ounces per square inch rule of thumb ??

[Miotch]

Just curious if there is a rule of thumb for weight of a stunt ship per square inch of wing surface.   I did a search and didn't really find anything.  Which doesn't mean it's not there.

I know there are a thousand variables, but when scratch designing a stunt ship, I'm just wondering about a rough target weight to shoot for.

Thanks, -Mitch

[Ken Culbertson]

The "standard" I have always been told is the proper envelope is 10-13oz a square foot.  That works out to roughly .07 to .09oz @square inch.  My question has always been what to count.  Just the wing, or all lifting surfaces.

Ken

[Brett Buck]

The "standard" I have always been told is the proper envelope is 10-13oz a square foot.  That works out to roughly .07 to .09oz @square inch.  My question has always been what to count.  Just the wing, or all lifting surfaces.

Ken

Almost all recent NATs of recent times have been 13-16 ounces/square foot as they were in flight. This is because they all use modern- quality power systems. Forget about those sorts of numbers if you use vintage engines. Wing loading is not the issue with old engines, but more like power/weight ratio. Give us some idea what you are doing and the collective knowledge of stunhangar can weigh in.

Brett

[Miotch]

Almost all recent NATs of recent times have been 13-16 ounces/square foot as they were in flight. This is because they all use modern- quality power systems. Forget about those sorts of numbers if you use vintage engines. Wing loading is not the issue with old engines, but more like power/weight ratio. Give us some idea what you are doing and the collective knowledge of stunhangar can weigh in.

Brett

Thanks everyone.

Not sure what I'm doing yet.  Part of the question was just wondering how heavy was my recent biplane build (570-ish square inches, 62 ounces with a Saito .56), but the other part was because building that plane kind of fed my dormant addiction to building and I'm eyeing some old kits, wondering what I can create out of them.  Maybe take a couple of old Buster kits and build a full fuselage Cassutt ??  Who knows what madness I will come up with. 

[Ken Culbertson]

Almost all recent NATs of recent times have been 13-16 ounces/square foot as they were in flight. This is because they all use modern- quality power systems. Forget about those sorts of numbers if you use vintage engines. Wing loading is not the issue with old engines, but more like power/weight ratio. Give us some idea what you are doing and the collective knowledge of stunhangar can weigh in.

Brett

Last time I was overly concerned with wing loading was the late 70's and that range was good for the .35-.46 era.  That was then, this is now.  Endgame III is now at a whopping 70 ounces and has a loading of 13.something with a 75 size motor that makes a .46 feel like a 1/2a.  I call it Mrs. Piggie but from what you are saying it is more mainstream than I thought.  I have been forgetting the fuel when I compare all the weights people boost of.  A 65oz Bear with a .75 in it is 71 oz at takeoff.  The difference, he gets to do the clover at 65oz, I am still at 70!...which I count as a +.  Question is "how do we measure power".

Ken

[Matt Colan]

Last time I was overly concerned with wing loading was the late 70's and that range was good for the .35-.46 era.  That was then, this is now.  Endgame III is now at a whopping 70 ounces and has a loading of 13.something with a 75 size motor that makes a .46 feel like a 1/2a.  I call it Mrs. Piggie but from what you are saying it is more mainstream than I thought.  I have been forgetting the fuel when I compare all the weights people boost of.  A 65oz Bear with a .75 in it is 71 oz at takeoff.  The difference, he gets to do the clover at 65oz, I am still at 70!...which I count as a +.  Question is "how do we measure power".

Ken

Ken, I flew 5.7 laps on Sunday in the dead 90 degree soup we had for air with a 72oz (dry) airplane and had power and lift everywhere in the pattern. It was awesome!

Point being, I wouldn’t worry about the plane being 70oz with a battery

[Brett Buck]

Question is "how do we measure power".

   The actual definition of "power" in terms of physics/engineering is almost universally misunderstood by stunt fliers. For instance, no matter what engine you uses, a full-sized stunt plane at typcal 60 mph takes about .45 HP, no matter which engine you use. How much power it is putting out at the shaft is wildly different depending on the prop, RPM, etc. The very least efficient systems (46VF with a 12-3.25 at about 12,500-13,000) put out enormous shaft power and can handle remarkably heavy airplanes.

   A 75, tuned for maximum power, might be capable of 4-5 HP, we only need .45, so how to you adjust it to be the most beneficial?
 
   It's not a matter of "how much?" as a matter of "how effective?" I gave up trying to have a sensible discussion about it along time ago, it's too hard to overcome the universal misunderstandings of 80+ years of "stunt wisdom".

   Brett

[Doug Moisuk]

650 square inches 65 oz or less
540 = 54 oz
Go by the designers square inches
I agree that modern engines can puss those numbers.

[Brett Buck]

650 square inches 65 oz or less
540 = 54 oz
Go by the designers square inches
I agree that modern engines can puss those numbers.

Depends on what your standard might be, these are on the high side for "vintage" systems and full stunt performance, and middle of the road for modern propulsion.

At the NATS, I was surprised to find my airplane was nearly the lightest "full-sized" airplane on my circle, it is 680 square inches and 63 ounces. It's a little distorted because mine was without fuel but the electrics were with battery, of course.

       Brett

[Tim Wescott]

Ken, if you're going to go by other people's measurements, model aviation seems to measure the area of the wing on the bench, before it's installed in the fuselage -- which is directly contrary to full scale aviation practice that measures the area excluding the fuselage.

Unless you're building something wildly different from normal (like a canard or a biplane) then I think you can just follow model aviation practice.  If you are building something wild, then you're a pioneer, and you should start by throwing together something easy to build because you'll be cutting it up and rearranging it as you learn.

[Dave Hull]

"Note that the fuselage section through which the wing is installed is included in the wing area calculation."

https://aerotoolbox.com/intro-wing-design/

http://john-golan.blogspot.com/2015/07/aircraft-peformance-part-2-basic.html