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Old May 20, 2009, 12:07 PM
Pusher jets rule!
crxmanpat's Avatar
Mesa, AZ
Joined Jan 2006
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Mini-HowTo
Profile pusher jet construction techniques/tips

I'm often asked about techniques I use to build these profile pusher jets, so I thought I'd start a thread that describes many of the techniques I use and tips I've discovered in the past few years in order to have all the information in a single place.

Keith Sparks has a wonderful book called "Building With Foam" that has many tricks and tips, and it is a highly recommended read. As well as all of the build threads that Steve Shumate has done for his wonderful parkjets. But these builds are typically for built-up foam planes, not the profile jets (although most of the techniques can be applied to the profiles as well).

My thread will focus more specifically on the profile mid-mount motor pusher jets like the Nico Hobbies Mini Pusher Jets, the 6mmflyrc Quick-Build Series, the Yardbird RC jets, the designs by Tomas Hellberg, and the planes and plans posted by people like "nac", "jetcaptain" and "rc cal", as well as most of the model plans posted over at www.parkjets.com.

The first tip involves printing the plans of the plane you want to build. Most designers offer a full size plan in a single sheet, and then Tiled versions for both US Standard 8.5X11 paper ("Letter"), and A4 paper that is used by most of the rest of the world. When printing the Tiled plans, make sure the "Page Scaling" option is set to "None" (see pic). Otherwise your plan may not be printed in the proper dimensions.

Printing out multiple pages and then taping them together can be tedious. Some people use the easier method of downloading the full plan to a CD or flash drive, then taking that to a place such as FedEX/Kinkos or one of the office supply stores for printing on a large format plotter. I take my plans to Staples as they can print up to 48x36 and are fairly inexpensive ($3 for 36x24 and $5 for 48x36).

Pat
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Old May 20, 2009, 12:38 PM
Pusher jets rule!
crxmanpat's Avatar
Mesa, AZ
Joined Jan 2006
17,203 Posts
Building Materials

Next I'll talk about a list of materials that I typically use for these builds. If you are downloading the plans and building from scratch, then you will need to buy foam. Most of these are done with 3mm or 6mm depron, and a good source is www.rcfoam.com. However, most hobby shops now carry sheets of depron as these planes have become more popular over the last few years.

There are other sources of foam that can be used, such as paper backed foam board that can be found at most craft stores (but you'll have to soak the board and peel the paper off), or fan-fold foam (or "FFF") which is normally found at home improvement stores. But personally, I like depron the best as it needs no prep.

Most builds typically have a carbon fiber tube for the wing spar. For my 6mm builds, I usually buy Midwest Products Item #5821 as that is what my LHS sells, and it has an outside diameter of 4mm, giving me 2mm of working room for epoxy when using 6mm foam. There are also times when using CF strips or smaller diameter tubes may apply, like my 3mm planes that use a 1mm x 3mm CF stick. The LHS may have a supply of various sizes of both tubes and strips.

The final material needed is lite ply for the motor mount. I use 1/8" lite ply (and I also have a source for laser cut ply mounts which are also 1/8"). If you buy a kit from 6mmFlyRC, Grayson Hobby or the like, you will most likely get the ply mount included (as well as a CF spar and control horns, etc). For my 3mm planes I use 1/16 ply for the motor mount.

For cutting the foam, I use a standard Xacto knife with a No 11 blade. I buy these in bulk as the blades go dull after a short period of time. And for anyone who's worked with covering, you know that when the blade goes dull it tends to tear the covering. The same goes for foam. Once the blade dulls it will tear the foam on the bottom side. So change that blade often. I typically use 2 blades per plan.

There are several types of glue that can be used. My favorite is UHU Creativ for Styrofoam (also called "UHU Por" in Europe). This stuff is very strong and holds up well over time. The only problem is that it's somewhat hard to find in the US. Right now RCFoam is carrying UHU Por, as is Hobby-Lobby.

My second favorite glue is Beacon 3-in-1 Advanced Craft Glue. You can find this stuff in 4oz bottles in most craft stores like Michael's or Jo-Ann's, and online at RCFoam. The only caution is that this stuff has a little acetone in it. A test of a glob on a piece of scrap depron revealed that it would actually eat the foam. But if you just put on a very thin bead, squeeze the parts together, separate and then press together again, you get a good bond. Dry in 20 minutes, fully cured in 24 hours. Great stuff. RCFoam also has another formula of Beacon glue called "Foam-Tac". It seems Beacon has specially formulated this stuff for depron (says so right on the bottle) and other foams. I have not tried any yet, but if it'd as good as the Beacon 3-in-1, then it will be a winner.

