I noticed a 2M with "Drela Derivative" airfoils at Sal's site: http://nesail.com/detail.php?productID=5125 Has anyone seen it in person yet? Looks promising.
On 8/1/06, Daryl Perkins <[EMAIL PROTECTED]> wrote:
Dave, What a great post. Thank you. You're right on about the MH32 being a poor choice for a 2M section. I don't like it for open class TD either. Drela has done a good deal of optimization on sections for us, and he's got a pretty good idea of what works in the real world. Definitely a good idea to try some of his thinner sections on a 2M. The key here would be LIGHT!!! I don't particularly like super low A/R 2M's... ala the Duck. Span loading ends up too high, wing loading too low... not a good combo. At least not my personal preference… you get a model that doesn't go anywhere... AND comes down quickly... woohoo!!! Your also correct about AUW. My old Lasers used to weigh in around 31 ounces, and they flew quite well (for a 2M). People seem to have gotten complacent about 40 and 45 ounce 2M's. Of course they fly fine... they're just pre-ballasted. Especially when you're only flying against other 40 and 45 ounce models. But remember, a 2M isn't much larger than a HL model. They're what? 25% larger? Who wants to thermal a 30 ounce HL? Or even a 20 ounce HL for that matter? That's tremendously over simplified, there are many other factors here, but you get my point. We can't build our 2M's light enough. Mike L's 2M Aegea weighed in at I think about 25 ounces (before the boom broke), and it was probably the best flying 2M I've ever seen. In the early morning light lift rounds, his was the only model that even recognized lift, as the rest of the field flew right through it and underneath him without even a bobble. V-Tails - still... no. The main problem with a V-Tail is that we all fly differing stability ranges. What I mean here, is that while I may prefer a less stable model, you may prefer a more stable model, and a beginner prefers a ludicrously stable model. Why am I talking about stability and not CG??? .. same thing for this discussion. You can't just oversize the V to be correct in yaw, and expect the model to fly right. It'll be too stable for me, and maybe for you... but perfect for the beginner. When I flew Super V's, I couldn't get the model "loose" enough. I'd cheat the CG way back, until I was happy with the performance and flight characteristics in pitch, and the model would tuck hard in slow cruise (harder as the speed increases). Not great for a TD model. Soooo... that's an indication that the model is overstabbed or too stable. So, I had to cut the V's down... then all my yaw stability went away. V-tails are a compromise at best. You can play games with the V angle to get it closer, but I've never got one right. They're fine for a one dimensional model - ala a slope racer, cuz you're never hanging the model on the wing. You don't see Drela's design's being V-Tails, do ya? ;-) The design challenges for a 2M are rather complex, and this makes it sorta fun. There are many compromises to be made. A/R vs. Area. Cruise vs. Hang. Cross tail... or... uh cross tail. (I'm not even gonna mention a damn V) I'm going to do a new 2M in the next few months. I'm not just going to focus on the wing, but on the fuse as well. We're seeing gains in F3B with small cross section fuses. I think I can shave some weight, and some drag here as well. I've broken up with multiple women in the last few months... need to do enough models to keep up with the naming process... ;-) Possibly "Lil Beeotch" - we'll see D __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off. Email sent from web based email such as Hotmail and AOL are generally NOT in text format
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