Airfoil comparison ISA571 & NACA4408

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jumpinjan

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Lucrum

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I'm looking for airfoil for my WWI replica design, and I want it mostly flat bottom, about 8% and no bad stall characteristics. I found the I.S.A. 571 and it looks pretty good....maybe too good to believe. Please compare the ISA571 & naca 4408.
Airfoil Investigation Database - Showing naca-4408
Airfoil Investigation Database - Showing I.S.A. 571
They are basically the same shape, but the 571 is superior? Is this data right and why the big difference, do you think?
Jan
That's a great web site. One disadvantage though is, I believe, their airfoil graphs only go up to a Re of 100,000.
 

flinote

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I'm looking for airfoil for my WWI replica design, and I want it mostly flat bottom, about 8% and no bad stall characteristics. I found the I.S.A. 571 and it looks pretty good....maybe too good to believe. Please compare the ISA571 & naca 4408.
Airfoil Investigation Database - Showing naca-4408
Airfoil Investigation Database - Showing I.S.A. 571
They are basically the same shape, but the 571 is superior? Is this data right and why the big difference, do you think?
Jan
Why are you using such a thin airfoil? This would imply a sharp leading edge radius with the accompanying sharp stall. Also, undercambered airfoils such as this have relatively high lift coefficients but poor L/D at the Reynolds numbers you'll be working with. Also, there's the issue of moment coefficient which is going to haunt you--the required tail coefficient is going to be abnormally high.

I believe a better choice for you is the Clark Y, for any number of reasons. It's an old section, but has been well-proven in many different aircraft of diverse specs. For you, the advantages would appear to be 1) it has a truly flat bottom; 2) the leading edge is of larger radius and will promote ease of building in that critical area; 3) a reasonably soft stall; 4) relatively high lift with adequate L/D--appropriate for a probable cruise speed under 100 knots; 4) the section thickness (11.7%) promotes decent spar depth; 5) lower moment coefficient, the Clark YH version (slightly reflexed) is even lower if you need that parameter augmented.

Google for Clark Y and look at all the relevant hits--there's a lot of info and most of it looks good for your app.

Etc, etc. There are also new, computer designed airfoils with tailored specs that will suit your needs. Remember, all aspects of the aircraft design and performance are interrelated, and you don't want to become overly focused on just one aspect.

Good luck and be careful.

Bill
 

jumpinjan

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Thanks Bill,
Okay, now look at the ClarkY and compare it to the ISA571. It looks like the 571 is just as good or better. Why is that?
Jan
 

flinote

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Thanks Bill,
Okay, now look at the ClarkY and compare it to the ISA571. It looks like the 571 is just as good or better. Why is that?
Jan
Better in what way, though? It's difficult to make a direct comparison because the website you're accessing for the I.S.A. 571 only shows performance at very low Reynolds numbers, suitable for model aircraft.

Do you know if this section has been used on any full-sized aircraft?

Bill
 

jumpinjan

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Well, could someone model these two at a cord length of 24" and see what their characteristics will be?
Jan
 

Dana

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From what I've seen, when it comes down to real world performance in, the classic sections like the Clark Y and the NACA 4- and 5-digit sections do jut as well as the fancy new sections in most moderate performance applications.

In this case, the ISA section has a higher Clmax, but the 4408 has a slightly better max L/D. The 4408 is also 8% thicker, which means 17% stronger.

Despite some adverse characteristics, a relatively thin, undercambered airfoil section woud look more authentic than, say, a Clark Y, while still being much better than the original airfoils used on a WWI aircraft. And hmmm... I've never seen any studies, but I wonder how the section thickness affects biplane interference?

BTW, the Clark Y is not truly flat bottomed, but very slightly undercambered... but most people build it as flat bottomed for ease of construction.

-Dana


Rules are for the guidance of wise men and the obedience of fools.
 

HumanPoweredDesigner

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A huge part of designing a plane that flies the first time is knowing how each part will behave. The Clark Y is very well understood. Probably books and books on it. Looks easy to fabricate too. It's like the difference between making a plane out of spruce or some new exotic material you don't have the specs for.

That website is made for RC airplanes. It is still somewhat useful though.
 

HumanPoweredDesigner

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Well, could someone model these two at a cord length of 24" and see what their characteristics will be?
Jan
I downloaded XFLR5, but I don't know how to run it. Someone on here should be able to compare both airfoils if you give them the Re you will be using.
 

jumpinjan

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Okay folks, here's a sample of why why I'm designing WWI aircraft replicas. It's about living history. Here's a short clip of the WWI aircraft & pilots flying their replicas over a simulated WWI battlefield.
This is a professional complied video clip that might become a weekly cable TV show.
http://www.weekendwarbirds.com/video/vid1.html
The thing is we want to get different types of WWI aircraft out there and that's why I'm designing some new ships to fly. I have now three designs in progress right now. We are having our fall event next week, by the way, so I'll be taking my laptop and I review my work with the other pilots & builders. The fall event is where the aeroplanes will make their runs over the trenches. It's like 1918 for 30hrs, next weekend! It's so cool!
Jan
 
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Jan Carlsson

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I tried to test them in DesignFoil, but the coordinates is to un even to get good result in this program.

4408 is just a 8% version of of 4412 with the same camber.
the 4412 is a mathematic version of ClarkY, 4412 I think have a kinder stall then ClarkY, but the ClarkY have little better L/D
But who can tell on a wing built with ribs and fabric?
the ISA571 looks autentic
You are flying these at Re Nr of 1 000 000+

Jan
 

wsimpso1

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I personally would not want to replicate the poor flight characteristics of airplanes from that era. Things like ailerons that are heavy and/or have poor responses, lousy stall behaviour, and nuetral (or worse) stability in all three axes.

