STOLing along

[kc]

In case any newcomers think we are just a bunch of 'anoraks' arguing over nothing it's actually the combined brainpower and archives of several aeromodellers trying to get things right so you can build a plane that flys well!

[PatMc]

Posted by reg shaw on 16/12/2014 22:18:37:

Yeah but....... in your doings above, the wing chord measurements are wrong, the larger span MkII wing is also wider in chord, where the pic above shows it to be narrower?

Ian.

I was careful to ensure that I was comparing like with like. The overlaid image of the common tail tip fits once I'd adjusted the Mk 2 drawing to the same scale as the Mk 1, also the rib spacing in both line up exactly.
If the Mk 1 wing was smaller in both chord and span it's outline would fit inside the Mk 2.

[jeff2wings]

Some better scans ,you can see the difference in wing chord and section.

both plans have the same number r/c 1190 the mk1 has not been available for decades ! lol

[Braddock, VC]

On my plan, measured with an old fashioned steel rule, the chord of the mk 2 is 8.75". The span, without dihedral is 55 and a bit inches but my plan has been stored subject to the vagaries of humidity but I seriously doubt it would stretch about .25" along the length of the plan and 3 or 4 times that on the other axis.

Incidentally the chord of the wing in the side elevation on that plan is 8.75".

The Mk1 stol, according to the peter russell article scanned in by jeff has a 48" wingspan and 7.5" chord.

Personally Reg I'd ignore all the quibbling and go ahead and build it as per the plan as you've redrawn it. Which you probably had done in any event. It'll still look flimsy and old fashioned but I suspect will provide more hours of fun than more modern models.

Just my 2p.

[reg shaw]

Like you say Braddock, none of this effects my plans and I'm pressing on regardless, it's just a bit of fun watching the discussion unfold! Jeff, your MkII plan shows the flap belcranks wrong like has been mentioned before. My MkII plan has them altered.

Ian.

[David Davis]

Posted by jeff2wings on 17/12/2014 07:43:09:

Some better scans ,you can see the difference in wing chord and section.

both plans have the same number r/c 1190 the mk1 has not been available for decades ! lol

 

 

 

Actually it is still available according to the myhobbystores website but it is rather expensive.

http://www.myhobbystore.co.uk/product/16565/rc1190--stol-mki

 

Haven't we done this to death now gentlemen. Either the Mark 1 is the same size as the Mark 2 or it isn't. Most of us will be building Mark 2s and that's that. Ian is an exception to the rule; he will be enlarging a Mark 2 in his own inimitable style.

Edited By David Davis on 17/12/2014 10:45:40

[kc]

Yes David we have finally resolved the problem---it is clear now that if there was any error it was on the Mark 1. As I proved yesterday to get the wing loading of 13.75 oz per sq ft with a model weight of 44 ounces ( as PR said in his 'Mark 1' article ) it must have 3.2 sq feet area - i.e. 55 by 8.75 inches allowing a little for wing tip rounding. So the Mark2 plan must be correct at 55 inches.. ( please check my maths and logic someone! )

I conclude that Peter Russel's original comments about 48 inch span by 7 must have been modified and enlarged to 55 by 8.75 by him before he built his model which we now term Mark 1. And the change of span was not noted anywhere! The first STOL plan sold in the hundreds according to PR and there was complimentary feedback for years in S&L but nobody seems to have mentioned that it came out larger than the advertised 48 inches! Strange but if a model flys well you dont bother to check the span do you?

[David Davis]

Well I'm pleased that's sorted!

[reg shaw]

Yes but if the......... and the......... could it be that the......

Phew, now crack on folks!!!

Ian.

[PatMc]

Posted by kc on 17/12/2014 11:18:33:

Yes David we have finally resolved the problem---it is clear now that if there was any error it was on the Mark 1. As I proved yesterday to get the wing loading of 13.75 oz per sq ft with a model weight of 44 ounces ( as PR said in his 'Mark 1' article ) it must have 3.2 sq feet area - i.e. 55 by 8.75 inches allowing a little for wing tip rounding. So the Mark2 plan must be correct at 55 inches.. ( please check my maths and logic someone! )

I conclude that Peter Russel's original comments about 48 inch span by 7 must have been modified and enlarged to 55 by 8.75 by him before he built his model which we now term Mark 1. And the change of span was not noted anywhere! The first STOL plan sold in the hundreds according to PR and there was complimentary feedback for years in S&L but nobody seems to have mentioned that it came out larger than the advertised 48 inches! Strange but if a model flys well you dont bother to check the span do you?

Actually, I don't think span for the Mk 1 was misquoted on the plan.

Just done some quick measuring of the better scans & I'm of the opinion that the old version was 48" span - confirmed this by checking against the wheel size. Against this the chord works out at 9.25".
Bear in mind that I'm working from a scan of a scaled sample image in a 40 year old mag. However the comparative accuracy of two given measurements, namely the wheel size & span were remarkably close which provides some confidence.

I know that in his June '72 article PR is quoted as saying that the span is 48" & chord 7.5" but that doesn't tie in with the wing loading he quotes in the plan presentation. Could it be possible that the journey between pen & publication included a glitch or two ?
I'm also aware that 9.25" chord still makes the area slightly than less the quoted wing loading suggested but not by very much & remember that PR's original drawing will have taken the same journey as his earlier article.

[PatMc]

Did a quick ditto of the Mk 2 from the better scans, again using the wheel as ref.
Works out as Ian (Reg ?) & Braddock said 55" span, 8.75" chord.

