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Old Jan 06, 2014, 06:37 PM
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Build Log
U-2C Spyplane build

I've been wanting to do this for quite a while now and I've decided to go ahead and get started with my build. I've spent the last few weeks working and playing around with drawings and drawing up a rough shape on the computer. I think I'm starting to get close but I am trying to nail down which fan/power package to use. The model will be about 75 inches long but I'd like to check a few numbers first before settling on an exact size. I'm currently considering using the E-Turbax 120mm fan and my research has this set up with a 15 sq in fan sweep area and about a 3.9 in diameter exit thrust tube (@ 80% FSA). Does anyone have any experience with these that could confirm this or add any additional info?

I've scratch built models before but this is my first EDF. I hope to post photos as I go along so please feel free to offer up any advice as I go... Thanks in advance!
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Old Jan 06, 2014, 07:06 PM
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Here's a quick screen shot of where I stand right now. Still lots of drawing to do but the fuse is starting to take shape...
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Old Jan 10, 2014, 02:31 PM
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Watt me worry?
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Good luck on the build....I am subbed.....
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Old Jan 16, 2014, 05:59 PM
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FYI the one I am building has a 69" fuselage, was scaled up from technical drawings and am planning on using a 90mm fan. It has room for a 100 but only has an 80mm outlet and that's fudging a little. I doubt I could get a 120mm to fit plus the outlet size would need to be way out of scale. The fuselage itself is just a tad over 5" diameter.

That said, I am modeling a R version, I see you decided to go with the C. Prettier by far but lacks the intake area for my liking or I would have done that version.

Great wishes on the project, I'll be paying close attention.

Rick
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Old Jan 17, 2014, 03:02 PM
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I'd love to hear how your build goes Rick. I picked the C variant because I just think it looks nicer plus I found one that seems to come with the larger inlets. I think the A and B versions had the smaller inlets and the C featured larger ones. Mine looks like it's going to be about 75'' long so I should have room for a 120mm fan. I'm working on drawing the inlet ducts now. My plan is to make a plug so I can make a glass fuse. Not not sure what route to go yet with the wings. I'd like to have them cut from foam but Im thinking I may get better results and a lighter wing if I build them up from balsa and lite ply. Keep me posted on how yours goes!
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Old Jan 17, 2014, 03:27 PM
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heres a photo of the one im modeling showing the inlets...
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Old Jan 17, 2014, 07:43 PM
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I'm in the process of planking the plug now though it's been on the back burner for a few months in favor of a scratched out Tiger Tail.

I am planning on balsa built up wings and tail feathers to keep the weight light as possible. I was able to thermal my old Phase 3 U-2 once it got to about 500'. Bigger ones should do even better.

I think the earlier models look better too but the R has huge inlets, 44% more wing area, longer tail moment and larger tail surfaces compared to the earlier versions. I debated hard over which one to do.

Rick
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Old Jan 18, 2014, 04:48 PM
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Quote:
Originally Posted by shootnstarz View Post
I'm in the process of planking the plug now though it's been on the back burner for a few months in favor of a scratched out Tiger Tail.

I am planning on balsa built up wings and tail feathers to keep the weight light as possible. I was able to thermal my old Phase 3 U-2 once it got to about 500'. Bigger ones should do even better.

I think the earlier models look better too but the R has huge inlets, 44% more wing area, longer tail moment and larger tail surfaces compared to the earlier versions. I debated hard over which one to do.

Rick
That sounds great. I think im going to try to make my plug from foam and then cover it with glass. I found a place that sells 2'' square aluminum tubing so I thought I could use that to support the inside of the fuse. I think I may fudge the wings a little to give them just a little more wing area too. You going to cover yours with glass? I figured Id use 2 layers of 3oz cloth.
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Old Jan 19, 2014, 09:39 AM
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Yea, I may cover it with some 3/4 oz cloth but since it's made out of basswood and ply it doesn't need any extra strength. I plan on finishing the plug with polyester resin and gelcoat.

I am (so far) making the plug 2 piece, right and left halves. Once I get it finished I will try to separate the two halves for mold construction. Never done it this way but if it works out it will make the mold making much easier.

One of my concerns for now is the wing tube running right through the intake ducting, going to reduce the area somewhat. I'm certainly not up on EDFs and their requirements for inlet/exhaust areas but I will learn as I go along, with help from this forum.

