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Old Jul 22, 2006, 10:47 PM
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Mig21 F8 Scratch Build EDF64

Been working on this scratch build forever, finally finished. Kinda lost interest for reasons unknown, but got tired of it taking up my bench space.

As far as this individual build is concerned, I think the design may have much more potential than this specific build may have. The idea was to make a front load design, with removable wings, necessitated by the need to have a fully empty fuse for internal component/fan assembly. I've seen designs where the fuse wing saddle and wings are a single piece, which splits the fuse straight down the center. I wanted to avoid that complexity, and the strength issues of attaching the wings to the saddle.

REMOVABLE NOSE
The nose section easily releases form the plane. The radar cone is mounted on a spring loaded fork, which is simply pushed in, to release the latches. Hopefully the pics make it a bit more clear than trying to describe it, but the fork arms basically slide in alum tubing, glued to the inner fuse walls, on each side. Each fork arm has a spring between its 90 deg bend and the tubing, keeping it outward. Pushed in, the fork arms simply get between the latching arms (part of the rear fuse), and the blocks on the nose section that they latch onto. This action unlatches them, and the nose can be pulled off for batt installation and component access.

The arms and latch blocks are made completely from CF spars. In the nose section, there are guides made from hard balsa 1/8" sq spars, to guide the arms into the nose section. At the end of the spars, an extra piece of spar is CA glued on to the main arms, to create a latch. The beginning of these small pieces is rounded off, so that they can ride over the latch blocks on the nose fuse walls, and latch. Its actually quite strong, and latches well. CF accepts CA glue for an incredible bond to inself, and anything else, for that matter.

The small wing leaders glued to the nose cone are made from aluminum oval tubing, cut into a wedge. The rear open inside portion of these wedges overlappes the very beginning of the delta wings, keeping them form sliding outward. The rear end of the wings still need to have something made, maybe magnets, to hold them tight to the fuse. They don't have much desire to slide outward, so they dont need too strong of an attachment.

REMOVABLE WINGS
The wings are constructed around round CF rods, which plug into the fuse. The rear plug-in is an aluminum tube, inserted and permanently glued across the fuse. The fan is slid into the fuse, all the way back, against this tube. The fuse was sized perfectly, for the fan housing to slide in. The front CF latch arms continue along the inner fuse to the alum plug-in tubing, and are also guides for the fan. Small notches are cut into the outer fan housing, to index with the CF spars. The spars also reinforce the main fuse section. Another notch is cut in the fan housing bottom, for the motor wires to route from the rear of the fan, toward the front of the fuse, where the ESC will be.

The front plug-in design has short bushings made form alum tubing, glued into holes in the fuse. This is necessary to slide the fan in, since nothing can be in its way. After fan and other component installation, a section of alum tube, which is the length of the fuse OD, is installed through both bushings, across the fuse. Now there is tubing across the entire fuse, for the front wing plug-in rods to install into. For additional strength, an extra section of tubing, the size of the fuse wall bushings, can be hand held in place between the bushings, as the inner alum wing rod plug-in tube is slid in. Now the tubing will be doubled. The inner section of tubing is sized for a tight tolerance slip fit, for the CF wing rods to plug into. The tubing sizes are incrementally sized K&S alum tubing, which fit inside each other with little slop. There are many available sizes of CF rods and alum tube, to use this design for many different scales of the model, if desired.

AILERONS
Since I've written a book already, the pics should show how this linkage is constructed, and can easily be installed after plugging in the wings. It has ball joints on the aileron arm end, and S-bends on the servo arm end. The servo is mounted in the fuse wall, and captured by the bottome keel, protecting it and the linkage from the ground. It could easily be cut out and changed, if necessary.

