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Build of a Steve Bage EDF MIG17 enlarged to 143%  Chapter 1

 

By a happy accident at a Prontoprint  facility, Steve Bage’s 17” span MIG17 was printed as ‘A3 fit to page’ and a 27” version was borne. I had not before contemplated a scale model but the excellence of the design impressed and I succumbed to the challenge of producing a free flight electric EDF scale jet, having never before been tempted by the ‘scale’ discipline.

 

The complexity of the design prompted me to engage Belair to laser cut 4 off kits for the Peterborough MFC as I was doubtful of my ability to produce the plethora of intricate formers and wing ribs that Steve’s design requires. Steve was happy to supply a 143% .dxf file that Belair needed to laser cut the kits. This was a good decision as the quality of the cutting was first class. However, the components require some adjustment as the jigging slots were designed for the smaller 17” model. This is not a build for the faint hearted and will require some modification of the Belair supplied components.

 

As supplied the Belair hardware appear as ……..

 

 

Sticking bits together result in….

 

 

These assemble as……….

 

 

 

Discussion

 

The plan calls for cutting the fuselage in half at the F7 junction to get access to the EDF. I was nervous about doing this , so I cut the fore and aft dorsal K1A member to achieve the same.

 

Having witnessed the state of a colleagues paper inlet and outlet ducts in damp weather, I am not going to use paper. I have ordered some clear acrylic from sales@clearplasticsupplies.co.uk to act as formers and I intend to plagiarise the gummed brown paper technique to build the ducting, described in the Free Flight Forum papers 2011. This can be damproofed using Johnsons Klear.

 

The parts assemble easily bearing in mind that the jig slots were oversize having used sheet thickness as per the 17” original. The method of wing retention is unique and esoteric, needs careful fitting but works well. I did however CA in a couple of magnets at the root rib.

 

Weight achieved

 

Airframe

 

Fuselage (90% complete)                                                  39.2gm

Stab                                                                                       4.1gm

Fin                                                                                         5.0gm

Wing right                                                                             11.0gm

Wing left                                                                               10.9gm

 

TOTAL                                                                                   70.2gm

 

For a complete wood only airframe                                    78gm

Allowing 20% for covering and finish                                  93.6gm

Assume 100gms for safety and self kidding         

 

Power system

 

AEO 6000 kv 44mm EDF with brushless outrunner         36gm

Kpaero Mk1 E30 controller with 2mm gold connectors    2gm

                           

Suppliers performance figures

 

Voltage           Current           Thrust       Energy

(volts)           (amps)          (gm)          (Watts)

   10                20.7             328            207

   11.1              23.7             374             263

   12.6             28.5             436             359

 

These figures are outrageous and I knocked out a test rig to see what the unit was really capable of. I used an E30 kpaero controller with a ‘wait to start’ feature achieved with a push button to the right of the controller.

 

 

44 mm AEO EDF test rig

 

 

44mm AEO EDF on test

 

Voltage           Current           Energy

(volts)              (amps)            (Watts)

 

7.4                   11.2                82.8

11.1                18.4                204

 

The suppliers figures are generous but not that far off.

 

Assuming 1.8 gm/Watt of thrust a 2 cell pack will give 149gm thrust.

A 3 cell pack will give over 363 gms of thrust ! (Way too much)

 

(Pay not too much attention to static thrust figures, a decent forward speed works wonders as does  good inlet and outlet ducting. At model sizes its not a science but an art).

 

A Hyperion G3 2 cell 550 mah is 65 x 18 x 15mm and will fit nicely within the battery bay and weigh 32gm for 13.7 amps (25C).

 

A Hyperion G3 3 cell 850 mah is 73.5 x 25.8 x 18.6mm and will require mods to the battery hatch to fit. It will weigh 69gm and offer 21amps (25C)

 

The 2 cell might be underpowered but nevertheless it’s the one I am going for. I will team this with a 19gm basic Robotbirds ESC capable of 25amps continuous. This recognises I might be wrong on the required thrust allowing a 3s battery change to get out of trouble. For a 2s battery I could fit a 12amp ESC and lose 6gm………not worth the effort.

 

Hence power unit weight will be  :-

 

EDF                                                                            36gm

Battery                                                                        32gm

Kpaero controller                                                      2gm

Loom, connectors, switches                                    15gm

 

 

Total    power unit weight                                          85gm

Total model weight                                                    185gm

Thrust on 2s                                                               149gm (Is this enough?)

 

Going 3 cell will be overkill and will add 37 gm to the AUW, probably destroy the balance and put the AUW to 222gm. Try the 2s , it might be OK.

 

 

 

 

Look out for Chapter 2 when I have made the ducting and installed the power unit.