The nose gear retracts forward and out of any ducting's way but the tailwheel is another issue I haven't worked out yet, not much room for it.

You picked out an airfoil yet?

Rick
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Old Jan 19, 2014, 08:36 PM
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Originally Posted by shootnstarz View Post
Yea, I may cover it with some 3/4 oz cloth but since it's made out of basswood and ply it doesn't need any extra strength. I plan on finishing the plug with polyester resin and gelcoat.

I am (so far) making the plug 2 piece, right and left halves. Once I get it finished I will try to separate the two halves for mold construction. Never done it this way but if it works out it will make the mold making much easier.

One of my concerns for now is the wing tube running right through the intake ducting, going to reduce the area somewhat. I'm certainly not up on EDFs and their requirements for inlet/exhaust areas but I will learn as I go along, with help from this forum.

The nose gear retracts forward and out of any ducting's way but the tailwheel is another issue I haven't worked out yet, not much room for it.

You picked out an airfoil yet?

Rick
Yup... I'm thinking about going with an N2312 airfoil at the root at least. Maybe the same at the tip. It looks like the real one had the airfoil cranked up at the root so I may do the same. I figured having about 2 degrees of positive incidence at the root and zero at the tip. I have wondered about using a wing tube thru the fuse but I think I have enough room to use two shorter tubes for each wing that wont interfere with the ducting. Not exactly sure how to do this yet but I'm thinking about using some sort of carbon structure to support the shorter wing tubes and distribute the load around the ducting. I've also wondered about the tail wheel assembly. I made a prop-jet version of the U-2 just a little larger than what you are looking to build and I used a Hobbico mechanical nose retract and modified it with a shorter strut. It worked great. I may do something similar for this one too. I'm going to use Robart mechanical retracts for the mains. I found a supplier that sells titanium rods that will fit the retracts so I figured that would be a good way to save some weight without losing any strength. I was also thinking about using lighter weight mechanical retracts in the wings to replace the "pogos". My prop version had two hacked digital cameras on board that I triggered with trainer button on my transmitter. I planned on doing the same but with a different set up. I plan on using a small microcontroller to control 2 to 3 higher resolution camera modules. I plan on having everything housed in a removable module in front of the main gear.

How do you plan on making the clear canopy for yours?

Rene
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Old Jan 19, 2014, 11:16 PM
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Quote:
Originally Posted by shootnstarz View Post
...One of my concerns for now is the wing tube running right through the intake ducting, going to reduce the area somewhat. I'm certainly not up on EDFs and their requirements for inlet/exhaust areas but I will learn as I go along, with help from this forum....

Rick
Check out the other U2 build thread -- this is the way it is typically done from what I have seen: http://www.rcgroups.com/forums/showp...&postcount=115
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Old Jan 20, 2014, 09:09 AM
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How do you plan on making the clear canopy for yours?

Rene[/QUOTE]

I plan on making the canopy area removable from the plug. I'll leave it attached while I do the final shaping and finishing then use it detached as a plug for a vacuum formed canopy. But at first I'll mold the fuselage with it in place for testing, then cut it out later. That's the plan anyway, could very well change.

I also thought about using two short wing tubes but will have to study how much room I have after the ducting is designed. It's not like these things will be doing 8g turns, the full scale ones are very frail. As Clarence Johnson said "Anybody can build a plane strong enough but it takes a genius to build one that's JUST strong enough".

I'll be using fall away pogos to start, see how that works out. I also haven't worked out the wing incidence yet, the full scale has oodles of positive.

Rick
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Old Jan 20, 2014, 09:11 AM
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Thanks Bill, I've been following that thread too. He is doing an amazing job on his, extremely detailed.

Rick
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Old Jan 24, 2014, 02:23 PM
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Hey Rick... I'm getting to the point where Im trying to fit retracts. Looks like the main (forward) gear shouldn't be a problem but the tailwheel is going to be super tight. I'm thinking about using a Robart 590 electric nose gear for the tailwheel gear and there isn't much room. Which retracts were you thinking of using? I figured going electric would be easier and lighter. Robart has drawings of their retracts so Im going to make digital models of them and plug them into my drawing...
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Old Jan 25, 2014, 09:32 AM
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Looks like the main (forward) gear shouldn't be a problem but the tailwheel is going to be super tight
Does the servo have to be near the tailwheel? Closed loop guided wires with servo well forward? Might even be able to couple to main retract servo.

Regards Ian.
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