Dale


This is what David Gladwin posted on the subject.... i am sure he won't mind me reposting..

The strips were placed on the wing to produce pre-stall buffet, essntial on a trainer without a stick shaker and/or pusher. However these stall strip wWILL produce an earlier stall in the area of the wing to which they are attached (the Chipmunk is a classic example of this application) and thats good in that it stalls the root section before the tips, thus retaining aileron control and miniimsing unpleaant wing drop at the stall.

They may well work at the Reynolds numbers we are working at with models BUT how would we FEEL the buffet if we are not IN the aircraft ?

However, because the strips produce this earlier stall the penalty on the Hawk was a small increase in stall speed, around 4-5 knots, considered acceptable in view of the enhanced stall warning.

On the Hawk, spanwise flow contol was achieved by optimising the wing fence design.

If you think the Hawk had to be "fiddled" to achieve accptable handling take a look at all the aerodynamic fixes on the Jet Provost Mk 5 , roughened leading edges, spin strakes on the nose, root slats, all to make it fly, stall and spin like a trainer ! In the final form (although many changes in wing dressings were made to later Hawks and Goshawks) they were both a delight to fly !

Regards, David Gladwin.

Dale

This picture explains the airflow, about the best one i have seen on the Hawk it was originally posted elswhere i beleive by RC Asia?

On my Display Hawk I remade the fences out of slighty thicker epoxy fibre glass board and dremeled into wing just to get through the paint and glued them on with Hysol done this on another Hawk ..they will not get knocked off they are solid just got to spray them black...


Alan

Thanks, I appreciate the info. I know on ful scale they are critical and used for the exact reason you posted.

I had a Carf Hawk tip stall on me this weekend, no warning what so ever ( you usually do feel a buffet, even in rc ), the plane went knife edge and was able to catch but the nose dropped off fast.

Afterwards the builder brought me the fences that were'nt put on - I immediatley got that rotten gut feeling.

Dale

If you look at my video, after my bouncy arrival and staggering back into the air you can see the right wing dropped and I just caught it with left aileron wonder if the result would have been so good without the fences?

Alan

That was a small drop compared to what this did. The plane litterally went knife edge. The strongest wing drop I've yet seen with no warning.

I got my Hawk really slow and it was very stable. FWIW, I have the fences on my wings.

There is another person at our field that has one and have seen that plane fly extremely slow. I know I had this one a lot faster ( still slow though ) when in stalled. I was amazed at how fast it tipped without any warning, the fences definitely do their job.

Guys

The fences do a job, even on the model. I fly my Hawk really slowly and land at walking pace, but with all Hawk's there is a fine line between happy and sad, the all flying tail is really powerful and if you keep pulling it will bite. Things to look out for are the aileron neutral, its easy to have them drooped on the CARF Hawk-mine do not line up with the flaps when up, they are slightly above the flap.
If you push the balance back looking for a more neutral aeroplane in flight you can get into the point where its a little loose on landing, every pilot is different and has a different feel, there is no right and wrong, its just how you need it for your flying/landing style. Adding weight increases the stall speed, my Hawk is really bland with no extras added, so is really light. The great thing about the Hawk is it will land fast and not skip so you can start off faster and gradually slow it down to the nose high creepers.

Dw

When I first flew my Carf Hawk last year I had a few bumpy landings to start with even on atarmac runway but it never dropped a wing on approach.

Over the winter months I made some changes including movingthe CG back as It was dropping its nose a bit in banked turns and needed a lot of down elevator to fly inverted.

I have a scale cockpit (skymaster) and 1/5th pilot and the canopy /frame interior and pilot weigh 1 kilo so I have notneeded any nose weight never the less I have moved one of my rx packs (2 cell 3600 lipo) back from next to the nose legg to just in front of the tank bulhead (about 600mm 24 inches) I have also mixed in a small amount of crow (6 mm at inside line of aileron) with full flap and this has helped no end on landing approach.

The advantage as far as I see it is that with a small amount of crow you have in effect washout, so this will prolong any tip stalling at low speed.

