Airfoil selection for an aircraft out there?

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WARPilot

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I am looking to do some redesign on a WAR FW 190. The wing is 20’ and has an area of approx 77ft^2. Weight is an issue and the redesign will largely involve creating a mold and chunking the wood and foam. New empty weight will be around 550lbs. Gross TO weight will be 900lbs.
The performance I am looking for from the wing is a low stall speed, 50 mph, and a cruise speed of 180 mph. Power will be in the 100-130 hp range.
The current airfoil is a 23015, 014, and 012. There must be better airfoils out there.
The wing must accommodate the retractable gear.
I want to keep the FW190 look in the planform.
Any ideas out there?
 

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nickec

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Flaps. Consider Junkers flaps. That will get you part way. Though not far enough - in my opinion.

Some will say your requirements lie outside reasonable expectations. Can you name a common aircraft with a 50 mph stall, 180 cruise, using 130 HP?

The look you desire limits the likelihood of achieving the numbers you want.

A high level of engineering and complexity can get 50/180, however, given the HP/TOW you listed, the airframe would be much sleeker than the 190.

Again, in my opinion. I wish to avoid discouraging you in your quest. Consider being OK with somewhat lesser performance. yet still striving.
 

nickec

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"... A Cessna 172S Skyhawk’s speed ratio is typical for trainers at about 2.6:1. A sleeker and more powerful, normally aspirated Cirrus SR22 improves to about 3:1. A retractable-gear Beechcraft Bonanza B36 is, somewhat surprisingly, a bit less at 2.9:1. And a Van’s Aircraft RV–10 (such as the AOPA 2020 Sweepstakes grand prize) has an unusually broad 4:1 speed ratio. ..."

You are hoping for a speed ratio of 3.6 - which is quite high. One might say, rare.

In another article at aopa.org the RV-10 numbers claim a speed ratio of 3.3:1. So the 4:1 number is suspect.

 
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TFF

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Essentially it’s the same airfoil as most RVs and Taylorcraft. It’s going to be hard to beat. For just slow, the USA35B will be hard to beat but 230xx is better overall. Weight loss is your real work.
 

wsimpso1

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You have two things to work through:

How to land slow, and;
How to cruise fast.

Landing slow is almost always about low enough wing loading combined with effective enough flaps. Slotted flaps on pivots hung below the wing is the simple way to get a lot of Cl when deployed and low drag when stowed. See the flap chapter of TOWS. Then make the wings big enough (wing loading low enough) to get into your target landing speed.

Cruising fast is about low drag. Minimizing things like frontal area of fuselage, planform area of wings and tail, etc. Since you want the feel of the FW-190, the planform proportions are already set, but you could go with laminar flow foils. Get Riblett's book to select the right foil from his catalog. Harry's foils have the advantage of nice stall behavior. Read and heed the advice to use one foil from root to tip. A hotwired foam wing per Rutan methods can be pretty light and laminar in this size. Want it to look like an FW? Put the details on with an airbrush.

After that, the other big issues are interference drag, cooling drag, and gear sealing.

Interference drag is usually minimized with the fuselage vertical walled and straight section through the wing. Think Mustang, NOT Spitfire. Once you accept fuselage taper through the wing, you are committing to expanding root fillets and still big drag from separation. If you can keep the FW look without tapering through the wing, you will be faster.

Cooling drag is all about putting all the air through the cooling fins, good exit design, and the minimizing inlet area. The FW had that nice nose bowl with a reduced opening. You can make that in two pieces from a mold, make several with different openings, and play until you have the smallest safe opening, then paint it to look like right in scale.

Gear doors must fit tight with some preload and springiness. Sealing the openings from the rest of the airframe will reduce excresence in not only the gear, but for control surfaces too.

Big project. I want to see it fly.

Billski
 

wsimpso1

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TOWS (or Abbott and von Doenhoff) is THE BIBLE for those of us getting started on wings, airfoils, flaps, etc. Then you go to Riblett for modern low drag good behaving foils and wings.

All of these books are listed here:

 

microwaves

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I am looking to do some redesign on a WAR FW 190. The wing is 20’ and has an area of approx 77ft^2. Weight is an issue and the redesign will largely involve creating a mold and chunking the wood and foam. New empty weight will be around 550lbs. Gross TO weight will be 900lbs.
The performance I am looking for from the wing is a low stall speed, 50 mph, and a cruise speed of 180 mph. Power will be in the 100-130 hp range.
The current airfoil is a 23015, 014, and 012. There must be better airfoils out there.
The wing must accommodate the retractable gear.
I want to keep the FW190 look in the planform.
Any ideas out there?
Check out airfoiltools.com. They have tons of free airfoils that can be downloaded into Excel and scaled to your dimensions.
 

WARPilot

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Flaps. Consider Junkers flaps. That will get you part way. Though not far enough - in my opinion.

Some will say your requirements lie outside reasonable expectations. Can you name a common aircraft with a 50 mph stall, 180 cruise, using 130 HP?

The look you desire limits the likelihood of achieving the numbers you want.

A high level of engineering and complexity can get 50/180, however, given the HP/TOW you listed, the airframe would be much sleeker than the 190.

