Power checks into wind?

[Binks]

Most checklists require the aircraft to be faced into the wind before doing the "run up" checks, and indeed many of us teach this as a matter of normal operations.
However at a time when we are trying to warm the engine up and not keep it cool I see more merit perhaps in facing towards the runway whereby one can see that the runway is clear and have good awareness as to what is on the approach.
Also at wet grass airfields it minimises the amount of tight manoeuvring creating more mud and damage to the surface etc etc.

What do we think?

[downwind24]

I was always taught the checks were carried out into wind to enable cooling on the engine during the 1800-2000 rpm mag drop check as it would get very hot very quick , especially if you had to do it a couple of times or more (we had a 150 that fouled plugs very easily)

[Pull what]

A classic example of folk lore left over from the days of Tiger Moth flying.

Our regulations state that run up into wind should only be carried out above 15 kts and that is purely because with high wing aircraft there is an increased chance of them tipping in high winds when power checks are being made.

The other classic is the 360 degree turn at the holding point before lining up, great when no ATC but i have seen aircraft doing it at major airfields.

(we had a 150 that fouled plugs very easily)

That aircraft shouldnt be flying and fouling is more likely at idle than high power settings

[Intercepted]

However at a time when we are trying to warm the engine up and not keep it cool I see more merit perhaps in facing towards the runwayWarming the engine doesn't mean that you shouldn't keep the cylinders cool.

When we talk about warming the engine we are aiming to heat up the oil etc. On a hot day the cylinders can be "overheated" before the engine is warm.

[athonite]

I always thought power checks into to wind was a through back to aircraft like Spitfires where the engine could rapidly heat up.

I have always taught unless there is a strong wind, align the aircraft at forty five degress to the taxiway, and then there is no problem with the slipstream for following aircraft on the taxiway.

[Binks]

Interesting points guys. At our flying school we sre trying to maintain some standardisation and this is one of the sticking points.
Thats a fair point you make Intercepted, but most of the year in the UK we do not suffer with hot days.
I think its probably a case of airmanship, and should be SCD.

I do think the checklists that are mass produced and sold widely should read "Face aircraft into wind - IF REQUIRED and APPROPRIATE" or something to that effect.

[24Carrot]

I thought it was to test the engine at higher revs, though I can't remember where I learned this.

With no wind at ground level, your "airspeed" is zero, and a fixed pitch prop (or a fully fine CSU) will suffer much more drag (and so need much more torque) than in the air.

If you turn into the wind, it reduces the angle of attack of the prop blades, reducing the drag so they can spin faster.

If there is a rev-related accident waiting to happen, you are more likely to provoke it during power checks if you turn into the wind, because you are testing at higher revs.

And of course, you do take off that way...

[24Carrot]

Please disregard the above, as the blades will obviously not spin any faster during an into-wind power check at 2000 rpm, the engine just works less hard.

[Intercepted]

"Face aircraft into wind - IF REQUIRED and APPROPRIATE"A checklist is supposed to be used by all pilots, including the ones without an in depth knowledge of engines. "If required and appropriate" would leave a checklist open for misunderstanding and make certain checks less well defined.

On the other hand, if you have the required knowledge you can use common sense and personalise a checklist into whatever suitable for you. Based on a standard checklist I have changed the order, deleted and added items to suit my way of checking an aircraft.

By learning the hard way I had to add:

1. PPR.................................................MAKE PHONE CALL :)

[Big Pistons Forever]

Where the air going out the back of the aircraft is a going is a lot more important than the air going into the engine compartment. The most important part of aligning the aircraft for the runup is to make sure the prop wash will not impinge on another aircraft or other items affected by prop wash and ensuringit is parked in such a way so as to not unnecesarily affect other manoevering aircraft (ie don't hog the whole of a 3 aircraft wide runup bay or be half hanging out into the taxiway). If you can accomplish the above and be into the wind then that is the most desirable configuration. As for overheating; the best way to be nice to the engine is not to leave it running at runup RPM for excessively long periods. This is usually the result of a poorly prepared pilot fumbling around with the checklist. Personally I teach the runup as a cockpit flow backed up by a review of the checklist when complete

[DFC]

Personally I teach the runup as a cockpit flow backed up by a review of the checklist when complete


Exactly. Learn the flow / procedure and check that it has been done by using the checklist.

To be 100% correct if one wants to complete an accurate run-up, one needs to have the prop facing cross-wind (esp fixed pitch props). Otherwise the wind and variations thereto will vary the parameters.

