Stirling Undercart

Stirling Undercart

A few random comments. My understanding is that the Specification B12/36 (Stirling) wingspan, of 99 ft 1 inch, was an Air Ministry requirement that it should not exceed 100 feet. Shorts wanted to build the aircraft with a 112 foot wingspan. Why the restriction? Who Knows! Hangars could normally accommodate a span of 120 feet, and, as has been said above, other a/c such as the Lancaster (102 ft) had a span in excess of 100 feet. My info is that a small increase was OK-ed but in the event, as we know, the Stirling wingspan stayed at 99 ft 1 inch.

(It may have had something to do with the requirement for the aircraft to be broken down into 35 ft sections to fit into packing cases that could be handled on rail wagons. (!?))

Re-undercarriage length, I’ve no breakthrough to offer, but I note that Spec B12/36 initially called for a take-off envelope of 500 yds to clear a 50 ft high obstacle with an associated landing run of 250 ft coming in over the same 50 foot obstacle. This was evidently a bit unrealistic as, I read in Air Britain’s ‘The Stirling File’, by Dec 1938 the take off run was estimated at 790 yds.

An undercarriage collapse (first of many, I guess) marred the full-size prototype’s initial flight at Rochester in May 39 and the aircraft, L7600, was written off and cannibalised. I read that the u/c ‘appeared to have been designed by someone more accustomed to the creation of cantilever bridges…’, but the reason for that was the need to avoid large forgings at a time when the a/c manufacturing industry was already under pressure.

It was after this landing accident that it was decided to increase wing incidence by 3 degrees, and this obviously demanded an even stalkier undercarriage. (See lancman’s input above). The folklore hath it that many pilots (drivers: aircraft!) made perfect three pointers ten feet above the runway and it perhaps was to the designer’s credit that more Stirlings didn’t fold gracefully to their knees on returing to earth!!

Good Luck!

“The Stirling was restricted to 100′ span by the B.12/36 spec: ie by the Air Ministry, not Farnborough. Economy measure,for standard hangars! “

I didn’t blame Farnborough for the wingspan! I knew it was the spec but couldn’t remember the number so left it out.

However, it got me thinking. I remembered the Halifax being 98′, although it’s nearer 99′, and the Lanc being 102′ and thought 3′ can’t make that much difference.
Then I looked at the empty weights.
The Stirling was 27% heavier than the Lanc and 39% heavier than the Halifax.
I understand it was built like a brick ____house (insert word of choice) and I now see how they could do it. Come to think of it, bricks couldn’t have been much heavier!

Whitley attitude

The initial design of the Whitley had no flaps. To avoid excessive float on landing, the wing incidence was set high, result, a high ground angle. Flap development overtook prototype development, so the Whitley ended up with both, and that pugnacious “squat” in the air.

Nothing to do with Farnborough.

The Stirling was restricted to 100′ span by the B.12/36 spec: ie by the Air Ministry, not Farnborough. Economy measure,for standard hangars!

The undercart was all down to Shorts. The initial design study (the half-scale model with Pobjoys) had the wing shoulder mounted, Gouge flapped and in general very much a brother to the Sunderland construction. High wing layouts have some advantage for interior space, but impose tall undercarts, plus a high ground angle. Take a flight in an F27 and look out the window. When in production, the wing reverted to mid-fuselage (presumably in response to the Franborough view on incidence…but the undercart remained much as on the Pobjoy engined 1/2 scale aircraft!

Although most of the comments are right, and many say more than I know, I think the detail’s a bit wrong.

As I understand it, the wingspan was never reduced but was always 99ft to fit the hangars, although Shorts wanted more.

It was Farnborough that insisted on the increase in angle of attack but the prototypes were already in an advanced state of construction and the production jigs were made.

As an aside, wasn’t it Farnborough that caused the strange flying attitude of the Whitley?

My source is a book about the Stirling by, I think, Bowman from some years ago. I was browsing through it only a couple of months ago so am fairly confident but can’t remember any more detail.
My Dad bought it so that makes it mid 80s at the latest.
I can’t check at present as it’s still with my Mum and a 300 mile round trip to look at a book is too far!

Thanx for that Ant

Most people tend to forget that bit about not being a fighter and the control inputs neede to do even a simple manouever… i hadnt thought about that.

Ref the thick wing, I was building my own plane at one time and the ribs where huge height wise compared to the length and that was a fairly high lift design

Thanx again.

Hi Geedee,
Although the majority of the take off run would be done with the aircraft rotated to the horizontal,it would still have to be pulled skyward with a backward yank on the controls as it achieved flying speed.A heavily laiden Stirling certainly wouldn’t fly itself off the deck Ray Hanna Spitfire style,hence the long legs and the steep angle of attack for take off.
The Stirling also had a very thick wing,which under certain curcumstances helps to generate lift,so I’d imagine it’s stalling angle would be greater than many others.
I’m no aerodynamics expert by any means,but this is my understanding of it,feel free to correct me folks.

