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

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pictsidhe

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The wing area requirements for ultralights are listed in AC103-7.
But the appendix is only for rectangular wings. I'll have 114 sqft, with >50% split flaps, I'm expecting it to meet the stall requirement. If not, I'll flaperon the ailerons until it does. You don't actually have to use the flaps etc except to show compliance...
A 70% p-51 will have 115sqft, so >50% flaps and reasonably high lift airfoils should work on that too.
 

pictsidhe

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70% of 37 feet is 26 feet span. His post 118 has morphed to 16 feet.
I missed that. You are right, post 118 has about half the wing area needed to comply with 103.
Scaling the post 118 concept by 140% would put it in the ballpark, though. It would have a nice roomy cockpit then, unlike mine...
 

pictsidhe

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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.
So, how do you plan to get a CLmax of around 4 that is necessary to make this concept 103 legal?
 
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J.L. Frusha

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I guess you missed the changes to cut weight... That said, let me reiterate... SO FAR, it has only been based off art and approximations...

Meaning, I scaled the length from 50 % to 36%, especially after all the griping of 'it's too big to be Part 103, then I cut the span from 50% to 85% of 50%.

So, with all the griping, I pushed it too small... Ooooooh can't get it small enough to be part 103... Well, evidently, I managed to blow right down too small...

How about that? Y'all are so busy griping, you don't give a **** that someone is actually trying to adjust things to fit all the info he can get out of the conversation...

No, FAR 103 does NOT say I'd need 6.8 ft chord 16 ft wings there, sunshine. It gives a means of calculating the stall speed, then, damned if it doesn't SPECIFY that DEMONSTRATED power-off stall speed certified by a mechanic meets FAR 103...

... but, wth, lets throw weird numbers out just to see if someone actually READS the post (right?)...

Run the numbers backwards... Gross weight ~500 lbs... WHY? 254 + 30 = 284 Me? I'm ~215 Voila - 499, so round up for that after meal flight? (shrugs)

Now, looking at the images... Oh, looky, there One with flaps... 1.8... Call mean chord 3.8 ft. Call it max wing loading 3.4? Use something like this...? ~9.35% thickness... (Correct?) (Oh, look, Fowler Flaps)...

http://www.tspeer.com/Fisher/C506F.htm


Anyone want to calculate the area, then the span, based on the standard P-51 Mustang wing with a root chord of ~5 ft 8 1/2 inches, mean chord of 3.8 ft?

I'll adjust the span, then fiddle with the rest. How does that sound?
 

cluttonfred

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You gave a span of 16' so you established one key dimension. A P-51 has 37' span and 235 sq ft of wing area, at 70% scale that's 26' span and 115 sq ft area.

A proven, cantilever, legal Part 103 ultralight like the Sky Pup needs 31' span and and 130 sq ft of wing area to manage a stall speed of 26 mph with an empty weight of just 195 lb and gross weight of just 400 lb.

If you have a more typical Part 103 gross weight of 500 lb then you'll need about 160 sq ft of wing area. BBerson is being very generous...by my calculations you'd need an average chord of 10' to make this work at 16' span with a typical airfoil.
 
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cluttonfred

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I think this is a case where trying to make the aircraft too small will make achieving the mission goals next to impossible. If I were you I'd start with about 5/6 scale (83.3%) to get the span (31 ft) and wing area (163 sq ft) you need to fly 500 lb at Part 103 stall speed with a typical airfoil. Then the challenge is designing a very light structure to create that form at 254 lb empty weight. I think it could be done with wood and foam and fabric, perhaps with some carbon fiber in the spars, longerons and landing gear legs and a paramotor engine. Basically you'd be creating a true Part 103 successor to the Loehle 5151.
 

J.L. Frusha

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You gave a span of 16' so you established one key dimension. A P-51 has 37' span and 235 sq ft of wing area, at 70% scale that's 26' span and 115 sq ft area.

A proven, cantilever, legal Part 103 ultralight like the Sky Pup needs 31' span and and 130 sq ft of wing area to manage a stall speed of 26 mph with an empty weight of just 195 lb and gross weight of just 400 lb.

If you have a more typical Part 103 gross weight of 500 lb then you'll need about 160 sq ft of wing area. BBerson is being very generous...by my calculations you'd need an average chord of 10' to make this work at 16' span with a typical airfoil.

So, you totally ignored 2 of my posts just to maintain that 16 ft span... Especially the one directly above yours asking for help calculating the span...


Run the numbers backwards... Gross weight ~500 lbs... WHY? 254 + 30 = 284 Me? I'm ~215 Voila - 499, so round up for that after meal flight? (shrugs)

Now, looking at the images... Oh, looky, there One with flaps... 1.8... Call mean chord 3.8 ft. Call it max wing loading 3.4? Use something like this...? ~9.35% thickness... (Correct?) (Oh, look, Fowler Flaps)...

http://www.tspeer.com/Fisher/C506F.htm


Anyone want to calculate the area, then the span, based on the standard P-51 Mustang wing with a root chord of ~5 ft 8 1/2 inches, mean chord of 3.8 ft?

I'll adjust the span, then fiddle with the rest. How does that sound?
 

J.L. Frusha

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So, let's maintain that 16 ft span... 3.8 ft mac and use a calculator... Why not, seems almost the only way to get an answer around here that isn't aimed at discouraging people, right?

