Peterf's twin 90mm EDF Blackhorse Mig 29 build log

[PeterF]

 

The blackhorse Mig 29 is a larger sized ARTF EDF based around 2 x 90mm EDF units, and these need to be at the high end of the power output of 90mm fans. The model is about 1.45m wingspan and 2.0m long and will weigh about 8kg (17 - 18lbs) when fully laden with batteries.Mine will run off 4 packs of 4S 5,000mAh battery packs in an 8S, 10,000mAh configuration. Expected current will be around 100A per fan giving 6kW in total. The fans are from Exreme RC in Australia with machined alloy shroud, Jetfan rotors and HET motors. I visit Melbourne on business a lot so that made the purchase easy. I have so far emptied the large box, large enough for my 7 year old granddaughter to sleep in and put together the model on the workbench to take a look.

There are a few videos on Youtube such as the one below.

Edited By PeterF on 24/10/2017 20:26:46

[PeterF]

I have read on a German forum about wood issues causing one of these planes to go in so had a good look over. One of the formers that the fans mount on had several bits of the outer ply layer missing and lack of adhesion. I have rectified this by gluing a similar 0.5mm layer into the gap then adding a larger patch over the area. This flaw went right across this one former on both sides of the fan and through the central spine, meaning 6 patches were required. I have had a thorough check and not found any others.

Outer layer missing / not glued down

Patch repair

[PeterF]

I have put all the servos in the wings and rudders, Hitec HS5085 digitals. I have put them in for the slats, but there seems to be concern that these should not be used as they create a step at the top of the wing as they are bottom hinged. I am not sure if they are never going to be used, so perhaps I should have left them out and glued them up. The servo mounting blocks were all glued into the servo covers as supplied, which is good. I have had one previous ARTF where the servo mounting blocks were not glued to the ply covers. The control horns are nice CNC cut epoxy glass board and glue into the control surfaces. They are not very long, hence the push rods need to be closer to the inner end of the servo arm.

There were only 2 minor niggles, the slots for the flap hinges were too high on rear wing spar so the flaps would not raise fully as they hit the chamfered edge on the top of the wing, the pictures show this. It was easy enough to slit extra slots a little below the existing ones and all is now well. I have also swapped to better quality M2 links, the ones supplied had a poor internal thread and the threaded rod did not engage until half way into the fitting.

I have reversed the slat and flap servo on the one side, which meant I had to reverse one of the flap servo mounts, lifting off the covering and gluing it back on turned through 180 degree. Each control surface has two slots in it for the control horns in case you can not reverse the servos and need to rotate the mounts. Make sure you get the horns in the right slots for your plans.

Servo in mounting block

Flaps can not raise fully as supplied, ailerons at neutral

Flaps now sit level with ailerons, all servos fitted

Flap and slat servos actuated

[Thomas Barwick]

I had one of these on 10s and was a wonderfull bit of kit. Dont bother with the leading edge slats as they really dont work as they should and watch the flaps as they cause the nose to dive dramatically. I ended up not using flaps or leading edge slats at all .

[PeterF]

Thomas,

It certainly flies well and has no issue with grass runways as per other videos. Thanks for the note about the flaps, I had not read anywhere about the pitch down effect so I am well warned. That is about £100 of servos that will have limited / no use for the slats and flaps, if that transpires they will come out for something else.

[PeterF]

The elevator servos are the weakest part of this model. The hardware is not great and there are reports of the servo mount failing. I have swapped to Kavan 3mm ball links tfor a slop free connection, which meant making my own threaded rods as the Kavan links are shorter than the ones in the kit. When I first put the assembly together I found that with the inner hole on the servo arm the EPA settings needed to be 65 to 70% to give the required throw. This is a huge waste of servos such as these Hitec HS-7955TG servos. Therefore, I drilled an extra hole 6.5mm out from the axis on the servo arms compared to the 10mm position of the inner hole. This has allowed the full range of the servo to be utilised, also reducing the servo load with the greater mechanical advantage.

