Ballpark target weight for a stunt plane in relation to wing area

[John Cralley]

I know this may be a question that has been addressed elsewhere but doing a search has not revealed a generic answer.

What is a good target weight for a stunt model in relation to the wing area?

I realize that this may not be a linear relationship and that other factors such as airfoil, flap area, tail coefficient. aspect ratio etc. likely will enter into the picture. What I would like is a chart (graph) of wing area vs flight weight. Has anyone done this??

Just a "rule of thumb" would be OK. 

[Tim Wescott]

I don't have the answer, John, and I'm interested in what the experts have to say.

While you're waiting for the word on weighting (sorry -- couldn't resist), dig out your stash of Flying Models magazine and make up a spreadsheet that lists wing area and weight.  I'd put in engines, span, and maybe an estimate of engine power, in there too, because those all have bearing on performance.

For that matter, the wing span loading probably "means" more in the corners than the wing area loading (it certainly means everything with respect to induced drag in the corners, but by the same token induced drag certainly isn't everything going on in the corners, and corners certainly aren't everything going on in the flight).

Or just do what Howard Rush claims to do, which is to do whatever Paul Walker does.

[John Cralley]

Thanks Ty,

That sounds like what I had in mind. 

John

[Howard Rush]

Or just do what Howard Rush claims to do, which is to do whatever Paul Walker does.

That's getting tougher.  He's on a lightness kick.

[PJ Rowland]

Yeah - How about 22 oz for finished airframe.........

When mine weight that I've forgotten to bolt a wing on...

[Howard Rush]

Yep, that light and the wing might not have enough glue to stay on even if one remembers the bolts. 

[PJ Rowland]

I think his scales are broke..

[EddyR]

I have a 600 sq" plane that has a loading of 18 ounces per sq ft.  The wing is 2" thick. 20% tail. It turns fast and smooth. I truly expected this to be the dog of the century. It has a 60 motor turning a 13" prop. It goes against everything I have I had learned over the years. My Tucker at 9.5 ounces per sq ft does not perform as well.

Ed

[Larry Cunningham]

dabigatran etexilate mesilate..

L.

"Well, that's very different!" -Emily Latilda

[RandySmith]

It would be very hard to put a number on that , that really means something  that will translate to across the board stuntship wings, with all of the differant  wings flying, I have seen and flown some that will max out at about 62 ounces for 700 sq in, Then I have flown others that will carry 75 ounces at 675 sq in.
There are far more things than just area, these can and will effect weight carry ability tremendously..... A/R , size of flaps, the airfoil itself, tip shape, there are other criteria that will substantially affect weight to sq in relationship.

Randy

[John Cralley]

It would be interesting if someone at the Nats would compile a chart of oz. per sq. foot for the entries this year. That would give us a range of variation for what should be highly competitive stunt ships. I wonder just how big a range that would turn out to be. Do the current rules require a weigh in for the pull test or is that just electrics?? If so that would be a way to get the weight and then one only needs to know the wing area to build the chart.

I will not be at the Nats and I guess it probably will not happen. (the data collection that is   )

[Bob Reeves]

Heard through the grapevine that a well known Texan builds to 13oz/sq/ft. Most of my stunt ships (Legacy wing and numbers) have ended up right at 13 and can't seem to get it down any lower with my building and finishing skills.

For what it's worth, in my opinion 13 is a good number, enough weight to handle Oklahoma wind but still light enough not to have any issues making turns.

[Howard Rush]

I will not be at the Nats and I guess it probably will not happen. (the data collection that is   )

Data are stored in the tabulation program.  Ask David Fitz. for the weights after the Nats.  Wing area is another matter.

[Bill Little]

Hi John,

I believe that everyone would agree that the more modern "fatter", well designed and tested airfoils will carry more weight per area than the older thinner airfoils, on the average.  It really does differ from design to design.  A 700 sq.in. Patternmaster can fly well approaching 80 oz. while a 700 sq.in. USA-1 had better not go over 60 oz. to really fly the way it should.  I don't know what those respective wing loadings are, but it illustrates the theory.  Plus, "modern power" makes up for a lot of "sins".