With the outer wing (aileron section) now at a negative attitude compared to the main wing the sink rate is greater and much more like my Flash to land.

Bouncy landings are really becausewe tend toland too fast andthe plane wants to carry on flying, With crow on the Hawk once she is down she sticks so I am very pleased with this

set up.

On sunday I flew my Hawk at Wroughton and had a chance to try out another mod I have made which is fitting a Futaba GYA 351 gyro to rudder and nose leg steering.

All seemed well and I had the Gyro rate turned down to only about 40% with no hunting untill I started the turbine (jetcat 120SX) and the rudder was oscillating like mad

So I turned the gain down to zero and flew with no problems.

I had the gyro fitted next to the Jetcat ECU so I wonder if there was any RF from the ECU that was upsetting the Gyro?

Anyone had similar problems as I have not yet had chance to move the gyro away from the ECU with the turbine is running.

Phil.

Curious as to what people are doing to retain the CF elevator pivot into the fuse. Do you cut it flush, leave it full length? Are you pining it, glueing it etc?

I cut mine almost flush & applied a drop of cyno to one side. It has not moved & if I need to remove it, I am sure a little tap will loosen it.

So, how is everyone's Hawk flying? Mine is getting very close to completion.

Hi,
I am impressed with your flap hinges and wondered where I can get some. Also how are they attached to the wing in a secure manner in order to take the strain of the flap?

Regards

David

David

You talking about our dummy hinge vanes? I'll bring a set to the meeting tonight and you can see.

Dave

Mine flies great!

[youtube]http://www.youtube.com/watch?v=usA4IYY7ANQ[/youtube]

Finally managed to get my second flight in with the Hawk, with work, holidays and buying a motorbike weekends have been a bit busy

This is one nice flying plane and if anyone thinks you need gyros think again this plane is on rails!

Glad I chose the CARF Hawk and not the other ones! Thanks Dave getting used to flying the Hawk now.

[youtube]http://www.youtube.com/watch?v=I6p9pJmTh8k[/youtube]



Alan

Hi there,
Nice video, and I am about 1/2 way thru building mine.
What lights did you use as they seem very nice and bright ?

Regards

David

David

I used Reble 700mA in wing tips and strobes and a Luxeon K2 TFFC LXK2-PWN4-160 - neutral-white - 220 Lumen which pulls around 1.5A

Made the circuit PCB and I used MOSFET output transistors.

I posted some pics of the circuit a few pages back on this thread

I have offered to build these NAV Lights to anyone who is interested, controlled from Rx channel

Film I did in the dark and day

Alan

[youtube]http://www.youtube.com/watch?v=GKPjR3D4eBk[/youtube]

[youtube]http://www.youtube.com/watch?v=7UE_IlD31sI&feature=related[/youtube]

The lights are alot bighter to the eye as the camera device closes down alot when subjected to that amout of lumens! First pcb used for test the final one can be seen in the jet this has worked faultless and is supplied via a 4700mA LiON Duralite

Hi all, another Carf Hawk in the air, kindly maidened by DW at Abingdon. I'd incorporated pretty much all the suggestions and set up through the build thread and she flys like a dream. I'm really pleased, its an excellent model.

ps had to upload the picture of DW using my MPX TX..................he did give a wry smile though!

David

Always good to chalk down another Tx type...makes me realise again and again how great my DSX-12 is

More pics take of the maiden flight taken by Little Stevie

Great model, worked perfectly and just needs a set of my wing flap carriers to look perfect

DW

Interesting day when another Hawk kit arrived, turns out to be our 20th kit.

Dw

Hello!
Mine flew tthis week too!
All settings as written here so many times!
A real superb model plane!

Congratulations!

They do fly good!

They look even better when you get the cock pit detail and pilot in

Alan

That does look good! What cockpit and pilot is that?

Mike

Mike

The cock pit was from Der Jet through Motors and Rotors and the pilot was done through Phil at fighteraces UK, had the suit changed to black to match the 2010 Display Hawk both not cheap but if you are going to spend on CARF Hawk anyway you might as well finish off properly
They do transform the glass area.

Alan