Backup for dropping the gear

In a previous article, "Peter Duniho" said:
"Paul Tomblin" wrote in message
...
[...]
Actually, reading that again, it's possible that what is happening isn't
that it comes on at a lower speed if you have power on, but that the
propellor slipstream holds the gear up against the springs if you have
power on.

I don't know how the "propeller slipstream" could hold the gear up. The
only "propeller slipstream" I'm aware of is the helical movement of the air
around the fuselage, and compared to the other forces involved I doubt it's
all that strong.

The air coming off the propellor is going faster relative to you than your
air speed. If it wasn't, your propellor wouldn't be producing power.
It makes perfect sense to me. Being behind the propellor disk, the nose
gear (and possibly the mains) is experiencing more dynamic air pressure
when the engine is producing power than if you were gliding at the same
speed.


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Paul Tomblin http://xcski.com/blogs/pt/
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"Paul Tomblin" wrote in message
...
The air coming off the propellor is going faster relative to you than your
air speed. If it wasn't, your propellor wouldn't be producing power.
It makes perfect sense to me. Being behind the propellor disk, the nose
gear (and possibly the mains) is experiencing more dynamic air pressure
when the engine is producing power than if you were gliding at the same
speed.

Hmmm...I suppose so. It still seems to me like the gear enjoys such a small
portion of the overall prop thrust, and that the difference in prop thrust
airspeed and airframe airspeed is greatly reduced at or near cruise
airspeeds. But I admit, I can't imagine what else the POH could be talking
about.

Still, it doesn't explain why an engine failure would in and of itself cause
the gear to extend. Presumably the hydraulic pressure is still holding the
gear up; the prop thrust would be a backup for that, not the sole mechanism
for holding the gear up. The extension mechanism still would need to be
triggered by airspeed or MP changes.

Right?

Pete

In a previous article, "Peter Duniho" said:
Still, it doesn't explain why an engine failure would in and of itself cause
the gear to extend. Presumably the hydraulic pressure is still holding the
gear up; the prop thrust would be a backup for that, not the sole mechanism
for holding the gear up. The extension mechanism still would need to be
triggered by airspeed or MP changes.

Right?

If the hydraulic system was still holding pressure, then I think you're
right.


--
Paul Tomblin http://xcski.com/blogs/pt/
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