone.

 

 

[mnewbery]

Answer 2

 

Car gas has some polarity (like salty water) so it can carry a current as a liquid. Aviation petrol and kerosine is non-polar as a side effect of its other qualities. This also makes it less likely to mix with water, like cooking oil.

 

Car gas has a higher vapour pressure but petrol needs about 14 grams of air per gram of petrol to be explosive. In a car gas tank, the vapour is much more petrol than what is required to be explosive and any static charge will generally not result in an explosion because the right place for the spark to cause an explosion isn't near the filler neck. More likely the spark will be "wet" which means the static charge will leak into the vapour like on a cold humid day. Occasionally people use plastic jerry cans and fill them without putting them on the ground. Empty plastic container not earthed the same as the pump plus hot dry day equals boom. But it's uncommon. Tell that to the people who have lost cars from dragging their nylon covered arses off their microfibre seat covers before a bit of self serve action.

 

Aviation petrol/kerosine WILL carry their own static charge. This means bigger sparks more often without grounding and in the case of a Piper Lance room for 170 litres of air mixed with petrol fumes per side. Cruelly, the right mixture for an explosion is often very near the filler cap for the average bug smasher.

 

Should I earth the petrol station filler on the car first? Touching the pump nozzle and a metal part of the car at the same time before opening the tank or dispensing petrol is enough. Even the plastic bits of the filler nozzle are weakly conductive. Plastic petrol containers need to go on the ground preferably away from the vehicle so if anything bad happens, you can drive a safe distance away.

 

Same with planes. Brakes off for refuelling if you can push/pull it. If the plane does catch fire it needs to get moved away from the rest of the petrol.

 

 

[biggles]

Car gas has a higher vapour pressure

Avgas has a higher Vapor pressure than Mogas ... Bob

 

 

[mnewbery]

So why can't I run car gas on a low wing plane without bigger lines and a stronger electric pump?