Syd,
I have measured a 3-view of the W-1 in "From The Ground Up" and
compared the location of the bottom of the pilot's seat to that of the
Coupe. In terms of the total distance from the ground to the top of
the respective cabins, the W-1 had the pilot's bottom a bit over
halfway (.53) up; and the top of the cabin was the BOTTOM of its wing
airfoil/structure. In the Coupe, this was a bit over a third of this
distance (.35) up.
The high wings of the W-1 and W-1A were of wood and fabric
construction. The 415-CA (wooden structure) Ercoupe was heavier than
the metal structure airframe. It is unlikely that the W-1 and W-1A
Wings were lighter (on a square foot basis or in terms of total weight)
than "factory" Ercoupe wings as each was finished out.
In the coupe, the centerline of the engine is roughly aligned with the
pilot's heart. In the W-1 and W-1A it is above the pilot's head. In
all liklihood, the fuel supply would also have been located similarly
high.
None of the above three realities appear consistent with your attempt
to dismiss the high wing W-1 and W-1A from contradicting the last
element of your stated theory. How do you define "low" in terms of
vertical CG? Some percentage of some "universal" structural height of
primary structure?
There would appear to be nothing "new" in stating that for crosswind
landings in a crab that:
(1) Tricycle gear is required (that appears to be the only way to
locate the MLG behind the CG in a lightplane)
(2) The MLG must have sufficient strength to withstand the forces
possible from the maximum possible landing speed AND the maximum design
crosswind capability (plus appropriate safety factor).
The "strength" needed here is much less than might appear necessary
because I see two separate forces to deal with upon landing. First,
there is the "maximum force of vertical sink", involving the
combination of structural strength and design shock absorption) upon
"arrival" in a calm wind condition.
Only secondly do we look at the additional twisting force present at
touchdown at the maximum design crosswind capability. This is not as
simple or straightforward because the airframe mass is (or should be)
traveling a course identical (aligned) with the runway heading
(tracking).
The moment the main tires touch in a crab the "lead tire" (most forward
main) takes the greatest "load" as its wheel and tire accelerate from 0
to 60 mph (as an example) over the time it takes for the trailing arm
gear to compress. I would speculate that this "transition is complete
before the oleo is fully compressed by airframe weight.
The other tire takes a lesser load because the "trailing tire" is going
to absorb part of that energy circumscribing an arc-shaped path as the
moving mass of the airframe forces the rolling main tires to align
themselves with the runway heading. It seems probable that the great
majority of "crosswind gust loading" energy is absorbed in the action
of the various oleos and the physical rotation of the airframe.
In this context, the sideloads of a 30 mph cross wind would probably be
little different on a main gear leg landing at 35 mph "forward" speed
on the W-1 or W-1A or one landing at 70 mph "forward" speed in a coupe.
Any specific loading trying to distort the trailing arm gear sideways
is brief and essentially self-unloading with very little mechanical
resistance. This is NOT the case with the Alon "spring gear", which
will take a "set" requiring replacement or shimming following undue
landing abuse.
Perhaps one of our "heavy iron" people has the necessary contacts at
Boeing to see if those landing gear designers assign a percentage to
these different forces, or if they simply find the normal "safety
factors" for handling "maximum force of vertical sink" adequate to also
handle "crosswind gust loading".
I just don't follow your assertion that a low wing design or low CG has
significance. Is a crabbed landing on the mains OK or a no-no for,
say, the Aero Commander (like Bob Hoover did his single engine and
engine out routines in a special version) or the Dehaviland Otter
turboprop commuter? (I don't know)
Regards,
WRB
--
On Apr 4, 2010, at 17:33, Syd Cohen wrote:
>
>
> WRB,
>
> You notice that I said "low vertical CG." The W-1 and W1A had rather
> light wings and the pilot's seat was fairly low to the ground. Also,
> it landed fairly slowly.
>
> Syd
>
>
>
> On Apr 4, 2010, at 5:02 PM, William R. Bayne wrote:
>
>>
>> Hi Syd,
>>
>> The W-1 and W-1A were of high wing design!
>>
>> Regards,
>>
>> WRB
>>
>> --
>>
>> On Apr 4, 2010, at 13:59, Syd Cohen wrote:
>>
>> >
>> >
>> > Frank,
>> >
>> > Trailing link or not, ALL tricycle gear airplanes have their main
>> gear
>> > located behind the center of gravity of the airplane. If it were
>> > ahead of the CG, the airplane would fall on it's tail whenever on
>> the
>> > ground. Taildraggers, on the other hand, have their main gear
>> located
>> > ahead of the CG, and the tail rides on the tailwheel.
>> >
>> > Three conditions are required for crosswind landings in a crab: 1.
>> > Main gear that has been engineered to take the side loads of the
>> > crosswind touchdown; 2. Main gear located behind the CG; and 3.
>> Low
>> > vertical CG of the airplane, such as a low wing design. The plane
>> > must have all 3.
>> >
>> > Syd
