Folland Gnat - Development & Derivatives

[Petrus]

I have just checked out in Tony Buttler's "British Secret Projects. Jet Fighters Since 1950" what is said about Gnat Marks 2-5. The book was published by Midland Publishing, which is an imprint of Ian Allen Publishing, so bearing in mind their over-sensitivity to the copyright issue I cannot simply quote the book. Instead I'll try to paraphrase it.

As for Gnat Mk.2, what differed it to the Gnat Mk.1 was thinner wing (6% compared to 8% of Mk.1), the Orpheus engine with afterburner with thrust of 5,750 lb (2,609 kG) and more internal fuel capacity.
The basic version of the Mk2 was to be armed with a pair of 30mm Aden guns, with possibility of carrying air-to-air unguided rockets (of unspecified type; my guess is that they would be 2" Microcell rockets that were used in Lightning and Sea Vixen) in EXTERNAL pods. Further modification would have a ranging-radar replaced with a true radar, probably Ferranti AI.23. According to the book the radar-equipped variant of Gnat Mk.2 would be designated Gnat Mk.2/4. "Another weapon choice was two Sidewinders" (hopefully they won't kill me for quoting the sentence).
The book gives some info on the aircraft's perfomance: it would have maximum speed of 858 mph (1,380 km/h), Mach 1.28 at 35,000 feet (10,668 m). Climb to 40,000 feet (12,192 m) - 2.7 minute (quite a good in my opinion). Span was to be 22.2 feet (6.8m) (there is no info on the plane's length). All-up weight was 7,865 lb (3,568 kg).

The Mk.4 would have even thinner wing (5%) of 160 square feet (14.9 m2). Its engine would be the Orpheus 6 (8000 lb/3629 kG thrust) or Orpheus 701.

The Mk.5 was to be the most advanced of the Gnat family, having two RB.153s giving with afterburner 5,000 lb (2,268 kG) each. Its maximum speed would be Mach 2.4, and all-up weight - 11,100 lb (5,035 kg). "The machine carried AI.23 radar and Firestreak or Sidewinder missiles". Tony Buttler maintains that "span and length were both 24 ft (7.3m)", which seems to me unlikely as for the length at least. I think that the span could have been such, but analizing the drawing of the Mk.5, I compared its length with that of the Firestreak missile, and concluded that the Mk.5's length was to be around 11.3 m, which sounds realistic.

Hope you'll find the above info interesting.

Best regards,
Piotr

 

[Maveric]

Hi all,

in L+K 1970 I have found this, but can´t translate. I hope our czech friends... ;D

 

[Petrus]

Perhaps the original captions to the drawing would be more readable. The picture comes from the "Flight" magazine of 22 November, 1957.


Best regards,
Piotr

 

[Maveric]

Good morning,

anybody have a good drawing and technical data for the Fo.140?

Regards

 

[Jemiba]

The "pre-Gnats" we had here : http://www.secretprojects.co.uk/forum/index.php/topic,769.30.html,
(#31) although I cannot give more data for the Fo.140, than the dimensions, based on the
drawings from flight. Just have added those projects with short-life engines in the meantime.
But, as it already is quite a while ago, perhaps one of you came across the very first proposals
in the meantime (#32) ? ???

 

[Petrus]

Interestingly there were wing-tip mounted fuel-tanks projected for the Gnat. As with other swept-wing aircraft (eg. the Hunter) the idea proved to be a failure due to aerodynamic problems.

Here is a drawing of the Gnat (Mark 2 for that matter) having such tanks on its wing-tips as well as air-to-ground weapons (3-in rockets and a bomb) under its wings. Obviously the picture comes from the "Flight" magazine.

Best regards,
Piotr

 

[Jemiba]

Am I wrong, or wouldn't the Gnat have carried both type of weapons at the same time ?
Ok, in the case of the versions armed with Firestreak, the missile was balanced with an
auxiliary tank under the other wing, too, but I thought, when firing the missile,
the tank would have been dropped more or less simultaneously. Releasing bombs and rockets
at the same time is not very probable, I think. So the drawing is a kind of "split view" ?

