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Help please with enlargment of pdf plans

Can't get percentages right.

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Phil B03/10/2019 16:51:51
167 forum posts
161 photos

I have downloaded the Sterling 64inch Stearman plans.

I wish to enlarge this to give a 72 inch wingspan. Why? Because I have a Great Planes Stearman fuselage that once had 72 inch wings, but now has no wings. I have / am repairing the fuse and tail.

So... I worked out 72/64x100 % = 112%.. The print shop produced this and.... Wingspan is 78 inch.

Now I plan eventually to build the 78 inch from scratch, but in the meantime I need to get a 72 inch span wing plan. Can some expert please explain the required calculation for the enlargement. In a way the span is less important than the chord, which wi need to be 11 inch, but my 12% enlargment produced a chord of 12.5 inch.

Phil B03/10/2019 17:00:21
167 forum posts
161 photos


Nigel R03/10/2019 17:05:47
3730 forum posts
583 photos

Where did the plans come from? It is possible they have not been sized correctly.

Anyway. If "112%" came out at 78 inches, then 103.5% should be very close to 72.

At 103.5% the chord will come at 11.5 inches.

Either of the plans may not be quite perfect scale outline - i.e. one of the designers may have added some chord to gain a bit more wing area.

Phil B03/10/2019 17:30:17
167 forum posts
161 photos

Thanks yes that helps.

The download was from Outerzone.

I will get a 103.8% print of one wing and check it is the right span and chord, before getting the other sheets done.

My other problem is to modify the cabane mounting system to suit the new wing.

The strange thing is that the original tail roughly matches the 112% plan one.

Bob Cotsford03/10/2019 17:34:46
8382 forum posts
463 photos

Sounds as though they enlarged it by 121%!

Phil B03/10/2019 17:37:15
167 forum posts
161 photos

Yes that makes sense mathematically, but I was sitting alongside when the lady put in 112% for the print.

kevin b03/10/2019 19:29:35
1823 forum posts
145 photos


PM me with your email address, the exact wingspan and chord width you want and I will resize it for you.


I also have the Royal / Marutaka kit, which is just over 68ins span as well.

Edited By kevin b on 03/10/2019 19:41:40

Simon Chaddock03/10/2019 19:41:41
5683 forum posts
3021 photos

Phil B

It is not unknown for an otherwise scale model to have 'over size' tail feathers on purpose. wink 2

Phil B03/10/2019 20:38:48
167 forum posts
161 photos

Thanks for the offer Kevin. Pm sent

Phil B03/10/2019 21:11:41
167 forum posts
161 photos

The lower wing seat in the fuselage has a chord of 11 inch or 280mm. That is the critical measurement. The finished wingspan for the lower wing should be 70 inch and the upper wing 72 inch. But a slightly less wingspan might be OK.

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