Scaling a stunt model

[George Grossardt]

So I am considering scaling a 720 sq. in. stunt design down to 630.  My question is do you just scale the thrust line to wing and tail center and nose/tail moment down at the same rate and call it good?  Or do you adjust the moments and thrust to centerlines to some other numbers.

Thanks,

George

[Dave_Trible]

For the difference you are talking about I'd just take your plans to FedEx Kinkos and shoot them down to the size you want and build.  You'll make minor wood size adjustments as needed.  If you were going down to something like a .35 sized airplane then you would need to fiddle with moments due to engine weight mostly.  There you would lengthen the nose and maybe shorten the tail.   

Dave

[Bill Hummel]

Hi George, I think this came from Mikey Pratt:
Scaling stunt plane
Decide size you want
Divide that by original wing area
Take square root of that number
Example:  630/720 =.875
Square root is .935,
So run your copy at 93%.
Hope that helps!

[Doug Moon]

Hi George, I think this came from Mikey Pratt:
Scaling stunt plane
Decide size you want
Divide that by original wing area
Take square root of that number
Example:  630/720 =.875
Square root is .935,
So run your copy at 93%.
Hope that helps!

I am not a math guy but always want to learn. And I am showing my ignorance here but....

Why do you use the square root of .875?  Why do you just use 87.5%?

[BillLee]

I am not a math guy but always want to learn. And I am showing my ignorance here but....

Why do you use the square root of .875?  Why do you just use 87.5%?

Makes it too small.

(Sorry, I just had to say that! 🙂)

[George Grossardt]

Hi George, I think this came from Mikey Pratt:
Scaling stunt plane
Decide size you want
Divide that by original wing area
Take square root of that number
Example:  630/720 =.875
Square root is .935,
So run your copy at 93%.
Hope that helps!

Using this formula, one would then just let the moments and thrust line to wing/tail centerlines fallout from the formula with no adjustments?

[Dave_Trible]

Yes.  Using photographic means to reduce the plans everything scales down or up by the same proportions,  leaving the same design but at a different size.  If you are manually drawing/scaling plans then you'd have to adjust everything down by the same formula,  lest you are altering the design which as I mentioned above you shouldn't have to do.  You aren't making that radical a change that other changes are necessary IMHO if you are going to use common standard fair motors in the .45-.61 size range which is what I'd target for 630 sq.

Dave

[Bill Hummel]

George and Doug, I’m far from a math whiz too, but I seem to remember the square root is needed because wing area is a squared function.  Or some other reason…

[Air Ministry .]

The FOURTH DIMENSION , ( volume / displacement : off atmosphere ) is what Gets Ya !  the Frogs ' portance ' ( support ) is what comes in here . Sweedish for GOOD is BRA . so that should help visualise it !.

Your left with a bit of leeway  , unless it was Classic in Aus . Where they get the ruler out . thought the Idea would be to build something with EVERYTHING say 3/16 in. OUT , and video the Judges consternation & astonishment  meauring it . the indignation might mean you had to get the ... out quick , however .
SOMEBODYS P 51 ( Walker ) threw 3/4 on the nose and threw the tailplane a inch & three quater ( measuerd )  back . Id wondered whyit looked  unpodgey like his last one . And lean athletic and so forth . ( will throw apictureon .)

The MORAL being , unless the gestapo say otherwise , build it HOW YOU WANT TO . To Fit . To Balance . to suit your timber . and other things too .



Thus therefore & so on , a example of ALTERED  if not SCALED , moments .

