Ts and Ps on the groud roll

[WrongWayCorrigan]

Does anyone else check the Ts and Ps on the ground roll? Just something I've always done...

[TheOddOne]

..plus airspeed increasing!
Perhaps even more important as it's the first opportunity to check it's working whereas most checklists will have had T & P check at least 3 times.

TOO

[SpannerInTheWerks]

... and heels on the floor - just to ensure you're not 'riding' the brakes ...

... plus flaps 'set' and carb air 'cold' - after a 'touch and go' ...

[fireflybob]

I also teach to check RPM (and Ts and Ps) after selecting full power. The pilot should be aware of a "normal" figure and be prepared to reject the take off if actual RPM is significantly below this figure.

[Big Pistons Forever]

I also teach to check RPM (and Ts and Ps) after selecting full power. The pilot should be aware of a "normal" figure and be prepared to reject the take off if actual RPM is significantly below this figure.

Unfortunately not very many pilots, or their instructors :(, actually know what "normal" RPM should be at the start of the takeoff roll.

A fixed pitch propeller will show considerably less than redline RPM at the start of the takeoff role. The "right" amount of RPM is the published POH static RPM figure. For example 2300 - 2420 RPM for a C 172P.

So at the start of the takeoff roll the throttle should be smoothly increased to full ( this should take 2 -3 seconds ) then the RPM checked for that it is indicating within the published static RPM range. If it is not the takeoff should be immediately aborted.

[fireflybob]

Unfortunately not very many pilots, or their instructors , actually know what "normal" RPM should be at the start of the takeoff roll.


I could not agree more!

[Big Pistons Forever]

Further to my last post checking the oil pressure should be more than " somewhere in the green ". Oil pressure is correlated engine RPM and with oil temp, so if the oil temp is 180 F ( or normal operating temp ) the oil pressure I would expect would be mid range in the green ( no unit markings) or around 80 PSI. Very high or very low pressure, even if in the green, should prompt a low speed reject and further investigation

The only time I have rejected a takeoff in a light SEP was due to high ( on or maybe slightly over redline). It was a checkout in an owners airplane. A cold day, very short taxi and checks done quickly but correctly did not give the oil time to warm up. This was exacerbated by the use of straight 100 oil instead of a multi grade.

Returning to the run up bay and letting the engine warm up for a few minutes resulted in a normal oil pressure reading when full power was applied

[India Four Two]

I always make a point of not moving after start, until the oil temperature is in the green.

[Big Pistons Forever]

I always make a point of not moving after start, until the oil temperature is in the green.

I am wary of absolute rules in aviation. Like many things in aviation this is IMO one of those "it depends" things".

Lycomings direction is the engine is warm enough to fly if it will go to full power without stumbling. All of the small Lycomings will do that with no oil temp showing on the gauge.

I am certainly not criticizing your practice of waiting for oil temp to register before taxing and that is certainly a non optional practice for radial engines or any of the bigger turbo charged flat engines, however I see no problem with taxing any of the simple flat 4/6's a soon as the engine has stabilized after start

Again the oil is the key. Are you running multi grade or a thick single grade and how cold is it ? The oil pressure gauge will tell you were you are at in terms of when you can increase power.

The flying club where I used to teach had a bunch of C 172's. They ran them to 3500 hours between overhauls with no problems and I can guarantee with the hobbs running nobody waited until oil temp showed on the crappy Cessna gauge before taxiing.

[fireflybob]

PA 38 POH states "Warm the engine at 800 to 1200 RPM for not more than 2 minutes in warm weather and four minutes in cold.....Take off may be made as soon as the ground check is completed and the engine warm."

Other types may have different advice in the POH.

As BGF states there's no absolute rules but I tend to go with IFT of not moving till the oil temp is beginning to nudge into the green.

[Big Pistons Forever]

PA 38 POH states "Warm the engine at 800 to 1200 RPM for not more than 2 minutes in warm weather and four minutes in cold.....Take off may be made as soon as the ground check is completed and the engine warm."

I believe the intent of this POH advice is to avoid spark plug fouling, a particular issue with this engine, due to excessive operation at low engine speeds where the engine can't scavenge the lead in the fuel.

My experience is that for the first flight of the day (ie cold oil) you probably won't see any movement on the oil temp without exceeding the recommended time limits in the POH. I find you generally start to see oil temp starting rise off the peg during the run up.

As an aside airplane owners should be aware that low oil temps in flight can be as damaging as high temps. In flight oil temp should stabilize around the 180 deg F mark in flight (this is the value for the unmarked white line in the middle of the green arc in Cessna oil temp gauges). Excessively low oil temp will cause higher than normal oil pressures as well as fail to ensure that the corrosive water vapor trapped inside the engine doesn't get boiled off.

[BigEndBob]

Makes you wonder how technical all this is, probably some opinion of someone at Piper, Cessna etc versus the engine manufacturer.
Someone had to come up with advice or is it based on in the field operations during testing. So what happens if you are held at the hold for ten minutes, engine blows up!

[Big Pistons Forever]

I think the take away is to be aware of what is happening under the cowl and pay attention to, and understand, what the gauge readings are telling you

Speaking of gauges I don't make a point of noting the airspeed is working as the instrument is not required for safe flight. I got all of my students to fly a full take off circuit and landing with the ASI and the Altimeter covered up.

