Weight Limit

[s.vannostrand at kodak.com]

Yep!  That's just one of the many tradeoffs that is part of a design.
There are other issues as well.

--Lance

Won't equipping larger wings effectively decrease the tail moment and hurt
stability?

 ----- Original Message -----

   From:  Buddy Brammer

   To:  discussion at nsrca.org

   Sent: November 11, 2002 3:38 PM

   Subject: Re: Weight Limit


   Lance

   I think my numbers went over most peoples head. None the less once they
   spend the time and money to build / design  a competative pattern
   airplane they will come to the same conclusion that I have. wing loading
   not weight limit is the limiting factor and I believe that even if we
   removed the weight limit entirely pattern design would would not see
   radical changes with the 2 meter size limit we now have.

   Buddy

   >From: s.vannostrand at kodak.com

   >Reply-To: discussion at nsrca.org

   >To: discussion at nsrca.org

   >Subject: Re: Weight Limit

   >Date: Mon, 11 Nov 2002 12:38:06 -0600

   >>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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