Weight Limit

[s.vannostrand at kodak.com]

Buddy, 
I like opinions that are backed up with data and not just perceptions.  My 
experience as a designer, like yours, leads me to the conclusion that 
there is a limit on how much airframe volume can exist in a 2m box and 
still have a precision aircraft.  This limit may be larger than what we 
have today, but not much larger.  A cubic airplane will not have the same 
stability as a monoplane or biplane.  Also, a heavy plane with a bigger 
engine won't necessarily fly better either.  As you state, there is a wing 
loading target that must be maintained.
  The cost of "exotic" materials in an airframe is not the expensive part. 
 Too many people focus on this and forget where their money really goes. 
AeroSlave has carbon fiber planes for the same price or less than other 
manufacturers glass planes.  I think the prices paid for carbon fiber 
exhaust systems have much more of a price premium than the premiums 
assessed on airplane kits.  The emergence of digital servos has also upped 
the ante.

Thanks for the numbers,
--Lance

===============================
Ron and Georgie 
Good point! Except before any conclusions can be made reguarding weather 
raising the weight limit while keeping the 2 meter size will result in 
larger airplanes and increasing cost you must first study the limitations 
of a high performance pattern airplane.

If you accept the fact a high performance pattern plane will have a wing 
loading of 100 sq. in. per pound then a 13 lb airplane will have a 1300 
sq. in. wing area . Lighter loading will result in less than acceptable 
fligh charesticts especially in higher wind conditions and I think that we 
will all agree that heavier wing loading will degrade performance. 

Adding a fatter and taller fuse and larger wings will certainly add 
weight.If you run the numbers this will be about a 15% increase in 
airframe weight for the 1300 sq. in. size.

I personally think that increasing the airframe size/ weight 15% will have 
little effect on cost.

Now if you increase size (Keeping the Maximum 2 meters limit ) you may 
need more power!  and that will possibly result in engine design changes 
or the ability to adapt gasoline engines to pattern. If a gasoline engine 
can be used then it's a no brainer the cost of flying will be reduced . 
the more you fly with gas the more the average cost of pattern is lowered. 
If you  fly 8 flights per gallon @ $16.00 per gallon the cost is $2.00 per 
flight. Gasoline @ $2.00 per gallon 25 cents per flight a savings of $1.75 
per flight. The savings there  could reduce the cost of flying pattern by 
30% 

As a designer and builder of pattern airplanes given the current 2 meter 
limit  I think the only reason for me to consider a larger design would be 
to cut my cost  since I can find no other reason to go larger. If anyone 
has a valid reason speak up I am listening. 

       And we have the age old argument that raising the limit will make 
many of the current near 2 meter size ARF's legal for pattern and bring 
more people into pattern at a reasonable cost. I think that  may be true, 
and once they are hooked they will opt for a true pattern design. 

Buddy
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