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Old Sep 18, 2008, 01:45 AM
Pusher jets rule!
crxmanpat's Avatar
Mesa, AZ
Joined Jan 2006
17,638 Posts
Awesome Steve. Is the kit mfgr the usual suspect, or someone new?

I was picking away at mine tonight. Did a lot of sanding edges round, hinged the tail surfaces, got the motor pod done except for the top and did the final preps to join the fuse to the wing and tail.

I'll probably be gluing lots of pieces together tomorrow. I might even get a maiden in this weekend.

Pat
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Old Sep 18, 2008, 01:53 AM
Park Jet Guru
jetset44's Avatar
Seattle, WA
Joined Jun 2002
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Glad to hear yours is coming along, Pat! The kit maker is someone new. The usual suspect has their hands full right now selling park jets!

Now that a kit is in the works, I'll be especially interested to hear the problems and improvements you guys find as you build from the plans. We'll use those tips to make the kit even better. So please post any tips you have as you go!

Steve
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Old Sep 18, 2008, 02:07 AM
Park Jet Guru
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Seattle, WA
Joined Jun 2002
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Don't fear the flat plate wing!

I've already received a couple messages from folks asking about putting an airfoiled wing on this model (same question I get regularly on my park jets). As a professional aerospace engineer with 20+ years airplane design experience, I can tell you with authority--DON'T!

There are some very good reasons why the flat foam wing performs so well on this model, aerodynamically as well as structurally. I keep meaning to write a detailed post/thread on when and where the flat foam wing should be used and how it compares to an airfoiled wing at this scale, but just haven't had the time yet. But the Polaris is an ideal application for the flat foam wing, given it's very light wing loading, small size, parkflyer speeds, and highly swept and low aspect ratio wing. If you were to spend the effort to build an airfoiled wing for it, I think you would be hard pressed to notice the difference in flight--and it might even be worse due to the weight penalty. If this model were bigger and faster and more heavily loaded I wouldn't be using a flat wing, but that's not the case.

So enjoy the ease of construction and excellent performance of the flat foam wing on this model!

Steve
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Last edited by jetset44; Sep 18, 2008 at 03:08 PM.
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Old Sep 18, 2008, 04:11 AM
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Del-Dredd's Avatar
Near Aberystwyth - Wales
Joined Aug 2004
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Just a thought after looking at the pictures, does the lower rear end have to narrow to a point so much for a particular reason, or just aesthetics (maybe helps tracking in the water?).

As you have plenty of room between the center line and the start of the aileron, you could move the sides wider apart and have a blunt rear this would provide more room for the wires and control rods.

It would also enable easier setting up and clearance of moving parts to wires.

Securing the wires would be a good idea, as if they move you could get a control restriction or insulation wear and eventual shorting.
I work on full size military jets and we have regular inspections in certain areas looking for chafing damage and security of cables that are close to control runs.

Del
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Old Sep 18, 2008, 02:29 PM
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Ky
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Very nice Steve, congratulations on another great design. I've been looking for a combination water/snow plane. Thanks for sharing it.
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Old Sep 18, 2008, 03:02 PM
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jetset44's Avatar
Seattle, WA
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Quote:
Originally Posted by Del-Dredd
Just a thought after looking at the pictures, does the lower rear end have to narrow to a point so much for a particular reason, or just aesthetics (maybe helps tracking in the water?).

As you have plenty of room between the center line and the start of the aileron, you could move the sides wider apart and have a blunt rear this would provide more room for the wires and control rods.

It would also enable easier setting up and clearance of moving parts to wires.

Securing the wires would be a good idea, as if they move you could get a control restriction or insulation wear and eventual shorting.
I work on full size military jets and we have regular inspections in certain areas looking for chafing damage and security of cables that are close to control runs.

Del
Good thinking, Del. Yes, the back end comes to a point both for low drag and for aesthetics. I really like on the Northstar how the fuselage blends directly into the base of the vertical tail. I gave some thought to trying to widen this area for more clearance, but didn't like what it did to the looks. And because there WAS just enough room to get everything in, I stuck with these lines. However, I did deepen the hull a little bit in the aft end, both for more rotation capability as well as to provide a little more room for the electronics installation.

Good catch on securing the wiring, too. I forgot to mention that I used dabs of CA and epoxy to secure all the motor and servo wiring against the sides of the fuselage to keep them from rubbing against the aileron horns.
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Old Sep 18, 2008, 03:03 PM
Park Jet Guru
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Seattle, WA
Joined Jun 2002
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Quote:
Originally Posted by Dave Barrow
Very nice Steve, congratulations on another great design. I've been looking for a combination water/snow plane. Thanks for sharing it.
Glad you like it. Post pics of your model if you build it!

