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Aggregate A9 (A4b)

Old 12-23-2015, 11:37 PM
  #51  
quorneng
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The 55mm EDF starts to go in.
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The hub of the 55 is exactly the same diameter as the 70 so the inner part of the duct is unchanged but it will take a bit thinking how best to blend the outer surfaces to meet the EDF bell mouth.
As the actual inlets are unchanged and the 55 mm has just 55% (coincidence?) of the 70's FSA the duct losses should be just that bit lower.

Last edited by quorneng; 02-14-2016 at 10:44 AM.
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Old 12-25-2015, 12:07 AM
  #52  
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The 55 mm EDF installation completed.
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The 70 mm EDF occupied the entire of the rear surface.
From this view the 55 mm EDF installation looks identical as before simply because the same inlets are used.
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It does however require a bit of extra internal ducting to smoothly meet the smaller fan casing.
It looks like the lighter EDF will enable the 1500mAh 3s LiPo to be used but it will have to be squeezed in right at the front to achieve the required CofG.
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Old 12-30-2015, 12:19 PM
  #53  
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The nose opened up to give access to install the battery and ESC.
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Both will have to go right forward to achieve the desired CofG.
Being an EDF the ESC has to work quite hard and will have no forced cooling so it had been given a new, fingered heat sink that has many times the heat dissipation capability of the original.
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The ends of the fingers have been 'contoured' to match the fuselage profile and will stick out a couple on mm in to the air stream.
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Old 01-02-2016, 06:32 PM
  #54  
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The motor wires neatly secured along the bottom of the fuselage.
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The heat sink mounted along side the battery with its fins just protruding into the air stream.
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The rebuilt leaving a long battery hatch to slide the battery right up to the nose and to give space to make the connection.
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Both the radio and battery hatches are secured with small magnets.
Finally black paint.
Not quite true to scale. The original checker board arrangement was to highlight any rotation but as a plane be able to identify "the right way up" is more important so the scheme has been altered so all the undersides of the wing and fins are black as are both sides of the vertical fins.
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The final issue to be addressed is how to hand launch it. There is nothing to hold on to!
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Old 01-04-2016, 09:59 AM
  #55  
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That's looking amazing. Grab it on the belly with a finger behind the wing, maybe? Make sure you get some video!
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Old 01-04-2016, 10:40 AM
  #56  
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The problem is the fuselage is to wide to get a grip.
I had exactly the same problem with the V-1 - its fuselage is virtually the same diameter - so I will adopt the same solution.
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Two stout fuselage strakes positioned just ahead of the CofG so they can be gripped comfortably between the thumb and 2,3 & 4th fingers with a shallow 'indent' just behind for the tip of the index finger.
The thumb and fingers provide a steady support leaving the index finger to provide the "push" on the launch.
Being all Depron it adds very little weight and negligible drag.
The only issue is because of the lower fin on the A4b the strakes do not touch the ground when at rest whereas on the V-1 they act as 'skids' during the landing slide.
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Old 01-11-2016, 10:56 PM
  #57  
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This is how it is held to launch.
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And this is the result!

I make no apologies for keeping rather high initially (this is its maiden flight!) so there is not much to see at times. It is a bit better in full screen.
It glides really quite well but then it was intended to!
With the appalling weather over the last 3 months I am rather out of practise so just one short flight, quit when ahead and wait for things to improve before exploring its characteristics further.

Last edited by quorneng; 01-12-2016 at 10:58 AM.
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Old 01-12-2016, 01:09 AM
  #58  
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Congratulations!
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Old 01-12-2016, 02:41 AM
  #59  
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Looks like it flies nice! Do you have enough thrust to do a vertical ROG?
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Old 01-12-2016, 04:16 AM
  #60  
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Wouldn't that be more of an SOG?
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Old 01-12-2016, 10:56 AM
  #61  
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Thank you each for the kind words.

At the moment its thrust is less than its weight so no vertical.
I believe it might be possible using 4s but the neither the fan or motor are rated for such although it might just be able to sustain it for a few seconds. It would also need a very high C 1200mAh battery as well.

