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SeppoK

Member
Joined
Jul 8, 2021
Messages
7
Thank you and bonus points for being the first one to directly answer the question :). Your experience is what I expected but was surprised to find the Pajno books published since 2016 to use the kgf (MKFS system) for force and kgf/mm^2 for stress. Perhaps it has more to do with the vinrage of the author :) . Good books though and worth reading. Any other with a European aircraft design background?
The Glider by Stellio Frati from 1946 uses kg for force, which is OK for strength, but in fluid dynamics you have density as kg s^2/m^4, which is almost as confusing as slugs. Maybe Italy was slower to adopt, they had barely abandoned Roman numerals. :)
 

User27

Well-Known Member
Joined
Apr 5, 2015
Messages
173
Location
England
Love all the comments and as the OP don’t mind at all the drift but would love an answer to the original question :
Of course theUS uses a mishmash of units but my understanding was Europe was uniformly SI but my two contemporary European design books use the old MKfS with kilo force. Is this common or very unusual within the European airplane design community?
Perhaps it depends very much on the preference of the Engineering Chief and how he was educated? As long as the whole design team uses a consistent system there should not be too many problems. I have seen variations across European companies still. I deal with German, Austrian and French companies, while they are all basically SI but there are small differences.

The significant problems occur when trying to integrate equipment from outside suppliers - I was programming in assembler in the late 90s for an airborne application, our aircraft used US imperial units, LSB was always 1 ft. We had a targeting pod where the LSB was 2.5m!! Initially the thing would never track properly at short ranges as it thought it was going nearly 10x quicker than it really was.
 

Riggerrob

Well-Known Member
Joined
Sep 9, 2014
Messages
2,655
Location
Canada
Perhaps it depends very much on the preference of the Engineering Chief and how he was educated? As long as the whole design team uses a consistent system there should not be too many problems. I have seen variations across European companies still. I deal with German, Austrian and French companies, while they are all basically SI but there are small differences.

The significant problems occur when trying to integrate equipment from outside suppliers - I was programming in assembler in the late 90s for an airborne application, our aircraft used US imperial units, LSB was always 1 ft. We had a targeting pod where the LSB was 2.5m!! Initially the thing would never track properly at short ranges as it thought it was going nearly 10x quicker than it really was.

Trying to use two different measurement methods on the same project is silly.
This reminds me of a conversation with an Airbus technologist who was loaned to Boeing. He was designing heavy-duty cargo floors for Boeing, but suffered problems with rounding numbers. His project used a mixture of Imperial and metric units. Accumulating rounding-errors (dropping the third or fourth decimal place) produced floor boards that were 3 or 4 inches too long or too short.
 

wrmiles

Active Member
Joined
Oct 13, 2019
Messages
30
When we designed the F406, which is a mixture of 404, 441, 425 and new parts, for production at Reims in France, they came back to us wanting to approve sheet metal in the nearest metric equivalent, eg. 1 mm instead of .040". We ended up refusing because it would have been a paperwork and structural certification nightmare.

Another problem with metric in aircraft design, is what to do about the bookshelves full of inch based standard parts standards.
 
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