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Author Topic: Lee's Hobbies Bristol Scout Kit  (Read 7739 times)
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« Reply #25 on: December 09, 2017, 05:44:26 AM »

Hi Jon,

No Problem!  I was more concerned that you might have wanted to use the same angles and got it wrong, so I thought it best to point it out to you.  Smiley

Cheers

Andrew
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flydean1
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« Reply #26 on: December 09, 2017, 07:47:51 AM »

There are two things which transformed my Peanut Scale (Always Capitalize) models, learned about 40 years ago from reading the McCombs books, Flying and Improving Scale Model Airplanes, and Making Scale Model Airplanes Fly

First, move the rear rubber anchor forward so that changing motor length/cross-section doesn't result in CG changes.

Second, provide some form of pitch trim adjustment; usually in the form of an over-height slot for the stab so that shims can be used to change the stab angle.  This is generally a lighter option providing wire-hinged moveable control surfaces.
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Jack Plane
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« Reply #27 on: December 09, 2017, 12:13:58 PM »

Second, provide some form of pitch trim adjustment; usually in the form of an over-height slot for the stab so that shims can be used to change the stab angle.  This is generally a lighter option providing wire-hinged moveable control surfaces.

The other thing about changing stab angle rather than the stab section (i.e. up or down elevator) is that the force on it isn't affected by airspeed, whereas the force with elevator trim will alter across the speed range... complicating things.
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« Reply #28 on: December 09, 2017, 05:24:16 PM »

Uh...respectively beg to differ.  Whether you move the whole stab, or just part of it, changes in airspeed will change the effect.
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Jack Plane
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« Reply #29 on: December 10, 2017, 03:08:55 AM »

Take a stab with flat (or fully symmetrical) section in isolation from the rest of the airframe:
(i)   With neutral elevator there will be no force generated perpendicular to its surface at all airspeeds.
(ii)  With a fixed amount of slight down-elevator, the perpendicular force upwards will increase as airspeed increases, i.e. there is an aerofoil effect.
(In both cases there will also be drag effects, but these will differ - the stab with deflected elevator will have greater drag at all airspeeds.)

Take the same two examples and fix them to the datum line of an airframe (where there are now moment relationships between it and the thrust-line and the main wing-incidence):
(i)  Set the whole no-elevator stab slightly up relative to the datum line (i.e. positive incidence), so the airflow will be striking it's underside at a slight angle - the increase in force won't be linear as the airspeed increases, but there won't be any aerofoil effect as such.
(ii)  Set the down-elevator stab directly on the datum line, so now there is also a slight positive incidence relative to the datum line (roughly comparable to the flat stab's up-angle) - but there will now also be an aerofoil effect and also increased drag as the speed increases.

In a full-size aircraft the elevator trim-tab can be adjusted to maintain level-flight as speed increases, but in a FF model it can't, so surely the option that has the least unwanted exponential effects (lift and drag) as speed alters is the better one?
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cvasecuk
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« Reply #30 on: December 10, 2017, 05:25:37 AM »

Sorry Jack even a flat plate is an "airfoil". If placed at some incidence it will generate lift and drag and these forces both vary as the square of the speed. If you replace the flat plate with some cambered airfoil the only significant thing that changes is the size of these forces., if the speed is the same.
If you use a symmetrical airfoil as, say, a rudder it will need to be deflected more at the trailing edge than would a hinged rudder to generate the same force at the same speed but in both cases the force is still speed dependent.
Ron
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Jack Plane
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« Reply #31 on: December 11, 2017, 03:00:44 AM »

Fair enough both.  I stand corrected and now better informed - thanks!  Smiley

----

In the meantime, I've carefully sized the interplane struts according to my desired wing incidences and temporarily fitted all the parts together.  This looks superficially fine (except the stabiliser which needs salt added and a new one made), and shows that the basic CG is more or less okay.

However careful eyeballing of the four wings' leading- and trailing-edges, both separately and together, reveal a quiet cacophony of small but differing 'steps' where each wing meets its centre-section, plus minor but variable bare-bones warps in each (before the slight wash-out built into each wing).  Some of this is due to my lack of experience when originally making the wings - but is also an outcome of the 'advanced' method of construction where the basswood spar runs from tip to tip and there's no doubling of the ribs where each wing meets the CS, just a 'glued-crack' in the spar and leading/trailing-edges.  So, given the minimal structure of each wing, any pull on it to get its struts to seat correctly in their tabs (even just by 0.5mm) upsets its at-rest tension and compounds the issues in it and across to the other wing.  And all this before covering - which will be extra challenging as the ribs are undercambered.