Steve
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Old Sep 18, 2008, 04:58 PM
Pusher jets rule!
crxmanpat's Avatar
Mesa, AZ
Joined Jan 2006
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Flat plate wing.

Steve,

I agree with you wholeheartedly. After building a few of your birds, and all of the 6mm Quick Build series, I too agree that flat plate is better at this scale.

The one thing I have learned though, is that you really want a good stiff spar across the wing, as well as stiffening rods behind the leading edges. I like to use large square CF sticks for the main spar, and then insert flat CF sticks for the leading edges. Your plan locations for the spars works perfectly! I have a nice stiff wing that won't warp over time. I'll post a couple pics of my Polaris wing tonight.

Now I'm going to have to go back and rebuild some of my older birds using this method as the wings are getting warped pretty good.

Pat
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Old Sep 18, 2008, 05:46 PM
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Near Aberystwyth - Wales
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Thanks for the comments Steve, thought it would be aesthetics, as long as theres room no problem.

Thought i would mention securing the wires as maybe somebody would not realise to do it, better safe than sorry.

Probably not much chance of chafing unless using metal rods with the points outwards, more likely a control restriction which could be dangerous.

Del
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Old Sep 18, 2008, 06:23 PM
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larryross's Avatar
Grand Junction, Colorado
Joined Dec 2007
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Quote:
Originally Posted by Del-Dredd
Just a thought after looking at the pictures, does the lower rear end have to narrow to a point so much for a particular reason, or just aesthetics (maybe helps tracking in the water?).

As you have plenty of room between the center line and the start of the aileron, you could move the sides wider apart and have a blunt rear this would provide more room for the wires and control rods.

It would also enable easier setting up and clearance of moving parts to wires.

Securing the wires would be a good idea, as if they move you could get a control restriction or insulation wear and eventual shorting.
I work on full size military jets and we have regular inspections in certain areas looking for chafing damage and security of cables that are close to control runs.

Del
Build a 2x scale and you will have all the room you need.
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Old Sep 18, 2008, 06:56 PM
BEC
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Auburn, Washington USA
Joined Jan 2001
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Quote:
Originally Posted by walt b
HELP PLEASE:
I need a sorce for blue foam or 6 mm. depron within 30 miles of Puyallop washington.
I tryed all the Lowes stores in the area and Lumbermens Building supplys.
thanks
Walt
The new Lowes in Renton stocks PBIII (the skinned-on-one-side Dow blue foam).
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Old Sep 18, 2008, 07:35 PM
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Seattle, WA
Joined Jun 2002
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Hey, great to see you poking around in this thread, Bernard!
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Old Sep 18, 2008, 08:50 PM
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Columbus, Ohio
Joined Jun 2005
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Quote:
Just a thought after looking at the pictures, does the lower rear end have to narrow to a point so much for a particular reason, or just aesthetics (maybe helps tracking in the water?).
It looks to me the main reason it goes in tight in the rear is to support the vertical stabilizer/engine pod. Would also allow more air to hit the rudder in flight
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Old Sep 18, 2008, 09:47 PM
Pusher jets rule!
crxmanpat's Avatar
Mesa, AZ
Joined Jan 2006
17,638 Posts
Here's a couple quick pics to show my wind spar and reinforcement CF. The main spar is 5mm sq CF (I normally use larger but my last piece was not long enough), and the leading edge pieces are 5mm x 2mm stick. For those I cut a 2mm wide slot in the foam, put packing tape over one side, ran some 5 minute epoxy into the grove and then inserted the stick and taped over it.

The horizonal stab has the same size stick in it.

Oh, and I decided to hinge all my control surfaces. GWS just came out with some nice plastic hinges that work well with foam. They're in the latest A-4 and J-10 jet kits. I had some left over, so I decided to try them in depron.

First I cut the hinge slots in the control surfaces, then I sanded the control surface as needed to allow free movement. Once satisfied I simply epoxied in the hinges. Turned out pretty good.

Pat
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Old Sep 18, 2008, 11:34 PM
BEC
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Auburn, Washington USA
Joined Jan 2001
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Quote:
Originally Posted by jetset44
Hey, great to see you poking around in this thread, Bernard!
Yeah, when I shoulda been doing something else.....

Saw your name and the configuration of the airplane and had to take a look.
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