Topic: folland gnat

I never got round to trying ele/flap mixing as the one event where the aircraft was well on its way to a full bunt was quite enough for me.  However, i suspect that the full size did have some form of interconnect because an ex Gnat pilot pal of mine says that he never noticed a big trim change.  With the all moving tailplane an enlarged area may not be needed.  I suggest you try it out (cautiously) before deciding.  I will be fascinated to hear what you find Gordon!

Oh.  So I guess that you didn’t roll it inverted either, to see if deploying the flaps would loop it   

Interconnecting flap with elevator was probably more commonly used back then than we might think, and in the past I have come across diagrams which showed that the Me 110 and Fairey Gannet both had this interlinking achieved mechanically.  As I mentioned earlier, the Gnat’s u/c door airbrakes were linked with the tail, and it’s likely that the electric tail trimming system is slaved to flap movement as well.

Incidentally, I’d expect the engineering staff to have a better appreciation of the tail trim mechanism than the aircrew, who wouldn’t need to know any more about it than any grandma would need to know the mechanical aspects of the steering wheel mechanism on her car.

The lowering of flap increases the angle of the downwash behind the wing.  If the tailplane is sitting in the airflow affected by the flow, it experiences a large change in angle of attack and produces a lot more downforce.  Since the tailplane has a lot of lever arm compared to the location of the flaps, it can often more than compensate for the nose down pitch caused by the flap camber, and a nose up pitch is the result.  That is why some planes pitch nose down, and some pitch nose up when flap is applied.  A high wing, low tail puts the tailplane deep in the downwash so it generally pitches nose up, a low wing and high tail keeps the tailplane out of the downwash so it generally pitches nose down.  The CAP is a low wing with a high tail, so lowering the flap will generally cause a nose down pitch.  The Gnat is a high wing with low tail so you would normally expect a strong nose up pitch when flap is applied.

Further to Harry’s explanation, it was the same reasoning that led me to increase the tail size on the CAP 21 mentioned earlier.  Since it was clearly a lack of down force on the tail that was causing the nose-down tendency, I reasoned that since there must be some downwash from the wing otherwise the wing wouldn’t generate any lift, a tailplane of increased area would capture more of this downwash and thereby create more downforce at the rear.  The fact that doubling the CAP’s tail area transformed the nose-down tendency into a slightly nose-up one seemed to validate my solution, if not the way I arrived at it.

Gordon

Incidentally, I’d expect the engineering staff to have a better appreciation of the tail trim mechanism than the aircrew, who wouldn’t need to know any more about it than any grandma would need to know the mechanical aspects of the steering wheel mechanism on her car.

Unfortunately I don't know any engineers who worked on Gnats.  Anybody got the manuals?

Incidentally, I’d expect the engineering staff to have a better appreciation of the tail trim mechanism than the aircrew, who wouldn’t need to know any more about it than any grandma would need to know the mechanical aspects of the steering wheel mechanism on her car.

Unless its near shift change when I doubt they have an appreciation for anything other than going home 

I must have more time on my hands than is really healthy ... but I have a soft spot for the Gnat. My first vivid aviation memory was seeing the Red's really close up and personal at a families day at RAF Tangmere way back in the distances of time (bu**er me it was probably probably 45 years ago!). Dad dragged me out of bed one sunday morning to go and stand on the dispersal to watch them arrive. In those days there weren't many strict rules about distance or hieght from a crowd. It was and still  is the best display I have ever witnessed.

Incidentally - it was 1965 and it was the first display season of the Red's .....

Anyway - I digress ... I found this on the web and thought I'd share

http://gnat50years.in/category/design-development

Some interesting views of the development from an Indian AF perspective.

Unfortunately I don't know any engineers who worked on Gnats.  Anybody got the manuals?

I worked on them during training, but no flight control functionals apart from the airbrakes.  The closest was the ruddy Hobson unit - AAAAAAAGGGGGGHHHHHHH

The manuals are available at Amazon

Happy new year all!

I have now taken on the project from Dennis.
The wings, tailplanes, canopys and ABS center sections are all done. I need to get the materials etc to make 9 more fuselages, the formers will also need to be cut 10 sets, so probably CNC.
Slight modifications have been made to the formers after consultation with Keith.

This will be a builders kit with work still to do and not an ARTF.

Dennis always intended to do 10 kits, one has already gone to Keith. Other than costs for materials the proceeds of these kits will go to Christine, the wife of Dennis.

Anyone who expressed an interest to Dennis or anyone interested in a kit please pm me.

Russ

Hi all well after a long cold spell i have managed to do a bit more on the GNAT,just the engine to install now and it will be ready for the maiden regards Keith ps if any body needs some good pic,s of GNATS, go to AIRPLANE PICTURES.NET

Keith

Let me know when your heading out for test flights and i'll bring my camera

Steve

Hi Steve thanks for the offer,i will take you up on that as i hope to do a article for R C J I on the GNAT and some flying shots would be great regards Keith

You bringing it to the Jet meet on March 13?

Hi yes should have done the maiden by then and got it sorted  :xxregards Keith

Looks great Keith!!

Hope to see you at the meet.

Russ

That Gnat looks great Jetjock and thanks to Russ for putting me on the list.

Matthew

It's just like seeing an old friend after years of separation!
Good luck with the first flight.
The DF version always was a peach to fly, and land.

Don't forget to let us know what happens.

