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Feb 08, 2019, 03:11 PM
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Build Log

Sport Spitfire (The Spirit Of Biggin Hill)


While searching OZ for ideas, I often hit on some smaller free flight designs which would make a great enlargement to 200% as an R/C electric model with some semi-scale thrown in. I like the idea of round formers and plenty of stringers to form the shape.

To save me the hassle of the enlargement, I bumped into this Sptfire by Don Srull at 72" (bit larger than I hoped) which is a scale up of the Earl Stahl Spitfire free flighter.

This build from the Don Srull plan....

https://outerzone.co.uk/plan_details.asp?ID=8613

The Earl Stahl plan.....

https://outerzone.co.uk/plan_details.asp?ID=8609

I think Don Srull has done a good job of enlarging the design while retaining the typical laminated leading and trailing edges, round formers and stringers. For the eagle eyed they will spot that it is on 3 function throttle, elevator and rudder which also keeps it within the vintage theme.

Flicking through the R/C comics, I see adverts for foam Spitfires embellished with enlarged plastic kit mouldings (from a giant Airfix model) and after the 4 basic functions, channels for flaps, gear, lights, etc.

I am aiming for a simple light weight build, and a Spit which floats about rather than blasts around at full chat, and the building challenge of round formers, stringers and laminated structures just like a giant free flighter.
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Feb 08, 2019, 03:26 PM
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Some web searching revealed the original build article in the magazine....

The pioneering Astro flight motor, reducer and ni-cads will be replaced by a brushless motor and lipo in my build.

Can't wait to get into that fuselage build shown on attachment 7.
Feb 08, 2019, 03:41 PM
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Made a start on those formers.

Plenty of cutting, sanding and notching to get them done

OK, normally I would start on the tail to get my eye in, proceed to the wing and end up on the fuselage during a build. However in this case, I may crash and burn on the fuselage build, so I am starting on the difficult part first.
Feb 08, 2019, 06:04 PM
Summit Model Aeronautics
Steve85's Avatar
Gere,

Looks fabulous. I had no idea Don Srull had done this to an Earl Stahl plan; talk about pedigree! I love the KISS principle...

Steve
Feb 08, 2019, 08:44 PM
B for Bruce
BMatthews's Avatar
I'd never seen it either.

If I were doing this for RC I think I'd alter the airfoil to a more semi symmetrical option with less camber to enhance the inverted performance. In fact looking up the Spit airfoil seems to show that it used a NACA 2213 at the root and a 2206 at the tip. And the 22nn series is an option with a pretty well proven record in model flying circles. So you could switch back to the proper scale airfoil and gain a lot of good things with your build. The 2212 being a pretty popular choice on a lot of the early "full house" aerobatic pattern flying models way back in the late 50's and through the 60's and in other sport models on and off since.
Feb 08, 2019, 11:04 PM
I'd rather be flying.....
JeffMac's Avatar
Nice ! Following.....

Best regards,

jeff
Feb 09, 2019, 02:32 AM
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Quote:
Originally Posted by Steve85
Gere,

Looks fabulous. I had no idea Don Srull had done this to an Earl Stahl plan; talk about pedigree! I love the KISS principle...

Steve

The rivet counters will not give my model a second glance.

I will be happy with a camouflage finish and some roundels. Provided the passing dog walkers call it a Spitfire, then it's good enough.
Feb 09, 2019, 02:48 AM
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owlsabie's Avatar
Fantastic! Will be following with interest. Always been curious how a "heavy metal" warbird would turn out if built like an old timer
Feb 09, 2019, 02:50 AM
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Quote:
Originally Posted by BMatthews
I'd never seen it either.

If I were doing this for RC I think I'd alter the airfoil to a more semi symmetrical option with less camber to enhance the inverted performance. In fact looking up the Spit airfoil seems to show that it used a NACA 2213 at the root and a 2206 at the tip. And the 22nn series is an option with a pretty well proven record in model flying circles. So you could switch back to the proper scale airfoil and gain a lot of good things with your build. The 2212 being a pretty popular choice on a lot of the early "full house" aerobatic pattern flying models way back in the late 50's and through the 60's and in other sport models on and off since.
Thank-you for the ideas, I will give it some thought when I get on to the wing build.

As an aside, the early Spitfires did not have great inverted performance due to the throttle valve getting flooded as the plane turned upside down.

This video explains the science if you skip in about a minute..

The Spitfire's Fatal Flaw (4 min 40 sec)
Feb 09, 2019, 03:08 AM
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Originally Posted by owlsabie
Fantastic! Will be following with interest. Always been curious how a "heavy metal" warbird would turn out if built like an old timer
I would estimate that a 6 foot Spitfire would typically come out at about 10 lb, but the plan and article for this one says only 5 lb. It will be interesting to see how slow it flies, hopefully more like the one in taxiing in the photo rather than the Typhoon on touch and go (RAF Coningsby Sept 2018)
Feb 09, 2019, 03:28 AM
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Printed some of the plan off in sections to suit the bench and taped them together. Very pleased that the plan is nice and clear - thanks OZ.

Placing the formers on the plan to check sizing prior to building the vertical crutch has shown up a gremlin. Former F2 is almost the same height as F1 and way shorter than it needs to be. I will have to develop my own version of F2 using F3 and the size view.

Also the central crutch notches on F7 and F8 seem out of alignment.

The formers were made from extra printouts glued to the balsa and then sawn, sanded and notched. Off the make some replacements
Feb 09, 2019, 06:51 AM
Blueplaidcanard flyer
formers can be a pain but you'll get there.
Feb 09, 2019, 03:04 PM
I like real wooden aeroplanes!
Sundancer's Avatar
I like the look of this GS and will be following progress. Looks like my kind of airframe.
Feb 09, 2019, 04:57 PM
B for Bruce
BMatthews's Avatar
Quote:
Originally Posted by Gere Sport
I would estimate that a 6 foot Spitfire would typically come out at about 10 lb, but the plan and article for this one says only 5 lb. It will be interesting to see how slow it flies, hopefully more like the one in taxiing in the photo rather than the Typhoon on touch and go (RAF Coningsby Sept 2018)
But look at all the wood in those more typical scale builds. You're doing something that is VERY different.

I'd go so far as to suggest that with even reasonable care that your Spit might well come in at under 5lbs and end up flying much like an old timer free flight spark design.

You can't really consider the top speed either. A light model can fly fast but a heavy model can't fly slow. So you can up the speed in flight to mimic the scale speed of the real thing. But unlike the heavy typical scale versions you'll be able to slow down to a more proper scale landing speed. If you haven't already watch a few of the full size Spit takeoffs and landings with an eye to seeing how many fuselage lengths it moves forward per second. It's not that many. Then fine some scale RC flight videos and get a feel for how many fuselage lengths per second those manage to use up. I suspect your 5lb'er will be closer to scale then the usual 10lber.
Feb 10, 2019, 03:04 AM
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Quote:
Originally Posted by rabidrue1
formers can be a pain but you'll get there.
Thank-you for the encouragement. I put the laptop down and made some replacement parts, so now I can continue making progress.


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