KR> wing design question
Fred, By scaling the airfoil only in one dimension (since you want to keep the same chord length) you are essentially changing the airfoil and consequently changing the aerodynamic characteristics. I think you would need to work out the characteristics of this new airfoil to figure out what the washout should be. I would imagine washout would be the least of your worries with an untested airfoil at your wing tips. Even if you keep the same airfoil shape (means you scale in both dimensions) the reduction in Reynold number would be enough to warrant an airfoil analysis and a washout to delay a tip stall. Ameet Savant Omaha, NE - Original Message From: Fred Johnson To: KRnet Sent: Mon, November 23, 2009 1:31:52 PM Subject: RE: KR> wing design question Mark, I did mean same airfoil, just thinner profile out to the tip. Like say 18% at the root and 14% or thinner at the tip. All the same chord. The drag at the root would be slightly higher but would the lift be slightly greater also because of the thickness? You are correct, the AS is as good an airfoil as you could design based on the flight parameters of the KR. Fred Johnson Reno, NV
KR> wing design question
I am referring to two things, one is an article from Barnaby Wainfan in Kitplanes a few months back talked about it and the other are RV's. unless I am mistaken?? I know sailplanes will change the entire airfoil to a higher lifting airfoil at the tip from the root. Where the root will be fat up to 24% thick an the change to higher lift but thinner airfoil at the tip. Fred Johnson Reno, NV Tom wrote: If I may... --- Fred: "(if) a barn door no taper wing doesn't require washout," Old Piper Hershey-bar wings I've looked at have washout. Which ones are you referring to that don't 'need' washout? Washout is one strategy to helping the root stall before the tip. Hershey-bars aren't immune from this need. --- Fred: "(what would a no taper wing need if it just changes thickness from root to tip but not chord?" It's long been my understanding, an alternative to washout for almost any (general aviation, Hershey-bar or tapered) wing would be to have the chord/thickness ratio become 'fatter' as you near the tip, not thinner. This allows the tip to keep flying while the root stalls. Seems I first heard about this approach from the BD-5, which had a tapered wing. (I could sure go for a Hershey-bar now)
KR> wing design question
If I may... --- Fred: "(if) a barn door no taper wing doesn't require washout," Old Piper Hershey-bar wings I've looked at have washout. Which ones are you referring to that don't 'need' washout? Washout is one strategy to helping the root stall before the tip. Hershey-bars aren't immune from this need. --- Fred: "(what would a no taper wing need if it just changes thickness from root to tip but not chord?" It's long been my understanding, an alternative to washout for almost any (general aviation, Hershey-bar or tapered) wing would be to have the chord/thickness ratio become 'fatter' as you near the tip, not thinner. This allows the tip to keep flying while the root stalls. Seems I first heard about this approach from the BD-5, which had a tapered wing. (I could sure go for a Hershey-bar now) Tom
KR> wing design question
Mark, I did mean same airfoil, just thinner profile out to the tip. Like say 18% at the root and 14% or thinner at the tip. All the same chord. The drag at the root would be slightly higher but would the lift be slightly greater also because of the thickness? You are correct, the AS is as good an airfoil as you could design based on the flight parameters of the KR. Fred Johnson Reno, NV Mark L Wrote: Well apparently you're talking about a different airfoil root to tip so the answer would be "that depends". Obviously the thickness ratio will have to get smaller if it's tapered going out, while retaining the same chord length. If the two airfoils are from the same family and the lift coefficients are anywhere near each other, the answer is almost certainly "no washout required". I suppose it's possible you could have two completely different airfoils and the one out on the tip is creating lots more lift than the inboard, but you'd have to try pretty hard to find that combination and screw it up that bad. As you mentioned before though, you'd be hard pressed to improve on an airfoil designed by one of the leading airfoil experts specifically for the KR2S. See http://www.krnet.org/as504x/ for details on that.
KR> wing design question
Fred Johnson wrote: > If a tapered wing requires washout to keep the tip from stalling first, > and > a barn door no taper wing doesn't require washout, what would a no taper > wing need if it just changes thickness from root to tip but not chord? Well apparently you're talking about a different airfoil root to tip so the answer would be "that depends". Obviously the thickness ratio will have to get smaller if it's tapered going out, while retaining the same chord length. If the two airfoils are from the same family and the lift coefficients are anywhere near each other, the answer is almost certainly "no washout required". I suppose it's possible you could have two completely different airfoils and the one out on the tip is creating lots more lift than the inboard, but you'd have to try pretty hard to find that combination and screw it up that bad. As you mentioned before though, you'd be hard pressed to improve on an airfoil designed by one of the leading airfoil experts specifically for the KR2S. See http://www.krnet.org/as504x/ for details on that. Mark Langford n5...@hiwaay.net website www.n56ml.com
KR> wing design question
I have wing design question maybe someone on the group will know: If a tapered wing requires washout to keep the tip from stalling first, and a barn door no taper wing doesn't require washout, what would a no taper wing need if it just changes thickness from root to tip but not chord? Fred Johnson Reno, NV
