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P-51C at ~70% scale as ultralight?

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J.L. Frusha

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At the same approximate scale, it has about 75% of the vertical stabilizer as the Marske Monarch, which is still roughly 35% more that the Ultracruiser, about the same Horizontal Stab as the Ultracruiser
 

Saville

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Do you think that would work as an ultralight? I'm guessing it would be about a 1000 lbs too heavy!
Well the idea being that with something like an RV-8 you have the balance and rough dimensions worked out. You would go with lighter materials and a smaller engine.
 

cluttonfred

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If I were really doing this and trying to stay legal under Part 103, I'd go with Sky Pup construction and about a 30 hp paramotor two-stroke to keep the weight down. I'd have a base structure that looked like a cross between a Sky Pup and a Volksplane: box fuselage, windshield bow/roll bar, gently straight-tapered wings, conventional fin/rudder and stab/elevator tail surfaces. Then I'd use just the fin/rudder shape and non-structural elements (cowling, turtledeck, canopy, radiator scoops, wingtips) to give a hint of a Mustang/P-40/Spitfire/Hurricane/Me109/Ki61 etc.
 

J.L. Frusha

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Not sure if I plan an all metal design, composite, or combination, however I am planning it as either Moncoque, or Semi-Monocoque construction.

I like the Rand KR fiber-faced reinforced foamboard technique, but I haven't looked into the relative weights for the strength. I do know that all-metal and all composit both methods can result in adequate strength, light-weight structures.

I don't see any advantage to making a core and tacking on features to imitate a general shape. Just sounds like added weight, for the sake of appearances, to me. Depending on the power source, when built, the Mustang's belly radiator scoop could be an intake and cooling air supply for a fuselage mounted generator, if series hybrid electric, or as a possible oil cooler for a tractor-mount 4-stroke powerplant. Either way, it won't be just for looks.
 

cluttonfred

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The "avantage to making a core and tacking on features to imitate a general shape" is that the work you would to to develop the basic design could be applied to other WWII fighters besides the P-51. You could create a whole cartoon squadron!
cartoon squadron.png
 

pictsidhe

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The full size Hurricanes used a boxy steel frame fuselage with wood and fabric shaping. If I wasn't pursing the crazy idea of a Coroplast monocoque, I'd likely follow that idea. Monocoque is hard to do for a 103, trust me, I'm doing one with maths. There is no way you will do it by guessing.

My 'radiator' will be quite fake. It's added complexity and and weight to put any cooling in the radiator housing. Getting rid of unnecessary weight is absolutely vital in a 103. Forget all and any notions of building it functionally like the full scale plane and work out how to build it light as you possibly can while still looking like the full size plane. 103s don't need the huge cooling flow of the real warplanes. As my "radiator housing" is in reality a detachable baggage pod, it does not contribute to the empty weight of the plane. Not only will my cooling system be simpler and lighter, but the 'radiator' will have a legal weight of 0lbs, whatever it weighs. It'll be handy for bulky light things like sleeping bags. it's rather far behind the cg to load with much weight. Fortunately, I have lots of accessible space in the wing root leading edges to balance it.

My cooling plan is an annular air intake between spinner and cowling. 15" spinner and 17" cowling will give a good amount of pressure recovery. I could also incorporate an annular diffuser in the cowling with a 2nd wall if I have the weight and halve the annular intake for aesthetics and a little drag reduction. Cooling air exit will be via the exhaust stubs. Ones of around scale size are about right for cooling air ejected by the real exhaust. That also varies air flow with power, giving low drag loss at cruise. The Meredith effect at UL speeds is miniscule, but the ejector pump will save fan or drag power loss, likely worth a few hp.

Visual external changes from my full size plane are an enlarged cockpit canopy so I have an acceptable view. Much bigger ailerons so it will roll a little faster than a glacier. Slightly smaller wheels as the ones I've found have a huge weight advantage over correctly sized ones and the cooling air intake. I'm hoping to get double takes from 200 yards...
 

Jerry Lytle

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Since we seem to be departing the reality of Part 103 how about making a silhouette P-51. A rollover could be contured to look like the canopy line, bent knees would allow the feet to be concealed by the silhouette of the radiator, (if the landing gear holds you might not break both legs.) A hopped up Olsen 65 for power and presto! Wear camo pants that match the paint job and it might pass the 100 yard eyeball test.
To me this makes as much sense as some of the ideals put forth. No not yours Pictsidhe.
Oh, oh, I forgot the air conditioning. Back to the drawing board.
 

pictsidhe

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Air conditioning? That's a bag of ice in a basket in the cabin air intake. Though I probably won't bother, the canopy will open. If I'm really lucky, it will even shut too. ;)
 

Dennis K

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These guys sell plans for a 2/3 scale P-51. Years ago I watched a fellow build one of thier FW-190's. Plywood fuse, foam blocks to fill out the shape with a VW engine. They had others like the F4U using the same basic construction but different shaped foam blocks and wing configurations.

www.falconaravia.com
 

radfordc

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mcrae0104

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The Loehle 5151 Mustang is the closest existing design to a 70% ultralight Mustang....and it's far from "ultralight".

https://en.wikipedia.org/wiki/Loehle_5151_Mustang
That is true. But I still hope the OP won't be deterred. There is value in the design process even if the outcome is not what one expects at the outset. I think a "cartoon Mustang" would be a hoot even if it came in at 400 or 500 lb.
 

J.L. Frusha

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Since we seem to be departing the reality of Part 103 how about making a silhouette P-51. A rollover could be contured to look like the canopy line, bent knees would allow the feet to be concealed by the silhouette of the radiator, (if the landing gear holds you might not break both legs.) A hopped up Olsen 65 for power and presto! Wear camo pants that match the paint job and it might pass the 100 yard eyeball test.
To me this makes as much sense as some of the ideals put forth. No not yours Pictsidhe.
Oh, oh, I forgot the air conditioning. Back to the drawing board.
I actually considered something close to the FlyBike (sp?).

As for accusations of departing from Part 103, there are a number of all aluminum planes that are close and one that is already discussed, which are close to the same approximate dimensions being considered.

Yes the Loehle, at 50% scale is larger than the 36% scale length that a 50% reduced further would represent a decrease in weight, but, I guess shorter aircraft weigh more, given the accusation...

No, it CAN'T be done, if nobody tries. Part of the purpose of this thread is to help explore the POSSIBILITY that it CAN be done, not argue over why each 'thinks' (unproven determination) it cannot be done.
 

BBerson

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How does 16 feet span comply with FAR103? Need about 110 sq.ft of wing. Which is about 6.8 feet chord average.
 

J.L. Frusha

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All I've done is scaling and comparisons.

I do not see how you equate FAR 103 with 110 sq feet/6.8 ft chord. To me, that's like saying You have an apple and ketchup is necessary.

What is needed is a wing that will perform the necessary functions, not some arbitrary chord and area. Chord at the root, as depicted is approximately 5 ft 8 1/2 inches.
 
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