Reality setting in
08-09-2009 | 09:54 AM
#1
Thread Starter
Senior Member
My Feedback: (1)
Reality setting in
At another forum here, reality is setting in for a couple of readers/respondants.
Apparently they were thinking that just because the box top says "Uses a NACA ____ Airfoil !!" it was the same from root to tip.
Naw.... that ain't necessarily true.
See we have to adjust things a bit out near the wingtip, such that a common 1/4 inch thick slab can be used full length. A 1/4 or 1/2 inch high wing spar does not often get cut down or tapered over the entire length either. All this in order that these easy to find common wood parts can be used with a minimum of sanding or other modifications. We make the airfoil thicker (higher) so that you do not have to sand away everything then in order to make fit or reduce the thinness of the rib/spar sockets.
All this was thought of way back when, and is still being done today. You need not worry any more. That expressed airfoil is only printing then.
Wm.
Apparently they were thinking that just because the box top says "Uses a NACA ____ Airfoil !!" it was the same from root to tip.
Naw.... that ain't necessarily true.
See we have to adjust things a bit out near the wingtip, such that a common 1/4 inch thick slab can be used full length. A 1/4 or 1/2 inch high wing spar does not often get cut down or tapered over the entire length either. All this in order that these easy to find common wood parts can be used with a minimum of sanding or other modifications. We make the airfoil thicker (higher) so that you do not have to sand away everything then in order to make fit or reduce the thinness of the rib/spar sockets.
All this was thought of way back when, and is still being done today. You need not worry any more. That expressed airfoil is only printing then.
Wm.
08-09-2009 | 10:17 AM
#2
Senior Member
RE: Reality setting in
Actually, semi-smart designers make the spar cutout deeper when they wish to use that spar without having to taper it.
Furthermore, smart designers understand how sensible it is to taper a spar thickness and do the work necessary for optimum weight vs strength.
Personally, if I knew that a kit cutter didn't understand the value in following the plans as printed, I'd find another kit cutter. And I wouldn't use plans that had a spar that was just as thick at the tip as it was at the root on a tapered planform. But then I figure the model's performance is more important than doing the kitting at absolute minimum cost and effort.
Furthermore, smart designers understand how sensible it is to taper a spar thickness and do the work necessary for optimum weight vs strength.
Personally, if I knew that a kit cutter didn't understand the value in following the plans as printed, I'd find another kit cutter. And I wouldn't use plans that had a spar that was just as thick at the tip as it was at the root on a tapered planform. But then I figure the model's performance is more important than doing the kitting at absolute minimum cost and effort.
08-10-2009 | 09:45 PM
#3
RE: Reality setting in
This reminds me of how very many variations I've seen for RAF32 airfoils on old time rubber models. With many of them other than the name being given you'd have no idea that they were meant to be the same airfoil.... 
Coos', since you've been doing a fair bit of OT stuff lately I'm sure you're well familiar with many similar "freedoms" having been taken with the science of aerodynamics.
Coos', since you've been doing a fair bit of OT stuff lately I'm sure you're well familiar with many similar "freedoms" having been taken with the science of aerodynamics.
08-12-2009 | 10:53 PM
#4
My Feedback: (60)
RE: Reality setting in
Here's an easy way to do a "tapered" spar. Laminate it! This is on my Yak-11 wing which gets very thin at the tip. The spars are laminated out as far as they will go without cutting the rib completely in half and then the top lamination carries on from there. A laminated spar is very strong as well.
