The A4b - a V-2 with wings on!

[Simon Chaddock]

As I discussed in the EDF topic I wanted to see if I could make a scale EDF "plane" that had no inlet at all.

The winged V-2 seemed a suitable subject in that it is instantly recognisable as a rocket, was actually flown (just) in winged form.

It was actually built and tested twice right at the end of the war, although not very successfully.

To fly as a reasonable RC plane with its limited wing area it will have to make extensive use of the lightness of Depron.

Using a 70mm EDF positioned right at the back and occupying all the available fuselage diameter the A4b comes out at 48" tall with a span of 20".

My intention is to keep to the scale control surface configuration with convention elevons but to add aileron control to the rudders as well - rudderons?

As I have no idea how the EDF will behave using only cheat hole inlets the first task is to build just the tail end of the fuselage as a test duct. It will look something like this.

The 70 mm AEO EDF delivers 690g (24 oz) on a 3s so the test duct should give an indication as to how much static thrust is lost by the inlet ducting.

I hope to get the all up weight to close to 20 oz so with a thrust to weight close to unity it should have an 'adequate' performance as an RC plane! .

[Stephen Jones]

Hi Simon,

Good Luck with this one you don`t make things easy for you're self do you.

Just a thought you could try using a mesh material rather than a hole.

that way the structure would look the same as the body if painted black .

Steve

[mightypeesh]

Wow - not seen this before, I think Gerry Anderson had though!

Interesting project for sure. What sort of flying pattern do you invisige though. Being a missile would it not be,

• launch
• fly very quickly in huge arc to target
• 'land' nose in and explode?
• 

Good luck, Cheers, Simon

[Simon Chaddock]

Stephen

I think you would find at the tiny pressures used in an EDF duct the airflow through a mesh would only a small fraction of an open duct of the same dimensions.

A start on the test duct

No its not a Depron pie funnel but the core of the duct!

In position in front of the hub of the EDF.

Of course in the completed duct the cone will not actually touch the EDF hub.

[Simon Chaddock]

 

The EDF now supported by 4 fins.

Note the planking goes right to the end of the EDF body.

The exterior planking showing a completed inlet.

No great science involved, just a compromise between area of intake and structural strength.

The view down one inlet.

It is only a test piece to simply test the aerodynamics of the inlets and the method of EDF installation.

It does not have the appropriate internal stiffness to carry the big external fins particularly as they will also be carrying all of the aerodynamic control surfaces.

It does look more or less like I intended and it is very light at just 15g.

All that is now required is to test it

Edited By Simon Chaddock on 02/12/2015 10:38:11

[Stephen Jones]

Hi Simon ,

Those are big cheat holes .

While caring out you`re tests, could you wrap some thin wire mess over those holes , just to see how much reduction in thrust there is .

Steve

[Simon Chaddock]

It is probably wrong to call them cheat holes. I did so simply because there is no 'direct entry' duct.

It would probably be more correct to call them 'submerged inlets'.

I have done a bit of testing.

On a 2200mAh 3s it draws 44 A showing 421W. and generates 26 oz (737 g) thrust which is surprisingly close to its 'free air' figures of 45 A and 462 W suggesting the duct is not costing that much performance..

In any case if the A4b's target weight of 20 oz is achieved it should have plenty of ooomph as a simple RC plane!

[Simon Chaddock]

 

To achieve anything like a 20 oz all up with a 70mm EDF the A4b has got to built very light indeed.

My favoured solution to this problem is Depron planking over 'ring' formers to create a hollow stressed skin structure.

As the A4b body is circular creating the ring formers from the plan is relatively easy. It will be built in 3 sections, nose, centre - carrying the wings, and the tail which has to hold everything else!

First the nose section. Its significant taper has the advantage that the smaller formers can be cut from the 'centres' of the larger ones.

The larger formers have an inner flange so when the skin is in place they in effect become circular "I" beams.

With a truly symmetrical structure it is possible to built it vertically and as one piece.

It looks a ridiculous way to build what will become a load bearing structure and it is very wobbly to start with but the end result is structurally very efficient.

Next the formers are glued into place. Their exact position has been marked on the inside of each plank.

Of course each plank has to be shaped so it covers the same proportion of every former. A rather slow and tedious operation creating quite a bit of Depron dust. To make matters worse sanding gives each particle a electrostatic charge so it gets (and sticks) everywhere!

Edited By Simon Chaddock on 03/12/2015 16:45:57

[Simon Chaddock]

The nose section planking (all 28 of them!) complete.and a start on the actual nose cone.

The nose is a 'right' cone so each plank is just a simple triangle.

It weighs 0.85 oz (24 g)

Next is the middle section which will carry the wings.

All the formers are similar but it is slightly barrel shaped so are 136, 138, 140, 142, 140, 138, 136 and 134 diameter. Cut as a complete ring would use a lot of Depron so each was made up from quadrants..