... which ends up being a turbine rotor blade design, because of a maintained fiction of 16 ft...
 
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radfordc

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He does seem to know all the answers, so input from more experienced people seems not to be needed. But, if this project ever gets beyond the "internet argument" stage I will be surprised. If it gets built I will be amazed. Best of luck to the OP.
 

J.L. Frusha

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It seems you know everything and reject help. Good luck with your project.
I asked for help and seem to be getting negativity. I SAID that I screwed up and over shot getting too small, because of all the comments on weight, but I guess that's not good enough for you...?

I ASKED for someone to help recalculate based on the Root Cord of 5 ft 8 1/2 inches, Mean Cord of 3.8 ft at 500 lbs gross, etc.

Instead, I get a snarky comment about 16 ft AFTER I asked for help recalculating the wing..., so, I found a way to get snarky right back.

Y'all are so busy discouraging the attempt, that you don't seem to give a **** about an honest effort to learn and adjust accordingly.
 

cluttonfred

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Or maybe you could read more carefully....

I think this is a case where trying to make the aircraft too small will make achieving the mission goals next to impossible. If I were you I'd start with about 5/6 scale (83.3%) to get the span (31 ft) and wing area (163 sq ft) you need to fly 500 lb at Part 103 stall speed with a typical airfoil. Then the challenge is designing a very light structure to create that form at 254 lb empty weight. I think it could be done with wood and foam and fabric, perhaps with some carbon fiber in the spars, longerons and landing gear legs and a paramotor engine. Basically you'd be creating a true Part 103 successor to the Loehle 5151.
 

pictsidhe

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103s have conflicting requirements.
They need to stall slow, that needs a certain amount of wing area, depending on the CL you can achieve.
They need to be light, that requires using mostly air to build them.
How I sized mine was first to decide on my high lift devices (split flaps like full size), estimate the CL the wing would achieve at a 103 Reynolds number (2 - 2.1) then calculate the area and from that I came up with 2/3 scale to be Baby Bear's porridge.

Anyone thinking of designing their own ultralight who can't manage that design stage should pick a set of plans and follow them.
 

don january

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Frusha. The persons you slash back at probably have more time on the "shitter" between flights then you have in the air. I think you OVERLOOK on big factor with a plane you are hoping to design and build with a tail moment so short I think pitch control would be more then a pilot could handle. Why not just buy one of these and build a proven design ? Personally I'
m rather sick of dreamers that have nothing better to do then talk the walk but never mix some glue or fire up the torch. My 2 centsp 51 toy.jpg
 

poormansairforce

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So, let's maintain that 16 ft span... 3.8 ft mac and use a calculator... Why not, seems almost the only way to get an answer around here that isn't aimed at discouraging people, right?

... which ends up being a turbine rotor blade design, because of a maintained fiction of 16 ft...
Ok, so you just posted a graph at a Reynolds number that indicates 100 mph. How about one at 26 mph?
 

J.L. Frusha

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Or maybe you could read more carefully....
Is that 31 ft based on the changes, or a suggestion? I'm not a mind reader. Not trying to be snarky, but asking an honest question. Not sure if we both arrived at 500 lbs by the same means, but, it works.

I have asked for and continue to ask for real help and have tried to adjust and give the real info that I CAN find/figure out, to work with.

I've found what I could. All the calculators in the world for Reynolds numbers don't tell me diddley about calculating the span from area, load and the chord at 2 points in the span that are root and middle of each wing, but nothing to get length between those points, or total span.

Frusha. The persons you slash back at probably have more time on the "shitter" between flights then you have in the air. I think you OVERLOOK on big factor with a plane you are hoping to design and build with a tail moment so short I think pitch control would be more then a pilot could handle. Why not just buy one of these and build a proven design ? Personally I'
m rather sick of dreamers that have nothing better to do then talk the walk but never mix some glue or fire up the torch. My 2 centsView attachment 85397
... and, still, I'm getting snarky comments.


I already compared tail area to the Ultracruiser and beat it in area with a visual comparison with both vertical and horizontal stabilizers, plus the LE and weight are in almost exactly the same place, with only a slightly shorter tail length and brought the nose back even further, reducing the tail moment to move the engine moment around the LE. Bit more leverage and area to use to move the lever...

No, I have not flown very much. Dropped out of flight school 31 years ago, because I had a daughter on the way. I'm a grandfather, now, not some snot-nosed teenager.

On the other hand, out of thousands (hundreds of thousands?) of pilots, very few attempt to build their own aircraft, while there are successful amateur-built aircraft dating literally back to the Wright Brothers, successfully and safely flown for totals of countless thousands of hours, by people with limited experience starting out.

-------------------------

Despite all the negativity, I AM trying to learn and have shown that. I admitted where AND WHY I screwed up. If that's not good enough, at least I have a few people in this thread that are and one person in messages and email from all this that is trying to help and I am grateful for that.

YES, it CAN be done.

The hard specs so far:
500 lbs MTOW
LOA ~13 ft 6 in
Root chord: ~5 ft 8 1/2 in
Mean Chord: ~3 ft 9 1/2 in
Loading of ~ 3.4 lbs per sq ft
Area(?) ~ 147 square ft(?)

If it's a rectangular wing, using the root chord, is the span 25 ft 9 1/2 inches? What would it be with the tapered planform? I still have no idea how to get that span.
 
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