Short Knuckleduster

[PMN1]

Wandered into this aircraft form another link

http://en.wikipedia.org/wiki/Short_Knuckleduster

According to the wiki article (I know, I know), the Goshawk was part of the contract, is this true as the competing Saro and Supermarine designs had Pegasus engines?

If The Knuckleduster managed to avoid the Goshawk, what are the chances of it entering service?

 

[Stargazer]

The aircraft was submitted to Operational Requirement OR.3 (Specification R.24/31) which called for a "General Purpose Boat Seaplane."

There were only three known contenders as follows:

• Saunders-Roe A.27 London
• Short S.18 Knuckleduster
• Supermarine 230 Southampton V

Now you're asking whether the Knuckleduster could have been successful if it had used Pegasus engines instead of the Goshawks? I don't know. I guess so. The weird arrangement of the engines and their tall, ungainly radiators placed high above the engine nacelles, may well have contributed to a loss in performance.
The Knuckleduster remained a prototype, but it contributed much to the design of the Empire and Sunderland flying boats. The Saro London, which entered service with the Royal Air Force in 1936, did use the Goshawk but only 31 were built, so the engines do not explain everything. The Supermarine Southampton V was initially turned down but Supermarine proceeded with the type as a private venture, and renamed it the Stranraer. It didn't fare much better than the London, as only 17 were produced for the RAF, with an additional 40 produced in Canada.

All three designs relied on the old biplane formula, with the engine located on the upper wing, and were the last of their kind, being soon superseded by the likes of the Sunderland monoplane flying boat.

 

[PMN1]

The Londons also used Pegasus engines, you can see that in the pictures.

If 31 Londons were built with Goshawks, that has used 42 more Goshawks than were built give or take a couple.

The question is whether Shorts were forced into using the Goshawk by the Air Ministry and if they hadn't and could have used the Pegasus of the other designs whether a useful design is the result.

Another question is given the hull design for a military flying boat rather than one used for commercial ops needing more internal space whether the gull wing design is better than the parasol wing design that the PBY used?

 

[robunos]

From Putnam's 'Shorts', pp. 280-285 :-
"Three prototypes to R.24/31 were eventually ordered, the Saro and Supermarine designs being biplanes with Pegasus engines, while Short Brothers received a contract for a more ambitious monoplane with experimental Rolls-Royce Goshawk steam cooled engines...it was necessary to to mount the engines high enough for their large diameter geared down airscrews to be well clear of spray at take-off; water tank and wind tunnel tests showed that the best compromise was likely to be a gull wing geometry...inner wings growing out of the hull at a dihedral angle of 30 degrees, the engine nacelles being faired into the leading edge at the wing joint, or 'knuckle'...
The 'Knuckleduster' [NOT an official Type Name] was not expected to win a production order in the R.24/31 competition..."


cheers,
Robin.
It did, however, provide valuable data on the steam cooling of engines and the handling of monoplane flying boats. It is interesting to speculate what it's performance might have been, for instance, with close cowled Perseus engines...

 

[DWG]

The weird arrangement of the engines and their tall, ungainly radiators placed high above the engine nacelles

Not that weird when you look at the immediately preceding Shorts designs such as the Sarafand, KF1 (H3K2) and Singapore. Shorts had been mounting radiators either above or below the engine for a while - and had flown the Singapore II with one radiator above to port, and one below to starboard, to work out which layout had the best aerodynamics - above turned out to be superior. What makes the Knuckleduster look odd in comparison to its predecessors is the lack of an upper wing above the radiator.


Interestingly the Singapore II was used to test evaporative cooling in 1932, which must have been in parallel with the design of the Knuckleduster. It's stated in Shorts Aircraft Since 1900 that the gothic radiator/condenser was a RR design and caused much more interference drag than the more box-like Shorts design.


The radiator layout actually makes a lot of sense in a biplane with engines between the wings, where there has to be a vertical structural girder in that position to brace the engine, so you might as well take advantage of the pre-existing drag and put the radiator in the same place. That advantage disappears in a monoplane and it looks odd without a wing above it, but it probably represents a known quantity in terms of airflow behaviour and cooling efficiency in what is already a very experimental design.


The Knuckleduster was good value for money for the RAF - they got to test both a monoplane flying boat and the Goshawk, and they effectively hid the expenditure within an operational requirement. Nor did Shorts lose out when the orders came around, picking up a repeat order for Singapores IIIs (with above engine radiators) at around the same time. It's possible the RAF wasn't ready to order a monoplane boat for operational service, but knew they were likely to have to do so in the relatively near future, so made sure the MAEE had one to play with. What would be interesting to know here is how much of the configuration originated with Shorts and how much with the Air Ministry/RAF/MAEE, but Shorts Aircraft Since 1900 is uncharacteristically reticent on the origin of the design.

 

[Stargazer]

Thanks DWG for this very interesting and relevant analysis.

 

[DWG]

I was lucky, I'd just re-read that section of the Shorts book, now that I've got a copy of the British Aircraft Specifications File to cross-reference with it, so it was all fresh in my mind.

 

[theponja]

DWG anyway is an excellent clarification. The Short_Knuckleduster looks very interesting. Anyone has a 3d view?

 

[Arjen]

From Putnam's 'Shorts'

 

[theponja]

Thanks!!! Seems to be a difficult one. I just found online a couple more of images.

 

[Arjen]

The weird arrangement of the engines and their tall, ungainly radiators placed high above the engine nacelles

The radiator layout actually makes a lot of sense in a biplane with engines between the wings, where there has to be a vertical structural girder in that position to brace the engine, so you might as well take advantage of the pre-existing drag and put the radiator in the same place. That advantage disappears in a monoplane and it looks odd without a wing above it, but it probably represents a known quantity in terms of airflow behaviour and cooling efficiency in what is already a very experimental design.

Having the radiators on top of the engines kept them clear of spray. Radiomasts on top of the radiators attracted even more attention to a crowded bit of aircraft.

 

[Schneiderman]

Another thread back from the dead

The radiators are actually a Rolls-Royce design patented by them in 1932. Placing the radiator above the engine was advantageous for an evaporatively cooled engine as it reduced the possibility of steam being drawn back into the engine or reboiling occurring in the pumps. All the Goshawk-powered F7.30 contenders that had low-mounted condensers suffered from these problems