Unfeathered propeller performance

[RichPa]

I would like to talk a little about the engine failure event where you might not be able to feather. I'm a multiengine student and I would like to know some climb/descent rates figures from your experience, what performance can be achieved in case of an engine failure after takeoff where you can't feather the prop? I guess in light piston twins there is no climb at all, but what fpm descent can you expect?

And what about part 25 large turboprop? Is there such a large drag from an unfeather propeller? I'm thinking about a King Air, Dash8, Saab or an ATR or other big turboprops like these, would you get a high rate of descent like that having no engine at all? I mean, if you have a double engine failure, let's say you get a 1500-2000 fpm glide, but if you have one engine failed and unfeathered, and the other doing full power, what are the figures? Let's assume medium values for weight and outside temperatures.

Thanks!

[barit1]

Well, one must consider that the DC-3 was originally certified (1936) with a non-feathering constant-speed prop. The Hydromatic full-feathering design (http://www.ctmuseumquest.com/?page_id=17576) wasn't available until a year or two later.

[AdamFrisch]

I get about 200-300ft of climb out of my Commander with one unfeathered. If the gear is out, it's down to about zero, maybe the slightest climb in ideal conditions. This is at SL.

So if something happens at rotation, gear still out and you can't feather, then it's a little problematic. Close the other and land straight ahead.

[low n' slow]

If your asking for values, you need to be more specific. JAR 25 aircraft have performance requirements that need to be fulfilled for the various climb segments, of which the second segment is usually the more limiting. Those figures would normally be the lower end values that you might see. The Saab 2000 for example I would imagine being well above the climb requirements under any circumstances. I guess it is up to the manufacturer during design and the operator during operation to make sure that these values can be complied with, be it unfeathered or feathered. Usually the performance manual states the conditions under which the values of climb performance are valid.

[RichPa]

I'm asking because as I know part 25 climb segment performance requirements are for feathered propeller, so it doesn't cover the case which you can't feather the prop.

I'm just flying a DA-42 at the moment because I'm in training and there is a 200-300 fpm loss with the prop unfeathered, but I guess the figures are very different for big turboprops due to bigger props and otherss and also different certification.

[Chris Scott]

AdamFrisch,

Is that a piston-engine Commander? Although the OP seems to be referring to turbine a/c, it sems to me the situation is generally worse in pistons. That may seem obvious, because most turbines have a higher power-to-weight ratio. What I have in mind is that the drag on an unfeathered piston is probably greater than on an unfeathered turbo-prop. But I stand to be corrected.

[Lyman]

My uncle Colonel Ed, returning in his B29 from Tokyo to base, had a prop freeze in flat pitch, #3.

It sped crazily to unknown rpms, requiring alot of ad hoc handling, whilst the Magnesium cowl ignited, and caused an ungodly vibration and din. It eventually parted the shaft, like a frisbee, turning wildly like a saucer, forward, up, left, and over the fuselage to narrowly miss taking off the talfeathers.

Yep. Pistons.

[Neptunus Rex]

Yep. Pistons.No, Lyman - Propellors

[RTN11]

The added drag could be compared to a 20% increase in weight. So if you're light, it will probably be fine, if you took off at MTOW, you could be struggling to keep level, or maybe just about get 2-300'/min out of it.

[RichPa]

Thanks everyone, very interesting answers. I would appreciate also if anyone here has any values regarding part 25 turboprop.

[Oktas8]

Dash-8 turboprop.

With autofeather inoperative, therefore assuming an unfeathered propeller following an engine failure at V1, we must reduce our TOW by about 30%. (This is quite approximate you understand; there are several pages of tables to look up for any specific WAT combination.)

In practice it means that the payload is reduced to just about zero!

[Tu.114]

On the DH8-300, it is as Oktas8 has written. On the -400, there is no MEL item allowing a release without working Autofeather function (the autofeather is an integrated function of the PEC).

A windmilling propeller on the -300 about kills all the performance - in straight and level flight, the simulator could be convinced to climb at 100fpm maximum. On the -400 it is not nearly as bad; while the yaw moment is rather nasty, a noticeable rate of climb is achievable. Again, this is experience from the simulator, I have not tried this in real life.

[43Inches]

SAAB 340 penalty for inop auto-coarsen/feather is almost 3 ton (around 20-30% of MTOW, so very similar to the dash). As with the dash controllability becomes very difficult at low speed requiring substantial increase in Vref if the system is inop. The normal SAAB coarsen system does not actually feather the prop during a failure, a computer cycles the prop at optimum RPM for fast drag reduction.

Most piston twin engine aircraft at mid to high weight will have negative climb rates with a wind-milling failed engine (dependant on atmospheric conditions of course).

What I have in mind is that the drag on an unfeathered piston is probably greater than on an unfeathered turbo-prop. But I stand to be corrected.

That would be very debatable as turbo-props tend to have much larger and more efficient props which in turn cause more drag when being driven by airflow. The reason for the piston lack of performance is more to do with lower power output to start off with. ie, a PA31-350 at max weight struggles to climb on both engines, take one away and add unnecessary drag and the result is predictable. Take same PA31 and strap on 500hp turbo-props (PA31T3) and the aircraft performs much better.

To complicate the situation most turbo-props have a power "push" system that allows operation above 100% power for limited periods during engine failure situations, some over 20% additional power.

[Baron 58P]

The SAAB 2000 has auto feathering on engine failure. It also has auto rudder on engine failure and all the pilot has to do is establish positive climb - very impressive climb to be sure. It is very similar to a modern jet aircraft.

[Dufo]

In Saab 340 sim, negative autocoarsen just after V1 is interesting at high weights. Not deadly but you don't climb until you feather the b1tch.

And when your sim partner manually feathers the wrong prop.. then it's reset time :E

[compressor stall]

Investigation: 200000624 - Beech Aircraft Corp 58, VH-NTG (http://www.atsb.gov.au/publications/investigation_reports/2000/aair/aair200000624.aspx)


It may not fly well at all....