To address the concerns over delamination of the servo mount ply I added an aluminium strip to the back, screwed through to extra wood blocks glued to the ply servo mounts. The aluminium strip fits into the small recess between the ply doublers. I also added gussets around the edges of the ply plates on both the servo and mounting pivot. The final thing, not mentioned in the instructions was to drill some small indents in the carbon rod so that the grub screws positively engaged.

This took an inordinate amount of time, but I am pleased with the result. It is a significant model to rely upon less that ideal elevator servo mounts.

Elevator with solid carbon rod axle glued in

1/4" gussets added around the elevator pivot block

Aluminium strip on reverse of servo mount plate screwed through to additional wooden blocks

The aluminium strip sits in this recess

The completed servo installation

[PeterF]

The fans have been installed, which was straightforward, what more can be said. The model came with a pair of nice light fibre glass thrust tubes that fitted well into the model. The tail cones were fitted after the fans were installed, with the thrust tubes fitting inside these. The only issue is the fans do not easily accept a bell mouth inlet because they are designed to fit into a ducted set up. The Mig 29 is hard (maybe impossible) to build with a fully ducted inlet, so I had to adapt a pair of Jetfan inlets to fit.

Fans as supplied by ExtremeRC of Melbourne, Australia

Fans installed in the model

[PeterF]

The build continues. I have installed the retracts. The kit lists a set with plastic bodies, I bought the same size with aluminium bodies for ruggedness as I fly off grass. These turned out to be slightly larger and I have had to sand the slots larger to fit them, but all has turned out well. I have fitted 8 pin multiplex plugs for the wing connections, slats and flaps servos along with the aileron ones, I did not want to gang all the power for 3 digital servos together. Yes, I know, I may end up taking out the slats servos. I used the Emcotec set up where a small PCB is soldered to the multiplex connector to give a better connection for the wiring, click for details. I have the ESC to motor wiring done and I have tested the fans, impressive, close to 6kW in total. The remaining work is really getting the electronics in and the flight batteries and then balancing the plane.

Nose gear

Main gear

Wing connections

Assembled plane

Assembled plane

[Simon Chaddock]

Very nice!

[PeterF]

Well, it has been a while since I touched this, I put my Tiger Moth on the bench and got completely carried away with that doing all the scale detail, which you will know if you followed that thread. Anyway, the Tiger Moth has been completed and completed its initial flying tests.

With the Moth gone, the Mig 29 could get back on the bench. The outstanding work from 2017 was putting in the BEC, back up battery, BEC / battery switch over unit, RX, telemetry and the gyro. I am not going to write a detailed explanation of all that as it is not plane specific. The Batteries are 4 x Turnigy Heavy Duty 5000mAh 4S, run in 2 sets of 2, giving 5,000mAh at 8S per fan. That is 2.35kg (5lbs 3 oz) of total battery weight, which is a significant portion of the all up weight. The ESCs are YGE 120Amp HV without a BEC, hence I have installed a 40Amp Jeti BEC, which should have enough overhead for the plane. Due to its size, there is a back up Rx battery with auto changeover circuit. There is telemetry on the flight battery voltage and the Rx voltage so I know if it has dropped down to the back up battery. I have an iGyro 3e installed as well.

The plane has been out to the field but it did not take off. The nose wheel is too soft and it maintained a nose down attitude. I had forgotten about this as it has been noted on other forums. I have since added some cable ties onto it to stop the nose dipping. Ideally it could do with a new spring with a much higher spring rate. I will have to go back and try it again.

[Biggles' Elder Brother - Moderator]

Wow! Simply stunning!

BEB

[Nigel R]

That is an impressive looking bit of kit. All the best with the maiden!

[eflightray]

Beautiful looking model, ..... but 5Lb-3oz of battery

My scratch built Mig 144(ish) flying weight is only 4Lb -10oz, at 64" span, 74" long, and flying on 500 watts, EDP, (Electric Ducted Props).

But then I'm the ultimate cheapskate

Ray.

.

[PeterF]

I am very impressed by that Ray, as large as mine and about 30% of the weight, it must be a floater. I assume it is built from Depron. It also highlights the inherent inefficiency of EDF, it is always better to accelerate a larger volume of air to a lower velocity for a given amount of thrust.