Tony's BIG Concorde build page

Flying the Concorde that I built winter 2009/2010 (details here) is great. It does fly well and looks very majestic. The only niggle I have is that it turns into a small white dot in the sky very quickly, which means you can't fly it more than a few hundred yards away. I do like to fly further and higher than that so the logical solution is to build something bigger so it can be seen (and controlled) from further away.

During winter 2010/2011 I started building a 150% size copy of that Concorde. This means the new Concorde will be approx 90 cm wide, 180 cm long, and it will have sufficient room in the engine nacelles to fit EDF55 electric ducted fan units. Using the same plans, same materials etc. The only difference is the propulsion (electric ducted fans instead propellors) plus I have added some lights. Here is a summary of the build of what I've now called "BigC".

General building

The plan used was exactly the same as the other Concorde, scaled to 150% size by means of a photocopier. 6mm depron is used, a 6mm carbon fibre reinforcement rod; glues used are UHU POR, Aliphatic resin, superglue, and 30 min epoxy.

	Here is a size comparison, showing both nose cones on the left, and a side-by-side comprison on the right.
	The wing is scaled up in size but not in thickness; it still consist of 2 sheets of 6 mm depron glued together, trapping in between them the wiring and the 6 mm carbon fibre rod. I also fitted a strip of pine wood to the leading edge again, as it gives a neat finish and adds some strength.
	The model is approx 180 cm long, nose to tail. To make transport easier I've made the nose cone detachable. This could well be the world's first model Concorde with detachable nose cone ! Using epoxy glue I fixed 4mm dia aluminium tube to the four inside corners of the nose cone, and then superglued short 4mm carbon fibre rods inside them. On the fuselage side it has the same aluminium tube, into which the carbon fibre then fits (not glued on this side!). As the nose cone carries nothing but its own weight this is suffiently strong. I also hope that in the event of a crash the nose will break away cleanly, limiting the damage to the fuselage.
	Just for fun I also added navigation lights. This is the one on the left wing tip (before painting). That one is red, there is also a green light on the right wing tip, a white light under the nose cone, a white flashing light on top of the cockpit and a red flashing light just in front of the tail. The lights can be switched on and off with the radio control. Here's a short clip of it at dusk.

Propulsion

	The size of the model was deliberately chosen so that the engine nacelles would be big enough to hold an EDF55 unit and here it is. On the left is the view from behind, showing the EDF itself (black), the aileron servo (blue) and the speed controller (yellow). The motor/EDF combination uses approx 180W when the fan is running around 45,000 rpm. On the right is the view from the front, which is the air intake. The top and bottom of the fan shroud is sunk 2mm into the depron which adds to its strength.
	There is an EDF unit in both engine nacelles.

Finishing

April 2011 - finishing the plane, are a few bigger pics of the result to date, hope you enjoy the result so far.

Test flight #1

June 2011 - after a long wait the conditions were finally right. Made the final checks at home and took the big C to Chobham Common. After final checks on-site I slowly opened the throttle until it was fully open and then launched her in the air with a firm and steady throw. She stayed level but instead of taking off she slowly glided back down to the ground. I checked the inlets, outlets and controls but everything looked OK to me. A second attempt had exactly the same result. As if the engines didn't have any power. I decided to leave it at that, packed up and went home. Time to do some more thinking.

T-h-rust me, I'm a Concorde !

In the weeks following, I did some measurements and lots of online research. The 2 EDF units were together producing approx 500 gr of static thrust at almost 500W, or 1 gramme of thrust per Watt , which is nowhere near as efficient as it could be. Also 500 gr thrust on a 1700 gr plane equates to less than 30% thrust/weight ratio, well short of the 40-50% guideline. Consensus on the various forums seems to be that both the outlet duct and inlet duct need to be as smooth as possible. So that's what I worked on first.

The servos and the ESCs were moved from the inside of the duct to the outside, and I made a tube from clear acetate (for overhead slides) which has a super smooth surface. This tube takes the air from the outlet of the EDF to the end of the duct, see pictures below; 'before' is on the left, and 'after' is on the right.

This took the thrust per engine up from 255 gr to 365 gr, which is a 43% increase.

Next I decided to repeat what I had done for my Learjet a few years ago : make the 6-bladed EDF propellor into a 3-bladed one by carefully removing 3 of the 6 blades. Result was that thrust remained the same but instead of drawing 23 Amps that same thrust now took 19 Amps, which is a 21% improvement.
I also made a little cone for the back of the motor but that made no measurable difference.


