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FFVS J-22 Anyone?


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Morning all,

 

Flushed with success from my Spitfire/ Harmony mash up that ended in a 42" Spitfire that flies really well, and encouraged by Peter Miller, I have a project...

 

The original design brief for the 'Harmfire' was to replace my Cambrian funfighter spitfire. It did indeed fight. Me. It can be challenging to launch and although it flies really well, the stall is quite, er abrupt so needs to come in quickly. Our strip can be unforgiving, and the cost of broken propellers was getting out of hand!

 

So, with Peter's help I grafted the wing from 'Harmony', thickened to 14% to accommodate retracts onto the fuselage of Ian Peacocks funfighter spitfire. I modified this massively to make the model one piece and to keep the tail light and get the battery forwards. It's really successful and I now fly it by taking off from the wheels, but belly landing like a funfighter to protect the retracts from our bumps. I have landed on the retracts with no problem though.

 

I've also developed a fascination for the lesser known aircraft of WWII. With that, I'm going to design and build a 42" version of the FFVS J-22. A swedish aircraft that looks like a happy accident between a bearcat, an FW190 with an LA7 tail! There are good reasons to select this design. The rearward retracts fit nicely into the fuselage and provide a decent grip for hand launching, and the large radial cowl gives good cooling and space to get the 3S 2200 pack well forward.

 

With half an eye on making the plan available, I am drawing this up. It's ages since i've done 'actual' drawing and it's taking rather a long time, so don't hold your collective breath.

 

Is anyone interested in a Blog, and possibly other similar size oddities?

 

Graham

 

ffvs_j22 3view.gif

FFVS_J22.jpg

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Hi Eric, are you well sir?

 

I'm going to need to simplify a little to keep the weight right down to achieve similar performance to the 'Harmfire'. I'm going to use flat sides for the rear fuselage but make a round profile towards the front. I'm also taking some liberties with the undercarriage. The forward mounts will make use of f2 for strength, but I think the wheel wells whilst behind the CofG will still be a decent launch grip. Hopefully though, if it comes out light then it will take off from it's wheels.

 

The Harmfire get's airborne in a very un-scale manner; 6 ft and she's off! No less scale than being flung though...

 

Graham

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Yes, of course, Graham. A building thread would be fine ?

 

There are several simplified EPP versions flying in Germany, built for EPA aircombat contests. I also remember pictures of more detailed ones in 1/12 scale, built by Swedish aircombat pilots for WWII class.
https://www.rc-network.de/threads/eine-einfache-aber-konkurrenzfähige-epa-einmot.722578/

 

Timo

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That's a nice variant Timo. 

 

Thanks to Peter Miller for a set of airfoil plots to save me a huge amount of time. As a result, I'm now underway.

 

I have started with the wing in the usual Peter Miller method of starting with the lower sheeting and building up from there. What you can't see are the washout wedges. There are 2; 1 degree at R6 and 2 degrees at R10. Once this is set, I will pull up the forward sheeting, add leading edges and add the servo frame and then the top sheeting. It stays pinned down on the washout wedges until the top sheeting is fitted. That keeps it warp free.

 

Note the liteply mainspar and foamboard ribs...

 

Graham

j22 build 01.jpg

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Sorry for the delay. Pesky C-19 got in the way.

 

So, a bit more has been done.

 

The wings are straightforward. Slotted liteply spars and foamboard ribs. Ailerons are built in, to be separated later. They can stay in one piece until I'm ready to do a bit more on the wing. There are no tubes for the servo leads. I don't find them essential on a wing this size as it's easy enough to pull a new lead through with the old one. You can see the slots in the top of the ribs; I turn the wing over and gently tease out the old cable if it becomes necessary. I do test the servos beforehand though!

 

Servos are mounted on 1/16 ply plates as simply as possible; wrap of insulation tape and gorilla glue. Works a treat and saves ply blocks.

 

You can see now that the wings are pretty much done. Sheeted, joined and sanded. I am considering a strip of lightweight glass cloth to reinforce the centre, but that may be overkill. I didn't bother with the Harmony/ Spitfire hybrid and they are solid. The model will be one piece, so the wings will be glued into the fus; it's likely to be plenty strong enough at the target weight of 2lb 12Oz.

 

Next stop; the fuselage...

 

Graham

J22 060921.jpg

J22 080921 1.jpg

J22 080921 2.jpg

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Fast forward because I forgot to take pictures of the nose ring!

 

I created the circular profile by fitting a nose ring of lightply and laminating soft balsa to the front. Some formers to the sides of the fuselage and then sheet with 1/16" balsa.

