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InnsbruckFlyer
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Hand Propping a Dash 8

Sat Mar 24, 2018 4:21 pm

Hi All,

A few days ago I was on a Dash 8 (I won't say the airline in case it gets them in trouble) in Europe. I noticed that while doing the walk around, the First Officer hand propped both propellers. My flight instructor says that this is a complete no-no. Is it okay to do this on a Dash 8? Is it safe?

InnsbruckFlyer
Last flown aircraft: E195 OE-LWO < A320 OE-LBX < A320 OE-LZF < DH8D OE-LGJ < A21N TC-LSK < B738 TC-JVZ < E195 OE-LWQ < DH8D OE-LGN < DH8D OE-LGI < E195 OE-LWE < DH8D OE-LGI < A320 D-AIUR < A320 D-AIZM < B738 PH-HZJ
 
jetmatt777
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Re: Hand Propping a Dash 8

Sat Mar 24, 2018 4:29 pm

A turboprop will not have any compression surges like spinning the prop on a reciprocating engine. It literally just spins. A turboprop is a jet engine that drives a gear that turns the prop. A recip is like a car engine that drives the propellor, so moving the prop on a recip will be pushing the pistons up and down in the cylinders.
 
dc10co
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Re: Hand Propping a Dash 8

Sat Mar 24, 2018 4:32 pm

As the other poster said, two different stories with a turboprop versus a piston engined airplane. Inspecting the propeller on turboprop aircraft is pretty a much standard part of any commercial carriers pre flight checks. Done to make sure there is no damage to the propeller blades from FOD
Listen Betty, don't start up with your white zone shit again.
 
T1a
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Re: Hand Propping a Dash 8

Sat Mar 24, 2018 4:57 pm

Considering your username the FO might have been me or any of my colleagues. On our Dash-8 fleet it is standard procedure to turn the propellers to check them for signs of oil leakage, grease leakage or cracks in the blades. All propeller blades have to be inspected every turn-around, so they are spun every turn-around. As said before, on a turboprop that is a complete non-issue, you simply spin the propeller itself, the reduction gear box and the low-pressure turbine. It's not connected to the combustion part of the engine, at all. In strong cross-winds (like more that 30kt) you can also see the propellers windmill.

Greets,
T1a
All views expressed under this username are mine as a private person and don't necessarily reflect the views of my employer.
 
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InnsbruckFlyer
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Re: Hand Propping a Dash 8

Sat Mar 24, 2018 5:49 pm

Thank you for all your responses!

InnsbruckFlyer
Last flown aircraft: E195 OE-LWO < A320 OE-LBX < A320 OE-LZF < DH8D OE-LGJ < A21N TC-LSK < B738 TC-JVZ < E195 OE-LWQ < DH8D OE-LGN < DH8D OE-LGI < E195 OE-LWE < DH8D OE-LGI < A320 D-AIUR < A320 D-AIZM < B738 PH-HZJ
 
ushermittwoch
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Re: Hand Propping a Dash 8

Sat Mar 24, 2018 5:52 pm

InnsbruckFlyer wrote:
Hi All,

A few days ago I was on a Dash 8 (I won't say the airline in case it gets them in trouble) in Europe. I noticed that while doing the walk around, the First Officer hand propped both propellers. My flight instructor says that this is a complete no-no. Is it okay to do this on a Dash 8? Is it safe?

InnsbruckFlyer


flyBE do this all the time.
Where have all the tri-jets gone...
 
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bluestreak
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Re: Hand Propping a Dash 8

Sat Mar 24, 2018 6:58 pm

We used to have to spin the props on the Jetstream 31 after engine shutdown. The TPE-331 suffers from shaft bow if the engine is not rotated by hand after shutdown. If I remember correctly, the top of the engine tends to cool quicker, causing a 'bow' in the shaft. Spinning the props creates more even cooling.

Also, on the walk around, it was standard procedure to spin the prop a complete round to inspect each blade. You can't do that with a piston engine, because of the risk of the engine starting, and the amount of compression on each cylinder.
"Well, we barely made the airport, for the last plane out, as we taxied down the runway, I could hear the people shout"
 
AR385
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Re: Hand Propping a Dash 8

Sat Mar 24, 2018 7:36 pm

Wow. One learns something new everyday.
 
26point2
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Re: Hand Propping a Dash 8

Sat Mar 24, 2018 9:37 pm

On the TPE 331 (a geared turbine....not a free turbine) there were 2 steps to avoiding uneven shaft cooling (Shaft Bow). After shutdown spin the prop mightily to purge as much residual heat out of the engine. Then 15 minutes later (or was it 30 minutes?) turn the engine shaft 180 degrees to even out the tendency for bowed turbine shaft. This was done by turning the propeller a fraction of a revolution so the geared compressor at the front which you see easily see also turned until it had rotated 180 degrees. Easy!
 