The real problem is the 55 mm EDF itself. It was a bit of a last minute job to change over from the 70 mm so I only checked it worked rather than worry too much about its balance and sods law it has about the worst balance of all my EDFs!
I fear it would break up (as others have found!) if run on 4s. It would need a new ESC as well.

So for a VTO it would really need another A4b to be built (possibly bigger!) using an EDF and 4s battery combination that had been bench tested for both duration and thrust levels.
It suspect it would also need a gyro stabiliser unit with a switch-able 'heading hold' option along with small control surface extensions into the exhaust stream. Overall not far removed from the system used in the original!

However its one thing to think about it, quite another to actually attempt it!
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Old 01-22-2016, 11:46 AM
  #62  
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Just to show things do not aways go as planned.
Flew again with the intention of flying low enough to get some good shots for the camera. All went well until.......

Still not quite sure why it did what it did. Did some thing go wrong? or was it me?
I made a 1/5 speed 'slomo' of the actual crash but it was really too far away to see the position of the control surfaces.

Fairly seriously damaged but one advantage of a full stressed skin monocoque construction is the stresses at any point are low so provided the glue is adequate the broken bits can be simply glued back together.
In the course of the repair I noted that two of the servos (LH elevon & lower rudderon) had suspect gear trains.
With the smaller EDF the torque at launch is not a problem so I decided to simply remove the lower rudder servo altogether and fix the control surface.
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The LH elevon servo was replaced.
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Not a simple task as the servo and its long wire were completely built in.
Finally the Orange RX3SM refused to bind. Went through the correct sequence but instead of the LED coming on continuous it simply went out! The gyro still worked.
The rx was replaced with a non gyro Rx so it is now all back together
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Next calm(ish) day we try again and keep a bit higher!
Atleast the A4b is doing what I intended -finding out what works (and what doesn't!) so if I ever build another ..........
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Old 01-27-2016, 03:52 PM
  #63  
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And what found out was Don't fly an A4b without a gyro!
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Well that is actually a bit of a simplification as it did fly but control was difficult, there was a bit of a breeze and I continued to "try to get it back" when I should have landed before it got too far away!
The result it went out of its park fly radio range and it disappeared behind some tress.
Fortunately it stands out quite well in the middle of a golf fairway!

The poor control was due to the modified control layout - a fixed lower rudder, upper rudder connected as an aileron. This gave the effect of severe adverse aileron yaw which when coupled with the EDF torque meant it would not turn right!
I would have done better to have to have just left the rudder as a rudder!

The twice repaired nose is now too badly damaged to be repaired again so it has been completely cut away to the original construction joint.
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The monocoque Depron structure did its usual excellent 'crumple' job so the rest is completely undamaged and all the electrics are operational.

All that is required is another new nose, a gyro and some control 'tweaks' .
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Old 01-27-2016, 09:13 PM
  #64  
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Man. It's always somethin', ain't it?
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Old 01-29-2016, 12:27 PM
  #65  
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A start on the new nose (its the third!).
The nose ring formers.
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Built vertically as before.
Very wobbly as this point
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Once the full set of formers are in the planking can start in earnest.
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As it now can be handled the intention is to build in the battery box and mount the ESC before the planking limits access.
On the original build the nose was completed and then cut open. Although this worked well enough it did seem rather brutal!

Last edited by quorneng; 01-31-2016 at 07:36 PM.
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Old 01-31-2016, 07:51 PM
  #66  
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The ESC mounted before too much planking is added.
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The battery box built in. With the improved access it can be better integrated with the structure than before.
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As the motor bullets have to be reconnected the nose has to be glued in place whilst there is still sufficient access to get at them.
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A quick check that the fan blows the right way and the motor wires can be secured in the fuselage.
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The planking can now be completed.

