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Aggregate A9 (A4b)

Old 11-12-2015, 08:20 PM
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quorneng
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Default Aggregate A9 (A4b)

Having built a pusher prop scale rocket plane (Bachem Natter) and several EDF jets I wondered if there was a scale rocket that could use an EDF.

The problem is of course that a rocket has no air intake so the EDF would have to rely entirely on cheat holes. It would also be rather nice if they could be covered with spring loaded doors when the fan was not in use!

So what is the Aggregate A9 ?
Its an A4 (the V-2) with wings on!
'Aggregate' in German means machines working together and they actually fired some!

Although officially called the A9 it was referred to as the A4b so scarce resources could be made available for it under the top priority V-2 programme.

My initial thoughts are for it to look something like this.
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A 70mm EDF right at the back (the exhaust tube is then exactly the FSA) with 4 cheat holes positioned between the fins to keep the duct length as short as possible.
No doors to start with and no ailerons either but elevons and rudderons - rudders also connected to act as additional ailerons!

Now if I can build it light enough, 3 axis stability and additional vanes in the exhaust it might even be a VTO tail riser!

The first task is to build just the tail section as an EDF 'test' duct to work out the best way to actually make it and to find out how much thrust is 'lost'.
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I am hoping to keep the complete A4b to no more than 600g (21oz)

We shall see!
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Old 11-12-2015, 08:53 PM
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I've seen a Space Shuttle done as an EDF with spring loaded doors on the sides for the cheater holes.

They were pretty much open even gliding with the motor off, but as soon as it slowed down enough (with motor off) the doors closed and made it hard to find the cheater holes.

Definitely more show than go... It flew but performance wasn't impressive.

So it can be done and look good.
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Old 11-12-2015, 10:16 PM
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A challenging and cool project. Best of luck if you decide to go forward with it.

Question - are you planning on being able to fly it around, like a plane? Or just launch and recover via 'chute? Or ...?
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Old 11-13-2015, 02:17 AM
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If I am right with a thrust to weight approaching unity it will not only fly from a hand launch but should be capable of modest, if rather non scale, aerobatics!
I was concerned about landing but even when resting on the lower fin the point of the nose is still off the ground so it should slide well enough on grass.
It may well end up a bit bigger at say 20" span with very little weight increase so with such a modest wing loading (about 8oz/sqft including fuselage lift) hopefully it won't have to slide very far.
Only if it proves suitably controllable would a standing vertical take off be attempted using a 4s battery.
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Old 11-13-2015, 04:47 PM
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Subbed!
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Old 11-14-2015, 10:39 PM
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A Depron pie funnel.
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Its actually the inner cone of the test duct.
Planked in 2mm Depron over ring formers. It weighs just 7g.
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This is how it sits in relation to the EDF but of course it will not actually touch the fan hub.
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Now comes the tricky bit of creating a structure that not only supports the EDF but includes the 4 inlet ducts leading from the cheat holes. It will involve some quite complex shapes.
I can visualise the sort of thing required but at the moment I have no idea how to actually make it using just 2mm Depron sheet!
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Old 11-14-2015, 11:30 PM
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Trouble designing the ducts?
With your skill in forming Depron?

You'll have it figured out in an hour.
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Old 11-16-2015, 12:23 AM
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All my 'visualisations' of the ducts either were virtually impossible to build or gave a rather poor duct shape.
Anyway I decided to proceed with a relatively easy to build duct shape on the grounds it might provide some insight on the building problems and it would at least it to be tested.
First 4 Depron 'fins'.
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These are the shape of the outer duct skin and provide location for the EDF itself.
The first planks are added over the fins.
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The planks extend right to the end of the EDF body.
Further planks start to form the intake itself.
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A view down one of the intakes.
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The test duct complete.
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Very light yet remarkably rigid.
Only tested at very low power (its after midnight!) to check the direction of rotation but it does seem to 'breath' pretty freely.

This is only a test duct and cannot be used in the final build as it does not have a suitable internal structure to support the tail fins but it has given me some indication on how it can be done and it has also given me some ideas on workable spring loaded inlet doors!
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Old 11-16-2015, 01:00 AM
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I'd have approached it "backward"... building a shell for the outside of the "fuselage" then seeing how to fit the EDF and duct inside.

Looks like you are just a couple of CF tubes away from supporting the fins...
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Old 11-16-2015, 01:31 PM
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Looking forward to the performance report!
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Old 11-18-2015, 12:44 PM
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Due to a fault (my own!) with the 50A ESC I had intended to use I cannot run the test duct at full power. While waiting for the replacement to be delivered I have decided to make a start on the A4b 'flight' version.
First the plan printed out at the required size.
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The 24" steel rule gives an idea of the scale.
A bit bigger than originally planned at 20" (508 mm) span and 48" (1220 mm) long.
I intend to build the nose section in one piece, vertically, in a similar way as I did with my Depron V-1.
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The 9 'ring' formers laid out on the plan.
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All but the smallest have an internal flange so with the planked skin in place they become in effect circular "I" beams.
There will be a lot on empty space inside!