N766UA
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Re: Hand Propping a Dash 8

Sun Mar 25, 2018 12:15 am

Turboprop propellors aren’t actually attatched to anything within the engine itself, save for a reduction gearbox. In effect, they basically run by being windmilled from within! Rotating the propellor is, to my knowledge, SOP on almost every turboprop ever made and is done to inspect the props themselves, check for leaks, and ensure the propellor spins freely. I also found it to be a bit of a ritual, personally.

On a side note, some guys I used to fly with would actually prop recipricating engines to check the cylinder compression. I never personally bothered, and our company didn’t actually teach or require that, but it’s not something that’s *never* done, either.
 
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tb727
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Re: Hand Propping a Dash 8

Sun Mar 25, 2018 1:10 am

As others have said, the TPE-331 it was required and that's what I thought about as soon as I read the title to this thread. Used to pull them through I want to say 10 times on the MU-2 and similar on the Volpar Beech 18 but I never flew those.
Too lazy to work, too scared to steal!
 
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smithbs
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Re: Hand Propping a Dash 8

Sun Mar 25, 2018 1:15 am

It could be an issue on a radial engine. Because of the gearing and length of the propeller being a lever arm, you have a lot of mechanical advantage. If the cylinder is full of oil, then you could end of applying a lot of force against a hydraulically locked cylinder and end up bending something. Best to ask the mechanic if it's okay.
 
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Starlionblue
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Re: Hand Propping a Dash 8

Sun Mar 25, 2018 1:18 am

N766UA wrote:
Turboprop propellors aren’t actually attatched to anything within the engine itself, save for a reduction gearbox. In effect, they basically run by being windmilled from within! Rotating the propellor is, to my knowledge, SOP on almost every turboprop ever made and is done to inspect the props themselves, check for leaks, and ensure the propellor spins freely. I also found it to be a bit of a ritual, personally.

On a side note, some guys I used to fly with would actually prop recipricating engines to check the cylinder compression. I never personally bothered, and our company didn’t actually teach or require that, but it’s not something that’s *never* done, either.


Whether the prop in a turboprop is attached to the compressor depends on the type of turboprop. In a free turbine turboprop (e.g. P&W PT-6) a free turbine drives the prop, and there is no mechanical connection with the compressor. In a single shaft turboprop (e.g. Allison T56) the prop shaft is driven directly by the compressor through a mechanical connection.

Either way there is no risk associated with moving the prop.

P&W PT-6
Image


Allison T56
Image
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opticalilyushin
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Re: Hand Propping a Dash 8

Sun Mar 25, 2018 9:14 am

I always wondered why the crew on J31/32s seem to frantically spin the props on the ground, more so than most other commercial types.
 
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SAAFNAV
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Re: Hand Propping a Dash 8

Sun Mar 25, 2018 10:21 am

The give-away between a free-turbine and single shaft turbo-prop plane is whether the blades are feathered or not on the ground.

Have a look at a C-130/Lockheed Electra/P-3 Orion/E-2 or a plane like a Jetstream with a TPE-331. The blades are always flat during start for minimum air resistance and least compressor load.
On a Herc, a small blade angle increase can lead to a bogged-down start and over-temping.

With a free turbine like a PT6, PW100 etc, the blades are feathered, and in cases like the ATR, can even have a brake on them to keep them from moving while the core is running.

On a T-56 you also will not be able to freely spin the prop as in a free-turbine. You can move it, but it takes a lot of effort as you have to overcome both the prop-brake, and all the friction of the gearbox and engine combined.
ex L-382G Loadmaster, ex C-130B Navigator, Möchtegern Flugzeugführer
 
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PW100
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Re: Hand Propping a Dash 8

Sun Mar 25, 2018 8:51 pm

N766UA wrote:
Turboprop propellors aren’t actually attatched to anything within the engine itself, save for a reduction gearbox.


That's not entirely correct. The PW100 RGB also drives the AC generator, hydraulic pump, overspeed governor and pump (providing hydraulic pressure to the propeller control system), and propellor controil unit.
So handturning the props on this Dash-8 will rotate the above RGB driven units, albeit so slowly that there won't be any noticeable effect.

There's no problem with hand turning PW100 engine props, not for the engine nor for any of the mentioned utilities. However forcing the propblade forward/backwards is generally "frowned upon" as axial movement can damage the hub seal of the prop blade.


