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Thread: Isaac spitfire

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    Isaac spitfire

    Hi all, Thanks for the kind welcome to your group. It's that time of year when I get out my Isaac Spitfire plans,do many sketches and calculations and then put them away again.
    Having been spurred on by Bill Pratt's Spit and not wanting to break tradition the plans are out again.
    The same stuff comes to mind, retracts,Flaps, Mini Merlin etc,etc ,though this time I am considering a shopping list.
    Many people on the replica spitfire site have said that the retracts are not possible though my calculations seem to suggest they are.
    So my first job is a mock up of the main spar and ribs around the U/C mounting points to prove it all fits.
    The Isaac plans have been bounced around for years, with most common complaint being its too small, though for me this means a project that I can realistically afford to finish, not a 200,000 monster that I will never afford the engine for, let alone finish

    I am lucky enough to fly a J3L4 from my back garden, so there is no need to rush the little spit, though "Low and Slow" doesn't always get the blood flowing.
    At the moment the plan is to finish the Spit as a Seafire47.


    Regards Darren
    CAA Licence A&C airplanes1

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    Re: Isaac spitfire

    Welcome aboard Darren Finlay !


    Isaacs Spitfire is very sporty aeroplane. I just named my design a SPITFIRE II for the semielliptical wing made it really look like one etherically.

    I have no idea how big the Isaacs Spit is but this little byrd here is now 5 m2 winged.

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    Registered User Autodidact's Avatar
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    Re: Isaac spitfire

    Speaking of Mini Merlins, I think an Autoflight universal PSRU adapted to a 3.0L Ford duratec v6 would be just about right - about 125-130 hp. All of this (retracts etc.) adds weight, though, but maybe not much if done well...

    Someone should design a Sea Fury along the lines of the Isaacs Spit for M14 power!
    I can't think of a good quote, today.

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    Re: Isaac spitfire

    Welcome! You have found a smart and talented group here.

    Any time of year should be good for rolling out Isaac Spitfire plans! I have always been a big fan of his Spit and Fury. Since only a few Spits have been built, I haven't read as much about it as the Fury, but it sure looks like fun! I have sometimes wondered if the Cjetcovik retractable gear would fit, if adapted for the correct geometry. I have a set of the landing gear plans in my "maybe someday" file. Are you thinking of swinging them "inside out" like the originals?

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    Re: Isaac spitfire

    For anyone wondering about the cjetcovik retractable gear.........
    http://www.cvjetkovic-aircraft.net/gear65.htm
    My avatar is a Thurston TA16 Seafire, not sure who built it, but if my project ends up as nice as this , I'll be wrapped.

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    Registered User craig saxon's Avatar
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    Re: Isaac spitfire

    Drawings for that gear are $25 which seems reasonable.
    CA65 Gross weight 1500#
    Last edited by craig saxon; January 14th, 2012 at 05:17 AM.
    My avatar is a Thurston TA16 Seafire, not sure who built it, but if my project ends up as nice as this , I'll be wrapped.

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    Re: Isaac spitfire

    Thanks again for the welcome, It's refreshing to have positive feed back on my project and good advice on powerplant and retracts (hopefully working in the same sense as the original). The weight is a concern as I want to keep it under 450kg AUW, So start with a wish list and see what I end up with.The big problem with the Isaac having retracts is space in the wing, I hope to get around this by modelling the aircraft on the Seafire47 which had large blisters on the upper wing to accommodate the U/C. If I can't get it Wright I just won't build it.

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    Re: Isaac spitfire

    You have the same problem that most RC Spits have, getting the gear right. The wheel goes where the main spar is. The choice is usually add weight through structure to get the wheel where it looks good, or move the wheel well forward to miss the spar. I think the pride of getting the plane built will out weigh any mismatch from a real Spit. I think when you get into it, other unSpit problems will come to light bogging you down if what you want is a real Spitfire to fly; only 50 owners in the world get that privilege.

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    Re: Isaac spitfire

    I totally agree with you, You will never make a real Spitfire from a wooden 6/10 replica, though What I would like to build is an aircraft instantly recognisable as a scaled down Spit and not something that vaguely resembles one. As long as it looks the part, as I gaze from the cockpit at 1500ft upon that elliptical wing,it would be real enough for me.

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    Registered User SpitfireBuilder91's Avatar
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    Re: Isaac spitfire

    Late to the party on this one, but why not fit the undercarriage to retract inwards? I might be wrong, but I think John Isaacs originally considered this.

    I've seen one Spitfire built this way (albeit a 75% scale one) and it seemed to work OK.

    Bill Pratt in the States is/was building his aircraft with a Jabiru 3300, which might go some way to ridding the aircraft of this bulged engine cowlings.

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    Re: Isaac spitfire

    a bit late, but ala, I have the isaac drawings for over 30 years, but never started. Reason: to small for happyness.
    The Isaacs ia allready upgrade from 100o lbs originally to 1100lbs. so all the eleastic used up! The wish for a bit more fuel
    finished ended with no spare weightspace left. any trial over this will end in trouble or much worse. The only way is to upscale
    the Isaacs to 70% what gives space for pilot and fuel. But all my efforts toget is done failed as it will be a complete new design
    and needs all calculated from the start over Cost: more as the plane cost to build! End of story.

    Bill Pratt has finished his Isaacs and must have passed the final inspection now. It is most likely that he made he first fight by now
    but I have not seen his latest news. He keeps me posted all the time.
    If you see it, you pull out the drawings once again!

    Remember: John O made the best of it 50 years ago. It is much closer to scale!!as most of you will believe. For his time it was absolute the best. All we have to do is scale it up to 70%. Someone out there who will sign for it?? I work on it for some time, and know what it will be.

    Don't compare the Mk26 with the Isaacs, the 26 is made for the US market with high power and lots of $$$. We talk a different language.

    regards, Harry

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    Re: Isaac spitfire

    I still have my plans for the Isaacs - wonder if I can build it in time for the 100th anniversary of the Spit's first flight??

    Anyway, maybe this will inspire some folks - and it DOES look good with the sprung aluminium undercarriage...

    Click image for larger version. 

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