TOPIC: Yak 23 & Jet Spifire

I got to take a look at Roj's YAK 23 at Old Warden on Saturday and upon re-reading this thread remembered that I had prevoiusly considered models of aircraft that where essentially piston engined aircraft fitted with under slung jet engines.

In March 1943 Focke Wulf considered a Junkers Jumo 004B engined design which used the wing, tailplane, rear fuselage and undercarriage components from a Focke Wulf 190A. The jet engine was to be fitted beneath the wing forward of the trailing edge, but this lead to the rejection of the design known as the P1 (Plan 1) for the fear that exhaust gases could damage the rear fuselage, sounds familiar.

I built a profile model as shown below believing that the layout may give me an extended glide phase but was not as succesfull as I had hoped due to to the fuselage being on the heavy side with a bend induced by laminating some carbon fibre tows into the fuselage which also made it impossible to straighten.




Another design that peaked my interest was the suggestion that in a step towards the F-84, Republic looked at fitting a J-35 engine into a P-47 Thunderbolt. Not sure if this was real or otherwise as all I found on line was reference to a 'Sharkit' resin set required for conversion of an Hasegawa plastic model kit.

It was enough for me to start drawing up a model, below you can see how far I got before interest moved to other things. Perhaps its something I should revisit again?

Roj has just sent me photos of progress with his Yak 23 mk2 which I've assembled into a montage:



Roj writes:

"I've sprayed the Yak [an authentic Soviet muted silver, it's a bit scruffy (esaki tissue sanded thru) to be honest, but it was a rushed build. With the motor pod, but less motor, it weighs a creditable 34 gms. I'm going to hide bad workmanship with panel lines and Russian decals.
A test glide in the garden was very promising but the amount of nose weight required was dissappointing. In hindsight the whole front of the fuz could have been infilled with balsa as I have had to use ballast. A heavy [ish] thrust tab might help and I hope it will fly well under power".
I commented it's not too late to add sheet infill to the nose as it's always a good wrinkle and means less damage to the nose on a hard arrival!

Here are the latest photos from the ever industrious Roj Reese:



Roj writes:

'I chickened out with marking up panel lines as the Esaki tissue too sensitive and Wing insignia too small. I think may cut a mask and spray over waterslides.'

Well, it looks pretty good to me!

Roj Reese was at Buckminster yesterday. Roj reports:
"It was as warm but blustery, with not too many free fighters but met up with Brian Lever. Sadly no rocketeers but moi.....
I had no success to speak of with my sport models but when the condition calmed I ventured a flight with the Yak 23 [mk 1]. Using a VMC L-2 it climed vertically and looped in large repeat circles travelling down wind at a rate of knots. The motor run was constant and the flightspeed was fast. The model ended up about 700 metres down wind and found a tree on the boundary . I found model, less left wing .



It is repairable, and Brian, who witnessed this impressive flight remarked how wonderful and exciting a flight it was. Looking over the model post-flight, I noticed the thrust tab was missing, which probably resulted in the looping".

I take this as a success - we've all had far less succesful and indeed disastrous maiden flights!
The thrust tab might of course have come off in the impact with the tree, but its absence points to the importance of preflight checks.
As to the looping .... this can also be cured by trimming in a little left or right rudder or aileron to (hopefully) get a climbing turn. The fact the loops were dead straight shows how accurately Roj had built his model and trimmed it for the de rigeur 'dead straight glide from a hand launch'.

I hope Roj is encouraged by this first powered flight and I look forward to seeing how his mk 2 (which is a bit larger and therefore likely to be less fiesty) behaves. But we will pick a calm day for its first flight and try out some less powerful motors first.

Onward and upwards!

Sad to see the tree damage but brilliant nevertheless, congratulations, the model looks great too.

Earlier in this thread I stated that I had dabbled with a couple of designs that where essentially piston engine aircraft with underslung jet engines. I had built a FW190 based FW P1 profile model and mentioned that I should probably revisit the design.

Well, late last year I did just that and have drawn up a full bodied design some screen shots of which can be seen below.







I have recently retired so hope to now get a few models completed. If and when I get around to starting this I will start a new thread.