Rgds,
PW100
Immigration officer: "What's the purpose of your visit to the USA?" Spotter: "Shooting airliners with my Canon!"
 
DashTrash
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Re: Hand Propping a Dash 8

Sun Mar 25, 2018 9:51 pm

smithbs wrote:
It could be an issue on a radial engine. Because of the gearing and length of the propeller being a lever arm, you have a lot of mechanical advantage. If the cylinder is full of oil, then you could end of applying a lot of force against a hydraulically locked cylinder and end up bending something. Best to ask the mechanic if it's okay.


We had to pull ours through nine blades worth before starting to pull the oil out of the bottom cylinders (R-985).
 
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glen
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Re: Hand Propping a Dash 8

Sun Mar 25, 2018 10:27 pm

bluestreak wrote:
You can't do that with a piston engine, because of the risk of the engine starting, and the amount of compression on each cylinder.


Well, you can. It's not the norm, but depending on the engine you even have to.
I had the chance to fly a Pilatus P-2 for a few years. The problem with its Argus-engine with its hanging V-12 arrangement was the oil accumulating in the cylinder-heads, when the engine wasn't running for a few days.
Thus you had to flood the cylinders with fuel with help of a primer-pump. Then you had to turn the prop manually over all 12 compression stages in order to flush-out every cylinder (this was a good credit towards your daily workout... :weightlifter: ).
It was definitely more work and more risk than turning a turboprop. Thererfore you had to make sure the aircraft was safely chocked and you were staying safe outside the moving area of the propeller.
The risk of an igniting cylinder in case of a broken magneto grounding remained (I never experienced it), however the risk of the whole engine starting up was close to zero, as the engine was very hard to start anyway - with still a lot of oil left even after the flush out procedure:
"The horizon of many people is a circle with zero radius which they call their point of view." - Albert Einstein
 
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smithbs
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Re: Hand Propping a Dash 8

Mon Mar 26, 2018 8:26 pm

DashTrash wrote:
smithbs wrote:
It could be an issue on a radial engine. Because of the gearing and length of the propeller being a lever arm, you have a lot of mechanical advantage. If the cylinder is full of oil, then you could end of applying a lot of force against a hydraulically locked cylinder and end up bending something. Best to ask the mechanic if it's okay.


We had to pull ours through nine blades worth before starting to pull the oil out of the bottom cylinders (R-985).


Did you ever have it stop or at least become very difficult to turn due to the bottom cylinders being full? I was told a long time ago by someone familiar with radial maintenance (a rare skill now) to turn it but never force it if it became very difficult.
 
DashTrash
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Re: Hand Propping a Dash 8

Mon Mar 26, 2018 8:30 pm

Never had much resistance turning it through.
 
DashTrash
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Re: Hand Propping a Dash 8

Mon Mar 26, 2018 8:31 pm

Never had much resistance turning it through.
 
jetstar
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Re: Hand Propping a Dash 8

Tue Mar 27, 2018 12:32 am

smithbs wrote:
It could be an issue on a radial engine. Because of the gearing and length of the propeller being a lever arm, you have a lot of mechanical advantage. If the cylinder is full of oil, then you could end of applying a lot of force against a hydraulically locked cylinder and end up bending something. Best to ask the mechanic if it's okay.


That is called hydraulic lock, when the lower cylinders of a radial piston engine fill up with oil. The primary reason for hydraulic lock is worn piston rings, but if a intake or exhaust valve guide or seal was worn or if oil was leaking into the intake or exhaust manifold, oil could work its way down to the lower cylinders. Watch when a radial engine initially starts up and there is a blue cloud of smoke coming out of the exhaust pipe, thats from oil settling into the lower cylinders or the intake or exhaust manifolds.

Back in my US Air Force days I was an engine mechanic on the 28 cylinder R-4360 and it was standard practice to walk the props, as it was called about 12 blades to check for hydraulic lock. The engine starter was powerful enough that if a lower cylinder had filled up with oil it could either bend the connecting rod or could even pop the cylinder right off of the engine, mostly by shearing off the cylinder mounting studs, either way it was engine change time.

Most of the times this was done by the flight line crew, but if they were short of help we would assist the line crew. If it was a warm day then walking the prop could be done by one person, but on a cold day it sometimes need 2 people. Moving all that cold internal metal lubricated by cold 50 weight oil made for a lot of internal friction.

Ah, the good old days, when approaching an R-4360, the first thing you did is check the direction of the wind, to make sure you are upwind so oil does not drip down on you.

JetStar

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