Electric Ducted Fan Jets Discuss electric ducted fan jets here including setup tips, power systems, flying techniques, etc.

Aggregate A9 (A4b)

Old 12-02-2015, 02:07 PM
  #26  
pmullen503
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Any idea what that fan would draw (thrust) in a more open installation?
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Old 12-02-2015, 04:58 PM
  #27  
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The EDF has now been extracted from the test duct.
In free air (held in my hand ) it draws 46A (466W) but the 'resting' voltage of the battery was slightly higher so presumably it had a slightly higher state of charge.
This result does suggest the 'cheat hole' ducting is not costing that much performance and probably little more than 'normal' ducting of the same length.

Just out of curiosity I repeated the free air test with the 2200mAh fully charged (4.2V per cell) and it showed an alarming 53A (535W). That would translate to over 400W/lb.
I am beginning to think that EDF is almost too powerful!
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Old 12-04-2015, 03:52 PM
  #28  
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The EDF mounted on the 'flight' tail section.
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at this stage the EDF is held in place just by the fins but there will additional support when the inlet duct is installed.
I have also stopped the duct diving wall some 20 mm short of the fan blades to both reduce the 'siren' effect and hopefully improve the efficiency a touch.
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Old 12-04-2015, 04:06 PM
  #29  
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Awesome!
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Old 12-05-2015, 04:23 PM
  #30  
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The inlets have a slightly different shape to the test duct.
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The inlet now maintains the same width as it gets deeper but gradually changes the cross section to a true quadrant at the same time.
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It should 'breath' just as easily as the earlier one but is less obtrusive, indeed when in flight hopefully they should not be visible.

Now just the other three to do on what is quite a tedious "fitting" job!
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Old 12-05-2015, 04:50 PM
  #31  
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A bit of yes and no about the duct "breathing". As speed increases that should work better, but it might starve the fan a bit at low speed.

Its a fairly common issue to deal with and shows up mainly as lower available thrust at high throttle than midrange when doing a static thrust test. something which you can get with any EDF even without ducting issues. Often we'll have a faster takeoff run at half throttle than full.
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Old 12-05-2015, 05:25 PM
  #32  
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Testing so far has confirmed that the static thrust is proportional to current suggesting that the fan is not being unduly constrained by the inlet ducting. There is of course no exhaust duct.
My concern is not so much the static thrust but by how much the inlets will be shielded by the larger diameter fuselage ahead of them.
There will be little or no ram effect indeed at speed the effect could be the opposite.

The saving grace is that with about 2 sqft of effective wing area the loading will be a modest 10oz/sqft so it won't have to fly particularly fast.
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Old 12-05-2015, 09:09 PM
  #33  
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Looks great! Should be another winner.
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Old 12-06-2015, 05:43 PM
  #34  
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I thought it was about time I stacked the bits on top of each other to see what it would look like.
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Its not actually that big. I am beginning to think I should have made it 25% bigger! i.e. 60" long, 25" span.
But I don't think I could face doing all again.
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Old 12-06-2015, 09:54 PM
  #35  
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Pretty sweet. Roll will be accomplished with the tail fins, right? How many servos? Elevons, Rudd-evons?
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Old 12-06-2015, 11:05 PM
  #36  
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Yes a servo in each fin.
Horizontal pair as conventional elevons, vertical pair as rudder and ailerons (rudderons?).
I intend to use stand alone mixers to do it so, if and when, a gyro radio is used (for vertical take off ) it will only 'see' conventional aileron, elevator and rudder connections.
A VTO is also likely to require control surface extensions into the exhaust stream as well - just like the full size!
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Old 12-07-2015, 05:32 AM
  #37  
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VTO would be impressive! Where do you put the CG on this thing? Swept wing and a disproportionally large horizontal stab.
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Old 12-07-2015, 05:51 AM
  #38  
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Originally Posted by pmullen503 View Post
VTO would be impressive! Where do you put the CG on this thing? Swept wing and a disproportionally large horizontal stab.

I would do the balance for a Canard. Find 30% MAC for both the fore-planes and tail-planes. Measure the distance between

Take the wing area of the fore-plane and the area of the tail-planes and treat them as weights at the ends of a beam of the distance separating them. Find where in the middle to place the pivot for that to balance.

That is the aft CG limit.

Perfect for canards and tandem wing aircraft.

Note that it has the tail-planes sharing the lift, so there are potential issues with stall/spin recovery. A canard depends on the tendency of a smaller wing to stall before a larger one. A tandem wing doesn't have that to aid in preventing or recovering from a spin.

It would probably fly with CG as far forward as 30% MAC of the main wing, giving this thing a VERY large CG range.

*********

There's a test we used to do with the little Estes rockets where we'd hang the thing in a string so it balanced then swing it in circles and see if it tumbled or assumed a proper nose-forward attitude...
If it would "fly" that way with an un-used rocket motor it would hold a vertical track on launch.
You might experiment with that and a miniature of the model.
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Old 12-07-2015, 01:45 PM
  #39  
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As I am more interested in it 'flying' capabilities than anything else I will almost certainly build a half size profile chuck glider in 6 mm Depron which what I did with my Concorde.
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It not only gives an idea of the the likely CofG but also what is likely to happen if it is a bit too far back.
It is an interesting point about how much the tail will act as a Delta lifting surface but then the area of the fuselage will have an input as well.