 

[Matej]

Hi all,

in L+K 1970 I have found this, but can't translate. I hope our Czech friends... ;D

The translation:

From the top left: section plans of the two proposals from the early 1951, two engined Gnat (September 1951), Fo.140/1 with the Saturn engine, Fo.140/2 created at the early 1952 ("horizontal tail still at the end of the vertical tail" - probably it means that this and previous proposals had vertical and horizontal tail as a joint construction structure while on the next proposal the horizontal tail is attached directly to the fuselage), nearly definitive project of the Gnat from the summer 1952.

 

[Petrus]

Am I wrong, or wouldn't the Gnat have carried both type of weapons at the same time ?
Ok, in the case of the versions armed with Firestreak, the missile was balanced with an
auxiliary tank under the other wing, too, but I thought, when firing the missile,
the tank would have been dropped more or less simultaneously. Releasing bombs and rockets
at the same time is not very probable, I think. So the drawing is a kind of "split view" ?

I think the drawing was to show the Gnat's ability to carry both kinds of air-to-ground weapons. Practically, I presume, it would have carried bombs OR rockets at the same time.
Just like in attached photos (by the way, the bombs in the pictures are of 250-lb weight, not 1000-lb).

Best regards,
Piotr

 

[zen]

Wow missed that one!

Did you see the compeleted Gnat model with different intakes?

 

[Stargazer]

Interesting to see the Gnat in Finnish colors. In Ilmavoimat this aircraft had a rather bad reputation, due notably -but not only- to its very poor longitudinal stability at low speed and generally dangerous controls. Maintainability was also a disaster. This also has to be taken into account when pondering why it did not sell nearly as good as the Northrop F-5 or why it was not developed further. The original design was severely limited and had some very serious flaws.

 

[Jemiba]

Especially interesting is the Fo.147 with conventional tail plus canards ! Haven't seen this
lay-out before. Is it just an illusion, or is the radom very slim, producing a kink in the
contour ?

 

[Jemiba]

With a belly pack, the camera installation would have been quite limited
in size, I think, due to the limited ground clearance. But it's a good clue
to an unknown version, thank you !

 

[JFC Fuller]

Sorry to bring this thread back from the dead but I have recently become fascinated by the Gnat and the type has the added advantage of being powered by Bristol engines which is another fascination of mine (yes I know Folland moved towards the Rolls Royce RB.153).

As consequence I would like to gauge peoples thoughts on an idea that struck me. It certainly seems that the Folland was hoping to use the Orpeheus BOr.12R in the Mk4 version of the Gnat but Bristols interest in this waned. The engine was impressive for its size producing 6,810lb dry. At the time the company appears to have been considering further variants that were lighter and more powerful.

Orpheus: http://www.flightglobal.com/pdfarchive/view/1959/1959%20-%200450.html

However after this interest appears to have switched the BS.75 turbofan, this has roughly the same dimensions but better fuel consumption and more thrust, 7,350lb with a potential development path to 10,000lbs. The intake diameter for this engine was 33.4 inches whilst the Orpheus had a total diameter of 32.4 inches. The BS.75 wieghed in at 1,525lbs and Bristol proposed a supersonic, reheated military version.

How feasible would the use of the BS.75 in the Gnat have been? It certainly seems to offer some advantages in terms of thrust and fuel consumption but would it have fitted?

 

[kaiserbill]

Sounds interesting.
Could possibly have been the first turbo-fan fighter in the world if it had gone ahead.
Almost like a TU RB199 class engine a decade earlier.
A video of the BS.75 being loaded onto the testbed.
http://www.bac2010.co.uk/film_clip_21.htm

 

[GTX]

Some additional images.

 

[Jemiba]

Good to come up again with this thread !
I tried to make drawings of those design shown in the Flight mag (#29),
here the early designs from 1951:

 

[hesham]

Beautiful drawings my dear Jemiba.

