[radlouni]

iconic fighter from the 60s, i saw a video on youtube of a build with twin 105mm EDFs

[DarthAnal]

Beanie's depron version or my version of John's Mig-25 via half-size KOTA drawings...… Hmmmm…. wirrr or roarrrrr…

Looks like I may wind up with two many projects and way too many EDFs in the workshop this winter.


BTW, John, how did the Mig fly?

[DarthAnal]

Spent the last week trying to get the KOTA half-size plans as well as Beanie's MiG-25 plans printed as well as reading this thread over and over again to glean any details that I could come up with.

One thing that I noticed about the KOTA plans is that the wingspan and fuselage width may have bee fudged, as I am getting a 28-inch wingspan for a 42-inch length. Considering that the original design used a Byroblaster fan unit (slang expression that I encountered about thirty or so years ago for the Byron pusher fan unit and it stuck), I think that the fuselage can be narrowed without impacting the overall design. The plan shows the Byron in sideview and has a size of 80mm, so putting in a 70mm or 2 50MM fan units should work.


Overall, the half-sized KOTA will wind up being about 55% of John's original design, which places it at about the same scale size as the Arrow (about 1/25th full scale).


Well, enough on this for Thanksgiving. First stop will be to get to Home Depot and see if I can find the sheets of foam that John's been using and play around with hot-wire cutting to see how easy it is an if I got the right foam.

Would be nice if someone has the brand name for the foam.....

[Dutkoski]

It's the blue extruded insulation foam, Dow makes it, if it's pink, then Corning makes it, all in all, it's the same. A couple of decades ago, I purchased a Mig-25 fuselage that was a KOTA product. Got rid of it soon afterwards though, it was poorly made, sloppy fiberglassing. So, that's all I had, no plans, foam cores, nothing....

[DarthAnal]

Plans weren't that much better. Should be good enough for a starting point and will need to print off a 3-view as my key reference so I can get the proportions right as opposed to the KOTA plans which was designed around using a Byron fan unit, which is likely putting the fuselage width off, much like Bob Parkinson's Arrow looked more like a pregnant guppy than the sleek thoroughbred that it was.

Thanks for updating me on the foam. Going to drop by the Depot this week and see if I can find a sheet and play around with it as well as getting a 3-view printed off.

Hope that your weekend was great.

[Dutkoski]

There are several line drawings of the Mig on the web, here are the ones I used, they look pretty well done. I enlarged them for the big Mig-25 that I started last summer ...... hmm .... I should get that project done too. The big one is made from the same insulation foam, the whole airframe will cost less than $150.00 by my estimate. The 1 oz fiberglass cloth and the urethane will be the big expense.

Just print out the drawings and take them to Paragon Printing, they offer good pricing and do it while you wait.

[DarthAnal]

Good evening, John. I've been diving through a lot of your half-inch foam sheet models, looking for design concepts and such, and noticed that you didn't post any more information on the first flight of this MIg-25. Can you post an update with the status of the model and what has happened to it since?

[Dutkoski]

Just saw your post in my email junk folder, seems all my notifications from R/C Canada gets sent to my junk folder for some reason.
Anyway, the 70 mm Mig-25 is having the retracts replaced. Originally, I installed a set that were too heavy, so removed them and sealed up the openings. Then found a smaller lighter set, very much like the ones used in the Habu, so opened up the openings and fitting in the replacement landing gear.
But, now the flying field does not have a finished runway, just grass, so the smaller gear may not work. So, it's hanging in my second workshop waiting.

[Dutkoski]

It’s been around 18 - 19 months since I toyed with this model, but, tired of looking at it hanging from the ceiling. So, took it down, made a cradle for it and resumed working on it. First on the list, re-install the main gear retracts. This was done fairly easily. Then when moving it around, noticed how tail heavy it was, too tail heavy. So, removed the EDF unit and made a new mount for it. I positioned it quite a bit forward, actually about 7” forward. And checked the CG with the battery in position just in front of the nose gear wheel well. This seemed to be much more reasonable to getting the CG balanced out later.

Next, getting the nose gear retract mounted. To get needed access to the interior of that long slim nose section, I simply cut away enough of the underside to afford me room to mount the retract rails and steering servo. One thing I did notice, the single tiller arm design will not work, sticks out too much. If I cannot get the needed clearance, I’ll have to make a pul pull bellcrank and use braided fishing line to do the steering.

[Dutkoski]

Fairly productive day, I designed and assembled a tray to mount the nose gear retract unit and the steering servo. Then epoxied the whole unit into the nose section. Because the nose wheel retracts rearward, the steering servo had to be mounted forward of the nose gear. The pull pull steering line therefore has to make an about turn at the rear of the retract position. This is so the line will go slack when the nose gear retracts. I trimmed a pair of small control horns so just the bottom hole was left. They then got screwed into position. This works really well.

The lower portion of the fuselage that was cut away was made into an access hatch. It’s held in position by a single nylon screw.

I then position the five cell battery inside the fuse and adjusted the location of the EDF unit until the airframe was balanced on the CG location. This gives me a good idea for the final location once the servos for tge ailerons, flaps and twin rudders are installed, which will affect further adjustment.

The model sits firmly on it’s wheels so far, very pleased with the results.