The Patternmasters & L J's are / were / do , ' scale ' . Like the P M 60 plan or Strega ) done to 54 inch , or 48 fora 35 or 36 fora .25 ! or 24 inch for .15 maybe . LJ at 48 for a FSR 25 maybe ,

BUT throwing the nose around shorter or longer to suit something , and tthe tail aft a bit , wont ead to a collapse of the global economy . You can even shift the canopy .

but STRUCTURAL stuff And Material Sizes & Bellcrank size / fit / position , and getting the horn arms in . Asin , if the Standard plan dimesion horn arm lengths will all fit in there in a littler one , they would .
So you would  likely use em , unscaled . with STIFF Flaps and no slop . and access for oiling even maybe .  You could just cut a few ribs out , instead . like the BEAR .46 if you have some good timber . UNSCALED 
Looking at a " CLEAN SHEET " your less likely to get caught out . Throw bits in photocopier , tape shuffle & trace .
https://stunthanger.com/smf/nostalgia-30/gieseke-nobler-46/msg613419/#msg613419

He just did a Cardinal like loose the center ribs trip , Mr Moon elaborates extensively on this in a low tech world beater thread .
https://stunthanger.com/smf/nostalgia-30/gieseke-nobler-46/msg613419/#msg613419

The pic of the red Bear 46 was built by my brother Doug. The two most inboard
ribs are removed, which leaves a wing are of 620 sq in.

https://stunthanger.com/smf/open-forum/new-clw-article-the-low-tech-world-beater-flipping-the-paradigm/msg103536/#msg103536

[Paul Wescott]

I am not a math guy but always want to learn. And I am showing my ignorance here but....

Why do you use the square root of .875?  Why do you just use 87.5%?

Doug,

Imagine a wing 720 SqIn
72” wingspan
10” chord
72 x 10 = 720  Good so far?

Desired size of new build: 600 SqIn

Divide Desired Size by Original Size
600 / 720 = 0.8333

This means the desired size is 83% of the original size.

Nice!

Let’s check those numbers…

72” span x .8333 = 60”
10” chord x .8333 = 8.333”

60” span x 8.333” chord = 500 SqIn !!!

How on earth did we reduce the span and the chord by the calculated reduction factor, then multiply them together and receive the WRONG result?  The result is not “wrong” it is exactly what the math gave us.  The logic in our head is what’s wrong.  We did not have as much (or at my age RECALL as much) of the math theory as Mr. Pratt did.  We have many very intelligent, educated, members who can explain how that “square root” step works, obviously there’s a step between one-dimensional math (the length of the wing SPAN) and two-dimensional math (the AREA of the wing) that we missed.  But do we want the lecture on math theory?  We may want it because it’s fun to listen to but honestly we don’t need it to get the answer.

To continue the math:

We need the square root of 83% or .8333
So we think hard and we calculate the square root in our head - Just kidding - Not us - We Google “square root calculator”, punch in the numbers, and get 0.913 as the new reduction factor.

Let’s check the new number

72” span x .913 = 65.74
10” chord x .913 = 9.13

65.74” span x 9.13” chord =  600 SqIn !!!

Bingo!  Take the plans to Kinko’s and have them set the reduction to .913%

Just don’t try to explain the math to the person operating the large format copier LOL.

[Doug Moon]

Doug,

Imagine a wing 720 SqIn
72” wingspan
10” chord
72 x 10 = 720  Good so far?

Desired size of new build: 600 SqIn

Divide Desired Size by Original Size
600 / 720 = 0.8333

This means the desired size is 83% of the original size.

Nice!

Let’s check those numbers…

72” span x .8333 = 60”
10” chord x .8333 = 8.333”

60” span x 8.333” chord = 500 SqIn !!!

How on earth did we reduce the span and the chord by the calculated reduction factor, then multiply them together and receive the WRONG result?  The result is not “wrong” it is exactly what the math gave us.  The logic in our head is what’s wrong.  We did not have as much (or at my age RECALL as much) of the math theory as Mr. Pratt did.  We have many very intelligent, educated, members who can explain how that “square root” step works, obviously there’s a step between one-dimensional math (the length of the wing SPAN) and two-dimensional math (the AREA of the wing) that we missed.  But do we want the lecture on math theory?  We may want it because it’s fun to listen to but honestly we don’t need it to get the answer.

To continue the math:

We need the square root of 83% or .8333
So we think hard and we calculate the square root in our head - Just kidding - Not us - We Google “square root calculator”, punch in the numbers, and get 0.913 as the new reduction factor.

Let’s check the new number

72” span x .913 = 65.74
10” chord x .913 = 9.13

65.74” span x 9.13” chord =  600 SqIn !!!

