Semi scale Mig-25 Foxbat, 70 mm - Page 6 - RCCanada - Canada Radio Controlled Hobby Forum
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Old 01-31-2016, 03:12 PM   #51
4stripes
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Re: Semi scale Mig-25 Foxbat, 70 mm


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What motors, fans and ESCs are you using JC? How many watts total?
Thanks Eric
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Zen thinking * It's rebuildable till it fits back in the box. **
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Old 02-01-2016, 08:57 AM   #52
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Re: Semi scale Mig-25 Foxbat, 70 mm

Except for the overall length, the wingspan is the same as the Habu. The long thin nose is what makes it a few inches longer. The Habu, when all decked out was about 60 oz. in all up weight, maybe a bit more with the 4500 battery. And it flew fine with the power system that was in it. The main difference in equipment is the retracts, which are the next size up and the aluminum struts, which are only slightly heavier, but a lot more robust.

As far as the basic airframe, it has a lot more lifting surface than the Habu, so, I am really hoping it will be a floater. If it's not a speed demon,mthats fine too, I want to enjoy flying it and not get greyer hair. I don't have a 80 mm EDF with me and a this point, don't want to buy one, trying to keep the cost down.

I hope to have the beast ready for painting by the end of this week.
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Old 02-01-2016, 03:40 PM   #53
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Re: Semi scale Mig-25 Foxbat, 70 mm

A little off topic, but something I needed. Since being in California away from my home shop, I've had to make do with things, including the work table. I've been using saw horses and sheets of chip board or particle board, even old hollow core doors. So, using about 8 - 2"x4"x8' timber and 4 swivel and lockable wheels, plus a half sheet of cheap chipboard, made myself an excellent work table, why I didn't do this earlier, I don't know. Now it's at the proper height so the old back doesn't get sore. And I now have a lot more storage for stuff. Whole project was under $50.00 , the work surface is 24" X 72". Took just over an hour to construct it.

Tonight, back on subject, mounting the EDF unit, ESC and battery mount.
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Old 02-02-2016, 11:04 PM   #54
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Re: Semi scale Mig-25 Foxbat, 70 mm

Tonight was EDF unit install. So, first placed the heavy times on and in the fuselage and got it balanced. Took measurements so I will know where to cut the bottom access hatch for the fan unit. I made the hatch a pretty good size so easy access to the unit and the two elevator servos, thrust tube, etc.
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Old 02-02-2016, 11:14 PM   #55
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Re: Semi scale Mig-25 Foxbat, 70 mm

Made the foam and plywood mounts and test fitted the assembly. Problem surfaced, the main plywood spar was in the way for smooth airflow to the top of the fan, so, got my Dremel and Dura Grit cutting wheel out and cut away quite a bit, but now it doesn't hang in front of the top portion of the fan.

Epoxied the assembly into the fuselage with five minute epoxy. When hard, removed the EDF unit and with System Three epoxy, lined the area and the inside surfaces of the foam rails with 6 oz fiberglass cloth.

Also, to hopefully return more strength to the modified spar, I laminated 8 strips of carbon fiber toe to the back side of the spar.
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Old 02-02-2016, 11:17 PM   #56
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Re: Semi scale Mig-25 Foxbat, 70 mm

Finished installation, neat, simple and easy access.

Tomorrow, I will install the two elevator servos and get those working.
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Old 02-03-2016, 01:17 PM   #57
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Re: Semi scale Mig-25 Foxbat, 70 mm

This's morning I was looking around to see what I could use to make a thrust tube and saw I had several sheets of Bristol board paper. I remembered an F-18 ARF I had purchased many years ago that was a 70 mm, the manufacturer used the Bristol board paper as a thrust tube. So, what the heck, gave it a shot.

Cut the paper to size, plus a 3/4" overlap. Also before cutting it out, the paper has a grain in it, it will bend easier one way other the other, that's the grain and make your pattern so the grain is going front to back. Also, there is a very smooth side and a Matt finish side. With glass cleaner ( which is what I used ) lightly spray the matt finished side, it will literally curl to shape which makes wrapping it into a tube very easy. Fit it onto the rear of the EDF. I used elastic bands to hold it in place. Use a small spring clamp at the exit end and adjust the choke to the diameter you desire. Let it sit til dry.

I then applied tape to the inside, opened the seam up, brushed in some wood glue ( paper is a wood product ) and then applied another full length strip of tape to close the seam.

Works like a dream, I might paint the outside with water based urethane paint, just to seal the surface. The trust tube is reasonably light and holds its shape really well. Where the wires exit the tube, I will reinforce the hole with more tape so the tube will not rip.
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Old 02-03-2016, 02:27 PM   #58
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Re: Semi scale Mig-25 Foxbat, 70 mm

Great info John. I have been looking for some type of material to use as the exhaust tube in my L59 and had not even considered Bristol Board. I will have to give it a try. This is why I enjoy reading everyones building threads. Some of the best techniques come from other modelers!!! Keep sharing ideas.

Thanks
Marty
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Old 02-03-2016, 11:32 PM   #59
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Re: Semi scale Mig-25 Foxbat, 70 mm

After some head scratching to locate the position of the elevator servos, I realized the plywood fan mounts would be ideal to use as a base. I cut the servo mount out of 1/8" aircraft plywood and epoxied the assembly to the rear section of the fan mount. As a safe guard, I also drilled and installed two screws, mechanically securing the servo mount to the fan mount.

Again, simple as it gets, easy access to the servos for any maintance.
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Old 02-05-2016, 11:34 PM   #60
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Re: Semi scale Mig-25 Foxbat, 70 mm

Was about to start the aileron and flap servo install. Was not happy with the amount of throw I could get from the control surfaces with the live fiberglass hinging technique, so, cut them off. Gluing 1/4" balsa on the leading edges and will reshape them to accept real hinges. Short delay.

Here is the amount of throw with the live fiberglass hinging technique, aileron isn't bad, the flaps would only be good for takeoffs.
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