Mac
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Post by Mac on May 10, 2003 13:12:41 GMT -5
Please help.... I have been flying gliders for a number of years, (I'm currently flying a Chris Foss Phase 6), and have recently decided to get into PSS. I went to Sussex Model Centre in Worthing, and purchased a Westfield kit of a BAe Hawk. The kit itself is for 25-32 size engines, but in the SMC catalogue, it states that it is ideal for converting to PSS, (which is why I bought it). The problem I have is that the kit plans are only for building with an engine Has anybody had experience with these models? If so, could you help me please? What do I need to do to convert it to PSS
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Post by Phil Cooke on May 11, 2003 16:21:15 GMT -5
I am not totally familiar with this kit - I presume it is designed for a motor in the nose (and not ducted fan?) - if so the biggest challenge is getting the Centre of Gravity right without the motor and tank up front whilst minimising overall weight - to do this you will need to move all the RC gear upfront, by redesign. With no motor or tank you will be able to shuffle everything as far forward as poss. As the loads are generally less on our PSS machines than power models you may well be able to lighten structures, remove certain bulkheads etc to keep the weight down. If the tail is wood then consider making it out of thinner/lighter material than that supplied - this will help further in both getting the CofG right and reducing the overall weight of your glider. Use snakes or full length pushrods to operate the elevator/rudder with servos as far forward as poss. Is it a foam or built up wing? If foam we are stuck with the section supplied unless you use the plan to have another cut with a more favourable section. If it is flat bottomed of not far off then it may do fine just as it is! If the wing is built up then do consider remaking the ribs with a better proved gliding section (Eppler 205 is my fave - as on your Phase 6) or try RG15 - good at compensating for draggy airframes like hawks with big air intakes! If the intakes are open then blank them off. Perhaps consider 'streamlining' them a little too, if poss, to reduce drag without detracting from scale too much. Hope these ideas help - let me know if it is fibreglass fuz/foam wings or all built up and I/we will be able to advise better. GOOD LUCK and do let us have a piccy of your results!!!! Phil.
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Post by Phil Cooke on May 11, 2003 16:41:35 GMT -5
ok - just done a search for the Westfield Hawk and it IS all built up, so I'd like to add the following to my previous note...
Build the wing as per the kit - it says it has been proven to fly well as PSS so no need to revise the section as I suggested might be needed earlier! Dont bother reducing the air intakes section - they look fine on the box...
Seriously, your biggest redesign is in weight distribution and minimising AUW - just get all the gear as far forward as poss, (from the front - Rx Battery, Rx, Servos) - take out any ply bulkheads and replace with balsa, or leave out entirely if you see fit - make up the nose to the right profile of the Hawk, careful sanding of balsa with reference to drawings to get the right shape - perhaps thin down (1/4" or 3/16" balsa will be fine for tail and fin) or reduce weight in the tail but other than that it should go just great!
A good PSS model will have a wing loading of about 16-18 oz per sq ft, so do try and minimise weight with this little wing and you will be fine!
Finally, in the true spirit of PSS, do try and finish your model in a scale manner, look at piccies of the full size machine, spend time adding obvious scale details (dont forget a pilot!) and you will produce a fine model!
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Mac
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Post by Mac on May 12, 2003 3:59:53 GMT -5
Thanks Phil. My other concern now that I have started to build the wings is that they are of balsa sheet construction, Cyano'd edge on. This gives a 'flat' wing section, aside from a very small amount of shaping. Is this still going to fly? Looking at it, it's not really going to produce any lift. AAAAARRRGH!
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Post by Phil Cooke on May 12, 2003 4:38:28 GMT -5
hmm, you might be surprised - if they are selling it as a PSS proven machine then I guess it must work... Draw lines approx 1/3 and 2/3 chord (parrallel with LE and TE) and sand as much of a section as you can between these lines, round LE and smooth, tapered TE. Take you time and it should work out ok.
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Mac
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Post by Mac on May 12, 2003 5:08:18 GMT -5
Thanks Phil. You truely are a star[glow=red,2,300]TEXT[/glow]. ;D Right, time to get cracking then............ Blinding site by the way! Having seen the photo gallery, and then seen that some of the aircraft are available via the plans service that's offered, I must have a go at an F86 Sabre! ;D ;D ;D Thanks again, Mac.
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Mac
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Post by Mac on May 12, 2003 5:16:36 GMT -5
By the way, I meant to ask, where did you see the picture of the Westfield Hawk? Was it on the SMC website? As it's my 'local' model shop, (it's ONLY 18 miles away!), I went in there and asked about the conversion to PSS, and who had tested it. All of the staff, who are most helpful, (NOT!), said, "We haven't tried it. we only go on what the manufacturers say!" Can you believe it, they didn't have a clue! Mac.
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Post by Phil Cooke on May 12, 2003 8:19:57 GMT -5
yeah the picture of it is on the SMC website - do a search for Hawk and the model is about the 3rd in the list... what is the span?? If its about 40" then you could speak to Andy Conway (PSSA member and designer of a great Hawk model) regarding obtaining a pair of foam wings with a proven section if you are still nervous (or have trouble with in future) your flat section wing. I can supply you with Andy's details if you so wish.
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AndyB
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Post by AndyB on May 12, 2003 10:29:34 GMT -5
Just thought I'd poke my nose in here to mention that someone had a Westfield MiG-15 at one of the Pendle events a year or two back, I seem to remember it flew Ok...