So, the only way to resolve this with any certainty is to sever the wings from their 'centre-sections' (i.e. the three lateral bits of wood each), then terribly carefully pin down and glue back together, and also add gussets.

The other thing that the lashed-together photo reveals is that the wheels are too small in diameter and lack convincing tyre-sections and cones, so they'll need re-making as well.

I'm reminded of the story of the traveller in [an island to the west of the island off the NW coast of mainland Europe] who asks a local for directions to a nearby place.  To which the local replied "If I was trying to get there, I wouldn't start from here!"
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« Reply #32 on: December 15, 2017, 03:57:42 AM »

Small but satisfying progress:

Effectively re-built the wing centre-sections and nailed down the correct 1/2" dihedral on each wing.  Steaming and bending then did the rest.

Covered and doped the fuselage with suitable cream-coloured tissue.

Stained the decking and struts with acrylic, added 'leather' coaming, made the blister for the right side of the cowl, filler cap on top and two paper carb access covers, and sealed and painted the motor and all the aluminium areas (the sliver-grey mix came out a bit dark, but will have to do as I refuse to add any more weight).

Need to pick out a few remaining bits of detail in black ink, drill teeny holes for the elastic cabane-strut rigging, and add a windscreen and instrument-panel.

Not yet sure if I'm willing to commit insanity by seeking to add stitching!

This Scout D will be unarmed, but will have to make a pilot of course...  Neville had a cousin in the RNAS don't you know?  Grin
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« Reply #33 on: December 15, 2017, 07:13:25 AM »

That's looking nice. Very Vintage.
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« Reply #34 on: December 15, 2017, 10:50:39 AM »

Love the Bristol Scout  -  don't forget the Ranken darts  Grin

If you want my decal file for the Scout let me know.

Ralph
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« Reply #35 on: December 15, 2017, 12:31:31 PM »

Cheers Ralph.  I've had a look again recently at your own Scout build thread - is it still in commission?

Decal files will be fab!  I'll PM you my email.

Jon
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« Reply #36 on: December 15, 2017, 01:55:07 PM »

Looks good Jon!  Grin

Andrew
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« Reply #37 on: December 15, 2017, 03:15:40 PM »

Thanks Andrew.

If it passes muster (i.e. flies properly enough for at least 15 secs and doesn't shout deviation-from-utter-scale too loudly) then it might just find itself on the apron for Open CO2 at next year's Nats...
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« Reply #38 on: December 15, 2017, 05:15:34 PM »

Good stuff!!

Dan.
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« Reply #39 on: November 05, 2018, 03:51:28 PM »

So nearly a year on, I finally got round to completing the Scout - which in fact is now going to be my Kit Scale entry for the 2019 Nats.

Truth be told, this model has taken me over four Shocked years to make!  It started off as my first ever model after a 35 year layoff, but proved beyond my initial skills so got put away.  When I finally resumed work last winter, I considered upgrading it to Open Scale but put it away again.  When work re-resumed this autumn I realised the only way forward was to build it as I fancied, i.e. as a fictitious generic late Scout D with my choice of features from various historic examples - taller rudder, single synchronised Vickers gun, larger engine with bulb on the starboard side of the cowling, etc, and Perry (Neville's cousin on his mum's side) as RFC pilot.

Despite the addition of some basic detail (rigging, simulacrum of an instrument panel, etc) , I've tried to keep the aesthetic well within the philosophy of the KS rules - impressionistic rather than hyper-real - and hope that these and whatever minor liberties I've taken with some construction decisions (which weren't intended to improve performance, just robustness and visual integrity) will be viewed kindly by those who give up their free time to judge our efforts....!