Last edited by quorneng; 01-31-2016 at 10:03 PM.
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Old 02-07-2016, 11:49 AM
  #67  
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Now complete - again!
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With only two servos the radio installation is admirably neat and simple.
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Just need some suitable weather to try again.
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Old 02-07-2016, 12:57 PM
  #68  
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Well done with the repairs. Better than new!
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Old 02-11-2016, 08:05 PM
  #69  
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First really calm day today so after its major rebuild it had its re-maiden.

Still not the easiest thing to fly - some of those more erratic manoeuvres were not completely intentional - I would probably benefit from a touch more nose weight.
Interesting it developed some gyro wobble - both the roll and pitch gains were set a maximum - so the roll gain will be turned down. With the heavy battery and EDF at the extremities of the fuselage I doubt pitch wobble will ever be problem.

Nevertheless the important bit was it went home without any damage apart from a small mud stain on the fuselage!

I would like to achieve a good few more flights with it to explore its flight characteristics.
A true 'vertical riser version' will have nearly twice the thrust to weight so is likely to be even more of a handful.

Last edited by quorneng; 02-14-2016 at 10:43 AM.
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Old 03-19-2016, 07:18 PM
  #70  
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On the calm days I have done quite a bit more flying with and without the gyro.
I have also added 30% expo on the elevator to reduce its 'twitchyness' a bit.
Still not the nicest thing to fly but it is quite capable of modest aerobatics.

As it now seems to be able to be flown repeatedly without damage I feel I can make a start on the bigger and much more powerful 'vertical riser' version!
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Old 06-24-2016, 03:45 PM
  #71  
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So next is the larger and more power "vertical riser" version using the abandoned 70 mm EDF which can for short periods be used with a 4s and generates about 45 oz thrust.
If the all up weight can be kept below say 30 oz (twice the weight of the smaller A4b) a vertical take off should be possible.
The issue is the control and stability during the critical initial part of the take off before the aerodynamics become significant.
I built this simple test rig to test a possible configuration of a 3 axis 'heading hold' gyro.

Note in this mode the servo arms maintain their deflection until the initial attitude is returned.
It does have limitations as any 'stick' input simply causes the gyro to take up a new heading hold attitude.
This means the gyro would have to control the take off and then switched back to ordinary 'stab' mode before any stick input is made.
This could be difficult to do in practise!
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Old 07-07-2016, 04:32 PM
  #72  
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To cut a long story short I built another A4b 25% bigger so it could carry the 70mm EDF without too high a wing loading.
Built in the same way as before and keeping with 2mm Depron meant it was proportionally lighter and even less crash resistant!
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The tail surfaces use long snakes so the 5g servos are positioned just ahead of the wing.
The battery is an 1800 mAh 30c 4s
Ready to go it weighs 24 oz (680 g)
For a vertical take off it sits on a simple stand.
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The only issue is it can only do this is really calm conditions!
The power figures are a bit frightening.
58 A 824 W (that's 568 W/lb!) and 42 oz (1190 g) thrust.
For safety the maiden was a hand launch and at rather less than full power.

The flight was kept short as I was not at all confident he electrics would hold together.
It was actually much easier to fly than the smaller A4b!
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Old 07-11-2016, 03:02 PM
  #73  
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With more really calm weather I plucked up courage to do a 'vertical' take off.

It proved to be a bit of a non event - it just went up!
As I was not sure about the 'heading hold' feature the take off just used gyro 'stab' with the result it rolled a bit initially from the motor torque.
In retrospect this roll might actually be an advantage as it would tend to neutralise and thrust line issues!
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Old 07-25-2016, 07:41 AM
  #74  
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Always interesting and informative to follow your builds...awesome project and congrats on the successful VTO....great job!
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Old 07-25-2016, 06:24 PM
  #75  
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DEG
Thanks for the compliment.

For its second VTO flight I left everything as it was but went a bit higher.

After the burst of power for the VTO (824W!) it actually flies on only 1/5 of that so can cruise about for quite a time.
It is remarkably well behaved, in fact the gryo was only used for the launch and the landing, the rest of the time it was switched off.
It does require very calm conditions for a VTO.

The next task is to see if I can find a way of eliminating/reducing the initial torque roll on take off.
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