As before each has an inner flange.

Edited By Simon Chaddock on 04/12/2015 16:46:40

[Daithi O Buitigh]

Just as an aside (and totally irrelevant) the design of the body was based on the bullet of a Kar98

Edited By Daithi O Buitigh on 04/12/2015 17:08:24

[Simon Chaddock]

I understand the fuselage of the Bell X-1 was based on the 50 cal machine gun bullet.

Edited By Simon Chaddock on 04/12/2015 23:25:09

[Andy G.]

Following this thread with interest!!

[Simon Chaddock]

The 'set' of formers for the centre section.

I judged it would be very difficult to build the formers in Depron with sufficient accuracy from quadrants so all were actually built slightly over size, the correct diameter marked with a compass and each then sanded down.

Accuracy was going to be important as with such a gentle barrel shape even a tiny error would be very obvious.

One advantage of being near parallel is that much wider planks can be used, probably only 16, although each has to be curved to match the former radius.

A start on the centre section.

At about this point I tell myself "this is definitely the last time plane I am going to build this way" but it never seems to be!

Edited By Simon Chaddock on 05/12/2015 10:26:39

[Colin Leighfield]

You never fail Simon, this will work. Seeing the notes about bullet shapes, the Miles M52 used the aerodynamic data available from research into ballistic rounds/shells. The shape of the wing tips was designed to fit exactly into the shock wave generated by the nose at supersonic speeds. Don't think you'll need to worry about that though, in fact this might turn out to be quite a floater!

[Daithi O Buitigh]

I just hope you don't adopt the sub-title of the autobiographical movie on von Braun called "I aim at the Stars" (but sometimes I missed and hit London)

[Simon Chaddock]

The centre section complete.

As I hoped it only needed 16 planks rather than the 28 used on the nose.

The wings have no ailerons, are symmetrical and rather thin so will be made with one piece skins over Depron spacers.

The wing complete.

Despite having no spar the wing is quite capable of carrying the anticipates full weight (20 oz) at its centre when supported only by the wing tips. This is my 'rule of thumb' test that is more or less equivalent to a 4g manoeuvre.

Having just competed the centre section it has to be almost cut in two to insert the wing.

A delicate operation requiring repeated fitting and sanding but eventually got there.

This complete section now weighs 1.25 oz (35g).

[Dave Hopkin]

Lovely "designmanship" and workmanship Simon, but yet again reading your builds I suspect you have a secret team of elves making those delicate structures.......

[Mowerman]

I doubt if Simon employs elves, just think having the chief elves and safety man there all the time

[Simon Chaddock]

I set the "elves" to work on the tail section.

Built as before but the 'Ogee' shape made forming the planks a bit of a trial.

The last plank!

It does show the rather extreme shape of each plank.

Finished it looks a bit like a Depron wine bottle!

The fins are similar in construction to the wings.

When fitted to the tail section they support the EDF.

Additional EDF support will be provided by the inlet ducts them selves.

[Andrew Price 2]

Simon, you just don't do easy do you?

[Simon Chaddock]

Now comes the tricky bit arranging the inlet ducts.

For the 'flight''version I will make the inlet longer and narrower with the duct itself gradually changing to a quadrant..

Between the fins they are not that noticeable.

Now I have just got to do the other 3 the same.

Edited By Simon Chaddock on 07/12/2015 23:12:14

[Simon Chaddock]

Next comes the servos, one for each fin.

The fins are virtually the same thickness as a 3.7g servo so they can be inserted through a shaped cut out in both skins. The servo wire runs inside the fin into the fuselage.

The scale control surfaces with a substantial overhang would be very vulnerable to damage on a model and in any case the low control surface would have to be cut back to allow for a belly landing.

So I have decided to cut them all back the same.

It does reduce the area by nearly 40% but at least they now stand a chance of surviving nore than one flight.

The control surfaces have a home made pin (literally) hinge at each end.

The pin is driven into the balsa leading edge although the excess length is cut off before final installation.

Very light and free moving.

Just the other 4 to do!

[Simon Chaddock]

I thought it was about time I stacked the bits on top of each other to get an idea of what it would look like.

Its actually not that big. I am beginning to wonder if I shouldn't have made it 25% larger (60" long, 25" span) or used a smaller lighter EDF.

I don't think I could face doing all that planking again but it would be just about possible to put in a smaller (64mm?) EDF.

Maybe during the rebuild after its first crash!

Edited By Simon Chaddock on 10/12/2015 01:04:30

[Dave Hopkin]

Coming along at a speed there Simon, just as well, Santa needs those elves back pretty soon!

[mightypeesh]

Looking great there simon. I know you will have been asked this a million times already - what adhesives do you use on these builds - Is it all uhu por or are there other ones in the mix?

Cheers, Simon