I also added a tube to the inlet to see what difference that made :

Result : thrust up from 365 gr to 415 gr for one engine, another 19% of the original, making a total thrust improvement of 62%.
During testing one of the fans came off and was damaged so I had to order another EDF unit. This was a slightly different design which proved less efficient. Total thrust is now 725 gr which makes a thrust/weight ratio of 725/1700 = 42% which *should* just be sufficient.
Efficiency is now 725/380 = approx 1.9 gr/W, nearly twice as efficient as before.

Test flight #2

Next opportunity for a test flight was on 29 July 2011. Off to Chobham Common where there was a slight steady breeze. First attempt resulted in a long glide again, about twice as long as that very first attempt in June. For the second attempt one of the other model flyers launched it with both hands leaving my hands free to control the plane through the launch. It dipped to about 3 feet height and then very slowly started gaining height to about 20 feet; at that point it had flown so far that I had to turn it back which meant a downwind stretch.... during which it lost most of its height again. I did 3 long circuits like that at full throttle with much the same result so I landed the plane; time for another rethink, as yet more thrust is required.

I don't think there is much more that I can do to optimise the airducts; one option is to use 4S batteries instead of the 3S batteries which would give more power, more revs and therefore more thrust. Another option is to try and make that second EDF unit more efficient. Third option is to fit higher revving motors, and final option is to buy a matched pair of EDF units complete with matched motors. The set that I found claims 470 gr thrust per unit at 190W, which would give over 50% thrust/weight ratio which should be more than sufficient in theory.

Test flight #3

I found a suitable shaft adapter which enabled me to re-use that original fan. Worth a try as it would save extensive surgery to fit entirely new units. Total thrust slightly up (by 10%) to 800 gr which makes for 47% thrust/weight ratio, worth a trip to Chobham Common, it might just be enough.... 23 September 2011. Steady breeze. First launch was a disappointing steady glide back down to earth. Second launch was more powerful and she lifted off but struggled to climb to 30 feet. Very stable but still not enough power, resulting in a lot of height loss during the downwind stretch. I landed her after just 1 circuit, no damage done. Looks like that major surgery is unavoidable....

October 2011

Found some interesting brushless motors on the net : Turborix D2627 . These are outrunners designed for EDF, 5000 Kv, approx 250W, amazing value at approx £8 each. It took most of a day to fit them, but initial measurements are looking promising : at full throttle they use 24 - 25 A (260-280 W), producing around 480 gr thrust each. This makes a total of 960 gr thrust; this means a 56% thrust/weight ratio, and a 1.8 gr/W efficiency. Even the noise levels are now approaching that of a real Concorde as the rpm must be approaching 50,000.....
Here they are as fitted (front view and back view) :

On 14th October (2011) it was a nice morning so time for another attempt to see what these new motors do. Surely that little bit of extra power would but sufficient ? Unfortunately not. All 3 attempts ended in a quick but steady glide back down to earth, as if we had less thrust instead of more ? Luckily my daughter caught all 3 attempts on video, and here it is.
What next ?

November 2011

6 November - quick update. Decided to add a 3rd EDF unit using one of the original motors; this will be a short (= efficient), all white (= hard to see) nacelle in between the 2 existing nacelles. It will take power from both existing batteries so the load is shared and no extra battery is needed; the throttle for that 3rd unit will be switchable independently so it will only consume power during take-off. I'm hoping this will take us close to 70% thrust/weight ratio.

17 November - the third EDF is now fitted & all wired up, here it is :

I did some initial (static!) testing in the back garden and it sure makes a powerful leaf blower !! The extra thrust from the 3rd EDF unit is quite noticeable. All-up weight is now 1900 grams. Static thrust has increased to 1150 gr, which makes 60% thrust/weight. Total thrust is 200 grams less than I was expecting and it is not (yet) clear to me why. Switching that 3rd EDF on and off shows it contributes approx 300 gr of thrust which means the two others must be producing 425 gr each.

10 March 2012 - SUCCESS

A beautiful spring day so I went to Chobham Common for the first attempt with that 3rd EDF unit. Quite a few other flyers around and quite a breeze, albeit steady. Everything was OK with the pre-flight checks so the moment of truth had arrived. I fully opened the throttle and with a firm toss into the wind big C was away. After an initial dip she recovered beautifully and steadily gained height. Success! Once at height I turned her slightly right and then into a wide left turn for a downwind stretch ; this had been tricky in the flights without the 3rd EDF unit but this time she did maintain height very well. After that it was 4 minutes of steady circuits to explore flight behaviour, after which I noticed a drop in power so I landed her onto the heather. Phew, what a buzz to see this thing finally fly. Compared to my other Concorde this one has 50% more wingspan which together with the increased weight results in a more stable flight behaviour which in turn looks even more majestic and scale-like. The only thing that needs adjusting for next time is the COG as she is a bit nose-heavy at the moment.