Again, in my opinion. I wish to avoid discouraging you in your quest. Consider being OK with somewhat lesser performance. yet still striving.
I’m told the FW 190 flew at 165mph with a continental O-200 by the previous owner. It is heavier than what I am proposing so I “just thought” 180mph was achievable with so e aerodynamic cleanup and a better airfoil.
 

TFF

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I think you need to look at it first and ask if a WAR can be lighter within the budget ,and deliver that type of performance. How much deviation are you allowing from the shape or contours? You won’t have the speed, but the Loele P-51/P40 does some of what you want. Same idea. There is also Scalebirds P-36 is probably closer to what you want. For the most part, you have to pick a speed as more important. Fast and slow ends up where it does, or slow and fast is what it is. Airfoils are important but there is no magic without wing area. You need to set a reasonable wing area and tune it with the airfoil.
 

WARPilot

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Sounds like you are willing to put in the work needed. I look forward to the end product. Keep us informed. Your efforts will interest many members.
I am friends with a composites engineer who has a company that builds a single seat aircraft. He is also has a new design that he will debut at AirVenture 2022.
Based on his other single seat kit he builds from molds, he believes a new kitted WAR FW 190 would weigh in at approx 550lbs, ready to fly less pilot and fuel. Thus the weight would be over 200 lbs lighter than any other WAR produced. Time to build would be approx 500 hours.
We don't want to change the design much but want to improve stall speed and cruise speed if possible. The FW would be molded to accept a Verner S7 Radial with 110hp continuous and 280ft-lbs torque (the o-320, 150hp engine makes 280 ft-lbs).
Flaps are possible but add some complexity.
 

WARPilot

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I think you need to look at it first and ask if a WAR can be lighter within the budget ,and deliver that type of performance. How much deviation are you allowing from the shape or contours? You won’t have the speed, but the Loele P-51/P40 does some of what you want. Same idea. There is also Scalebirds P-36 is probably closer to what you want. For the most part, you have to pick a speed as more important. Fast and slow ends up where it does, or slow and fast is what it is. Airfoils are important but there is no magic without wing area. You need to set a reasonable wing area and tune it with the airfoil.
A WAR can be much lighter and much easier to build! The wing loading is approx 13lbs/ft^2
A lighter aircraft with 77ft^2 area would be 11.5-12lbs/ft
The proposed engines would produce about 110-130hp.

Im just seeking advice for how to proceed on aerodynamics, for speed and descent flight quality.
 

BJC

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Streamline the engine and cooling air path as per the real -190. That is the biggie. Ensure effective sealing of all openings - LG, flap and aileron gaps, canopy, etc. optimize decalage to minimize trim drag. Build a smooth, wave free forward half of the wing.

Don’t worry too much about the airfoil, especially if it is a low pitching moment a la the 230XX.


BJC
 

Dana

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The 230XX series airfoils have a long record of successful use on well behaved airplanes that go faster than their peers on the same power. If you're changing the airfoil, and changing the structure, it's not a WAR aircraft any more, it's a completely new design that may share some features. The big selling point of the WAR series back in the day was the simple construction that could easily be cosmetically altered to replicate different designs.

You might want to look at NACA Technical Report No. 530, which compares the 23012 with the Clark Y, one of the most common low speed airfoils of the day. The 23012 has a Clmax of 1.6 to the Clark Y's 1.7, which would give only a 3% difference in stall speed.
 

llemon

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imho there is no reason not to swap the NACA airfoil for the related Ribblet section. It should improve stall slightly with no degradation anywhere else.
 

TFF

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If you are going composite it’s a new design with the exact same shape as a WAR. 500 lb would be impressive. The firewall forward is going to be 250 lb engine, prop, cowl, and other stuff. 250 lb airframe will be impressive, especially with retractable gear. At least for the shape and surface. I’m sure you can loose some weight, substantial I’m sure. Half weight is pretty ambitious. Easier to build once the moulds are done, sure; but building the moulds is part of the job; I bet it’s not zero hours. 500 plus 1000 making moulds probably another 500 for systems. Canopy, flight control runs, fuel lines, landing gear, wiring is not going to be free time. If you are turning it into a kit, I bet plenty will be able to capitalize on your hard work laying everything out, but the first one will not be that quick.
 

WARPilot

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The 230XX series airfoils have a long record of successful use on well behaved airplanes that go faster than their peers on the same power. If you're changing the airfoil, and changing the structure, it's not a WAR aircraft any more, it's a completely new design that may share some features. The big selling point of the WAR series back in the day was the simple construction that could easily be cosmetically altered to replicate different designs.

You might want to look at NACA Technical Report No. 530, which compares the 23012 with the Clark Y, one of the most common low speed airfoils of the day. The 23012 has a Clmax of 1.6 to the Clark Y's 1.7, which would give only a 3% difference in stall speed.
Easily altered was great but it left all the heavy structure that can be designed into a fully molded, easy to build, and to fly with better performance. There is no support from WAR in the form of parts. Most builders never finished due to the daunting challenges. I am finding out from this group that the WAR designers picked a good airfoil. I was just thinking there had to be a really good, modern airfoil that would improve slow and fast speed performance.
 
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