Flyer Posted October 29, 2015 Share Posted October 29, 2015 Hi lads, Is there a general consensus of which rib profile is well suited for PSS models? Or could someone push me gently in the right direction. Am being brave (or very stoooopid) in attempting to design and fly my own design PSS, and am trying to make things a little easier for myself. Thanks Adrian Quote Link to comment Share on other sites More sharing options...
Andy Meade Posted October 29, 2015 Share Posted October 29, 2015 Oooh nice What sort of size aircraft are you looking at? (wingspan and weight if possible) Quote Link to comment Share on other sites More sharing options...
Flyer Posted October 29, 2015 Author Share Posted October 29, 2015 Looking at around 50 inches or so, not sure on weight yet, as I can always add church roof!! Quote Link to comment Share on other sites More sharing options...
Andy Meade Posted October 29, 2015 Share Posted October 29, 2015 Want it to fly fast like a fighter or float like a bomber? Quote Link to comment Share on other sites More sharing options...
Flyer Posted October 29, 2015 Author Share Posted October 29, 2015 It's hoping to be based on a fighter, if my reflexes are up to it !! Quote Link to comment Share on other sites More sharing options...
Andy Meade Posted October 29, 2015 Share Posted October 29, 2015 I'd stick with something along the lines of an Eppler 374, or an SD6060 then. I have also used an MH32 (built without the camber at the back) with pretty good success. Oh, all of these as long as it isn't a delta / flying wing by the way Quote Link to comment Share on other sites More sharing options...
Flyer Posted October 29, 2015 Author Share Posted October 29, 2015 Thanks Andy, would the SD6060 work with a forward sweep? Quote Link to comment Share on other sites More sharing options...
Andy Meade Posted October 29, 2015 Share Posted October 29, 2015 Eeek. FSW's get a bit funny, but from what I can remember of Andy Lennon's model design book, there is no special requirement. The root can stall before the tips I think, which creates a pitch up that you might not be able to recover from. You may need to wash-in at the tips! Can we start guessing what it is yet? Edited By Andy Meade on 29/10/2015 13:58:56 Quote Link to comment Share on other sites More sharing options...
Andy Blackburn Posted October 29, 2015 Share Posted October 29, 2015 I wrote a piece in the PSSA Magazine back in 2001 that's now on the pssa website, it's called "The Jet Fighter as a Marginal PSS Subject", and it was updated it last year. It might be useful (depends what your application is, of course) but in summary: Think about the pitching moment as well if it's a swept wing - if the section has a lot of camber you might find that you're having to use a lot of stabiliser angle to balance out the pitching moment, or that you have to use a downward-lifting tailplane, either of which will generate drag that you'd probably rather not have. I like E178, E180 and SD6060. For models with straight wings, Clark Y and Selig S7055 are nice. If the wing is less than (sweeping generalization coming up) about 7 inches in chord, think very carefully before using a section like E205 or E374 because they're not that efficient at smaller wing chords. Other than that, they're usually very good. Swept wings are much better with washout; if you leave it off, you may regret it unless you have the c.g. further forward than optimum and are therefore living with a bit more drag, or unless you always fly it fast. Straight wings are also better with a bit of washout, particularly when thermalling, sctarching on the slope edge or in the landing circuit. Other people may well disagree with this, but that's my two penn'orth. Quote Link to comment Share on other sites More sharing options...
Flyer Posted October 29, 2015 Author Share Posted October 29, 2015 The full size had the problem of the root stalling before the tips, in part due to the whole wing flexing. I'm going to try and make a wing that resists flexing without adding too much weight. As I say, its at the design stage, so a long way to go. The wash -in may be the way to go. If you don't try, you'll never know. Quote Link to comment Share on other sites More sharing options...
Andy Blackburn Posted October 29, 2015 Share Posted October 29, 2015 IMO, a FSW with SD6060 should be fine - the root should tend to stall before the tip but depending on the wing chord (airfoils generally tend to change their characteristics at smaller wing chords) I'd still be thinking about washing out the tips a bit. Is it an X-29? Some Luft46 exotica? ... Quote Link to comment Share on other sites More sharing options...
Andy Blackburn Posted October 29, 2015 Share Posted October 29, 2015 But, you want the root to stall before the tip, don't you? Because if the tip stalls first, there will be A Problem, the gravity of which will depend on height over terrain. Why don't you try a smaller-scale free-flight glider from 1/16" sheet first...? Edited By Andy Blackburn on 29/10/2015 14:09:29 Quote Link to comment Share on other sites More sharing options...
Andy Meade Posted October 29, 2015 Share Posted October 29, 2015 I thought the root stalling before the tip produced a big pitch-up that just worsened the matter - the main reason FSW's spin so very well and rarely recover. Sukhoi 47? Quote Link to comment Share on other sites More sharing options...
Flyer Posted October 29, 2015 Author Share Posted October 29, 2015 Thanks Mr Blackburn, there's a lot for my little mind to take in. And from a quick look at the link to the PSSA I may be ok with a wingspan above 50 inches. It is an X-29A I'm looking at , always been interested in it, so seems that PSS may be the way to go. I'm looking at proving the concept with a corex model first, then move onto something more accurate, but by using a 'proper' aerofoil'. Something for those dark winter nights. Thanks for your input. Quote Link to comment Share on other sites More sharing options...