 

[Jemiba]

Based on the same source, the RR Derwent powered design:

 

[Abraham Gubler]

All the recent drawings: Gnatastic!

 

[Jemiba]

Missed one, but it isn't designated as "Gnat": The Fo.148, with its swing wing
working in the same way, as in the Fo.147.

 

[hesham]

Although I had all those projects from many years,but my dear Jemiba's drawings
have a good taste.

 

[starviking]

Lovely drawings Jemiba!

 

[Petrus]

Some additional images.

What is the source of the drawings?

Piotr

 

[Arjen]

Drawings from 'Folland Gnat: Sabre Slayer and Red Arrow' by Victor Bingham.

 

[Delta Force]

Apparently the Gnat had maintenance and reliability issues in Finnish service. Does anyone have any information on what those issues may have been and if they posed any problems for other operators? India and the United Kingdom found the type interesting enough to warrant further development as a light attack aircraft and trainer, respectively.

 

[perttime]

The Finnish Wikipedia article on Gnat Mk.1 has a general statement on the problems, and a description of one particular incident, referring to
Hävittäjälentäjä by Lauri Pekuri, 2006, ISBN10: 9510319074, ISBN13: 9789510319079.

The general statement is that the Mk.1 design had remained immature as RAF and aircraft manufacturers focused on Mach 2 aircraft. The performance and agility of Gnat Mk.1 were considered good but "technical issues" and the difficulty in obtaining spare parts hastened its withdrawal.

The particular incident was a loss of hydraulic pressure that resulted in a crash landing and a pilot paralyzed for the rest of his life. My translation/interpretation:
A design flaw (lack of a valve?) in hydraulics allowed a "low-pressure" situation to develop in a reservoir, at higher altitudes. The aircraft lost hydraulic pressure and the landing gear had to be lowered using a back-up system. On landing approach hydraulic pressure was lost from elevator control. Using "manual" control, the pilot continued the landing but hit the runway at 20 degrees, instead of the normal 3.

 

[overscan (PaulMM)]

Folland FO 147 Brochure via Luciano Alviani.

 

[overscan (PaulMM)]

more

 

[overscan (PaulMM)]

more

 

[overscan (PaulMM)]

last

 

[hesham]

Wow,very beauty my dear Paul.

 

[Hood]

Loading and C.G. diagrams of the Folland Fo.140/1 and F.140/2 ground-attack fighter designs from 1952.

Source: AVIA 65/100

 

[hesham]

Loading and C.G. diagrams of the Folland Fo.140/1 and F.140/2 ground-attack fighter designs from 1952.

Source: AVIA 65/100

Wow,great find my dear Hood.

 

[Pioneer]

Folland ‘Sea Gnat’ advertisement

Regards
Pioneer

 

[hesham]

Nice find my dear Pioneer,

and we must merge those topics;

http://www.secretprojects.co.uk/forum/index.php/topic,769.15.html

 

[Petrus]

Here is an article "Evolution of the Folland Gnat" from the "Teesside Aviation News" of November 1979 (the bulletin's archive may be found at http://www.dtvmovements.co.uk/Archivesmonths/Archivemonths.htm). In the article there are information on the very early projects that led to the Gnat beginning with designs with two short-life engines having only one power setting (in fact they were on-off devices) and the pilot in prone position through more standard two- and one-engined (Saturn/Derwent) projects. Armament options (underbelly gun-pack/rocket-pack) and tactics are briefly mentioned as well.

Piotr

 

[RAP]

Aviation Week article from 1959 indicating the Mk2 was going to compete against the T38.

 

[Petrus]

In the Aeroplane monthly of September 2008 (Issue No 425) there is the Aeroplane Database - Folland Gnat, which includes an article ('The Nordic Gnats') on Gnats in Finland's service. The article contains a brief info on an unbuilt reconnaissance variant of the Gnat under consideration by the Finnish Air Force that was to have a camera suit in the ventral bay.

Here you have an excerpt from the article.

Best regards,
Piotr

 

[TsrJoe]

see reply #52 for Jens speculative reconstruction of a ventral camera Gnat