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Turpopop Run-Ups?

Thu May 04, 2000 7:47 am

I have a question that was raised by reading last week's Flight International Dash-8-Q400 flight test. I'll quote;
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While taxiing, an area was found to run up the engines and check the propellers, including the airspeed govenors, and arm the auto-feather system. The aircraft must stay within 30 degrees of any significant surface wind and a clear area is needed behind in the region of the propeller slipstream.

Once the first-flight-of-the-day run-up has been done, subsequent takeoffs demand a shorter checks and experienced crews should accomplish this quickly and smoothly. This chore is inescapable with a turboprop and puts it at a disadvantage to turbojets sic, which generally don't require a run-up.
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OK, I basically want to know what the run-up is for, what exactly it accomplishes, and why it isn't required on jets. I understand what the auto-feather is, but that's about it!

Also, all DHC-8-Q400 takeoffs, have to be brakes-off, rolling start. Is this something unique to this aircraft or truboprops in general? Why is this so?

Sorry to ask so many questions, but I really don't understand props in any great depth   

Cheers,
James
 
Guest

RE: Turpopop Run-Ups?

Thu May 04, 2000 12:20 pm

Well, as you probably know, autofeather changes the blade angle of the prop on the affected engine to one which minimizes the amount of drag caused by a unpowered prop after an engine failue. The triggering mechanism for most autofeather systems is a torque sensor which, at a minimum torque (how power is measured on turboprops) value and with the power levers at an approximate takeoff angle, engages an electric feathering pump and automatically dives to the most coarse (highest) blade angle available. This minimizes drag and allows the aircraft the maximum single engine climb capibility. Autofeather is normally only armed for takeoff and go-around.

In most turboprops a full autofeather check is done prior to the first takeoff of the day which checks the ciruitry, logic and the actual functioning of the feather pump. This check usually takes about a minute to a minute and a half. In every turboprop I have flown there is also an abreviated check that can be doe merely to check the circuitry and logic as it is not necessary to check the acutal feather pump function and blade movement more than once per day. This check is many times accomplished before engine start so it has no effect on taxi times.

I don't know where this magazine gets it's info, but to say that an autofeather check must be fully accomplished prior to every takeoff is probably inaccurate. To say that this check also greatly effects taxi time and thus jets are better is rediculous. Jets will never ever be suitable for many routes and airports.

As for the rolling takeoff procedure... most aircraft will "hop" at high power settings with the brakes on and light loads. Also, when the aircraft is stopped the props suck in lots of foreign matter that can damage them and reduce aerodynamic efficiancy. In an aircraft with outstanding short field performance like the Dash 8, I don't think that locking the brakes at the end of the runway would be necessary anyway.

Hope I answered your questions.
 
dash8
Posts: 389
Joined: Sat Aug 27, 2005 8:23 am

RE: Turpopop Run-Ups?

Sat May 06, 2000 3:53 am

I agree with ATRpilot. We do a full autofeather check at the gate on the first flight. Power is left at idle and the test is performed on both engines. And the test isn't performed for the rest of the day.
Also the only time we depart statically is when we're light. But it doesn't include setting TO power before brake release. After 40% torque (read TO power for the turboprop challenged) brakes are released.
The only reason this is done is to allow the pilot-non-flying (the one setting TO power and talking on the radio etc etc) enough time to monitor the TO progress after setting the power. Otherwise rotation speed is achieved before you're finished. Now slam an engine failure right at rotation and you can see that it's a cause for confusion in the cockpit.

So I also don't know where FI gets this info. On an aircraft as advanced as the -400 I'm sure no autofeather tests are required every TO.
What I have in mind is that because this a new type, SAS is stipulating the tests every TO for a short period of time, and that the magazine misinterpreted this.
p.s. I'v flown the -400 sim in Toronto and........WOW !!
Electrical trims, advanced EFIS. Geez, even the radio selector panel is LCD. And the power is amazing !!!!
You guys know Bombardier climbed this thing from runway to 25,000 feet in 5:10 !!!!!!
Of course it was on a cold day, empty and everything maxed out. But still an initial ROC of 8,000 FPM is very impressive.

Regards,

Xander
F/O Dash8-311
 
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Dash8

Tue May 09, 2000 2:14 pm

Hey You a Piedmont driver? I might be coming to visit you all here soon... maybe to try and find a home!

8000 ft/min???? Holy Cow!!!!
 
Buff
Posts: 1066
Joined: Fri Mar 16, 2007 1:29 pm

RE: Turpopop Run-Ups?

Wed May 10, 2000 2:43 am

deHavilland (now Bombardier) philosophy regarding Auto Feather systems was to test it prior to each flight. At my last place of employment, we operated Dash 8 102's and until about 1991, an A/FX test was required prior to each flight.

One of the fears of people flying the original Dash series was DHC's poor autofeather system on the Twin Otter. On more than one occasion, it screwed up and sent props into feather on take-off rolls. A prominent northern Canadian bush operator was so disgusted with the DHC-6 A/FX system, not only was the system deactivated, but all associated wiring was removed from the engine.

So in answer to the original question, I believe the AFM suggests a checklist that incorporates autofeather and other tests after engine start. Operators however have been freed to modify as necessary some of these checklist requirements, and relegate them either to once per day, or maintenance.

Hope that adds to the discussion!

Best Regards,

Buff

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