BIG Bear
RNMM/AMM

[Ted Fancher]

Hi John,

I believe that everyone would agree that the more modern "fatter", well designed and tested airfoils will carry more weight per area than the older thinner airfoils, on the average.  It really does differ from design to design.  A 700 sq.in. Patternmaster can fly well approaching 80 oz. while a 700 sq.in. USA-1 had better not go over 60 oz. to really fly the way it should.  I don't know what those respective wing loadings are, but it illustrates the theory.  Plus, "modern power" makes up for a lot of "sins".

BIG Bear
RNMM/AMM

The most important factor re wingloading for a stunt ship is the power train's ability to maintain airspeed under load.  Wings that worked best with a Max .35 at low to mid .40 oz weights can easily carry half again more with a modern engine set up such as a high rev/low pitch tuned pipe .40 to .75, strong elex, properly propped four stroke etc.  Lift goes up (or down) as a square of airspeed.  The Trivial Pursuit is ~660 Square inches and will fly competitively up to the low 70oz range with the proper power train.  Put in a tire ST. 46 at the same weight and it gets much more problematic.

The original T.P. flew its best back in the early .90s with a .40 VF and a 12X3.25 Bolly two blade at 68 or so oz.   That’s 14.8 oz per square foot!  (Launch RPMs were very high and noisy.  Didn’t own a tach in those days but I’m guessing 11.5K or so.  Randy Smith timed the laps at 5.8 in Lincoln that year.  It placed second at that Nats.

Ted

[Brett Buck]

It would be interesting if someone at the Nats would compile a chart of oz. per sq. foot for the entries this year. That would give us a range of variation for what should be highly competitive stunt ships.

   There are posts here that do that, and Noel Drindak's surveys also have that information. The answer, for competitive stunt planes in the last ~25 years, is somewhere in the range of about 12.5 oz/square foot to about 15 oz/square foot. There were competitive planes lighter than this but not many. The winners are clustered in the 13.0-13.5 range.


    Brett

[John Cralley]

Thanks Ted, what you say may explain part of the surge in use and success of electric power as seen at Brodak's Fun Fly, the Nats and the World competition this year. Electric motors can have that extra reserve "umph" for smoothly completing speed killing maneuvers.

Brett, your figures for this year's Nationals seem to verify what Bob Reeves quoted in an earlier post (13 oz/sq/ft).

[Brett Buck]

Thanks Ted, what you say may explain part of the surge in use and success of electric power as seen at Brodak's Fun Fly, the Nats and the World competition this year. Electric motors can have that extra reserve "umph" for smoothly completing speed killing maneuvers.

   Actually the issue with TP engines is getting *too much* oopmh, in many cases. Most of what my buddies and I have done in the last 15 years with TP engines is try to moderate the negative aspects of that.  The thing electrics can possibly do is keep the speed up in the corners without the danger having excess acceleration at other times.

    Brett

[Andrew Tinsley]

Don't be caught out with the mantra "Lighter is better". My planes were always way overweight until I decided to do something about it. I finished up with a wing loading of around 10.5 oz per square foot, on my next plane.
It flew well in calm conditions, but was awful in windy weather, got blown all over the place. I finished up having to put ballast on the CG (no easy thing!) and that improved windy weather flying no end.
Now, no how, do I even claim to be a good pilot, actually the reverse! That build was a salutory lesson for me. I still wonder if I had done something else wrong!

Regards,

Andrew.   

[RandySmith]

It is not nearly so simple as adding weight, that works sometimes... but not all, and some "light" planes work very very well, Billy's P-47 weighed 54 ounces and was 700 sq.in, It flies exceptional in the wind, My Katana was 59.5 ounces when it flew in 2 extremely windy NATs with winds approaching 30 MPH, it is 675 sq in
Curt Contrata's  SATONA weighed  48 ounces and was 640 sq in, about the same wing that Dave Fitz has in his new ship. It flew extremely well in 20 MPH plus winds, I flew it several times with 2 being in high winds.
I have personally flown other very lightly loaded ships that perform very well in high winds, Bears included.  This is not to say heavier ones don't work, just adding some realistic facts to the thread.
The only place where the heavy ships have any advantage over "some"  of the lighter loading ones are in the landing, When the power shuts down, sometimes its a B**** to land a very light plane in turbulent high winds.

