Stephen and KR Netters, Take a look at my web site and you will see what I did, may help you with your decision. Adrian
Stephen Jacobs wrote: > Now I am torn between following the manual or using something less than > 3.5 degrees to yield a more "normal" in-flight nose up/down attitude. > Then I ask myself, "If I use less than 3.5 degrees at the fuselage, what > happens to the normal wing tip washout of +.5 degrees...does it become > negative? stay the same or what?" > > +++++++++++++++++++++++++++++ > > Bernard > > You have received several replies to this question, most of them address > elements of the topic but I am not sure that you have heard enough help > you make a firm decision. > > If this is old hat ignore, but just in case. > > As you know, washout means setting the wing tips at a lesser incidence > angle (than the inboard side). The purpose for this reduced incidence > at the tip is to ensure that the wing tips stall last (relative to the > rest of the wing). This reduces the likelihood of "tip stalls" (wing > dropping) and makes the airplane less likely to spin when stalled. > Loads more could be said about this, but that is the gist of washout. > > Because it is the improved stalling characteristics at the wing tip that > we want - some airplanes have little (or no) angular washout as such - > instead they have a different wing (airfoil) section at the tip that > stalls at a higher angle (and thus delays the outboard stall). It is > also true that there are aircraft with zero washout of any nature. > > How much washout? Any amount of washout will contribute to the above > advantage, but as we add washout (reduce incidence over some of the > wing) we also reduce the amount of lift the wing is creating. As such, > washout is good - but only to a point. > > I would suggest that somewhere between 1.5 and 2.5 degrees of reduced > incidence at the tips would NORMALLY be about right. But normally the > washout (wing twist) would start where the wing "starts" - right by the > fuselage. > > Because the KR has a centre section, the washout only starts where the > outer wing panel starts, so we need to get in a bit more twist over a > shorter distance. The angular amount should thus be a bit more - so > maybe 2.0 to 3.0 degrees for a KR. The optimum amount is effected by so > many things (wing section, wing span, wing loading, speed range, mission > requirement, etc.), but I believe that anything in this zone will do the > job. > > To refine your decision, have a close look at web sites like Langford > and Reid - they discuss their reasons for what they have decided on - > these are informed opinions. > > Above we talk about the angular relationship of the wing tip to the wing > root. Your other question is about incidence - the relationship between > the whole wing (washout and all) to the fuselage. > > Kenny made it 3.5 degrees (root) and hundreds of KR's are happily flying > about like that. The little bird looks a bit like an Apache helicopter > on a beat-up, but the nose-down "sit" is a part of the KR character. > So, for openers, the plans way works just fine. > > It is however also true that 3.5 degrees is not very efficient for the > KR as it has evolved, particularly for the airplanes that are aspiring > to 140mph and more. It does not sound like you are using the new wing > section so it is less significant for your KR, but 1.5 to 2 degrees less > than the plans call for may be a good idea. > > Ask 10 guys and you will get 11 different answers. The 12th answer is > (RAF 48) 2 degrees at the root with 2 degrees washout (0 at the tip). > > Take care > Steve J > > > > > _______________________________________ > to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net > please see other KRnet info at http://www.krnet.org/info.html > > . > -- Adrian VE6AFY Mailto:cart...@spots.ab.ca http://www.spots.ab.ca/~cartera