Think of it like this - set 2000 RPM straight and level and then increase airspeed by 20 Kt (lower the attitude)....what happens to the RPM!!! Now imagine what you engine is doing on day 1 (calm day) into wind at 2000 RPM compared to day 2 (20Kt wind). You are not comparing like with like when checking the performance!!!!! Imagine a strong gusting wind.

Pointing into wind does stop the controls flapping about a bit though!!!

[TurningFinals]

My flying instructor told me that its also because it means your prop wash isn't being aimed at the aircraft behind you, and so that in the event of a brake failure while the engine is above idle you go off the taxiway onto the grass, rather than on to the runway or into the aircraft infront of you.

[24Carrot]

DFC, I think I understand your point about turning crosswind for an accurate run up, but I think it brings another complication.

When the blades are vertical one blade will be advancing into the crosswind. Let's say it's top one, so the bottom one will be retreating from it. The top blade (thought of as a wing) will have a higher airspeed and generate more lift than the bottom one. This will generate a bending torque on the propeller shaft, which disappears as the blades go horizontal and then bends the shaft back the other way as the blades go vertical again, etc. Sounds bad in principle.

This is the effect that causes "flapback" in helicopters, except they have flapping hinges so the disc tilts intead of stressing the rotor mast.

I have no idea if this is a real problem, rather than a theoretical one. Can anybody enlighten me?

[fireflybob]

I always understood that pointing into wind for the Power Check (aka Run-Up) was important in tailwheel a/c such as the Chipmunk and, of course, keeping the stick fully aft whilst doing so. If you are downwind in a strongish wind is there not a risk of the tail lifting?

Maybe running up into wind also stems from the days when engine cooling was more critical. Personally I would always teach the run up into wind at the ab initio stage since he might go and fly a tail dragger one day and also it gets the student thinking about where the wind is.

[Binks]

DFC it is interesting that you mentin a "crosswind runup". Occasionally I do C of A air tests and the form requires the power checks to be done cross wind for exactly that reason, so a good point I think.

Somebody mentioned Tiger Moths and having no brakes the power checks on these aeroplanes are done on the chocks outside the flying club. Into wind or not.

Of course all airfields are different, and the wind varying from calm to 30 kts plus (should we be flying?) but some great points here.

I shall continue to teach power checks facing the runway (subject to all clear behind) unless the wind is 10 kts or more and turning into wind would not cause a problem of any sort - Subject to Captains Discretion. As ever airmanship is key.

[Big Pistons Forever]

To be 100% correct if one wants to complete an accurate run-up, one needs to have the prop facing cross-wind (esp fixed pitch props). Otherwise the wind and variations thereto will vary the parameters.



I am quite puzzled with the importance you seem to place on achieving an exact consistant RPM in the runup. The point of the student runup is to check the operation of the engine not to fill in a normalzed engine performance parameter engineering test card. The direction the wind striking the propeller will have no effect on the mixture or carb heat/ice checks and while theoretically it could slightly change the magnitude of the mag drop, IMO if the very small wind caused variations in the RPM make the difference in passsing the mag drop limits or not, than you should not be flying the airplane anyway. Students have more important things to worry about.

[24Carrot]

He might have been referring to the max static rpm test in a check flight?, see eg p53 in:
http://www.caa.co.uk/docs/1455/CheckFlightHandbookIssue2Point2-April2009.pdf

Anyhow that same document says:
NOTE: Technical reasons why a short run-up should not be carried out crosswind are rare. so it seems the prop shaft bending stress I asked about is a non-issue .

[Skipping Classes]

CFI - Insights "Hot Weather Engine Cooling" (http://www.principalair.com/article%20-%20hot%20weather.htm)

"
As the Cessna 172M POH says, “Since the engine is closely cowled for efficient in-flight cooling, precautions should be taken to avoid overheating during prolonged engine operation on the ground.”
Increasing idle rpm on the engine may add some slight additional airflow over the engine. It will also increase the heat production. For the most part, the air accelerated aft by the propeller does not increase cooling very much. The cowl openings are too close to the hub of the propeller and airflow is minimal. Prop wash may slightly increase the negative pressure at the cowl flaps and do a bit to assist cooling, but don’t count on too much help from higher rpm.
The engine cooling system is not designed to operate efficiently while the aircraft is on the ground. We want to ensure proper operating temperatures are reached before takeoff, but we do not want the engine to overheat while running on the ground without proper cooling. Try to point the aircraft into prevailing wind for run-up and monitor temperature gauges. If you are equipped with cowl flaps, these will normally be in the open position while taxiing, during run-up and for take off to increase airflow over the engine."


Depends on the a/c type I suppose?