Arrows 64mm 6cell Mig-29

Konrad · November 1

This is one of my guilty pleasures, bashing foam ARFs. When I visit the family in Denver I need something to do to vent the pressure from the family madness. I often have an EDF project scheduled for the visits. My visit earlier this year, had an Arrows Mig 29 waiting for me. I got this on sale and with the savings I purchased a pair of Freewing 2500Kv inrunner motors.

Historically I've thought of the 64mm EDF as fun entry level models, with two exceptions, the Freewing 4 cell 6 blade Stinger and the Banana Hobbies SR71 running Don's RC outrunners. Both of these models would place a smile on my face that would take a long time to wear off.

Well, I'm here to say that the Arrows Mig 29 is the third 64mm EDF model in this class. In stock form with the SMC 4400 6 cell I'm sure she will provide any enthusiast more than ample performance. I think I mentioned that I was flying my Arrows Mig 29 at over 6k more like 7K feet altitude. As such there is a huge performance hit with EDF. This was the single strongest reason I upgraded to the Freewing 2500kv inrunners. With the SMC 4400 6cell hot off the charger I witnessed near positive thrust from the 64mm EDF units. (I was at a static positive thrust if I left off the canopy and nose cone.) I was drawing drawing 120 amps. I was a bit surprised that the batteries didn't show much if any voltage drop between a single engine run and a dual engine run. So as a propulsion exercise I'm ecstatic at how this worked out.

This took a lot more work than I anticipated. First was the purchasing of Freewing components. The description on MotionRC's sales page are just wholly inadequate There is little in the way of engineering data to help make the selection. I ordered 2, 64mm Freewing EDF units only to find that they have 4 piloting points that will NOT allow the new Freewing inrunners to fit. Also the collets found in the EDF units don’t fit the larger 4mm shaft of the inrunner motors. So Freewing to Freewing parts don't work. I got lucky in that the Arrows 64mm EDF units will allow the Freewing motors to center in the housing properly. Note that the Arrows 64mm EDF housing has a set of stators that are about 4mm longer than the Freewing 64mm EDF housing. This is great but one needs to chamfer back the motor tube a bit at 45° for about 4 mm. This is easy to do and rather uncritical work. From a design point I like the longer stators. I also liked that the Arrows EDF unit is stiffer, in that the inlet bell mouth is molded in to the housing. So while it was looking like I was going to have a problem with the EDF units the use of the Arrows EDF units allows for easier installation of the 2500kv inrunner motors. Freewing, really what does v2 tell anybody. There is no mentioning of the motor body diameter or of the collet/adaptor diameter. By the way this is the Freewing EDF unit P0643 that fits the inrunner. I still think the Arrows EDF unit is the better unit (longer stators).

A big surprise was that 2500KV motors weighed 53 grams more than the stock Arrows outrunners. The surprise was that Arrows added a 105 grams of lead in the aft section of the fuselage. I love trading dead weight for functional mass! So by the removal of the 105 gram lead plate, the upgrade to inrunners was a wash when it comes to weight. Actually the mass is shifted aft a bit as the motors sit a bit further aft than the location of the lead plate. This is a much needed shift in weight.

Freewing states that the 2500Kv motor in the Freewing 64mm EDF unit needs at least a 60 amp ESC on six cells. I had a set of Hobbywing ESCs laying around after upgrading my Freewing SU-35 to FMS fans, so I choose to use them. They are a bit wide for the ESC/wire tunnel, so I had to remove some foam to fit the Hobbywing Spacewalker 60 amp ESC. I think a better fit would have been the ZTW 60 amp Slim ESC.

At 6K feet altitude the Arrows 64mm fans on 6 cells (26.1v) are drawing 57 amps each after a 10 second run with the timing set on low. One of the few real problem with the Arrows Mig 29 is that the battery compartment is too small and place a bit too far forward. As a result to get any duration the model ends up nose heavy. To minimize this I'm using the 592 gram SMC 4400HV charged to 4.35v per cell . I had to remove the 6mm foam that makes up the rear of the battery compartment. I couldn't remove more as I was hitting the nose retract. Please note that these batteries need a charger that can charge HV Lipos. I'm using an iCharger x12

My initial CG setting was at 118mm at this setting the Mig 29 is still pulling up out of a dive indicating that the model is still nose heavy. But at the low elevator dual rate setting in the manual I can still snap at the top of a loop. I'll need to cut down on the elevator throws if I move the CG any more aft. On the subject of throws. I changed the controls to elevons for the tail with the elevator taking 35% of the mix and allowing the aileron to have the other 65% of the mix. I kept the wing ailerons, but cut down their motion to about half the manual's value. The flaps go down to 90° just because I can get them that far down. With the flaps at 90° I can dive for the runway flair into a high alpha landing profile and modulate the sink with about 30% throttle. The Mig 29 like the Su-27/Su-35 and F-18 uses the LEX very well to keep the airflow attached at high alpha values.

