M14P and SR
Posted: Fri Feb 17, 2012 8:27 pm
After the discussion on the group and Mr. Murphy's note, it got me
thinking. (_Always_ a bad thing.)
First, why the increase in Vne? Takeoff power for the M14P is
360HP, but that's only for five minutes max. From the maintenance
manual on the GeSoCo page, the 'Nominal I' power is 290HP and
'Nominal II' is 240HP. 75% 'Cruise I' is 180HP. Would only 40HP
more than the O-540 push the plane past the established Vne?
Also, I wondered, what would have to change if there was an
increase in gross weight and no structural changes? Assuming the
fusalage is strong enough for the higher load, then the real impact
is on the wing and landing gear. (The later, literally.)
So say the wing is designed for +5.7 and -3.8G's ultimate. That's
+17,100lbs and -11,400lbs at 3000lbs gross. For the same
strength margins, you'd have +4.9 and -3.3G's as the limit. My
Cessna is rated in the normal catagory at +3.8, -1.52G's.
Assuming ultimate is 150% of rated, that's +5.7 and -2.28G's, so
that puts me below normal catagory.
Nuts.
Still, it could be flown here, as long as you keep the plane below
those G limits by adjusting the V speeds. Vs0 and Vs1 would
have to go up, due to higher wing loading. Vfe might not change, if
the loads on the flaps don't change much with aircraft load. Va,
Vno and probably Vne would change, but I have no idea by how
much or which way. Normally, Va would go up 4% with the
increase in gross, but since we've changed the G limits, that
probably doesn't apply anymore. (This is where my ignorance
shows. I don't really understand how V numbers relate to the
physical structure.)
The landing gear depends on how often and how hard you bounce
the plane, so full tilt boogie landings on sandbars might be out...
I bet headgame stuff like this gives designers heartburn. :)
---
David Parrish
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thinking. (_Always_ a bad thing.)
First, why the increase in Vne? Takeoff power for the M14P is
360HP, but that's only for five minutes max. From the maintenance
manual on the GeSoCo page, the 'Nominal I' power is 290HP and
'Nominal II' is 240HP. 75% 'Cruise I' is 180HP. Would only 40HP
more than the O-540 push the plane past the established Vne?
Also, I wondered, what would have to change if there was an
increase in gross weight and no structural changes? Assuming the
fusalage is strong enough for the higher load, then the real impact
is on the wing and landing gear. (The later, literally.)
So say the wing is designed for +5.7 and -3.8G's ultimate. That's
+17,100lbs and -11,400lbs at 3000lbs gross. For the same
strength margins, you'd have +4.9 and -3.3G's as the limit. My
Cessna is rated in the normal catagory at +3.8, -1.52G's.
Assuming ultimate is 150% of rated, that's +5.7 and -2.28G's, so
that puts me below normal catagory.
Nuts.
Still, it could be flown here, as long as you keep the plane below
those G limits by adjusting the V speeds. Vs0 and Vs1 would
have to go up, due to higher wing loading. Vfe might not change, if
the loads on the flaps don't change much with aircraft load. Va,
Vno and probably Vne would change, but I have no idea by how
much or which way. Normally, Va would go up 4% with the
increase in gross, but since we've changed the G limits, that
probably doesn't apply anymore. (This is where my ignorance
shows. I don't really understand how V numbers relate to the
physical structure.)
The landing gear depends on how often and how hard you bounce
the plane, so full tilt boogie landings on sandbars might be out...
I bet headgame stuff like this gives designers heartburn. :)
---
David Parrish
*-----------------------------------------------------------------------------------*
The Murphy Rebel Builders List is for the discussion
between builders and owners of Murphy Rebel aircraft.
Archives located at:
http://www.dcsol.com/murphy-rebel/lists/default.htm
*-----------------------------------------------------------------------------------*
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