Markings are pen for control surfaces etc, coloured tissue for roundels (chalked white tissue) and acrylic for cowling, struts, pilot, official number, etc - all compliant with the desired impression.  Of course Perry's silk scarf is a bit of kitchen roll secured with CA!  Grin

There are some aspects of the build that I'm not entirely happy with, but I've got work and other projects pressing for attention, so will let them be and move on.  There was an awful lot of re-doing (and re-doing again!) along the way - nose, cowling, decking, rear fuselage, complete new wings, new U/C, new wheels, etc, etc - so I'm feeling jolly glad it's finally all done!!

Total airframe weight 16.5g plus Gasparin G-28 (inc prop) 7.2g = 23.7g AUW.  This is heavier than I'd have preferred, but the model seems spot on in terms of static balance and the wing area of 56 sq in gives a loading of 0.42g/sq in... which isn't too shabby... I hope!  Shocked

And one final thing:  test glides onto the bed were a nice little thill, and I'll be trimming indoors for the first time later this week - all of which is excellent in terms of getting this one under the wire and into the WW1 Cookup thread before the absolute deadline of 11am this Sunday 11th.

Jon
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« Reply #40 on: November 05, 2018, 03:54:44 PM »

And the rest of the piccies...
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« Reply #41 on: November 05, 2018, 04:04:03 PM »

The Scout looks really good Jon, very nicely finished... Personally I think Perry looks to be more than up to the job particularly now he's equipped with a decent scarf - his mum will be pleased
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« Reply #42 on: November 05, 2018, 04:48:55 PM »

That’s really nice Jon.  Good luck with the trimming  Grin

Andrew
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« Reply #43 on: November 05, 2018, 05:02:26 PM »

Lovely job, Jon. I love Bristol Scouts, and that one really captures its charm perfectly. Well done!
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« Reply #44 on: November 05, 2018, 05:10:46 PM »

Thanks chaps!

Finishing what one's started is an awful affliction...  Grin
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« Reply #45 on: November 05, 2018, 07:32:10 PM »

Fine effort Jack - nicely finished. Very neat rigging. Good luck with the trimming.

John
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« Reply #46 on: November 06, 2018, 02:16:01 AM »

Lovely. And the serials have worked well too.  As I have said elsewhere, "We expect flight reports!" Smiley
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« Reply #47 on: November 06, 2018, 05:16:31 AM »

Nice to see another Scout finished.  Pretty little aircraft.
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« Reply #48 on: November 06, 2018, 06:02:17 AM »

You're right Ralph, the Scout is indeed a pretty little aircraft.  (As you can see, I used tissue and acrylic rather than transfers for the markings, but thanks again for kindly sending me the file you made for your's.  How is it these days?)

With hindsight, making it from the Lee's Hobby kit design was a bit frustrating in some aspects (e.g. would have preferred a two-part lower wing), but it gave me good experience at working to surface accuracy and reasonable detail at small scale, including all that rigging!

The real proof of my efforts with the Scout will be in the flying.  Although I was aiming for 20g AUW but came out 20% higher (lots of reasons but including the use of domestic rather than esaki), this isn't a peanut for rubber duration.  It just needs to take off, gain a decent enough height, and fly relatively realistically before landing in an orderly fashion - all for a minimum of 10 secs, but preferably around 30 secs.

In the event my incidences were set at 1.5deg lower wing (as per plan) but 2.5deg top wing (plan had zero).  There is currently no wash-in/out as I've tried to keep everything neutral for now. Once trimming, will experiment with gurney strips under the left inside wing(s) and tip-weight on the outside wing.  The single-piece rudder is currently hinged to allow for optimum setting of the yaw before being fixed, and the CO2 motor is set at  3deg down and similar right - both adjustable.

At some time in the future I've an idea to build another Lee's Hobby peanut kit, an opposition aircraft of roughly the same early/mid period of the war as a 'companion' piece, powered by a Brown A-23 I recently picked up.  So, at a very modest £15 each from SAMS, I've added a Halberstadt D.II and an Albatros D.II to my collection... inclined towards the fish-like Halberstadt with the rhino-horn exhaust, done in field-grey tissue with a black-clad chap called Ernst perched in his cockpit with a single Spandau at his disposal...  Grin

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« Reply #49 on: November 06, 2018, 05:49:56 PM »

That's really rather nice, has captured the character of the full-size and is distressingly well-executed; you weren't thinking of entering it in next years Kit Scale nats, were you?...  Smiley
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