Re: [RCSE] Re: 2M Rambles
Actually Dave, this is a perfect place to go into detail. There has been so much dribble and little info that it is refreshing. David Register wrote: It's a little tough to go into too much more detail on RCSE. Also probably not of general interest to everyone on the list. Is this topic of sufficient interest to open a 2M forum on RCGroups where some more detailed numbers, graphs etc. can be posted. Or does such a forum already exist? -- Jeff Steifel 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
Re: [RCSE] Re: 2M Rambles
From: David Register [EMAIL PROTECTED] Good luck with the girlfriends. In 1963, Jimmy Soul had a #1 hit with some interesting advice along those lines. = Which said: If you wanna be happy for the rest of your life Never make a pretty women your wife Go for my personal point of view Get an ugly girl to marry you 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
Re: [RCSE] Re: 2M Rambles
From: David Register <[EMAIL PROTECTED] /> Good luck with the girlfriends. In 1963, Jimmy Soul had a #1 hit with some interesting advice along those lines. = Which said: If you wanna be happy for the rest of your life Never make a pretty women your wife Go for my personal point of view Get an ugly girl to marry you Just don't let your wife know that's your philosophy if you want to go on living!George Gillburg Bakersfield, California 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
[RCSE] RE: 2M Rambles
Allegro broken with negative G's Brent, What was the mode of failure? How would you build the wing differently if you wanted to survive a quick and too deep dip into the bucket? Aradhana Singh Khalsa Espanola, NM 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
RE: [RCSE] RE: 2M Rambles
I really wouldn't change much beyond my launch technique. If I do build another, I would be a little more careful with my spar wrapping and glueing of the center section, the centermost 6 inches in particular. I might consider adding a little more carbon in that same area if I had some thin prepreg available, inside of the bottom spar? It would just take a little sanding down of those shear webs a bit. Again, it's pretty darn tough, but avoiding a deep dip is probably a pretty good idea any way. Good luck! Brent 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
[RCSE] Re: 2M Rambles
Actually, I think, given the AG airfoils, optimum aspect ratio is probably a function of your vision. Given very good vision and very good skill with composites, optimum aspect ratio is probably upwards of 12, as in the original Agea 2M. More realistically, maybe a bit over 11. Wing loading shouldn't be an issue, given enough building skill, as 21 oz. can be acheived. Maybe 25 oz. for all the other really good builders besides Mark. You can add ballast on windy days. Carbon tailbooms and some of the other more sophisticated building tricks keep the weight down. Most of those old airfoils are now obsolete, aren't they? (I saw a new foil, a thicker one, on the yahoo xfoil group, which behaves just like a thinner AG, though) In local contests, I end up competing against Mark. One of these days I want to see what happens if I have a glider almost as good as his is. From: David Register wrote: snip snip Beause of it's size, a 2M is not going to be able to roam as far or as high as an open class ship - it's simply harder to see at distance. So, like DLG, it's going to be more of a close-in ship. Consequently, it probably should tend to better minimum sink and max L/D rather than having great 'legs' for roaming all over the sky. This tends to drive the design towards lower aspect ratios. Due to the span limit, a high aspect ratio 2M may start to run into Re problems. Carrying more wing area will allow a lower wing loading with modest attention to building techniques. This should also help with the launch as more area would help to carry the tow weight better. The airfoils often used for 2M are not particularly well optimized for this class. If you run X-Foil snip So a couple of suggestions; - Look to lower aspect ratio designs. An evaluation discussed in RCSD a few years back suggests the 8 to 11 range is about right.snip - Sort through the Drela sections, many of them are much better in the intermediate speed range than any of the sections commonly used for 2M, snip - Work a bit on keeping the weight in the 30oz range. A ballast box is great for the windy days but it's tough to add lightness. snip - Dave R 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
[RCSE] Re: 2M Rambles
Daryl (and list), Thank you for the comments on 2M design. Your input is extremely valuable as both a designer and competitor. The stability issue is well put. Just to clarify aspect ratio a bit, some design work was done 2 years ago that suggests optimal AR for 2M is somewhere between 8 and about 11. The range and boundaries are 'soft' depending on the pilot's preferences. This was done on the basis of a fairly detailed polar analysis which uses UIUC airfoil data or X-Foil results, a modestly detailed description of the planform and some assumptions about parasitic drag and fuselage wetted area. Why such a broad range? Well, once a design is set, decreasing AR increases wing area (and the associated tail volumes) which increases the weight (but reduces the wing loading), increases induced drag, reduces profile drag coefficients a bit due to Reynolds number, etc. etc. It's an interesting interplay but one has to consider that weight is not an arbitrary parameter but is tied to the planform once a general construction method is adopted. The span loading issues that you mentioned are not addressed in this type of analysis. Nor are handling, turning, stability, etc. etc. So there's a lot more to the picture once the general planform parameters are established. Field experience and the pilot's preferences are the deciding factors. The other thing that comes into play (for 2M and smaller) is the flow attachment on the airfoil. The Drela sections are just better designed that way than just about anything that preceded them. You can compare X-Foil with UIUC data for those sections where measurements have been made. The result is generally gratifying. Extending that analysis to the AG sections leads to the observation of separation bubbles in many of the popular sections used for 2M. The bubble generally appears at modest Cl values so the problem is not high drag at high Cl (low speeds) but in the intermediate speeds (cruise). Consequently, airfoil choice for 2M will be particularly sensitive in the mid-speed range (generally higher than max L/D - about the range where you want to scoot to cover ground). At these Cls, induced drag is not really an issue (AR is not terribly important at lower Cl). Profile drag is the big issue and the non-Drela sections are generally not great in this range. When you go to open class, the chords and speeds go up enough that the problem tends to go away. Bottom line, there are a lot of trade-offs. Input from guys who have your level of field experience are invaluable to the design process. Polars look real good on paper but if all it does is run great in a straight line then it's not much use. However, a polar is a useful starting point and the calculations are generally supported by what little field data there is. It's a little tough to go into too much more detail on RCSE. Also probably not of general interest to everyone on the list. Is this topic of sufficient interest to open a 2M forum on RCGroups where some more detailed numbers, graphs etc. can be posted. Or does such a forum already exist? Thanks very much for the feedback Good luck with the girlfriends. In 1963, Jimmy Soul had a #1 hit with some interesting advice along those lines. - Dave R 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