Andy Meade Posted October 29, 2015 Share Posted October 29, 2015 Good choice The X29 certainly is a looker (in my book at least). There is a PSS plan for one out there, if you didn't want to do any of the testing and development heavy lifting. https://www.myhobbystore.co.uk/product/16174/rc1518--grumman-x-29a Edited By Andy Meade on 29/10/2015 14:30:41 Quote Link to comment Share on other sites More sharing options...
Harry Twist Posted October 29, 2015 Share Posted October 29, 2015 Some coincedences are amazing! I was thinking of asking a similar questions to Adrians' ref a model I have in mind to scratchbuild also. So... while wing section thoughts are fresh and apologies beforehand for riding on the back of Adrians X29 thread ... what profile would you suggest for ( I'll let you work out the aircraft!).... A flying wing - with rearward swept wings approx 30 degrees sweep, approx 6 degrees dihedral plus some washout , winglets with approx 20 degrees anhedral. With upright small fins on each wingtip. Aim span 46 inches all balsa built up fuz aim weight 2-2.5 pounds. I dont want a rocket ship and want it to be able to fly in medium ish (13-25mph) wind speeds approx. I have read up on some recommended sections but got a little brain blown between RG15, E374 and others. That, plus the confusion of the addition of anhedral winglets led me back to thinking of keeping a simple Clark Y profile for the main wing!!! Any thoughts? Regards H Edited By Harry Twist on 29/10/2015 15:53:55 Quote Link to comment Share on other sites More sharing options...
Andy Blackburn Posted October 29, 2015 Share Posted October 29, 2015 Harry - have a read of the link above before using a heavily cambered section like Clark Y on a swept-wing; it will probably give you problems with a swept wing, possibly severe problems if its tail-less. Personally, I'd consider a "proper" flying wing airfoil such as E178 or E180. Quote Link to comment Share on other sites More sharing options...
Andy Blackburn Posted October 29, 2015 Share Posted October 29, 2015 > I thought the root stalling before the tip produced a big pitch-up that just worsened the matter - the main reason FSW's spin so very well and rarely recover. Yeah, but it's a matter of degree, is complicated by airfoil behaviour at small wing chords, the very aft c.g of the full-size (wasn't it one of the first unstable fly-by-wire aircraft?) and I haven't got a wind tunnel, so I have no idea what a conventionally-balanced one is likely to do. Hence the suggestion of a much smaller profile model from 1/16" sheet. Good point, though... Edited By Andy Blackburn on 29/10/2015 16:03:51 Quote Link to comment Share on other sites More sharing options...
Andy Meade Posted October 29, 2015 Share Posted October 29, 2015 Harry, my Horten 229 uses (I believe) Eppler 330 at root, and fully symmetrical at the tip. No wussy fins on that baby though! Soo...Blohm & Voss 215 / 209? Edited By Andy Meade on 29/10/2015 16:09:11 Quote Link to comment Share on other sites More sharing options...
Andy Blackburn Posted October 29, 2015 Share Posted October 29, 2015 I think it's a B&V 212... ?? Quote Link to comment Share on other sites More sharing options...
Mark Kettle 1 Posted October 29, 2015 Share Posted October 29, 2015 Eppler 330 is very similar to the section I use on the Vulcan. Look at NACA 23012 a well, a good section albeit make a little slimmer say 8 - 9% and flatten out at the tip or like Andy's Horton make it symmetrical at the tip. Quote Link to comment Share on other sites More sharing options...
MattyB Posted October 29, 2015 Share Posted October 29, 2015 For a Horton I would try one of Martin Hepperle's MH sections, or maybe one of the older EH sections - either option should do the job nicely and offer more performance than the older Eppler sections. Quote Link to comment Share on other sites More sharing options...
Harry Twist Posted October 29, 2015 Share Posted October 29, 2015 Hi All, Many many thanks for the suggestions it's a BV 215 I have in mind. Ugly but also lovely. I may lessen the sweep to 25 degrees, increase the wing area slightly (10% ish) - hopefully both these things wont detract too much from a scale like appearance. I dont really want to over complicate production so will probably stick to a constant section throughout. Just a thought on winglets - anyone think these should be a flying section also? I think they should but happy to be recommended otherwise. I will go away and study some of the suggestions made. Thanks again. Regards H Quote Link to comment Share on other sites More sharing options...
Flyer Posted October 30, 2015 Author Share Posted October 30, 2015 Thanks for all the input; I think I need a bigger drawing board !!! At 1/7th scale the fuselage is 2.1m long with a wingspan of 1.184m. Suppose it should be big enough to utilise the SD6060 and still be manageable to launch. Luckily, my new workbench in 2.4m long...... Work will be nuts now until end of January (but can fit in drawing up plans ), so looking at starting construction in Feb 2016, although with my rate of build it may take some time. He who dares............fill's more black bag's....... Quote Link to comment Share on other sites More sharing options...
Andy Meade Posted October 30, 2015 Share Posted October 30, 2015 Good on ya That's a pretty good size - will be impressive! Are you including the strake flaps on the back of the fuselage? I saw a depron build yesterday on RCGroups that used them. Quote Link to comment Share on other sites More sharing options...
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