STOLing along

[jeff2wings]

O.K, thought it would be a good idea to start a general chat thread for Peter Russell’s STOL so people can swap ideas both structural and aerodynamic on this very adaptable design, so to start off with I’ve scanned the original May 1973 article so people not entirely familiar with PR’s design will have a better idea where he was ‘coming from’ with his STOL concept. I will go through my back issues and see if I can find other STOL related articles.

And of course it will also stop me from ‘photo bombing’ other peoples threads !

[john stones 1 - Moderator]

Turn page over Jeff I've read that one

John

[kc]

Jeff, the burning question is ---does the article show the wingspan? ( the heading and part of the plan are obscured in your photo) Is it 48 inches as shown on the later article plan or 55 inches as the current issue Mark 2 plan?

[Ernie]

Do I remember correctly? I think that Pete Russel made the first electric powered flight in the UK or maybe even worldwide. In a modified STOL?

ernie

[GONZO]

No, that was Col Tapplin with a plane that used cells that cost an absolute arm and a leg and could only be used once as soon as the electrolyte was added. Think they were something like silver/zinc or silver/chloride. PR did, however, convert a STOL to electric power. I think the motor was called a 'sea pup'. All this is pure memory so could be less than accurate.

[GONZO]

**LINK** Colonel H J Taplin, Radio Queen with silver-zinc cells and RC.

Edited By GONZO on 15/12/2014 13:45:39

Edited By GONZO on 15/12/2014 13:47:25

[jeff2wings]

K.C.'s the mk 1 is 48" and the mk is 55" span ,the plan has a typo !! the mk 2 has a extra rib bay in each panel

mk 1

mk 2

[reg shaw]

Wow, thanks for posting that, I was beginning to fear for kc's sanity!!! Is the wing chord narrower too?

Ian.

Edited By reg shaw on 15/12/2014 20:10:52

[jeff2wings]

And for those that like to drive too their flying site in a smart car, there’s this neat solution would be perfect with modern E.P. setups

[jeff2wings]

Got a good memory Gonzo !

[PatMc]

Posted by GONZO on 15/12/2014 12:42:38:

No, that was Col Tapplin with a plane that used cells that cost an absolute arm and a leg and could only be used once as soon as the electrolyte was added. Think they were something like silver/zinc or silver/chloride. PR did, however, convert a STOL to electric power. I think the motor was called a 'sea pup'. All this is pure memory so could be less than accurate.

You're right Tapplin did use a silver-zinc battery & it was very expensive (aprox £30 in 1957) but it would have been rechargeable.
It was Sanwa in the early 1960's that used a silver-chloride cell to power their Electra small f/f model. This cell came with the electrodes contained in a plastic bag with a cloth separator between them. It was activated by adding a little salt water to the bag, remained useable for about 45 mins or so & could deliver about 1.5A at just over 1v for around 1 min. It was a primary cell, meaning of course, single use only.
IIRC Pete Russel described the above in an article in an AM annual.

[jeff2wings]

Ian , wing chord on the mk 1 is 7.5" .

[David Davis]

Posted by jeff2wings on 15/12/2014 19:50:09:

K.C.'s the mk 1 is 48" and the mk is 55" span ,the plan has a typo !! the mk 2 has a extra rib bay in each panel

mk 1

 

mk 2

So that deals with the question of the different wingspans. The Mk 2's wing chord is 7.5 inches as well.

Now to the fuselage dimensions. The fuselage of the Mk 2 is 39 inches long including the rudder and omitting the spinner.

Is the fuselage on the Mk1 the same?

 

Edited By David Davis on 16/12/2014 10:23:17

[reg shaw]

So that deals with the question of the different wingspans. The Mk 2's wing chord is 7.5 inches as well.

Now to the fuselage dimensions. The fuselage of the Mk 2 is 39 inches long including the rudder and omitting the spinner.

Is the fuselage on the Mk1 the same?

Edited By David Davis on 16/12/2014 10:23:17

....err no it isn't!! The MkII chord is 8.75 inches. On my plan anyhoo!

Ian.

[David Davis]

Quite right Ian, I stand corrected! The Mark 2 chord is indeed 8.75 inches.

That still doesn't answer the question of the length of the STOL Mark 1 fuselage.

The Mystery Of The STOL Dimensions continues...

[reg shaw]

The plot certainly thickens, kc, how are you sleeping at night!!!??? When you look at the two wing plans in the post above, they are massively different in aspect ratios, more than 7" on span and 1.25" on chord increases would suggest.

Ian.

[David Davis]

I hesitate to offer a contrary opinion in such exalted company but 48 divided by 7.5 equals 6.4, while 55 divided by 8.75 equals 6.3, so the aspect ratios are not really very different, at least not according to my calculator!

Does that mean that the Mark 2 is a stretched version of the Mark 1?

We need to know the length of the Mark 1 fuselage Holmes!

[kc]

Thanks for your concern Ian, .I sleep well due to a clear conscience!......been out flying today so I could not reply earlier. As you all realise it is something of an obsession with me to get the facts right on these plans and thereby correctly preserve our aeromodelling heritage.

Peter Russell said in his Mark 2 article " Mark2...totally different structure but the same planform" so I feel it is clear it should be same chord & span as the Mark 1. PR just changed the wing on his own model. I reckon that someone - not Peter R - added an extra rib bay when redrawing the plan for RCME and nobody noticed! Whether anybody built a 48 inch Mark 2 or not we dont know, maybe they all built 55inch! There were comments from STOL builder for many years in Straight & Level but I have not yet found anything which mentions wing span or chord What a pity we are a year or so too late to ask PR himself.