Randy

[Andrew Tinsley]

Hello Randy,
I take the point you are making. My question would be "would those lightweight planes have flown better in high winds, if they had been heavier"?. I tried the experiment and found that my lightweight plane flew better in high winds with ballast, I suspect that in the cases you quote there would have been some improvement if the experiment had been done.

Regards,

Andrew.

[RandySmith]

Hello Randy,
I take the point you are making. My question would be "would those lightweight planes have flown better in high winds, if they had been heavier"?. I tried the experiment and found that my lightweight plane flew better in high winds with ballast, I suspect that in the cases you quote there would have been some improvement if the experiment had been done.

Regards,

Andrew.

NO they don't fly better in high winds with added weight, Some may but these did not, I have tested that out on 3 of my planes ,and one other plane, made them worse, or no differant at best, but did not improve anything, however I didn't go to the trouble of adding back flap area or movement, tweeking controls and others.
I think it maybe if I had much thicker wings that adding weight may help in high winds, but this is not the case.
 I have also flown the same design at many different weights, when setup and trimmed properly the light ones are normally better in my case with my ships.
Also when you add weight to a big ship. it becomes a real handful to hold in high winds, and stresses get much much higher.
This is much different than Ted adding weight to a hyper light ship too. Although trimming the flaps and adding elevator would have also helped that ship too.

I have also did this experiment many times with slow and fast combat ships years back, the lighter ones were much better than the heavy ones.

Randy

[Andrew Tinsley]

Thanks for that information Randy, food for thought! I wonder why some planes do fly better with added weight. In my case the difference was very marked. Must be some other factor at work, I wonder what it could be?

Thanks again,

Andrew.

[RandySmith]

Thanks for that information Randy, food for thought! I wonder why some planes do fly better with added weight. In my case the difference was very marked. Must be some other factor at work, I wonder what it could be?

Thanks again,

Andrew.

Hi Andrew

It is several and not just one thing, The weight, if  if is  too light or too heavy, for instance, and if you have a hyper light plane with 1 to 1 controls, you will most times have too much flap and not enough elevator, what you can do is add weight until you use the extra lift made by the flap deflection, or you can increase the ratio of the elevators and decrease the flap ratio. This will do much the same , as it balances the flap v elevator relationship in getting the right amount of lift and turn.. or you can do a combination of both.
Another example , many many people back in the late 70s and early 80s went to the ST 60 and built heavy ships, these dropped in corners and did not work well in hard turns, They then made new flaps with about 1/4 inch more chord all the way across, this small amount, added just enough lift  to stop the dropping and cleaned the corners right up. Others that used 3/4 to 1 ratios just changed them to 1 to 1, still other I talked with and helped added more flap than elevator.
So there are many many different types of problems you can come up with. And many many ways to trim them to perform properly.

Randy

[Andrew Tinsley]

Randy,
Thanks for taking the time and trouble to outline some scenarios for me. With my particular example it appeared that wind penetration suffered and in fiercce gusting conditions, the plane would be blown down. With the added weight, penetration was improved and blowdown in gusting conditions was markedly less. It almost seemed to be a straightforward application of Newton's laws of motion. More mass gives more inertia and hence for a given force (windspeed) the deflection of the mass (aircraft) is less.
  I am talking here of extreme conditions, where perhaps most people would elect to remain grounded. Fairweather performance was good with either the original mass or the ballasted version. In fact, apart from the expected decrease in acceleration, I could not see much difference in performance at the different weights. But then my piloting ability is such that I probably didn't notice what would be obvious to a top class pilot.

Thanks again,

Andrew