Bingo!  Take the plans to Kinko’s and have them set the reduction to .913%

Just don’t try to explain the math to the person operating the large format copier LOL.

This makes sense!
I have in the past tried to reduce numbers using basic logic like you described and it never worked out. Now I know why.
Thank you
Doug

[George Grossardt]

Gentlemen,

Thank you for the comments and insight.  This has been helpful.

George

[Ken Culbertson]

Another method I used to upscale my Surveyor design from a .35 to a .46 size was to take the area * 110%, the chord by 110% then divide the area by the chord to get the new span.   Everything else was a function of the chord differences.  In my scenario, area was the most important variable.  As it turned out, simply drawing a bigger version is about as good as trying to get a perfect % increase/decrease.  Whatever you do, don't expect the planes to fly the same.

Ken

[Air Ministry .]

Shoulda just chucked the .46 in the . 35 plane . 

Being a cheapskaatre & doing A3 enlargements of crucial areas , with a few variations , you can shuffle them about . ( sticky tape on the back , ALIGNED )

some photocopiers / printers TWIST things . So . . . percentage across can be incorrect . But a X - Y axis varieble one , YOU can ' twist ' it to differant across & along % .

Think Mr Moons " leave out the middle " outlook , leaving the large tailplane , isnt a bad way to GET RESULTS .

Scaling up the Folkerts Direct got a can of worms  . 1.15 od linear to get 1.3 od area . the VOULUME got twelve extra ton of timber . Technically the 80 Oz was the same loading as the 57 Oz ;
But you know when youve got 80 ounce , The inside of the Sq 8 is where it gets you . ( on other things besides ) .

So douing a Tom Morris ( where He just uses the Root for the Template . ( or doing your prefered templates ) and sizing Fuse to suit engine , spinner tank etc  ,
sticking the drawing on the wall for a few weeks , to see if its got the better of you , ( upside down occasionally ) you can ascertain ' the sit ' to see if youve  won .

Or just throw it together & shuffle the flying surfaces to suit ( moments ) .

[Larry Fernandez]

The FOURTH DIMENSION , ( volume / displacement : off atmosphere ) is what Gets Ya !  the Frogs ' portance ' ( support ) is what comes in here . Sweedish for GOOD is BRA . so that should help visualise it !.

Your left with a bit of leeway  , unless it was Classic in Aus . Where they get the ruler out . thought the Idea would be to build something with EVERYTHING say 3/16 in. OUT , and video the Judges consternation & astonishment  meauring it . the indignation might mean you had to get the ... out quick , however .
SOMEBODYS P 51 ( Walker ) threw 3/4 on the nose and threw the tailplane a inch & three quater ( measuerd )  back . Id wondered whyit looked  unpodgey like his last one . And lean athletic and so forth . ( will throw apictureon .)

The MORAL being , unless the gestapo say otherwise , build it HOW YOU WANT TO . To Fit . To Balance . to suit your timber . and other things too .



Thus therefore & so on , a example of ALTERED  if not SCALED , moments .

The Patternmasters & L J's are / were / do , ' scale ' . Like the P M 60 plan or Strega ) done to 54 inch , or 48 fora 35 or 36 fora .25 ! or 24 inch for .15 maybe . LJ at 48 for a FSR 25 maybe ,

BUT throwing the nose around shorter or longer to suit something , and tthe tail aft a bit , wont ead to a collapse of the global economy . You can even shift the canopy .

but STRUCTURAL stuff And Material Sizes & Bellcrank size / fit / position , and getting the horn arms in . Asin , if the Standard plan dimesion horn arm lengths will all fit in there in a littler one , they would .
So you would  likely use em , unscaled . with STIFF Flaps and no slop . and access for oiling even maybe .  You could just cut a few ribs out , instead . like the BEAR .46 if you have some good timber . UNSCALED 
Looking at a " CLEAN SHEET " your less likely to get caught out . Throw bits in photocopier , tape shuffle & trace .
https://stunthanger.com/smf/nostalgia-30/gieseke-nobler-46/msg613419/#msg613419

He just did a Cardinal like loose the center ribs trip , Mr Moon elaborates extensively on this in a low tech world beater thread .
https://stunthanger.com/smf/nostalgia-30/gieseke-nobler-46/msg613419/#msg613419

https://stunthanger.com/smf/open-forum/new-clw-article-the-low-tech-world-beater-flipping-the-paradigm/msg103536/#msg103536



Holy cow! How far away are those power lines?

