Weight Limit

[Adam Glatt]

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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