 

Similar under the wing. The wing is fixed, then formers added and 1/8" ply plates for the retracts before 1/16" sheeting.

 

J22 140921.jpg

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And now nearly finished...

 

Top hatch is my current favourite style; nose ring to behind canopy. Suits a fixed wing model and makes access a doddle. Hatch is made on a 3/32 balsa sheet with lightply and foamboard spacers, then 1/16" sheet.

 

Canopy is an FW190 one I had knocking around. 

 

With all the gubbins, but without covering and finishing and pushrods and horns, she weighs 2lb 7Oz with a 2200 3S battery.

 

 

J22 1 150921.jpg

J22 2 150921.jpg

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A bit more progress...

 

All covered (38gsm matte doculam).

Control surfaces hinged and pinned and control horns fitted prior to a couple of light coats of primer.

 

*Note: Halfords grey primer is not the best over doculam. Despite a good keying, it chips off rather easily. And has also caused blooming with the first coat of MIG acrylic paint over the top. I used Ambersil Acrylic primer before and it's much better. A little lesson learned...

 

Pilot is fitted and a modified FW190 canopy is waiting for the canopy glue to dry. I have used a couple of screws into lightply reinforcement strips as it's under a bit of tension to get it closer to the J22 shape.

 

Starting the top coats now, so not far to go now.

 

Graham

 

J22 210921 1.jpg

J22 210921 2.jpg

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Hi Graham, 

Looking good, rapid progress at this rate you will get the test flight in while the weather is good. I have been away so catching up now.

I am keeping well, getting ready for the winter builds and repairs, I have ordered a Hurricane from Richard so that's November sorted, hoping to build another twin over the next few months, not decided what yet. 

Cheers Eric.

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Hi Eric,

Glad to hear all is well with you.

Yes, progress was indeed quite brisk. I tend to get excited once I get started. This is my first own design scale (ish) model, so there was a lot of time on the drawing board before I could make anything. All being well I'm just a week or so from a scary test flight.

 

I have various half-kits from Richard so have plenty of options. He gave me a P51 that wouldn't fit in the bin too, so I've got that to refurbish. I'm not short of projects!

 

Graham

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  • 1 month later...

Hi all,

 

Apologies for the radio silence, but a lot has happened with the J-22...

 

Initial flights were, er, sub-optimal. The aircraft would simply not fly. Launches either from the hand or from the ground resulted in the model climbing but having no control at all. Day 1 resulted in 2 very short flights and steep landing approaches. My first thoughts were that the large cowl and 10" prop were preventing meaningful airflow across the tail surfaces. A 900kv motor and 11" prop were procured and another go had a similar outcome, but this time the damage was extensive. The main spar was broken and the front of the fuselage rather broken.

 

I considered scrapping it at that point, but the rear end looked good and what would Iearn from binning it?

 

I rebuilt it, and discovered that I had indadvertedly introduced several degrees of positive incidence in the main wing. This was clearly a smoking gun as the wing was almost certainly fully stalled at launch. It's a one piece model, but the rebuild gave me the opportunity to reset the incidence. 

 

After the rebuild, the maiden was relatively uneventful although I needed a huge amount of aileron trim. This later bit me as I tried to fly the model slow enough to record some video, and it stalled during a turn. The damage from this was minimal, but I decided to find the cause of the excessive aileron trim. It transpired that I had built in a twist in the right wing during the rebuild. I was luckily able to remove the twist with some vigorous heatgun work.

 

I'm please to report that the model now flies really well. It has hit my personal brief, which was:

  • Build an unusual subject
  • Build a warbird that will fly on a 3S 2200 pack
  • Suit our bumpy strip
  • Have retracts (even if I hand launch and belly land)

 

It takes off from the wheels very well. It has less torque swing than my Harmony/ Spitfire hybrid and it's easy to get it to rattle along the strip before easing away. Landings are also dead easy as the large cowl provides plenty of drag to help slow her down. There's little risk of ripping out the retracts as it can be slowed nicely, but also because there are nice solid mounts for the retracts in the underwing fairing.

 

I built in slightly too much dihedral during the rebuild, but this has made the model great at wide, flat turns that look great. It is very stable in roll, so it is stubborn to roll from flat, but very urgent from inverted!

 

The coolest thing though is the buzz of satisfaction of seeing this unusual model in the air, and knowing that for better or worse, it's all my own work!

 

My next project is even more obscure...

 

361856138_J-22flying1.thumb.jpg.27e3d602b4b3102b26d48dfdcca973a9.jpgGraham768703390_J-22Flying3.thumb.jpg.dbce9e41e728bcf512ecf4e5b60659aa.jpg

 

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