This proved to be a significant issue with by Bachem Natter with its CofG ending up at just 20% chord.
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And even then it tends to rear up at high angle of attack!
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Old 12-09-2015, 12:49 AM
  #40  
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I have been considering this for a couple of days.
The scale control surfaces have a big overhang which would make them very vulnerable in a model plane.
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In any case I would have to cut the lower control surface back to allow a belly landing.
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So I have decided to cut them all back flush with the fin. It does reduce the area by nearly 40% but should still be big enough.
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Each has two pin (literally) hinges.
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The pin is driven into the balsa leading edge although the pin is cut short before installation.
Simple, free moving and very light.
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Old 12-12-2015, 11:41 AM
  #41  
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With all four surfaces installed along with the horizontal and vertical mixers a full control test.

As everything but the battery will be permanently 'built in' each fuselage section has to fully complete and tested before it can be joined to the next. There is no easy going back if something has been overlooked!
Next are the long motor to ESC wires.
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Old 12-12-2015, 10:39 PM
  #42  
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An amazing build, sir.
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Old 12-13-2015, 02:54 PM
  #43  
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As they are so long (24", 620mm) the motor wires are actual solid 'magnet' wire which is polyurethane insulated. For the same copper cross section it is only half the weight of normal multi strand silicone insulated type.
They run externally for a short distance along the base of the lower fin before entering the fin and passing into the fuselage.
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They then run along the bottom through the formers.
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It all a bit ungainly as the wires have to be long enough to reach right up to the nose where the ESC and battery will be. The problem is the exact position of the battery is not yet established!
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Old 12-13-2015, 09:36 PM
  #44  
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Consider small ply plates so you can screw the sections together and thus be able to take off the front for access to that cavern.
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Old 12-19-2015, 08:52 PM
  #45  
quorneng
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The Orange 3 axis radio and the stand alone mixers are wired up together in a Depron Box.
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The four servo leads plug into the front, the ESC plugs in through the top.
This box will be glued onto the wing at the CofG.
As the gyro gains will need to be adjusted (and possibly to re bind the Rx) a hatch is provided in the fuselage above the wing.
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The centre and rear sections could now be permanently joined.
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With just a small internal flange it is a simple "skin to skin" joint to ensure it has the same strength and stiffness as the rest of the monocoque structure.
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Old 12-21-2015, 12:14 PM
  #46  
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At last the nose can be fixed on as well.
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With an access hatch over the radio the basic structure is complete.
A substantial 'opening' will have to be made in the nose to install the battery box and the ESC.
It will then be made good leaving just a 'minimum' battery hatch.

The next task to to try and ascertain where the CofG should be as this will determine the exact battery position.
As the EDF version is not really robust enough to survive much 'testing' a simple 1/2 size 'profile' chuck glider made of sheet Depron is a cheap & practical way to proceed.
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Old 12-21-2015, 12:23 PM
  #47  
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Reduced the tailplane size by chopping the control surfaces... its going to be close to 30% MAC of the main wings

Maybe a little ahead of that.

BTW... looks a lot like the ship from the movie "When Worlds Collide"

http://www.imdb.com/title/tt0044207/ See 4th photo
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Old 12-21-2015, 04:27 PM
  #48  
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30% MAC may well be right.
The concern is the the 'tailplane' is in effect a low aspect ratio 'delta' in its own right so could provide some lift that would be a long way behind the wing.
Then the relatively big fuselage will also generate some lift and heavens knows where the CofP of that will be.
Perhaps even more important is the effectiveness of the elevators. The tail surfaces are very close coupled although the elevators are a reasonable distance back.
Finally there is the issue of how it behaves at the stall and the recovery.
I hope the chuck glider will provide some confirmation on the above.

I had the same problem when I built my scale Depron Concorde. In that case the half size chuck glider demonstrated not only a likely CofG but also its remarkably benign gliding characteristics.
An important issue when you are about to hand launch an EDF that has taken lots of hours to build yet has zero crash resistance and marginal power!
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Old 12-21-2015, 06:39 PM
  #49  
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Looks great!

But I wonder how easy it will be to keep it level in the roll access. It looks like it will have a wicked roll rate and without dihedral, will have no way to "self correct". Maybe a gyro to damp roll rate (or even a "failsafe" type to level the wings) might be a good precaution.

Either way, a good paint scheme is a must for good visual orientation.
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Old 12-22-2015, 08:00 PM
  #50  
quorneng
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The chuck glider was remarkably simple to make just 10 pieces - and that includes the 2 elevators.
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Made of 3 mm Depron it weighs just 0.8 oz (23 g) so it should survive 'test' flying. The 'rudders' are part of the fuselage but the elevators are 'bendable'.

It would appear that the German rocket team knew what they were about as it actually flies quite nicely!
The swept wing seem to give reasonable roll stability despite having no dihedral.
Without any elevator reflex the CofG is quite critical to achieve longitudinal stability. Just a bit back and it virtually 'parachutes' down, too far forward and it 'lawn darts'!
With some up elevator the CofG can go forward but as I feared they are not very effective and may explain the shape used in the original.
The chuck glider seems to work best with a touch of up elevator and a CofG at 40% of the wing root chord (where the wing enters the fuselage).
However I suspect the cruciform fuselage actually gives a bit more lift than the scale round one so for the EDF version it will be set a bit further forward, say 37%.
Even this may be a bit 'rearward' but on such a fragile plane a stalling tendency is easier to manage than running out of elevator authority.
The 70 mm EDF cut out.
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Now to start rebuilding the rear end but with a 55 mm EDF!
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