Hi Timbo

I guess its not quite the most clearly worded post

After doing a bit of reading on RC Groups it seems to be quite a common rule of thumb that a inrunner can disipate the heat generated by input power of 4 watts per gram of motor weight and a outrunner 3 watts per gram of motor weight.

As the motor and controller used by Richard is  2.5 ounce  I took the motor as being 2 ounce

 2 ounce * 28.3 *4 = 226 watts for a inrunner or  2*28.3*3 = 170 watts for a outrunner

Ah. Well  I have never heard of that one - and personally find it a little strange to factor in the heat dissapation properties of a motor when calculating powertrains - surely too many elements will have a bearing on this such as cooling. The quality of the motor will probably also affect this "rule" as well, with the better quality items having better bearings, windings and terminals, not to mention the magnet retention and flux. Loss of magnetism and therefore performance is the main product of overheating our motors, and these fixings vary tremendously across different motors. As with most things modelling though, I still try to aim for all my powertrain components to be wiorking WELL within their claimed tolerances, and as with LiPos and C rates etc, personally I reckon around 50% - 70%  of maximum C is a good target. If I was worrying about whether my motor was capable of the heat dissapation required, then I reckon I am overcooking it!

Interesting nonetheless, thanks for that SA Allen.

Hi David......that looks like an excellent model......just one problem....you appear to be attempting to run two brushless motors from one ESC. This will not work. Unlike brushed motors brushless ESCs rely on initial feedback from a motor to establish the timing points....with two motors the ESC cannot determine which motor to "fire" & when.

Suggest you need to add another ESC !!!!

Just another thought (because EDF facinates me although I've never got around to actually building one.....yet!!)...how are you going to feed air to the fans? My (limited) understanding tells me that a good straight run feeding lots of air to the fan is required. From your pics is seems as though the fans will have to suck air past a load of wires, structure etc......

Not a criticism I'm just keen to know your thoughts/solution....

Very nice picture, David -- impressive looking model, and I just love the colour scheme!

 I se what you mean about the 2 ducted fans -- this obviously took some building, and you have taken a more ambitious approach to redesign than I had thought.  I'm sure it will pay off as you will have massive excess power with the two fans, assuming the model is otherwise similar in size to the original plan?   Have you increased wing area to keep wing loading down, etc?

I'm a little worried about the inlets to the fans - is the from path clean enough?

Here is my construction so far, based on a single fan, same size, model concept ---

you may be interested in the EDF Mig forum where we have been having an extended discussion of EDF conversion:

<img title="This is one of our busiest threads" src="http://www.modelflying.co.uk/forum/images/hotthread24.gif" />Mig -25 EDF conversion
Discuss converting Tony Nijhuis' Mig toducted fan By Richard Sharman
Topic: Electric Flight

aaarrgh!  After many successful flights of the Mig-25 pusher-prop plane built from the plan, I finally ran out of juice downwind on a windy day with the following result :    (I've removed the covering on the nose to show the details, and the nose has rotated by 90 deg):

It would seem that the nose being just a 1/8th sheet balsa box is not quite strong enough, especially bearing in mind it's carrying the weight of a battery!  So, suggestion is - if anyone else is embarking on building from the plan, do put a little strengthening in - laminating with 1/64 ply, or some carbon fibre stringers should do the job.

The model flies(flew) well, and I was told that the final crash looked "very scale-like, an authentic downing of a foreign intruder",  so someone was pleased!

With some nifty work involving CA glue, and some ply doublers in the nose, the Mig is repaired and flying again, now fitted with a  KMS 380/20 and 6x4 prop, not to mention the sunny weather.

Hey David, ditch the 60amp esc for two 35 amp escs, run them froma Y lead off the throttle outlet.

I like the idea of incorporating cheat holes in side of the fuz just in front of the fans, as well as above the fuz, but you won't get enough air in there. Also the square box in front of your esc will cause a lot of vortices. See the way Richard has tapered the same area from the point at the top of the inlets as far back as the first of the twin formers.

 Richard, very nice, but wouldn't you get better air if the fuz at the inlets was slightly concave so that the most air can cram into the duct opening like a real Harrier, you wouldn't see it in profile or from above, maybe the esc/s could sit against some slots inboard of this with, with air let in past the nose wheel (also allowing some battery cooling). 

Timbo said the same as my thoughts, choc-block connectors, one esc, and no inlet for the fans!

Is that brown colouring in the scheme red ochre or rust?

to Martin:

you're probably right, and any step in the direction of making the inlet cross section smooth and round, without sharp angles, would be good.  However, in this case I wanted a "simple" construction idea that could be quickly built, but not too bad, aerodynamically.   Here is (an early) picture of the duct when it was in construction, and you'll see what I mean:

The result is that I get a tremendous draft of air down the duct and out the back, so much in fact that a tiny bit of gravel gor sucked in and blew the fan to bits (as in an earlier post). I made and tested a "homebrew" fan, as you probably saw, but now the pukka carbon fibre replacement jobs have arrived in the post so I can get back to work on it!