JohnC

Hi all Gnat did not fly this week end to much wind  :-\but here are some install pic,s regards Keith

Hi All The Gnat had its maiden today all went very well with no problems, it is well over powered with the super sport but man is it quick but flying around at half throttle was a breeze and a lot quieter.Weight came out at just under 16lbs with a full UAT.Landings were good once i reduced the elevator throw and put in 35% expo,i might try moving the C/g forward a bit. i am well pleased with the model it was certainly worth all the effort regards Keith

Excellent news, congrats!

A great result Keith and congratulations 

With all the thrust you have available I wouldn't be surprised if your Gnat would accelerate OOS in the vertical 

Gordon

thanks Ian......looks as if someone has beat us too it!....can't wait to see the photos

so would that be about 44" wingspan at 1/6 scale?.......just seems a bit small?.....can't remember what JC's was....we flew that on a 14lb wren...went lovey

cheers

dave

I have loved the Gnat ever since the dead sparrows flew them in the 1960-1970's.
I am really into 'Vintage' jets and would love to build my two other favourite aeroplanes, the Jet Provost and the F86 Sabre; sex on wings or what!!

Well done Keith, you must be chuffed to bits after a successful maiden.
Any chnace of a few more details of your equipment installation, especially retracts please?

Well done Keith, glad to hear it went ok.

Hi All thanks to every one for the replys,the retracks i used are some beotec air up spring down which i had lying around,legs are 6mm piano wire and wheels are some spare fly eagle jet wheels which are pump up type but i did not put any air in them they were ok with out,these worked well and gave a little cushioning,i was also able to use the brakes that go with them.all will be revealed as i am in the proccess of writing a article for R C J I with all the details regards Keith ps any one from here coming to the JMA meet at West Raynam on the 13th of March?? We should have two in the air one, in the Yellow Jack colours

Thanks for the info Keith, most helpful.
My girlfriend bought me a subscription to RCJI for Christmas, so I'll look out for your article.

Well done Keith, shame about Sunday as my camera was all ready to go, looking forward to your next outing so I can get some shots for you.

Steve

Nice one Keith,

Got a Wren 70 which just found a ride!!!

Spoke to Russ, now waiting for a kit..

Some Pictures of Keith's Gnat.

Take-off



Flight

Fabulous!

What is that small 'blob' at the wing root under the leading edge?  Don't remember that on my prototypes, but it was a long time ago.

Great pics, more please (lots more)!

Nice one Keith. I love Gnats, and one day will have one of my own 
  Is it nose heavy, or is the incidence out? It sure looks to be carrying allot of up elevator to fly straight.
 Also in the head on shot, it sure looks like the post wing is leading edge low compared to the starboard.
. It might just be an optical illusion, but thought I would give you a heads up.
 Regards Al

Nice photos Steve you must have been rubbing shoulders with Lozza or Neilly

Nice photos Steve you must have been rubbing shoulders with Lozza or Neilly

Not even close to their standard unfortunately, but enjoy taking piccies with the gear I have got!!

Hi all the blob as you call it is the tank vent.
Ali you sure have sharp eyes and yes it looks like the wings are not in line,i will check the model,its not nose heavy but i believe the incidence may need checking,it may have been altered making the mold regards Keith

Hi Keith,
 Well something about me has to be sharp I guess 

  It looks great, none the less!  Well done.
 Regards Al

Superb shots Steve, with the Gnat beautifully positioned by Keith - you're a great team 

I love the plane and can't wait to receive my kit - blast that snow which prevented me from collecting it at the Dec CJ

Roll on the next CJ   

Gordon

What are you using for the nose light Keith?  I've bought one of those cheap 9-LED torches from which I'm planning to extract the LED block for the light in mine.

Godon

Gordon,

You not have your kit yet? i will be going to the JMA AGM, i think keith is aswell so could collect it for you there if you like? i travel to and from Culdrose every weekend so a meet up would be easy to arrange.

         Jamie

Hi Jamie

You're a star!!  Many thanks for the offer and I would certainly be very grateful if it was possible for you to collect it in this way.  I can't make it to the AGM, unfortunately.

We're a bit off the beaten track down here and it'd be a big detour from the M5, but I could easily meet up with you at Junction 25, which is the turn-off for Tiverton and Barnstaple, or at any other location, eg Taunton Deane.  Or I could drive over one weekend to Merryfield or Woodspring (I'm a member of that club) and meet you there for a spot of flying (assuming you live near/at Weston)

That would be FANTASTIC! 

Many thanks!

Gordon

No problem, happy to help. If you let keith know what is going on i will see him at the AGM. Any of the above will be fine so you should have it within the week.

Gordon

Didn't you have a Gnat kit from me back in the eighties, back in the ducted fan days?

John,

Pete Nye has let me borrow his videos of the DF meets back then, Ron Sweeney has also let me have some film as well. There are Gnats all over them! and quite a bit of film of yourself, Gordon, Pim, Ted Cooke, Pete Nye, Paul Gray, Dave Nieman etc etc

Pete was telling me about you, Dave N, himself and a blue Granada estate with a Phantom on the roof at Radlett . . . . . . . . sounded lke a really good laugh!

Hi John

I always wanted one but couldn't really afford DF back then.  After one (successful) foray with a scratch-built Supermarine Swift which ended up with a KB.75/Turbax I gave up for several years.  I put the 7.5 to good use in a 1/8th scale scratch-built Spitfire Mk 24, taking advantage of its rear exhaust to avoid having the silencer poking out of the side of the cowling.

BTW, I've moved back from electrics to i/c and have a Saito 36cc petrol awaiting the completion of a 27.5% Bucker Jungmeister.  I began building the Bucker for 12S electric, realised somewhat belatedly that owning enough huge lipos to get a decent day's flying was going to be massively expensive, and bought the Saito for less than the batteries would have cost.

Cheers

Gordon