Thanks for the info guys.

So increasing the undercart length gave a better angle of attack for take off / landings ? Very clever idea. Hadn’t thought of that one

I reckon though that the designers may have just probably got it a little bit wrong. Sat on the ground, the angle of incidence looks very close to 15 degree’s which I believe is the angle at which a wing normally stalls ?.

Also, once upto speed, surely the ‘plane wouldnt take off in 3 pointer attitude (or did it ?), it would tend to flatten out as the tail rose so less aerodynamic drag and greater acceleration resulting in faster airflow over the wings ?

I agree,she should have had a wing extension. Dammit, they did that to convert the Manchester in to the Lancaster, surely they could have added 5 feet each side on the Stirling, iether at the wing tips or by incvreasing the distance between the engines.

Shame we’ll never know

Well said, Ant-I think the Stirling could have been one heck of a machine, had they given her some decent wings and perhaps sorted the bomb bay out a bit.

The long,spindley and rather precarious looking undercart legs on the poor old Stirling were a result of the wingspan reduction which was insisted on by the Air Ministry,the original span not fitting in existing hangars.This loss of span resulted in loss of wing area and a corresponding loss of lift,and this meant that the aircraft would’ve taken a hell of a run before getting airborne.The solution was to lengthen the legs which increased the angle of attack available on take off before the tail hit the ground.
Aswell as the better known problems with undercart collapses,this change of undercart design also put extra stress on the electrical systems.The Stirling had an awful lot of gizmos which were electrically operated,the idea being to save the wieght and bulk of hydraulic systems.Even the flaps and landing gear where electrically operated.The problem was that the system hadn’t been designed to operate these bulkier legs,but at the same time it would’ve taken a major redesign to convert the system from electric to hydraulic,hydraulic lines needing larger holes drilled through structural parts etc etc.This dictated that Shorts would have to stay with the electrical system if it was to get the bomber into service within a useful time frame.In practice,this meant that it could take as much as two minutes to cycle the landing gear,and on numerous occasions the motors and/or thier associated curcuitry would burn out.This is the reason why so many Stirling’s had to belly land at some time or other,some belly-flopping more than once in thier career.
So complex were the electrics that Stirling squadrons actually had an extra electrical specialist assigned to each ground crew,and a new rank was even given to these specialists (unfortunately I can’t remember the name of the rank!).
All in all,the majority of the Stirling’s problems were caused by that initial reduction in wingspan,and it makes you wonder what the aircraft might’ve gone on to achieve had the Government decided to splash out on bigger hangars.As it was,the Stirling crews gave sterling service,and the aircraft’s deficiances should only serve to increase our respect for those who flew and maintaned them.

B*st*rds!

Doesn’t it make you want to vomit?

The locals are perfectly happy with their airport, there is substantial support and virtually no serious objection.

The council have gone through consultation after consultation, and when they have got answers that they don’t like – ignored them.

😡 😡 😡 😡 😡

Moggy – more furious than ever!

i dont want to flood the board but here is the bit about Rochester airfield…i had to shrink it a bit hope it’s still readible

how do you post more than 1 piccie?……anyone…..HELP

sorry i havent got the hang of posting piccies yet on this new-fangled bb

Welcome to the board mmitch, nice to see you come from the same part of the world as me..and of course rabie…anyway I recon that the stirling has big legs so the back of it clears the ground.. it has/ had a very big back-end ( see piccies below..hopfulley!) Compared to the lanc, which has a lovely sleek ass-end, as for the why’s and where-for’s of this I don’t know…just design maybe? But the stirling does seem to be a very big, or should that be fat, aircraft at the back ( or are the 6 can’s of fosters kicking in 😉 )
BTW I came across this looking at the local paper today……looks like after all the hard work Rochester is going to be a indrustrial park anyway or at least a bit of it is, and when that is built the council will say its unsafe for flying and build on the rest of it. Council !!!! I can think of a better name beginning with ‘C’

housing on airfiled hateing Dezz

The prototype Sterling made its first flight from Rochester, then as now a grass airfield. After a successful take off and flight it was written off when the undercarriage collapsed on landing. The next prototype had a strengthened U/C! The tail assembly was massive. Twin wheels on a retractable arm. The Medway Aircraft Preservation Society based at the airport had one brought to them that had been trawled from up the seabed.
Have you seen these Stirling websites. These links are from one comemmorating the ‘MacRoberts Reply’ Sterling.
See:- http://www.macrobertsreply.com/links.htm
In particular check the ‘Stirling Bomber’ one.
mmitch.

If I remember rightly, the Stirling’s rather silly legs were the result of increasing the angle of things for take-off, weren’t they? Anyone?