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Post by Phil Cooke on May 12, 2003 10:45:47 GMT -5
Hiya Andy, Did the MiG rely on a flat sheet wing too? And if so, you said it flew ok? That is Fireblades biggest concern with this model - if you can reassure him with experience of seeing it work that would be great! Fireblade I have checked again on the SMC site and the span of your model at 40" is identical to that of Andy Conways Hawk - if you did want to change to a proper foam wing then it would be easy to do so...
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Mac
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Post by Mac on May 12, 2003 13:36:37 GMT -5
Thanks Phil. I'll bare it in mind, regarding getting the foam wings, but I'll give it a bash with the built up wings first, just so I know what it flies like. Then I can let other know, because thus far, they seem to be an untested model. Looks like I'm gonna be the Guinea Pig again.
AndyB, dont suppose you have any photo's of that Mig 15, do you. That would be great to see flying!
I'm torn between that and an F86 Sabre for the next model. Does any body know which flies better?
Thanks again for all the help guys. And thank God I'm a nosey sod who was smurfing the internerd!
Mac.
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AndyB
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Post by AndyB on May 12, 2003 15:51:44 GMT -5
> Did the MiG rely on a flat sheet wing too? And if so, you said it flew ok?
Yes, from memory it seemed to. I've never flown a flat sheet wing but a Bradford gentleman of your and my acquaintance has, apparently they're fine they tend to be a bit "one speed".
Fireblade, I'd be inclined to try and keep it fairly light, particularly as a first attempt - you can always add a ballast box if it needs it. Unfortunately I haven't got any pics of the Westfield MiG 15, and I'm afraid I've no idea whether the Westfield Sabre or MiG 15 flies better. If you feel up to building from a plan, Ron Collins has an F-86 plan available from Nexus, I've seen several fly and they're all very good. You can get foam wings made (e.g. Pat Teakle) and I think it uses a commercial canopy.
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Post by rc-pilot on May 20, 2003 17:23:56 GMT -5
Hi Guys,
Sorry to have missed out on most of this conversation, I've been remiss in not logging on for some time.
Must pick up on a couple of points, though.
Phil: wherever did you get the idea that a good PSS model has a wing loading of 16-18 oz? A good PSS model has a wing loading that enables it to fly where and how you want it to, surely? As I fly off crappy local slopes mine are running at 11-13 oz/sq.ft, and fly just as well on bricklifters. Light = right, especially if you have a wing without a proper section (eg solid sheet balsa) the lower the wing loading the better it's likely to be. There'll be d**n all lift from it until it's at a high AoA, and then there'll be oodles of nasty drag to accompany it. Keeping the weight down enables the wing to generate sufficient lift at a lower AoA than if it were heavier, so less drag, better speed, lower stalling speed, no disadvantages that I've been able to discern.
Andy: I had a Westfield MiG29 some time ago, that had a built-up wing and was very cartoon-PSS. You wouldn't be thinking of that, perchance?
Fireblade: I am the "Bradford gentleman" with some experience of flat sheet wings, and as AndyB notes, they have proved to have a limited speed range, although the first one I tried flew in remarkably light lift - at its top speed of about 15-20mph. In a 20mph wind it was a hovercraft. Good luck with your Hawk, nice to have another convert.
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AndyB
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Post by AndyB on May 21, 2003 7:11:29 GMT -5
I was thinking of a "real" MiG 15, in fact I've found a photo of what I belive to be the model in question on the RVMSA website: www.rvmsa.co.uk/footmouth.html?1053518063593It's about the 5th or 6th picture from the top of the page. On the issue of wing-loading, I think it depends on the slope that you want to fly off. I'm in a similar position to rc-pilot with regard to wing loading; my local slope (Ivinghoe beacon) is OK but the wind is often quite sedate. I also attend quite a few PSS events and would have had quite a few wasted journeys over recent years if all my models had been in the 16-18 oz/sq ft range. This is what I currently have; Hawk: 12.5 oz/sq ft MiG 15: 13 oz/sq/ft Hurricane: ~14 oz/sq ft MiG 19: 12.5 oz/sq ft ...and here's what's planned P-51D: 11 oz/sq ft F-8 Crusader: 14 oz/sq ft.
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Post by Phil Cooke on May 22, 2003 10:06:45 GMT -5
yeah ok Steve - you are quite right of course! ...I was probably a little careless with my choice of phrase - I was talking about models I have flown in the past on the hills in and around our area - and my figures were based on my favoured style of flying too. My point was when built too lightly a PSS model can sometimes fail to 'get into the groove' properly and never attains enough kinetic energy to fly like a proper jet or prop powered aircraft should do (in my opinion)...and of course when built too heavy, the model fails to soar at all in anything but a howling gale. There is a definate target range of loadings... However, I did fail to consider flying on lesser hills, in less than perfect conditions, or in styles more sedate to my particular passion. Sorry if I mislead anyone...I guess there really is no correct answer as to the correct wing loading! ;D And Andy is right too, I have spent many an afternoon not being able to fly my models 'cos their wing loadings are too high for the conditions whilst others scratch around and thermal happily at the same event! Maybe we should all have a floater, a mid range and a heavyweight with us at every meet, thus catering for all thrown at us!
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