The A4b - a V-2 with wings on!

[Colin Leighfield]

Another labour of love, success is guaranteed!

[Daithi O Buitigh]

Well you could claim the landing was scale in that it descended nose first

"Where's the ka-boom? There was meant to be an Earth-shattering ka-boom"

[mightypeesh]

Thanks for an interesting build, good luck with the 'second maiden' looks great!

Cheers, Simon

[Simon Chaddock]

The new nose under way.

Built in the same way as before. As the damage obly extended back to former 6 there is a bit less of it than before but what there is is 1/2" longer.

As I now know exactly how to install the battery and ESC I will simplyleave part of the planking off than cut open the completed shell as I did the first time.

[Simon Chaddock]

With the top planking left off for access the new nose is glued on.

Next is to fit the ESC then the battery box.

The nose is exactly 1/2" longer than before and so will be the position of the  battery.

Edited By Simon Chaddock on 06/01/2016 18:34:40

[Simon Chaddock]

The ESC mounted as before and the battery box added.

Complete with all the planking made good.

II think I will wait for the mud to harden a bit (and the grass to recover!) before I try again.

[Stephen Jones]

Posted by Simon Chaddock on 07/01/2016 23:16:44:

The ESC mounted as before and the battery box added.

Complete with all the planking made good.

II think I will wait for the mud to harden a bit (and the grass to recover!) before I try again.

Yes ,

Best not to make a habit of blasting holes in the green

Steve

[Chris Barlow]

Been following in the shadows for a while now and have to say it's been an intriguing build. Can't imagine how it flies except fast?

What launch method did you use in the end? There looks like there's lots to hold on the nose to throw it like an oversized dart.

Can't wait for the next test.

[john stones 1 - Moderator]

Double 20

You'll have somebodys eye out wi that

John

[Simon Chaddock]

Chris

Remember it has a wing area of 1.5 sqft which gives a loading of a pretty modest 10 oz/sqft. Then there is any fuselage lift to take into account as well!

From the limited flight so far it hand launches easily like this

It has a minimum flying speed of not much more than 10 mph!

[_AL_]

Congratulations on a very interesting build.
I hope the re-maiden goes a little smoother.

Al

[Erfolg]

A Miles M52 would be nice, very similar in shape and could be just as scale,

I did not realise how big it is.

[Simon Chaddock]

I was never very happy with the geometry of the cheat hole intakes.

As the rear end has proved to be much more rigid than I feared I have decided to open out the intakes a bit.

The original intake

The 'opened out' intake

I am not sure it will make a huge difference but with the much reduced thrust resulting from the change to the smaller 55 mm EDF its 'breathing' needs to be as good as possible.

[Simon Chaddock]

Almost perfect calm this morning still lots of mud but here you go!

I make no apologies for keeping high most of the time but I am too out of practise to try anything dramatic particularly on its first 'proper' maiden!

A bit tricky to fly with no roll stability at all but it does glides remarkably well (but then it was supposed to!) and the landing speed is ridiculously modest.

The field is still so water logged and muddy I will wait for better conditions before exploring its characteristics any further.

[Colin Leighfield]

Nothing wrong with that Simon, it flies like a pussy-cat. You need to speed up the video about 20 times for scale effect though!

[Andrew Price 2]

Looking good Simon. Well done.

[Dave Hopkin]

Looks good Simon another keeper!!!

[Simon Chaddock]

Thank you each for the kind words.

What I am pleased with is the fact that although the first short flight ended badly I did manage to extract sufficient information to deduce:-

a} That it would fly

and

b) A relatively small CofG change would make the difference.

Whilst not the fastest of my Depron EDFs (that title belongs to the smaller cascade nozzle Harrier) it is still fairly quick and perhaps as no surprise it is rather more 'slippery'.

It biggest problem however is the EDF itself.

As the 55 mm was a quick 'replace' job I only checked that it ran rather worry too much about its balance. Sods law it is about the worst of any of my EDFs!

I fear that until the fan/motor is in better balance it would break up in any attempt to run on the 4s necessary for a possible VTO!

[Stephen Jones]

Well Simon ,

You know what they say ; You can not make an omelette without breaking a few eggs .

I bet you're browsing habits rings a few alarm bells back at HQ .

Well done Simon,

although i am a bit disappointed there was no big explosion at the end of its flight , not even a puff of smoke .

Congratulations Steve

[Simon Chaddock]

Colin

You are quite right. I do have something in mind but it is still only in the mind!

[Simon Chaddock]

My initial selection of the 70 mm EDF was based on its thrust to weight performance which suggested greater than 1 would be achievable.

The use of the smaller 55 was the only way that a practical CofG could be achieved on the A4b.

Compared to my other 'big' scale Depron planes the 46" (1168 mm) long A4b actually looks quite small so the best way to use the 70 mm EDF is to simply build a bigger one!

A 72" ((1829 mm) version should be impressive.

The discussion on the EDF thread "EDF exhaust tubes - why?" has opened up an intriguing proposition.

It has been shown by experiment that an exhaust of just 85% of the FSA raises the 'free air' thrust by 5%. The same also showed that although an FSA sized exhaust tube lost little thrust it did require over 1% more power to do it. This suggests that the 85% thrust tube is actually having to overcome losses before the net thrust rises.

In my 70 mm EDF the motor body extends past the shroud by 21 mm so what would happen if the EDF shroud itself was reduced in diameter over that distance to give an annulus of 85% of the FSA?

Something like this.

Even with the bigger EDF the thrust to weight is unlikely to be batter than 1.3 : 1 suggesting the initial vertical rise would be quite slow. This would almost certainly require control vanes in the exhaust stream coupled to a heading hold giro until sufficient air speed had been achieved.

Not that different to the full size!

Hmmmm1

[Colin Leighfield]

You're going to do it, aren't you?! Either that or a Space-Shuttle.

[Simon Chaddock]

My instinct is that it would be foolish to build such a big scale airframe without having some confidence that the stabilizing system for a slow vertical lift off actually worked reasonably reliably.

Like the full size such a lightweight structure will not be very tolerant to a launch failure!

So what is the simplest to build, lightest and stiffest structure that could emulate a 6 foot long A4b?

I do not envisage a vertical landing so it has still got to be able to fly and land conventionally.

Mi initial thoughts look like this.

A simple square box fuselage with a pyramid nose but with a cone leading to the EDF. The same fins and control surfaces but a simple 'plank' wing of equal area and CofG as the A4b.

With the same rear end it would also develop a suitable launching platform.

If I go ahead with this don't expect any 'failure' videos!

Edited By Simon Chaddock on 16/01/2016 13:12:02

[Simon Chaddock]

Calm(ish) this morning so the A4b had its second flight. A SW wind meant the only dry(ish) part of the field was in the lee of some tall trees so it had to be kept high to avoid the turbulence.

Hard to see but it rolls nicely.

Flew without the gyro for the first time. It tended to lift the nose very readily and adding down trim eat into the longitudinal stability so a bit of nose weight is required. A good example of how a gyro can 'mask' a fundamental issue!

On the final approach I noticed a dog making a bee line for it (the field was empty when I started!) so the final touch down had to be adjusted to full cross wind to ensure it landed close by.

Mud spatter but no damage.

This is not the best weather for 'test' flying. Roll on warmer and dryer conditions!

[Andrew Price 2]

Looks even better, Simon. The tweaks seem to have worked very well.

The dog reminds me of taking my Collie with me whilst I practiced my iron shoots. I had to stop as she was so fast there was a danger that she would actually catch one, as she was seriously trying to do!! How was I going to explain a toothless dog to the kids!