Reduced power Take Offs? - Page 6

OLDSAM · #51 02-26-2015, 01:49 PM

...a way to reduce my chances of having an engine failure on takeoff to less than 4%. I liked those odds...

Am I missing something? Why is it good to have an even chance of an engine failure on every 25th takeoff? Now I'm nervous, cause I am way, way overdue.

Did a decimal point, and maybe some zeros, get omitted?

Just wonderin'

Flying again! · #52 02-26-2015, 02:43 PM

Quote:

Originally Posted by OLDSAM

...a way to reduce my chances of having an engine failure on takeoff to less than 4%. I liked those odds...

Am I missing something? Why is it good to have an even chance of an engine failure on every 25th takeoff? Now I'm nervous, cause I am way, way overdue.

Did a decimal point, and maybe some zeros, get omitted?

Just wonderin'

What was said is the 96% of engine failures on TO occurred at full power. So now we need to estimate what the percent chance of engine failure is on TO. NTSB-AAS-72-10 shows that for single engine a/c the engine failure rate overall was 4.6 failures per 100,000 flight hours. It also said engine issues were responsible for 44% of those failures (pilot error, fuel exhaustion, etc. made up the rest). Engine failures during TO Are estimated to be to be 30% according to a Boeing study. This results in 4.6*.44*.30=.61 engine failures/100,000 hours.

If you assume one TO per 2 flight hours this is an engine failure rate at takeoff of .0012144%. So if 96% of engine failures at TO occur at full power, then the failure rate during full throttle TO is .0011658%. So reduced power TO compared to full throttle (if the 96% to 4% applies), reduces the chance of engine failure by .0000486%.

Slow day at work...lol

Maxrate · #53 02-26-2015, 04:46 PM

Thoroughly enjoying this guys! Starting my second bag of popcorn right now. BTW, what kind of primer is the best in everyones opinion.......kidding, kidding....

rjbob · #54 02-26-2015, 05:45 PM

Quote:

Originally Posted by Flying again!

What was said is the 96% of engine failures on TO occurred at full power.

It is unwise to take off in our type of aircraft with anything less than full power...period. In a non-turbocharged single, lessening the time it takes to get to a safe altitude is the main concern. For a Turbo-charged engine without an automatic waste gate, full power would be whatever the limitations are.

The 96% thing is a total non-issue because almost all takeoffs in our little planes are accomplished at full throttle...most likely over 99%.

fl-mike · #55 02-26-2015, 05:52 PM

As a fixed pitch flyer, I'm at less than max power at every takeoff, correct? Also, formation takeoffs are at reduced,power to give wing power margin. We do that all the time.

rjbob · #56 02-26-2015, 06:13 PM

Quote:

Originally Posted by fl-mike

As a fixed pitch flyer, I'm at less than max power at every takeoff, correct? Also, formation takeoffs are at reduced,power to give wing power margin. We do that all the time.

Should have said "Max AVAILABLE power.
Yes, there are exceptions such as formation takeoffs and high altitude training.

Thank you for catching that.

N427EF · #57 02-26-2015, 07:46 PM

I have never seen so many people ignoring factory advice.
In fact using full power for take off is not only suggested by the aircraft engine manufacturer but for once even the same advice is suggested by
APS's John Deakin.
These 2 entities are often at odds as to how to operate an aircraft engine.

Quote:

It is unwise to take off in our type of aircraft with anything less than full power...period. In a non-turbocharged single, lessening the time it takes to get to a safe altitude is the main concern. For a Turbo-charged engine without an automatic waste gate, full power would be whatever the limitations are.

It is just this simple

2 exceptions for me, noise abatement and formation take off.

BillL · #58 02-26-2015, 08:19 PM

Quote:

Originally Posted by engineerorange

That's usually because you are at max rpm (max piston speed/acc.) and when you let off the go pedal there is no boom to help turn the piston around and the rod and wrist pin have to do it all. You also get some shock cooling of the valves and every now and again a head pops off. Not to mention torsional reversals in the crank. Sometimes it gets ugly.

I believe that when I was 16, but now . . . it is just hand waving, and irrelevant to a reciprocating engine. Every other stroke is intake, no pressure there. Those valves get shocked each revolution with hot exhaust gas and cool intake gasses, again - no issue. All systems/components are designed for much greater forces, temperatures than a "throttle back".

One main reason I am building an RV and not buying a Corvette, is I can legally use the RV to it's design capabilities. And I will. What thrill is a 200 mph Vette, tooling along at 55 mph. That alone would kill me.

When I drive my old E28 M5, yes, I absolutely push the pedal all the way down . . . a lot! Can't keep it there, it just goes too fast. It is made for it. I love it, it's why I have it. It has 155k miles too, no overhaul yet.

Part throttle or reduced power take offs are possible, and might extend the life of the engine (that is an whole other thread to rehash) so why not? Do it if you are safe, and if you want to. Personally, I have not decided on what each TO will be but, I will likely throttle back at 400 ft unless on a cross country mission that will need the speed.

g zero · #59 02-26-2015, 08:47 PM

I didn't build a hot rod ,big horse power , constant speed prop RV to do reduced power Anything !

N427EF · #60 02-26-2015, 09:04 PM

Quote:

You also get some shock cooling of the valves

Not if you don't overheat them in the first place by lugging the engine with partial throttle, robbing it of the extra fuel needed for cooling as well as hot gas blowby heating the oil.

As I often point out, it is experimental aviation and you get to fly your engine any way you want