A modern airfoil designed for real airplanes (not RC's) can be selected that will give good stall behaviour and reasonable pitching moments. This allows you an airplane that is safe in a stall, has lighter ailerons that will roll the bird, reduced pitching moments allows a period correct looking tail enough authority and stablity to keep the pointy end forward. You can keep a relatively thin foil for a period look, but still gain some thickness for improved panel stiffness and strength at lower weights.

What is your intended cruise Cl? If it is about 0.3, then Harry Riblett's 30-312 should be about right, with low pitching moment, no cusps, soft stall, and 12% thick... His 30- series is based on the NACA 0015. If you are intending it for inverted flight, you could use the nice symetric NACA foils - 0008, 0010, 0012. They have been around a long time and are the basis for many cambered foils as well as tails, and symetric wings. The 0015 might be a bit thick for your period correct look...

I know, these are not flat bottomed, but being as most WWI aircraft had rectangular wings, you only need to build one jig to build each wing. And being as many of those planes also had nearly identical top and bottom, one jig would allow you build all four panels.
 

jumpinjan

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"With authentic aircraft, comes authentic risks", was quoted by a modern day Wright Biplane researcher/builder/pilot.
My (our) philosophy is to do as much research as possible to make the aeroplane have the authenticity on the outside, but design/build the inside with modern materials and apply the proper engineering processes on the inside. Some will build to factory plans and even fly with the original engine. Those pilots flying originals that I talked to, say they fly like a Piper Cub, but also say that you need to be on-top of it's control, or it will wonder right off, and you need to pick it up again (especially a configuration like the Fokker Triplane).
The subjects that I am designing, are scaled down slightly. That's because of the limited engine availability, and we want them to fit on light weight trailers, so we can easily transport them across the country. They are strictly flown like a Cessna 150, and as well as stressed to the limits of a 150; They are NOT aerobatic! Most cruise at speeds of 100-80mph, and typically weigh 900-600 lbs.
I wrote an article a few months ago for our club's newsletter on what I'm doing. It's basically aircraft homebuilding that most of you do.
http://janswerks.com/aircraft/albatros/GWAA.pdf
Jan
 

wsimpso1

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If you are trying to completely replicate a historic airplane, then replicate the entire airplane. I understand completely the issue of replicating it all, including the behaviour.

Once you deviate on scale and engine type and structure details and the way it is to be flown, you might as well fix stall behaviour, aileron reponse and forces, and stability.

Good stall behaviour in an 8% thick wing is as simple as adding Harry Ribblett's GA3 camber curve to the NACA 0008 form.
Pitch and yaw stability is only a matter of making sure that the CG is forward of the Neutral Point in pitch and yaw by about 10% MAC, either by CG adjustments or scaling the tail length/area a touch.

Roll behaviour, if it is a problem with the original is usually fixable by adding a touch of dihedral - easy to do on wire braced biplane.

If each of these is done gently, the airplane will still look right in profile, in plan view, and even while walking around it. And it will be more fun and less risky to fly.

I can help with the airfoil coordinates...

Billski
 

Lucrum

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"With authentic aircraft, comes authentic risks"...
While authenticity is certainly commendable if I'm not mistaken certain models of WW1 aircraft killed more pilots from accidents than were KIA by the enemy. The average modern low time private pilot is probably not equipped to handle many of the characteristics of some of those early designs. GL and be careful.
 

autoreply

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While authenticity is certainly commendable if I'm not mistaken certain models of WW1 aircraft killed more pilots from accidents than were KIA by the enemy. The average modern low time private pilot is probably not equipped to handle many of the characteristics of some of those early designs. GL and be careful.
Well, the guy that made that statement came really close to killing himself as well with his replica and was lucky to survive it.

Some people just don't believe in Darwin till he's done his work...
 

Autodidact

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Since the Albatross is almost (but maybe not quite) a sesquiplane, why not consider the Pietenpol airfoil for the upper wing, but thinned down a little? In the immediate post war period Gloster (the Grebe) built fighters designed by Folland that had a thicker upper wing for better stall and handling, a so called "high lift" wing. The Pietenpol airfoil has that sharp nosed, reflexed underside that is evocative of WWI era airfoils.

Personally, what attracts me to WWI era aircraft are things like varnished plywood, steel fittings, brass, etc. Especially in a scaled down version, a not quite authentic airfoil wouldn't detract from the beauty of the aircraft so long as the structure is authentic looking, but that's just me. I think I read somewhere that airplanes scale up better than they scale down.

Also, have you talked to Koloman Mayrhofer about the lower wing spar on his Austrian Albatros? Are you planning to strengthen it, or are you starting with a "clean sheet" for the structure?

I like the 3d models, sort of reminds me of a better proportioned Lincoln Sport. Neat.
 

NorthwestJack

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I am using a Gottingen 324 in my airplane design. I believe these airfoils were developed towards the end of WW1. I find the high Cl and larger Spar depth quite convenient. The only drawback was manufacture of a double recurve airfoil. But I think a lot of the WW1 foils were fairly similar.
Jacques
 

jumpinjan

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...certain models of WW1 aircraft killed more pilots from accidents...
Just about every TV show that I watch will bring this up time and time again and point to the Sopwith Camel's rotary (not Mazda) engine. Do to the procession of the flywheel (the engine itself was spinning around), your direction was 90 degree removed. So, if you yaw to the right, the plane would nose dive. I don't think the plane actually killed more pilots, than were shot down. I just think most of the accidents were just from the shoddy materials & workmanship and you went down with the ship, because there was no way to escape. You need to give these WWI pilots more credit for their flying skills, I think.
I'll take a look at this Mike Shuck article
http://www.imagedv.com/aircamper/pietenpol_fc10.pdf
jan
 
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