How wide for a side-by-side?

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How wide should a side-by-side cockpit be in a light, two-seat homebuilt?

  • 34" / 86 cm

    Votes: 0 0.0%
  • 36" / 91 cm

    Votes: 1 2.1%
  • 38" / 97 cm

    Votes: 0 0.0%
  • 40" / 102 cm

    Votes: 3 6.4%
  • 42" / 107 cm

    Votes: 12 25.5%
  • 44" / 112 cm

    Votes: 8 17.0%
  • 46" / 117 cm

    Votes: 5 10.6%
  • 48" / 122 cm

    Votes: 14 29.8%
  • Other (explain in a post)

    Votes: 4 8.5%

  • Total voters
    47
  • Poll closed .

Pilot-34

Well-Known Member
Joined
Apr 7, 2020
Messages
432
Ahhh, anthropometry - a vexed subject.

Here is a study of US military personnel from 2012, with many body distance measures. It is perhaps not representative of the entire US population as it selectively avoids very small (height and weight) and very large people (height and weight), and the elderly - they simply don't get recruited.


A short extract from the Bideltoid breadth table, p65, and reference to the statistical info p66.

Percentile Female Male
5 40.6 45.9
25 43.0 48.9
50 45.0 50.9
75 46.9 53.1
95 49.9 56.7

These dimension sets are close to normally distributed. Given one knows the mean and standard deviation AND the two people are selected randomly one can calculate statistically the percentage of the population that will fit a given cabin width. This is left as an exercise for the reader 🙃

Now we move into psychology. Clearances between people in various positions are a much more vexed and contentious subject. Quietly sitting people prefer to sit with a minimum of 3.5cm of clearance from a wall, and with about 5.5cm of clearance from another person. Allows a little wiggle room without frequently touching. If each person has something to do, then particularly the inter-person spacing increases. For instance, diners report a comfort distance between shoulder widths of approximately 18.5cm, rather than the 5.5 used here. Plant operators minimum is approx. 80cm and preferably of the order of 100cm and that is "to wall" as well.

People will sit jammed against a wall so as not to touch another person, particularly if they do not know them very well. So the minimum distance between a hard surface and the shoulder width could be considered to be zero. Equally, two people will sit with their shoulders touching (0cm), or indeed interfering (-1cm) . But this is tolerable only in the short term. Interestingly, there has been a study - but not peer reviewed - which indicates that, given no other issues - bo, sweatiness, bare skin - total strangers will tolerate this level of proximity for longer than people who know each other socially. Don't aske me how they defined the level of knowing! Also, if people know that there is a physical, practical reason for the space being cramped, they will tolerate a smaller spacing for longer, as well.

A cabin width of 106.2 cm (two 95 percentile males) will be wide enough to fit around 99% of randomly selected pairs. Adding "comfort" spacing of 12.5 cm gives a cabin width of 118.7 cm (or 46.7") - call it 120cm or 47.25".

A cabin width of 81.2 cm will fit two 5th percentile females, or around 1% of randomly selected pairs. Adding the comfort spacing of 12 cm gives a cabin width of 93.7 cm (or 36.9").

A cabin width of 114.3 (two 50th percentile males plus comfort) will fit approximately 93% of randomly selected pairs. (Or 45").

Please note that family members do not meet the randomly selected requirement. Friends typically do not, either (birds of a feather is a cliché for a reason).

Yeah I see that data is pretty well skewed
First off the military has limits on both the largest and smallest bodies it will take.
It also has limits on age and physical fitness
So in the real world that that is pretty well useless
If you’ve ever bought a military surplus vehicle it doesn’t take long to realize that they are designed for a skinny 18-year-old.
 

