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Old Jan 04, 2006, 07:21 PM
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Westchester County, NY, USA
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My Multiplex Microjet mods

I am so happy with my TwinJet I decided to take the plunge and buy a Microjet. It's powered with a powerful JustGoFly 400DF outrunner with a 22A ESC, also from JFG. I have a 5.5 x 4.5 Master Airscrew prop on it, but I might prop it down a little. I thought it would come out way too heavy with my mods, but it came out at exactly the manufacturers recommended weight of 16 oz.
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Old Jan 04, 2006, 07:24 PM
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This photo shows my CF prop guard and sandpaper finger grips. I have a similar setup on my TwinJet and it works well.
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Old Jan 04, 2006, 11:26 PM
BDR
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Nice to see another thread on the microjet. My approach to the MJ was to lighten it as much as possible to make it a possible parkflier. A 2-cell Lipo and Johnson 250 motor kept the weight just below 10 ounces. Launches fairly easy and can fly within 2 soccer fields. This is my first pusher jet so my concern was too much speed! Not much vertical performance but good for learning to cope with more speed and will upgrade motor in the near future. I like your turtledeck mod and will use it. Is the prop gaurd necesary? I've yet to break a prop and adding weight at the back is not a good idea. Keep the good ideas flowing!
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Old Jan 05, 2006, 12:44 AM
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You know the whole time I was building the MJ I was already thinking about making a second one. The next one will be much lighter, although not as light as yours. I would do away with a couple of mods in the interest of keeping weight down. I'm thinking of going with 3-cell 1320 packs, of which I have several. I'd also go with the 300DF motor from JustGoFly, which would draw half the amps of the 400DF. I think it's inexpensive enough that it might be a good idea to have one heavy and one light, as others have done.

As far as the prop guard, I did loosen the mounting on my TwinJet with prop strikes. Don't forget this 16 oz. version is going to come in hot and heavy compared to your's, so you might really never have a need for it. The CF really doesn't add much weight though. The epoxy holding it in probably weighs more than the CF rods.
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Old Jan 05, 2006, 07:47 AM
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Redondo Beach, CA
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I like your motor mount -- need to do something like that with my MJ. The stock mount doesn't hold up well.

How does it fly?
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Old Jan 05, 2006, 06:29 PM
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Yes, you can probably get that aluminum at any hardware store. One 3 foot piece can make a lifetime worth of motor mounts. Easy to drill also.

How does it fly? I haven't had a chance to get to the field yet. Working midnights and getting up at 3:00 PM doesn't give me much of a chance to get to the field before it gets dark. I may be able to do some flying this weekend though. I'll keep you posted. It should be a rocket!
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Old Jan 05, 2006, 06:49 PM
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Great mods, I will have to incorporate them into my MJ. I especially like the turtledeck idea...
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Old Jan 06, 2006, 03:42 AM
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Thanks Sal. Yes, I figured the turtledeck mod worked great on my TJ so what the heck.
The most time consuming part was the removable fins. I had to first insert dowels, then drill them out to fill with JB Weld, and then tap the hardened weld. I toughened up the JB Weld with thin CA before tapping. I guess I could have just tapped the dowel, but I thought tapping the weld would be more secure. It holds down those fins just fine. Hopefully they'll stay on at 60 or 70 mph!
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Old Jan 06, 2006, 09:14 AM
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Nicely done mods to MicroJet !

Danny great thread ! Great mods ! Let me know if I missed any of your mods.

I see the CF tail skid to keep the prop healthy - very nice ! I noticed on your other planes you used a complete loop. I wonder if this mod will cause the rod to slid backwards on the force of landing. I'm very interested in how this works.

I did notice the screws coming from the tail stabs. Will one screw be enough ?

Also the hand grips from sand paper. Nice !

I like the inboard mounting of the motor mount on a wood mount to fill in the slot and for mounting of an outrunner motor. What type of wood did yu use ? I know some might use paint stirrers for this, and you can get them for free at LHS. I used a smaller balsa fillet and on a crash it took a chunk of the foam and fillet with it. Your longer fillet will distribute the load over a larger area - nicely done. Looks like you used Epoxy ? Have you tried Poly-Urathane glue ? This is my fav glue, light weight and will give a little and crunch alot before letting lose. The Epoxy will crack and IMHO is strong enough, but not flexible enough.

I really like that you moved the outrunner closer to the center and see you were able to move the battery closer to center as well. But I wonder how well balanced this is with the battery behind the ESC. I also think you might need some form of blocking mechanism to keep the battery from crunching your electronics on a crash. A crash is bad enough without losing electronics to go along with it.

Looks like you embedded some wood to hold down the rear plastic cover - is that the "Turtle Deck ?" If so you already answered the question.

Looks like you have a insert in your front canopy - what is that ?

How are you holding the canopy's down ?

Nicely done and certainly all great mods for any MJ ! Now to straighten out my fuselage. I crashed on maiden after an insane 1 minute of flying and after re-inflating the EPP, and re-glueing it now looks like the concord with the nose slightly dipped down. I'm very tempted to fly it but think I should break and re-set the nose.

Vinnie
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Old Jan 06, 2006, 03:52 PM
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Vinnie,
Thanks for the compliments.
The motor base is made of 1/8" liteply. It's really a lot stonger than balsa, as you can imagine. I sanded the forward end to a point and just pushed it into the foam and then just epoxied it down. The thrust line is the same as the stock motor installation.