Incidentaly Ian, in my previous post when I said that you reckoned the chord 8.75" I wasnt doubting you I was in fact acknowledging that my measurements & calculations were subject to a number of inaccuracies, hence the smaller chord figure that I came up with for the Mk 2. Also the smiley wasn't intended it was the result of the carp software of this forum changing a close bracket symbol to .

 

Edited By PatMc on 17/12/2014 16:47:09

[reg shaw]

No worries PatMc, I never took it that way, but now you mention that I could, I will and am now offended

It is amazing how things have been changed over the years. One very simple plan can cause so much interest and speculation!!! That's historic aeromodelling for you! I never really thought too much about it before, but kc hit it on the head, it doesn't ACTUALLY matter, but it isn't what was originally designed and which might be lost over the years.

Ian.

[kc]

Nobody actually measured a proper fullsize Mark 1 plan but we just assumed the tiny plan in the mag was correct! It cannot have been!

Sooner or later these unintended 'smileys' are going to cause a war!

[PatMc]

Posted by kc on 17/12/2014 17:15:20:

Nobody actually measured a proper fullsize Mark 1 plan but we just assumed the tiny plan in the mag was correct! It cannot have been!

I think they were accurate, in fact the measuring I've done with the Mk 1 seems to prove that. The trick is using a definite known parameter to use as a start point & not taking the quoted scale as gospel. If there's no defined measure anywhere using a bit of common sense on the most likely size of some parts will often be key.

Anyhoo, I think that PR always held that nobody actually "designed" model aeroplanes. They were & still are planned empiricaly around known sizes to meet set objectives then developed by trial & error.

[Levanter]

Reg. That's two unintended smileys you got today with the return bracket. It really spooked me as I really didn't think I had gone to the smileys box. Anyway it's good to know I am less mad than I thought I was.

[jeff2wings]

I think by the time we have finished adding our own ideas it won't matter anyway now who would like to discuss flaps & slat options !!

[Braddock, VC]

What size were the slats?

[jeff2wings]

The right size !!

[jeff2wings]

Well I’ve received my plans for the mk2 stol , now to decide on the flap/slat options. First option is to build as drawn, not! So what other options are there?

I’m thinking full span slats with the outer part fixed and the inner part inter-connected with the flaps, but what type of flap? Peter’s plan flap are good and effective how about slotted flaps or Fowler flaps that increases the wing area

[Barnstormer 52]

Hi

I am building a Mk II and am trying to decide on a power plant for it and was thinking of an OS FS 26 that I have.

I have tried to find instructions for and the old OS 19 (or 25) two stroke that would have been in the original to get an idea of the output?

The FS 26 is rated at 0.41bhp.

Does anyone have the instructions of a view on whether it'll be powerful enough?

Unfortunately I haven't had the engine in anything yet to judge it by.

Regards

Geoff

[Braddock, VC]

IIRC a 26 FS will be adequate with one of the original 40 FS from 82 ish ideal.

In my Junior 60 a 26fs provides the same sort of performance as an OS 20 Fp, the J60 is/was significantly heavier than a STOL.

Fine pitch prop is essential, 26 fs happy with a 10x4 or 11x4, the 40 fs really happy with a 12x4, all apc btw. All with 10% nitro. On paper the 26 and 40 Fs have similar performance, in my mind the 40 trumps it. Similarly the 20 FP, on paper, outperforms the 26 FS but imho the 26 trumps it as it turns larger props.

[Braddock, VC]

IIRC a 26 FS will be adequate with one of the original 40 FS from 82 ish ideal.

In my Junior 60 a 26fs provides the same sort of performance as an OS 20 Fp, the J60 is/was significantly heavier than a STOL.

Fine pitch prop is essential, 26 fs happy with a 10x4 or 11x4, the 40 fs really happy with a 12x4, all apc btw. All with 10% nitro. On paper the 26 and 40 Fs have similar performance, in my mind the 40 trumps it. Similarly the 20 FP, on paper, outperforms the 26 FS but imho the 26 trumps it as it turns larger props.

[David Davis]

I am thinking of fitting an HP VT 25 in mine. I have had it in a much larger and heavier Junior 60 in the past so powering the STOL shouldn't pose a problem. It's supposed to produce 0.39bhp as opposed to the 0.34bhp of the original 21. However, I might just shove an electric motor into it for reasons of convenience.

[Barnstormer 52]

I have a FS 40 also but thought it may be too much.

The instructions quote 0.65 bhp for the FS 40 FS and 0.41 for the FS 26.

Th FS 40 has been in a 63" Barnstormer 63" since '82, it powers it quite happily and I am sure the prop is a 82 vintage grey Master Airscrew 12 x 6.

It is quite a heavy prop and the model weighs just on or just under the 5lb, I can't get near it to weigh it at the moment.

Attached is the guide for propellors for both

The 12 x 6 is right at the top end if you accept the above, but the engine seems happy, ticks over well, the model doesn't punch holes in the sky, but wasn't meant to.

Geoff

[Braddock, VC]

That 40 fs quoted there is the surpass version which is a completely different animal, the 0.65 hp quoted is also for the surpass version, at least it is in the instructions for my 40 surpass. IIRC contemporary engine tests stated 0.45 hp for the 40 fs .

As you said they are smashing little engines, extremely reliable and very frugal. Incidentally, the reason I suggested low pitch props is to provide the plane with the acceleration to get up to its flying speed pdq.