Unfortunately I don't have enough free channels in my TD-10 RX to allow me to separate the flaps. As a result of some linkage geometry issues I have a slight roll when deploying the flaps. I'll have to work out a flap to aileron mix to address this.

Now I have to address a real flaw in the Arrows Mig 29 design, other than the battery compartment. Looking at how the model sits on the ground and how the full size sits on the ground we can see a huge disconnect. I saw a lot of U-Tube videos showing how poorly the Arrows Mig 29 handles on the ground. In stock form you can see the model stays glued to the runway until the pilot gains far too much speed and then yanks back on the elevator. If he is fast enough (with the reflexes) the pilot will add forward stick before the model snaps right after take off. I traced this problem to 2 issues. First is that the rear struts are far too long. This not only make the Arrows Mig 29 looks odd on the ground but also results in a deck stance that is negative (the LE of the wing is lower than the TE of the wing)! This is why it takes so much speed (power) to get the elevator to respond to lift the nose at V1 speed. Combine this deck angle with the fact that the rear mains are far too far aft relative to the CG and it is all but impossible to get the Arrows Mig 29 to rotate smoothly at take off and to not bounce back into the air on landings!

The fix I came up with is rather easy. First I moved the main retract forward about 12mm to 13mm along the plastic hard point in the fuselage. I did have to regrind a pocket in the hard point ahead of the factory front mounting screw location for the bucket that receives the rotation pin. I wanted to reuse the factory mounting screw location as it has extra material for the forward retract mounting screws. As a result I had to drill a new set of holes in the retract just aft of the pin bucket. I reused the aft retract mounting holes by simply drilling a new set of holes into the hard point rails. Note these holes are under compression during a landing. So it isn't as critical that the screws bite into as much material as they did at the factory retract location. This moves the main axle much closer to the 118mm CG allowing for smooth take offs and high alpha low speed/low bounce landings.

Next I shortened the main strut about 16mm by removing all of the strut's top boss. This allows the wheel to fit back into the wheel recess and lowers the aft end of the fuselage ground stance. I think my wing deck is something like 26mm. That is the LE is now higher than the TE by about 26mm. Now the only tricky part of the modification was the need to drill and tap a new 4mm strut grub screw. Using a drill press and the flats for the trailing link mounts I was able to drill the holes so that the struts still maintained the required toe in without needing to grind new flats to the strut pins.

And last I cut the main springs 5mm to give the mains more range of motion before reaching coil bound.

Note that I didn't change the nose gear strut at all. Also you might see that the top of the main wheel is now even with the bottom of the fuselage when sitting on the ground. I can now hold the nose high at V1 all the way down the runway. I can also wheelie until I'm bored for the landing roll out.

In stock form there is little to complain about when it comes to the assembly of the model. But there is one glaring problem. The manual says to glue the vertical fin on to the fuselage. There is no caution as to how to set the fins. If you push the fins to make a solid bond with the fuselage you will end up with the fins splayed outwards like the F-18. But if you rig the fins like this the elevators will bind as they move. The vertical fins are to be rigged so as to be vertical. I'd like to see an addendum be added to state this. Also I'd like to see the factory mask the bonding area of the fuselage and vertical area to be free of paint. Glue doesn't bond well to paint!

As to the flight characteristics I'm again very happy with how the Arrows Mig 29 rotates at take off and how smoothly she lands even with 90° flaps! But I have to caution anybody wanting to fly the Arrows Mig 29 at high altitudes. The wing loading is a bit high. She will bite if allowed to slow down too much. My ship had a persistent stall with the left wing. I was also seeing a bit of left aileron to hold level flight. This leads me to think that the left wing is at a slightly higher angle of attack than the right wing. Further flight testing showed that the wings were not true to each other. I had to rework the wing hard points to allow for shimming the wing 0.5mm. With the re-shimmed wing the Mig now stalls true in both high speed and low speed flight.

The next needed upgrade to the model was to print some new nozzles, as the stock ones have what I think look like some performance robbing features. See the foam step and that the Swept Fan Area (WFA) is far too large. I found a set of 3D nozzles that remove this step and brings the WFA down to 100%. I still think the SFA needs to come down a bit more to around 90% SFA. I also needed to add a lot of up thrust, like 3.5°. This helped the up line and my power on high alpha landings.

As I said this was a way for me to hide from some of the madness that is family, so I never intended to do a write up. Much to my surprise I didn't see much on this model in the other forums. So I added this to the RCM&E forum.

P.S.

I really don’t know where the CG is, as flight testing was showing that at 118mm there was still a strong pull up out of a dive. I’ve since added about 49 grams of mass to the tail. She is now a real honest fun high performance EDF. I’ve since purchased the Freewing 64mm F-14. I can say that the reworked Arrows Mig 29 flies better. This is mainly do to the added weight of the F-14 (swing wings and much larger SMC battery 5900 mAh. I also have a Flyfans SU-27 that with the stock components actually flies better than the F-14 and Mig-29. Again this is because the SU-27 is lighter still. But for high powered, high speed flight the Mig-29 is the more enjoyable of the models to fly.