ELEVATOR HALVES
The elevator servo is mounted in the fuse backbone. This is a nice feature of the Mig21, for hiding most of the servo, but keeping it out of the air path, as there is enough in it already. The servo lead routes through the backbone, exits a small hole to the inner fuse, and plugs into the receiver, mounted at the top of the fuse inner wall, near this hole. I found this to be a convienient receiver location, for this reason, and also to keep it away form the battery, which mounts below it. The elevator halves use Sullivan gold cable, for linkage. The cable housing routes inside the fuse, and then back out, to each elevator. One exits below the first elevator half, and one above the other elevator half, so that they move in the same direction.

BATTERY
The battery mounts on the fuse floor, in the rear fuse section. The battery tray area seems to have ample distance to accomodate the CG, with different batts. Without the batt, the plane is tail heavy, and the batt area runs from behind the calculated cg, to the front of the rear fuse half, giving plenty of adjustment room.

I'll put the build in the next post, since this one's getting full.
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Old Jul 22, 2006, 10:48 PM
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The Build Materials, Details, and Pics

FUSE
The fuse is made of hard cardboard rocket tube. Extensive lightening holes were added before sheeting. To create the compound curves, tapered V-cuts were made to the front and rear tubing, and then CA glued together. some padding was added to the tube before sheeting, to tweak the outer shape. This is done by adding small sheets of light 1/32" balsa, and then sculpting to shape.

RADAD CONE/NOSE RELEASE
The radar cone is a cut down GWS rubber spinner, painted green. The mounting wire fork is bent in a loop, directly behind the spinner. A small bolt is mounted through the loop and nutted on the other side. The bolt is sized such that the treads will allow the push-on rubber spinner to be installed on it.

WING PANEL CONSTRUCTION
The wing panel construction was started with both haves built together. The common tie is the rear plug-in CF rod. This was done to keep symmetry on the panels, since they need to be accurately made to plug into the fuse. Holes were drilled in the wing formers for thr front spars to mount. A common is spar inserted across both wing panels, NOT GLUED IN PLACE, used for alignment and symmetry of the panels. Once far enough along, the rear spar can be cut, and the panels can be completed separately. At this point, the front spars can be installed and glued in.
CF spars can also be seen along the rear of the wing LE's, for reinforcement. Once sheeted, the panels are quite strong.
Not seen in the pics are 2 small cheaters under the wings, near the front. Not Mig21 scale, but hey. They are hidden behind by small intake collectors which are mounted on the wing, draw air in from the front, and fit nicely against the fuse contour. I guess looking a bit sort of like bifircated ducts.
I did document the wings, but would need to clean them up, if I were to make them into a plan format.
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Last edited by scratchandbash; Jul 22, 2006 at 11:31 PM.
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Old Jul 22, 2006, 11:17 PM
EDF rules... :)
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Joined Nov 1999
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Hi Scratch,

Nice work, how much did it come out in weight?

Eric B.
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Old Jul 22, 2006, 11:26 PM
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I need to put it on the scale. I'll get that and other specs posted soon. One of the reasons I lost interest is that it went a bit above what I wanted. Its not heavy, but I thought it would turn out a bit lighter, for the Maxx 2015-4100 and T-Bird 18 that are currently in it. At this point, I may swipe one of my 2025-5300 or near equivalent motors from something else. At this point, Im not sure if I want to pirate stuff, or blow more bucks, or maybe just plain lazyness may stop me. It still may go with 140W, or whatever I can abuse out of the 2015.

Edit:
Here's the basic specs:
AUW: 22.0 oz TP 3s-2100 Prolite (This is with roll gyro also)
Span: 22.13"
Area: 163.3 sq-in
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Old Jul 23, 2006, 03:17 AM
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Scratch,

Another of your fantastic models ( 'scuse the pun ) and with a wickedly simple - yet rather ingenious method to retain the front fuselage !

Smartarse

The model looks the business in that first photo...!

Keven.
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Old Jul 23, 2006, 09:40 AM
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Quote:
Originally Posted by keven64
Scratch,

Another of your fantastic models ( 'scuse the pun ) and with a wickedly simple - yet rather ingenious method to retain the front fuselage !

Smartarse

The model looks the business in that first photo...!