Riggerrob

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Joined
Sep 9, 2014
Messages
1,437
Location
Canada
Yeah I see that data is pretty well skewed
First off the military has limits on both the largest and smallest bodies it will take.
It also has limits on age and physical fitness
So in the real world that that is pretty well useless
If you’ve ever bought a military surplus vehicle it doesn’t take long to realize that they are designed for a skinny 18-year-old.
The latest ejection seats are designed to accommodate people ranging in size from 5 th percentile women to 95 th percentile men. Off the top of my head, a 95 th percentile man weighs about 220 pounds (100 kilograms) and stands about 6' 2" (190 ish centimetres). North American pilots tend towards the large end of the scale.
 

crusty old aviator

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Joined
Feb 17, 2014
Messages
238
Location
Grantham, NH
60”, or 152 cm. Butts are getting bigger and people with fast food addictions, thyroid disorders, and type II diabetes shouldn’t be discriminated against. Employing the old 1 to 3 ratio of fluid dynamics, a 5’ wide ride will be 15‘, or 4.6m long.
Need a longer fuselage? Widen it out to 6’ across and install a loveseat! Think of how many Wisconsin farmers will want to build your design so they can take their wives along? (I grew up in Wisconsin: it’s no stereotype! I knew many women, and some men, who were so wide they literally had to go through doorways, sideways.) They should be able to fly, too!
Carefully study the interior layout of the “new” VW Beetle. They’re very popular with big people because they’re roomy inside and have big doors.
Follow the 3:1 ratio on your fuselage and it will be just as fast and efficient as these scrawny little airplanes that, as Dick Collins once so eloquently stated, “They’re so small inside, you don’t even enough room to get up on one bun to fart.”
 

cluttonfred

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HBA Supporter
Joined
Feb 13, 2010
Messages
7,401
Location
World traveler
Without getting too technical, the point of this thread was to get a sense of what would be desirable cockpit width for a side-by-side, and it has given me plenty of chew on. Thanks, all, for the input. My "VP-21" concept now has a 48" fuselage width penciled in. ;-)
 

mcrae0104

Well-Known Member
HBA Supporter
Log Member
Joined
Oct 27, 2009
Messages
3,315
Location
BJC
My "VP-21" concept now has a 48" fuselage width penciled in. ;-)
Gotta start somewhere before the trade studies begin.
Personally, I cut out the second seat, not because the frontal drag cuts performance, but because reducing gross weight is the cheapest, most effective performance increase available. Also, it's easy to rent a 172 to take the occasional passenger. Your mission requirements may vary.
 

Grelly

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Joined
Aug 27, 2010
Messages
255
Location
Surrey, UK
For those wanted to transport 8x4 sheets, I have seen a few designs with a cargo pod strapped to the belly. The Comp Air 8, for example. It's an idea.
 

Pilot-34

Well-Known Member
Joined
Apr 7, 2020
Messages
432
Gotta start somewhere before the trade studies begin.
Personally, I cut out the second seat, not because the frontal drag cuts performance, but because reducing gross weight is the cheapest, most effective performance increase available. Also, it's easy to rent a 172 to take the occasional passenger. Your mission requirements may vary.
Remember you don’t have to design for one seat to get most of that performance .
When performance = getting stuff off the ground.
Just don’t put a butt in it.
 

autoreply

Well-Known Member
Joined
Jul 7, 2009
Messages
10,750
Location
Rotterdam, Netherlands
Just to mention it: Frontal area doesn't need to be a predominant factor in total drag in cruise if we pay attention to the shape of the airframe. Autoreply posted some pix of a sleek but spacious side-by-side sailplane when I was ribbing him about the sofa-width cabin he was specifying for his version of the Beetlemaster.

And a small gripe for Cessna: Okay, you made this C-152 cockpit 39" wide to reduce weight and frontal area. Got it. So why is the cabin so tall? I'm 5'11" and I could wear a top hat in here. How about moving about 4" of this height to the cabin width?
46" and half the frontal typical area of your typical Cessna-type:



I've flown gliders with a cockpit width of 21.5" and I personally wouldn't want to own a two-seater that's less than 45" or so.
 
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