31 August 2012 - Time for a rethink

A nice sunny day, with a steady breeze, finally it's bigC's turn again (I fly many planes, in rotation). Off to Chobham Common again with bigC. I had moved the CoG (centre of gravity) back a bit to see if it made any difference. A handful of other flyers around (hello Bob!) , and one of them kindly volunteered to launch bigC , perfect. Ground checks done, I opened the throttle, and bigC was launched with a firm throw. She dipped quite a bit and then, shock horror, we were back in old territory..... not enough power ! Even on full throttle and full up elevator she could not quite maintain altitude. As if we were back on 2 engines.
I managed to keep her in the air for 3/4 circuit but then we ran out of air and it was a fairly hard landing, a long walk away. Luckily she landed near the place where another plane (glider) had crashed just before, ands its owner picked up bigC on the way (thanks whoever you are, sorry I forgot to ask your name!). The damage to bigC is fixable (nose bent, plus batteries broke through the fuselage bottom) but I was obviously disappointed and pretty frustrated about this. I went on to fly one of my other planes (I always taken more than one, just in case!). Shortly afterwards at home I checked the total thrust and it had come down to 900 gr (from 1150 gr) without any obvious reason.
After giving it a lot more more thought I've decided to give up on EDF for bigC. Yes we can put bigger EDF units on, and by the time we've got it up to 1 kW it is guaranteed to fly like a rocket, but that wouldn't feel like an achievement to me anymore (just brute force). I managed to get the EDF efficiency up to 2 gr/W which is as good as it gets, having done extensive internet research on it. It is not difficult to get 2 -3 times that efficiency when using propellors, so that's the way I'm going to go. bigC will be changed to a twin-propellor set up, just like my smaller Concorde. I expect to get both more thrust and lower power consumption (= longer flight time) by switching to propellors. It won't sound as good but I'm sure it will be much less frustrating to fly. Guess what my winter 2012 building project is going to be....

November 2012 - Building again

	First I carefully removed the EDF's and the engine nacelles, compare left to right picture. They came off reasonably clean with the help of a Stanley knife. I was impressed with how strong the aliphatic resin glue was holding on to the nacelles, more than adequate, so that is what I will use to attach the replacement nacelles as well.
	I made up some new nacelles from 6mm depron and some custom made liteply engine mounts. This is just a single layer of 2mm liteply, held in place entirely by depron, glued with UHU POR. I reckon it's strong enough to hold 3-4 pounds of push (maybe more) which is more than adequate for the 2 pounds max of thrust that I am expecting per motor.
	My smaller Concorde has 2 normal propellors, but for this one I thought it might be nice to use folding propellors. They fold in when landing which reduces the risk of damage. I'm using normal 7.5x4 folding props, but fitted backwards as we use them as pushers (so the motor is pointing backwards as well). Hopefully the picture below explains it better than I can do in words.
	During flight (if we're gliding) and during landing, the props will fold in as on the left, which reduces drag as well as the risk of damaging the props. When the motor is running, the props will fold out as on the right and we have a normal pusher prop configuration. I had to remove some metal from the spinners to allow the props to fully fold out. I also added a little plastic strip (not visible) to stop the props from folding in too much (which could prevent them from folding out again).
All in all I'm quite pleased with the looks of those metal spinners, well worth the £4 each. At this point I just had to fire up those motors. They're sounding good, and are using approx 16A each at full throttle, a bit less than I expected. I haven't measured the thrust yet but there was enough there to accidentally blow the bedroom door shut ! December 2012 - Building done All finished and measurements done. All-up weight has decreased by 9% to 1725 grammes, thrust has increased by 50% to approx 1600 grammes, efficiency has increased by 150% to 5 gr/Watt (2.5 times more efficient than EDF) and ......thrust-to-weight ratio has increased by 50% to an impressive 92% (!). These are very good figures, showing that BigC now has ample power to take off and fly with ease. I can't wait to get her back in the air again.... 15 Dec - Windy conditions but no rain today so I just had to try her out over Chobham Common. Stood on the edge of Tank hill for a minute or so, holding up BigC ready to go, waiting for a 5 second break in the strong winds. Once that arrived, I throttled up, chucked her in the air and off she went. A bit wobbly because of the wind, but no dip and plenty of power, just great. I took her up to a safe height and flew circuits for about four minutes. She flew fine but the strong wind took a lot of the pleasure out of it, so I decided to land and take no further risks. The landing was straightforward; the strong headwind enabled a landing at very low ground speed. Those 4 minutes flying in strong winds have shown me sufficient to be confident that she will fly very well in spring, in more favourable conditions. Watch this space for the first video of BigC in flight in spring!

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