Keven.
Thanks Keven. I'm actually more excited about using these design concepts again, than this particular plane.
That's the idea too. I'm always telling myself "Keep it simple Stupid". Best thing I got out of engineering.
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Old Jul 23, 2006, 11:13 PM
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Scratch,
Great work!

Cheers---Stacker
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Old Jul 25, 2006, 01:09 AM
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Scratch,
Great work!

Cheers---Stacker
Thanks. Haven't been here much lately. What do you have going on?
Hey, I fianlly got the Arado going pretty good too.
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Old Jul 25, 2006, 10:40 AM
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Scratch,
Been pritty busy flying some of my planes this summer. Finally got my 262 going and designed a mig25 that flies real nice. I've started a B52 and a edf64 F104 starfighter but crashed on my bike riding to work and broke one of my sanding arms and thats been slowing my building down.

It's good to hear you got your arado flying, I've got my little edf40 down and dusted off for it's first flight maybe this week. Did you finish your Meteor yet?

Cheers -- Stacker
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Old Jul 25, 2006, 02:43 PM
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Quote:
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Scratch,
Been pritty busy flying some of my planes this summer. Finally got my 262 going and designed a mig25 that flies real nice. I've started a B52 and a edf64 F104 starfighter but crashed on my bike riding to work and broke one of my sanding arms and thats been slowing my building down.

It's good to hear you got your arado flying, I've got my little edf40 down and dusted off for it's first flight maybe this week. Did you finish your Meteor yet?

Cheers -- Stacker
Finished the Meteor. Been using excuses, such as lack of a strong enough batt. They are valid, but I kinda got that hangar attachment for the thing. You know how it is.
3s-2100 Prolite ain't getting it, with the 2 Hacker E series motors, in EDF 64s. Like every build, I had unrealistic dreams of it coming out lighter, so that I could power it with that batt. Its not estremely heavy, but too heavy for that.
Like all of them, eventually we get tired of looking at them and try them out.
Bill
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Old Jul 25, 2006, 03:01 PM
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Meteor sure looks good! Might want to look at on of the 20c 2100 packs, I puffed my only 2100 PL a couple of weeks age and had to buy on for my Mig25, It's a bit over a ounce heavier but cranks out the power.

Here is a picture of my B52 fuse with a micrfan powered mig21.

Cheers --- Stacker
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Old Jul 25, 2006, 11:42 PM
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The B52 is cool. EAM personally sold one a while ago, I think designed for 8 40mm fans. The build was partially completed. I thought about it a good bit, but the cost of the gear adds up. 8 EDFs would look/sound cool.

Like the little Mig25 there too.
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Old Jul 26, 2006, 10:04 AM
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Yea, multi engine planes are not cheap. I'm cheating on this B52, it's only got four motors with duel intakes and I'll try to run it with two speed controls.

Cheers --- Stacker
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Old Jul 27, 2006, 12:14 AM
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Quote:
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Yea, multi engine planes are not cheap. I'm cheating on this B52, it's only got four motors with duel intakes and I'll try to run it with two speed controls.

Cheers --- Stacker
That makes sense. Nobody will ever know the difference, as long as the nacelles look good. I've had success with duals on the CC25, although it seems to derate it to 20. That's a guess, I arrived at by realizing that the lack of perfect synchronization seems to derate it, as it gets noticably hotter. On the wattmeter, its about as hot at 20A with twins, as it is at 25A with a single motor. I ran it up above 20A for a short period, but did not like how darn hot it was getting.
I've flown the CC25 on twin EDF at 20A successfully in the past.
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Old Jul 27, 2006, 10:27 AM
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Scratch,
Be careful with the CC25 on two outrunners, I guess the early models had a problem with outrunners and it would cause them to heat way up and even make the suface mount parts all slide off the board. I've also heard that if you try running two motors on one controller you should over rate the controller by about 30%. I have had real good luck with a GWS A-10 and one CC18 thunderbird, but it is a pritty low amp setup (under 14 amps for both motors)

Cheers -- Stacker
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