A couple of questions

[Leon H]

hi all,

just a few hours in to my NPPL flying a C152 and enjoying it very much. Good instructor and friendly flying club. I usually arrive for my lesson with many questions to ask my instructor but a combination of excitement and nerves means I usually forget them till I am driving home. I do apologise if they seem a bit ordinary but I cant wait till my next lesson. so here goes.

1. Why is the aircraft turned into wind for pre-take off checks even when said wind is very light.

2. Are C152's twin plugged with one magneto serving each of the four plugs.

3. Why is the trim tab only on one elevator.

cheers all

Leon H.

[MSP Aviation]

1. The engine is air-cooled, thus keeping the pointy bit into the wind during runup helps avoid excessive temps as there is more cooling.

2. Two plugs in each cylinder. The right mag fires the lower right and upper left plugs, and the left mag fires the lower left and upper right plugs.

3. Both sides of the elevator are mechanically linked. Therefore, a trim tab on only one side is cheaper, simpler, and moves both sides the same amount.

[BEagle]

Re. turning into wind for power checks, don't forget that you're being trained for a SSEA Class Rating, not just a Cessna 152 rating. So generic procedures which would be essential on other types are also applied universally on others.

Good to read that you're both enjoying your flying AND asking sensible questions!

[IO540]

Why is the aircraft turned into wind for pre-take off checks even when said wind is very light.

This is an enduring folk tale, like so many in GA.

I have an engine monitor which shows the CHT and EGT for each cylinder, and can tell you there is no noticeable difference in engine temps before/after the power checks whether I park into wind or downwind.

The airflow from the prop (as seen at the engine air intake, when sitting on the ground) is many times stronger than any wind which one is likely to be flying a Cessna in. Also the engine tests don't take an hour...

Yet, most of GA has been taught this "precaution" and every time I fly I see people point (often laboriously/inconveniently) their plane into wind.

What is more important IMHO is to not have the wind flowing across the prop, i.e. not have it at right angles to the aircraft axis. This causes the top blade to see a different wind to the bottom blade, and causes noticeable vibration. Some planes, I gather, have a crosswind limit on their engine tests, for this reason.

So, if the wind is say 360, it's OK to do the engine checks when pointed at 360 or 180, but avoid 090 or 270.

[S-Works]

I tend not to turn into wind based on the same evidence as IO540. However when it is blowing a gale it is not wise to be sat cross the wind or tail in so on those occassions I do turn in.

A lot if these things are habit teaching on the part of flying Instructors as Beagle points out. Teach a generic habit that will work accross the crop.

The failing is actually on the part of the flying instructor for not explaining the reason why. This is either laziness or a lack of knowledge by the FI.

[Mariner9]

Dont disagree that turning into wind may not be required for engine cooling, but run-up areas tend to be on taxiways 90 deg(ish) to the rwy. Turning into wind (and therefore at an angle on the taxiway) prevents your propwash sand-blasting any a/c behind you in the queue. Good airmanship IMHO.

[Whirlybird]

The failing is actually on the part of the flying instructor for not explaining the reason why. This is either laziness or a lack of knowledge by the FI.

It could be. But don't forget that most students are on the verge of mental overload during every early lesson anyway. And if they're not, you tend to throw more essential or really useful facts at them. And this particular fact doesn't, IMHO, come under the heading of either "essential" or "really useful" for the low hours student.

If in the beginning you told every student everything that it would eventually be good for them to know, most of them would run away screaming, or at any rate be too confused to separate the wheat from the chaff and remember the basics of how the controls work.

[englishal]

What is more important IMHO is to not have the wind flowing across the prop, i.e. not have it at right angles to the aircraft axis. This causes the top blade to see a different wind to the bottom blade, and causes noticeable vibration. Some planes, I gather, have a crosswind limit on their engine tests, for this reason.

I agree. I often do runups not pointing into wind, but make sure the wind is not on the beam.

The runup on the twin star can be done on the taxy....just press and hold two buttons until the test sequence is complete

[On-MarkBob]

I agree with the post regarding 'generic habits'. This is important as some aircraft are more critical than others. To get into the habit will mean that you will respect this age old dicipline even when you change aircraft. Don't forget that this was born out of old aircraft, often light and delicate. Remember too that into wind the aircraft is less susceptible to wind enduced misshaps, bearing in mind that the increased airflow will also create some lift and thus the aircraft may be more likely to respond to a gust of wind. This of course is particularly the case in old taildraggers like the Tiger Moth and others since during high engine power a high pressure can build up under the bottom wing as it converges the ground. Into wind also means that all flying controls will respond fully to any potential need, whereas crosswind will mean that some control maybe already being used to 'protect' from a potential misshap. Checking the engine downwind in a taildragger is not a good idea since full down elevator is used to prevent the wind nosing the aircraft over yet, obviously, up elevator is required to prevent the same during the engine run.

[MSP Aviation]

turning into the wind isn't exactly effective, but engine cooling is the reason usually cited by FIs. perhaps this is a hand-me-down from people starting jet/turboprop aircraft when pointing into the wind to avoid hotstarts.

[IO540]

Unfortunately, a lot in PPL training is a case of "in the land of the blind, the one-eyed man is king".

Another nice topic / urban myth to pick apart is why one needs to have the ALT switch OFF during starting. Any offers?

[fernytickles]

Perhaps most of you don't notice a big difference on the turning into wind or not factor because you're flying where the temps remain relatively reasonable throughout the year.

When its hot here in the Midwest, I always try to combine turning into wind whilst not blasting whoever might be behind.

The departures during AirVenture can take so long at "rush hour" that plenty of engines overheat. If you angle it right, you can get a bit of propwash off the guy infront along with some natural breeze, which can help to keep the temps within limits until you manage to get off the ground.

[On-MarkBob]

Re: Alternator switch off for starting (above).

The main problem with an alternator is that it should never 'look' at an open circuit. If it does you will distroy it in a flash. The ALT switch controls the 'field' current that energises the elrctro magnet via the regulator. The unit produces Alternating Current which is turned into Direct Current to charge the battery and run the electrical system. It is the Rectifier that converts the AC to DC and it is the rectifier that is at risk from an open circuit. Leaving the ALT switch off for starting serves no particular purpose, while it might initially protect the Alternator, if there is an open circuit, it will ruin the unit the moment you switch it on in any case. The purpose of being able to isolate the ALT is due to the fire risk. If you smell electrical burning it should be the first thing to be isolated.

Just to note that I have had two in flight fires caused by the alternator or generator, one of which was is a Piper Cub and quite frightening, since I had a vision of being left at 2000' in nothing more that a framework where the fabric used to be!