For tailwheel training I make a point of telling the students not to look at the ASI on the takeoff roll. If they are looking at the ASI they are not looking out the windshield to keep the aircraft straight. You don't need an airspeed anyway the aircraft will tell you when it is ready to fly

[Piltdown Man]

I used to give tbe clocks a quick glance early on in the takeoff roll. My preference was make this check shortly after takeoff power was set. But to be honest, it was a quick glance as I preferred to look out if the window. Going gardening because you were looking at the clocks is not s good thing to do.

PM

[Shaft109]

Interesting question -
I have a mnemonic T R E A

Throttle to full and hold - feel / sound or response

RPM - check static RPM on fixed prop or as required on CSU

Engine T's and P's - as stated by others knowing what is right not just book figures

ASI alive

As an aside I fitted an oil temp gauge to my old car and interesting to understand what it tells you.

Cold start it would run straight to 64psi / 4 BAR at idle and then get checked by the OP relief valve and stay there. Once warmed it would slowly decrease at idle until about 30psi.

However if it was on the OPRV and you revved it it could go way beyond up to 80-90psi but once warmed it would stay at 64psi all day long under load.

It taught me a brief warm up period is needed but not necessarily 5 mins static. Just allow everything to stabilise and once you've finished taxying to the runway it should be something like.

[fireflybob]

I have a mnemonic T R E A


Why on earth would you need a mnemonic to remember basic stuff like this?!

[Shaft109]

Well it works for my simple brain - it was in the Flight Reference Cards of the first aircraft I learned to fly and do it to have a structured approach.

I say and action TREA so as not to hit one.

Next time I'll just gun it to see what happens

[ShyTorque]

I think you meant to say you fitted an oil pressure gauge.

[Pull what]

Most important thing to check on take off is that no one else is about to occupy or infringe the runway you are taking off on!

[Centaurus]

I also teach to check RPM (and Ts and Ps) after selecting full power

If the T&P were normal during the pre-take off engine run-up, then you are wasting your time to double check again a minute or so later after selecting full throttle. Concentration should be outside the cockpit during the take off.

However, agree that in a fixed pitch prop the minimum static RPM should be checked as full throttle is reached. There was a case in a Cessna 152 where during the take off roll the prop RPM exceeded the red line figure so the pilots used to ease back the throttle to keep it below red line. In effect a reduced "thrust" take off.:=

Many pilots flew that Cessna 152 in that condition without reporting the event. Investigation later revealed the propeller was genuinely over-speeding as the aircraft gathered speed on take off and in climb. It would have shown up if pilots had taken the trouble to check min static RPM range from the manufacturers POH before take off or during a full throttle run up if necessary. It would have shown the min static RPM was well out of tolerance at the top end of the tolerance.

The cause of the over-speeding prop was the owner. Over many months he has repeatedly filed the leading edge of the propeller blades to remove nicks in the metal and by doing so thinned out the blades of the prop. In turn less drag and thinner blades allowed the prop to turn faster. The result of all this over-speeding was engine various components were found to have been out of engineering tolerances which if not repaired would have eventually resulted in engine failure. The owner very reluctantly was forced to have the engine changed.


The moral of this sorry saga was as a pilot you should always record a defect using the appropriate legal document rather than a mere verbal report. if not, the next pilot to fly that aircraft could be the unfortunate sod who gets the engine failure.

[fireflybob]

If the T&P were normal during the pre-take off engine run-up, then you are wasting your time to double check again a minute or so later after selecting full throttle.

Sorry I can't agree with that - engines and attached components are more likely to fail at full power settings. Engine run ups are conducted at modest RPMs e.g. 2000 RPM.

Of course one should be paying attention to what is going on outside the cockpit but a well trained and competent pilot is quite capable of a quick check of the engine parameters as soon as full power has been selected.

[Centaurus]

but a well trained and competent pilot is quite capable of a quick check of the engine parameters as soon as full power has been selected.

"A well trained and competent pilot". Agree. But the problem is the solo student pilot who by definition is inexperienced. I would have thought the last thing he needs to do is having his head inside the cockpit at the start of the take off run and then half way down the take off run, searching for the oil pressure and the oil temperature an even a CHT gauge. And what are the tolerances of these gauges? How about the night take off or even a crosswind take off where pilot concentration on directional control is vital.

A student or inexperienced pilot usually remembers what his instructor tells him when it comes to important safety advice. If the instructor tells him to always check the T and P's at full throttle just where a early swing on take off usually will occur, then he could be setting the student up for a possible directional control problem. For an inexperienced pilot it takes only a couple of seconds of undetected yaw on take off to be in trouble especially if he happens to be looking at a particular engine gauge and deciding if what he sees dictates an abort.

For example if the oil pressure needle wavers at full throttle does that mean an abort? Will the oil temperature red line during a take off run when it was normal during the run up a few minutes early? I don't think that would happen.

Many years ago, there was a spectacular accident at Horn island in Australia where a Lockheed Hudson pilot happened to check his T&P's of his two engines during the late part of the take off run. He saw one oil pressure needle flickering significantly Everything had been normal during the run-up a few minutes earlier. He immediately closed the throttles and abandoned the take off run thinking he was about to have an engine failure.

The Hudson went off the end of the runway and was a write-off. Investigation revealed there was nothing wrong with either engine and the cause of the flickering oil pressure could not be determined.

For inexperienced pilots the priority during the early part of take off is not what a T&P needle may or may not show you, but directional control. That applies to jet transports as well as Cessna singles. IMHO, of course. :ok:

[fireflybob]

For inexperienced pilots the priority during the early part of take off is not what a T&P needle may or may not show you, but directional control.

Centaurus, I'm in agreement with you here. But in the long term I think pilots should be taught to do both with, obviously, emphasis on control.