# How wide for a side-by-side?

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

• ### Other (explain in a post)

• Total voters
47
• Poll closed .

HBA Supporter
Last edited:

#### robertl

##### Well-Known Member
Mr BB King, Built for comfort, says it all
Uh, that would be Willie Dixon, and I know what he meant.

#### Pops

##### Well-Known Member
Log Member
I don't read metic, just imperial. Grew up and still living in the U.S.

#### Pilot-34

##### Well-Known Member
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 Interestingly, there has been a study - but not peer reviewed - which indicates that, given no other issues - bo, sweatiness, bare skin - total strangers will tolerate this level of proximity for longer than people who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

##### Well-Known Member
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

##### Well-Known Member
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

##### Well-Known Member
HBA Supporter
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
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

##### Well-Known Member
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
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.

#### Bill-Higdon

##### Well-Known Member
I'd say look at Fred Keller's Explorer, he built it to haul stuff yo his new home in Alaska