The tail skid was a little problem. I had wanted to just use a loop as I did on the TJ but I found that when using the guage CF that was needed for durability I wasn't able to bend the CF without breaking. I actually was installing a piece and it snapped in my hand. Luckily nothing broke the skin, but it did sting.

You have a good eye, the rear motor cover is held down by the screws that screw into dowels expoxied in the foam. I always hit the hole with thin CA to give it strength. It also prevents the wood from spliting when tightening the screw.

As you can see in the photos the front of the deck cover is held down with rubberbands. To remove you just slide it forward and pivot. The cover is never removed, just pivoted. I thought this was the stock setup on the TwinJet, but maybe it was my mod?

I forgot to mention, the ESC is in the tunnel behind the battery, but you're right about the RX being in front of the battery. I think it'll be a goner if there's a nose-in crash. For my 300DF equipped MJ I'll mount the battery, the 1320 pack, forward of all electronics. I just couldn't do it with this setup without winding up nose heavy....

My other little mod, which no one mentioned, was with the control horns. I didn't like the stock setup so I reshaped the horns, drilled new holes and just used .032 piano wire with a "V" bend for adjustment.

Danny
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Old Jan 06, 2006, 07:46 PM
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Very nice ! I will use many of them on the TwinJet sitting on my build bench. I used magnets on the rear canopy cover and the clips on the forward canopy, but I like the rubber band mod. I've used electric heat shrink on CF to keep it from splintering and adds a little color. I use a CF loop below my Carbon Fiber IFO to protect the blade from strikes and for landing gear. I'll be going with dual 450TH motors on the Twin Jet and running the pair of 1700 on 7x5 prop and once I get used to the Jet running the 3000 Kv bell with a 5x5 prop and shoot out beyond 100 mph.

I was thinking of putting a CF rod through the wings to add more strength and adding some fiberglass re-enforced mesh across the bottom to keep the wing from flexing. I intend to pump it full of 4S batteries and push it very fast.

Let us know how the maiden goes !

Vinnie
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Old Jan 06, 2006, 11:21 PM
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hey guys ,

thanks for this MJ thread. I just found it.
my MJ came in yesterday. Ill be building it in a couple weeks. I just finished a 3D build "THE JUDGE" by Hobby Lobby Intl. this is my first 3d and first real plane with Arons so I dont know how its gonna go.

but any way I will be using Gorilla Glue on this MJ. I found that its stronger than epoxy and dries out like EPP. on my last MJ I just glued the mega 15/16/04 straight on w/out a mount and saved some weight there. dont take much either. If you havnt tried the GG get ya some
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Old Jan 06, 2006, 11:21 PM
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I have my receiver mounted up front also. So far I've nosed in twice, both times breaking the nose off just in front of the wings. So far the electronics have survived. At least with the 3S TPS2100 pro-lite packs I'm running, it's not possible to get the balance right with the packs all the way up front -- without adding weight to the back.
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Old Jan 07, 2006, 02:54 AM
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Vinnie,
That TJ is going to be a animal. I'd love to see that thing fly. We have a club member that owns a LHS and flys a TJ with twin kontronik (sp?) BL motors and it is also very fast. He uses smaller packs and I'm sure he's destroying them with what those motors are pulling, but I guess being a store owner he just has to grab another pack off the shelf when he needs it.
He also flys a MJ with a hot motor and I believe it's actually faster than the TJ. He had them at NEAT and they were clocked on radar, but I don't know exactly what their speeds were.
Both planes are a great platform for experimentation, and are easy to repair. BTW....to get your MJ back in shape try using a heat gun while applying pressure. You might be able to coax that fuse back into shape. It worked great on my TJ. The downside is the EPP particles kind of balloon up and remain that way. It really doesn't look to bad though, just different.
Also, great idea on covering the CF with heat shrink. From past experience I know you have to be careful when applying heat to CF since it turns rubbery if overheated.


Scott,
Keep us posted on how your's is going. I haven't tried GG yet but I always hear people raving about it. As far as motor mounting, the outrunners really can't be directly glued to the airframe. At least the majority of them. I know there is at least one outrunner now (Ultrafly?) that has a full enclosure, but other than that you have to devise another way to mount. Good luck with yours. If it flys like the TwinJet it'll be a winner.

XXrando,
I suppose we can glue a piece of balsa the exact size of the fuse so the force of the battery flying forward will be lessened since the balsa support will take some of the shock. Of course I won't do that until after I ruin the rx in a crash!
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Old Jan 07, 2006, 03:08 PM
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Ya Gorilla Glue - otherwise known as "Polyurathane Glue" is excellent for RC, since it is light and very strong. It takes longer to set than the more popular Epoxy but I think ideal for most uses. If you want to fill in gaps or recreate void areas mix in a little water to activate the glue and it will slowly foam up while it sets. Use the blue painters tape to guide it along a channel, break or to hold a stick in the fuselage while gluing. It's a bit more messy than some of the other glues, but a MUST for the RC building bench.

Heading out now to fly a couple new planes I built over the holidays but haven't had the weather or time to fly ! I have an hour of light. The TwinJet just stares at me wondering when I'll put it together. It's part of my bonding process Ya gotta read all the mods before building and learn of problems some guys have had, otherwise you have a crappy maiden and don't know why.

Vinnie
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