Larry, Buttafucco Stunt Team

[Air Ministry .]

Just looked at the google earth map , and scaled it . a good four hundred meters , i should think . Maybe 1/4 Mile . Tho nobody there can do a quater in 10 , or'd know how . Even If its beside the old
Mt Druitt RACE TRACK . Was a R A A F traing field in W W II . " Whalan Reserve " N S W , Australia . the Pylons are over by the Train tracks . must be the lense in the phone / camera , cetra .
The wooden One is Way Over , TOO . 150 metres , cr to cr . 70 ft lines are 20 metre , odd . so past 100 metre from far side of circe . 390 foot ( call it 400 from plane , when closest . )
Tho thankyou for your concern . Wooden Handle & lightning 3 mile off , a finger on a line gets a mild tingle . Lec Fence set for BULL . Gets you flat on your back  , when your 13 odd .
I Tried THIS ; ( FLAPS ) so ( as theyed ended up 1/2 wider than they were & the moments 1 1/2 longer , and it was never designed in the first place , It was SKETCHED & scaled up ) . the STRUCTURE was maybe designed .
The configuration was contrived .

and had a sore head . so I got a ruler and went um er 14 and 16 equals 32 er um half o.k. mark , look .
inner  hinge justt inboard , throw a straight ege in the hinge gap , mark across with a square,
notch rear edge , mark other side . Hacksaw one side abit , notch rear edge , hacksaw other side marked line a bit ,
start sawing . OOPS .
If we dont throw something in , it'll NOTCH the trailing edge . as we had a spatula / paint scaper out , that fit .CUT THE FLAPS TO HALF LENGTH .

Throw in sanded ' V 's with chordwise strips clamping ' aileron ' straight  ( neutral ) sand , throw on dope , attack & attempt to bog , throw on silver.
CRIPES the grooves are still there . Dig out cheap foot talcum , bog . ( Silver NOW actual ) Look for other as outta WHITE ( paint ) SO THATS WHERE
the " TALC " ( from art supply . no Oil or perfume ) . Lottsa Dupli coat cast offs . But No White . What'll it be . WE'RE NOT THAT FAR YET . Gotta sand it again .

the moral being , see that things fit . If somethings disagreeable you usually dont feel agreeable . looking at it . copy paste shift .shuffle , trace on lunch roll paper , or tape on a window in sunlight to see through paper .

[Dave Moritz]

Bill and Paul

How would you guys tackle the enlargement problem presented by Ken? Is his the only way, or is there something more elegant involving a square root or squaring function? Ah what fun this all is!

Dave Mo…

[Ken Culbertson]

Photo enlargement like Kinko's or using a smaller sizes like MS Paint give you an accurate "stretch" on the x,y axis.  If you have a 50" wing and you want a 10% increase you will get a 55" wing.  What will be the square is the area.

So, why are you up/downsizing?  If you just want a bigger/smaller version, pick a % and go to Kinko's then find the right size motor.  If your goal is to fit a larger size motor/engine then weight/lift is the issue.  Pick your desired area, subtract the old area and go to Kinko's and expand by the square root of the difference, measure and cut.  Now consider that the weight behind the CG has changed a lot and the weight ahead of the CG probably not so much and the center of lift - the wing is both thicker and much larger than the fuselage changes.

Is that really larger/smaller stab moved back/forward going to be enough, or too much to offest that massively larger/smaller wing?    

Seriously, a % change really creates an entirely different airplane.  Be prepared.

Ken

[Paul Smith]

I've gone through this on Scale Projects.

I compute the average chord from known area and wingspan data.
Then I set up an Excel spreadsheet and compute spans and areas in 1% increments within the possible range.
I then pick and area and wingspan that looks good to me.