I expect a considerable difference in performance if the span is increased by that much. Clipped wing might be lively and aerobatic, full span could be more like a trainer. In a way it does not really matter as long as we know which one flys well. The proof of the plane is in the flying. If you take the chord into consideration too it may make a totally different aircraft. Bear in mind PR himself used the same fuselage with both wings and the wing dowels determine where the wing sits. So the original Mark 1 wing chord must be the same on Mark 2.

So we need to calculate wing area and wing loading. But first we need an accurate chord for each plan also fuselage length.

[kc]

There is another way to solve this mystery and the clue is in this article above......

PR says the Mark 1 weighs 44 ounces and loading is  13.75 oz per sq ft. So that makes 3.2 sq ft.doesn't it? and 8.75 by 53 is 463.75 sq inches = 3.22 sq ft if my maths is correct. So even the Mark 1 must surely be 53 inch span by 8.75 chord?

Someone please check my maths and the logic! I seem to have destroyed my own argument by my calculations!

 

 

Edited By kc on 16/12/2014 18:52:47

Edited By kc on 16/12/2014 18:54:00

[Martian]

aaaaaaaaaaaaaaaaaaaaahhhhhhhhhhh

[David Davis]

According to jeff2wings, the chord of the Mark 1 wing is 7.5 ins and the span is 48 ins. Therefore, the total wing area is 360 sq ins or 2.5 sq.ft.

If the model weighs 44 ounces that means that the wing loading is 17.6 ounces per square foot.

The only way we'll find out is if someone measures the length of the Mark 1 fuselage.

I shall be building the bigger one and dealing with wing dowel problems as I go.

[PatMc]

I've taken a screen print of both the wings from Jeff's post, then increased the Mk 2 image by 10% & found that the tail tip shown at the bottom right in both images correspond when overlaid. I cleaned both images up, changed the Mk 2 to red outline & overlaid a reduced opacity section of it on the Mk 1 then increased the combined image by 50% with the result below.

By measuring the pixels & a bit of simple maths based on the Mk 1 being 48" span I've come up with the following : Mk 1 span 48" ; chord 9.4"
Mk 2 span 52.5" ; chord 8.46"

Allowing for the discrepencies between original mag scale image, the scan, line thickness etc it's likely that these figures can be rounded. I would image that Pete Russell would have been using conveniently sized airfoil drawings (No internet or even electronic calculators when the Mk 1 was drawn up) so it likely that the Mk 1 chord was 9.5" & the Mk 2 was 8.5" (though I note that Reg reckons his plan measures 8.75". Also I'm not adamant on the exact wingspans especially of the Mk 2 , an extra rib bay each side would have added 6" but each tip is 0.5" shorter making it the overall increase in span 5" - i.e. the Mk 2 works out at 53" span.

My conclusion is that PR designed & developed the models empiricaly. Since the Mk 1 was a success he probably tweaked the Mk 2 for ailerons & better flaps, increased the span by 10% to enable decent size ailerons, decided that the area was about right so reduced the chord by 10%. The increased aspect ratio would have improved the wing efficiency & the use of ailerons would have maintained the roll rate.

Incidentaly whilst resizing & comparing I noticed that the tail part I used as a yardstick had the same note above it in both images & even the line down from it are identical. My guess is that when preparing the new drawings the old wing was simply deleted to be replaced by the new wing with the left tip in roughly the same position in both drawings, hence the fin intruding into the right tip of the Mk 2 wing. If I'm right then the fuselage sizes won't have been altered except perhaps around the actual wing position.

[reg shaw]

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.

[jeff2wings]

Below is the scan from PR’s column of June 1972 that I quoted (sort of)

However, Peter must have changed his mind by the time he got to the building board. So I checked both reduced scale plans, the Mk 1 was at 1/7 scale and the Mk 2 at 1/6, and my figures are very close to PatMcs’ figures.So just go build the thing !!!

[kc]

PatMc note that one plan was said to be 1/6 scale in the mag while the Mark 1 was said to be 1/7 scale. Actually 1/6 was slightly wrong anyway when I measured the Mark 2 mag plan.

PR clearly said the planform was the same!

I am beginning to believe that the original Mark1 drawing was either incorrect or perhaps Jeff's copy is not a full size original. If so it's amazing that the Plans handbooks, adverts etc were wrong and nobody commented.

Electronic calculators were around in 1973 - Clive Sinclair sold pocket calculators before then but desktops were common in commerce in 1973 - P R owned a model shop - And of course mechanical calculators were around in the 1950's.but anyway educated people didn't ( & still don't) need calculators! But it's also possible he miscalculated the wing area.

However the bottom line is 13.75 ounces per sq ft is a good loading to aim for so 55 inch span and 8.5 means you need to build to 44 ounces = 2 pound 12oz to achieve that. A smaller wing would be much more difficult to achieve 13.75oz/sq ft. . So the Mark2 plan 55 by 8.5 surely is the size to build even if you build a wing without ailerons. Aim for under 3 pounds and accept 3.5 if it happens.  4.5 would fly but not be properly STOL I reckon.

Edited By kc on 16/12/2014 22:55:32