Last edited by quorneng; 11-19-2015 at 12:25 AM.
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Old 11-19-2015, 02:24 AM
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Very nice!
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Old 11-19-2015, 03:01 AM
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Maximum strength from minimum weight... Excellent planning.
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Old 11-19-2015, 11:38 AM
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quorneng
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This is a very odd way to build a fuselage!

The first step of the A4b nose.
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At this stage it is very delicate and wobbly but provided all four planks are exactly the same length it can be 'trued up' as the assembly continues.
Next is to add the remaining formers. Their positions have been marked on the inside of the planks.
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Old 11-20-2015, 11:06 PM
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Next the ring formers are glued in.
Name:  Nose2.JPG
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Then the boring bit shaping & fitting each plank individually. There are 28 all told.
When complete a start can be made on the nose cone.
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Rather simpler to do as it is a constant taper so each plank is just a straight sided triangle.
There is no internal structure so once the model is structurally complete with the EDF and servos in place there will have to be a substantial cut out made somewhere in the nose to fit the ESC, radio and battery to achieve a suitable CofG.

I think the wings will be next on the list.
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Old 11-21-2015, 10:19 PM
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The structurally completed nose section.
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It still needs a bit of filling and gentle sanding.

The wing has one piece skins.
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Fully stressed skin structure with no load bearing spars or ribs apart from one at the C/L and at each tip.
As it has no moving surfaces the whole structure will be as light as possible.

As far as I can tell the wing had a typical 'supersonic' section. Fully symmetrical. a sharp leading edge with its maximum thickness near 50% and pretty thin.
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Old 11-22-2015, 10:20 PM
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The wing internal structure.
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The completed wing.
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The tip section.
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With no ailerons it is pretty light at 34 g (1.2 oz) but it is still well able to support the predicted all up weight (20 oz) at its centre when supported just by its tips.

This is my simple strength test that gives a wing bending load at least equivalent to a 4g manoeuvre.

Fuselage centre section next.
Hopefully the ESC will arrive soon so I can start testing the 'test' duct.
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Old 11-23-2015, 02:49 AM
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Depending on expected performance envelope, I have supported wings at 1/2 distance between root and tip with up to 100X expected model weight on the centerline. (and that wouldn't be enough strength for some of the modern Dynamic Soaring models...)
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Old 11-23-2015, 03:47 PM
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For maximum performance surely the object is not to make it as strong as possible but just strong enough for the intended flight envelope.
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Old 11-24-2015, 12:31 AM
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Just pointing out its not that unusual to do a weight load test.
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Old 11-25-2015, 11:57 PM
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quorneng
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The fuselage centre section is next.
This poses its own problem in that it is actually slightly barrel shaped.
The formers are required to be 136, 138, 140, 142, 140, 138 and 136 mm diameter.
The issue is that with such a gentle curve even a slightly under or over size former would be pretty obvious when the skin was glued on.
In addition simply cutting full circles would use a lot of Depron!
An effective way to create a ring is to build it up from 4 quadrants as each quadrant can be efficiently 'nested' when cut from a sheet.
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To over come the accuracy problem all the formers will be made to the largest size. The required diameter can then be marked with a compass and the edge sanded down.
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One benefit of the formers being so similar is that much broader planks can be used although each plank has to be carefully 'formed' to match the radius.
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Still waiting for the new ESC.
It must be on a slow 747 from China!
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Old 11-27-2015, 11:20 PM
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The first pair of planks.
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Next the top former then the intermediate ones.
14 planks later (and a day and a half!) it looks like this.
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Having completed it the next operation is to virtually cut in half down the middle to create 'slots' for the wings to slide in.
It took quite a bit of repeated fitting and sanding for the slots to achieve the correct shape but got there in the end. The nose is just resting in place.
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Although this represents nearly 2/3 of the complete structure of course all these parts are 'dumb' with nothing inside.
The tail section on the other hand not only is it a much more complex shape with the intakes and four fins but it also requires quite a bit of the electrics and wiring to be built in as well.
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Old 12-01-2015, 12:48 PM
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A start on the tail section.
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Built in the same way as the others although the big change in diameter from front to back means each plank has a very specific highly tapered form.
The result is a large amount of offcuts and Depron sanding dust to achieve the correct fit.
Next to it a stack of the 8 fins skins.
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Old 12-01-2015, 10:36 PM
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Looking really cool, sir!
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Old 12-02-2015, 12:32 PM
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At last I have run the 'test' duct under full power.
It looks like it could have been designed for those kitchen scales!
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On a 2200mAh 3s it draws:
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giving:
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It generates 26 oz (737 g) of thrust.
So far so good and it is still on course for 20 oz all up weight so it should have 'adequate' oomph!
However at 43A it will need a good high 'C' battery if its capacity is say only 1500mAh.
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