But the trick to ALL of these glues is that they must be used properly in order to work. These are all "contact cements", which means that you apply a very thin layer of glue to the surfaces to be joined, press the parts together briefly and separate, allow the glue to get "tacky" (10-30 seconds), then rejoin the parts. All of these cure within 24 hours, so I like to glue a plane up in a single sitting, then allow it to cure overnight before removing any tape or continuing with construction.

Currently, here's the glues I use, and where I use them:

5-min Epoxy - Wing spar (and any other CF spars in the plane)
Hot glue - Motor mount, servos, control horns, control rod guides
Beacon 3-in-1 - All foam construction where the above glues are not used

Pat
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Old May 20, 2009, 12:59 PM
Pusher jets rule!
crxmanpat's Avatar
Mesa, AZ
Joined Jan 2006
17,203 Posts
Installing the Wing Spar

The first step to almost every build (once all the foam parts are cut out) is to install the wing spar. You will need:

Flat, level working surface
Knife
CF spar
Straight edge (I use a 36" metal ruler)
Tape (low tack 3M painters tape is best)
Glue (I use 5-minute epoxy)
Scraper (any straight edge scraper will work, I use old credit cards and such)

First, determine the length of your CF spar and cut as needed. Then, using the straight edge, cut your spar slot in the foam. Be sure to cut the slot a few milimeters longer and wider than the CF spar so that the epoxy can work around the edges.

Next, take a length of tape and entirely cover the slot, then flip the wing over. Now use some tape to "frame out" the slot opening. This is to prevent excess epoxy from sticking to the foam and creates a nice clean install. Before mixing your epoxy, be sure you have a nice flat and level surface to work on, as well as something to weigh down the foam. I use a couple thick heavy books to make sure the foam stays flat while the epoxy cures.

Now mix your epoxy and run a thick bead into the slot, making sure it fills the entire opening and is about 3/4 deep. Insert the CF tube and press down firmly so that the epoxy runs all around the tube. This should eliminate any air bubbles on the bottom. Then use the scraper to "smooth out" the top layer of epoxy so that it is flush with the top of the opening, being careful not to get overflow on the foam. This is where the tape framework helps. Place your weights on the foam so that it remains flat during the curing process.

After the epoxy has cured, remove the tape from both sides of the foam. You will now have a smooth and solid install of your spar.

Pat
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Old May 20, 2009, 01:21 PM
Pusher jets rule!
crxmanpat's Avatar
Mesa, AZ
Joined Jan 2006
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Basic Construction

Most of the parts on these planes are tabbed or slotted for ease of contruction and alignment. However, some pieces such as intakes, dividers and vertical stabilizers may require installation at an angle (for example, the vertical stabs on an F-22). Since you want to have as much surface contact as possible between the two pieces of foam, it's a good idea to sand the necessary angle in the contact surface as needed.

Before I begin gluing parts together, I always do a dry fit of the parts to ensure I cut the tabs and notches correctly. Now is the time to make any adjustments needed. You don't want to put glue on a piece only to find out it doesn't fit properly.

These jets typically go together in the following manner:

- Glue in wing spar
- Install control surfaces
- Glue on upper forward fuse
- Glue on lower forward fuse
- Glue on intake sides
- Glue on belly pan
- Glue on vertical stab(s)
- Glue on the motor mount and control horns
- Install electronics

Once you are satisfied with fit, apply glue to one of the parts to to be joined, then press the two parts together and immediately separate again. Rejoin the parts after the glue becomes tacky. But also read the directions for the type of glue used to make sure you are using it properly.

And of course, use tape where needed to ensure parts stay together until the glue cures. Scotch tape does not stick well to depron over long periods of time. Blue Painters tape works better for this.

Pat
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Old May 20, 2009, 02:23 PM
Pusher jets rule!
crxmanpat's Avatar
Mesa, AZ
Joined Jan 2006
17,203 Posts
Motor Mount

OK, mounting the motor has probably been one of the most challenging items that I've encountered on these builds, but I think I have it down to a science now. If you are cutting your own plane from scratch, DO NOT cut out any of the slots for the motor mount (just cut out the prop canyon). Instead, leave that foam in place until you get all parts cut out and can do some measurements.

My motor mounts consist of:

- 1/8" lite ply motor mount with 6mm notches cut in at each polar location (see pic)
- 6mm depron disc cut to match the ply mount

Step one is to measure the dimensions of the notches in your mount so you will know how wide to cut the slots in your foam. Next you will need to take your motor and attach the cross mount and prop adapter/prop to it. Then take the depron disc, ply mount and assembled motor and determine the cut distance needed so that the prop hub winds up in the middle of the prop canyon when looking from front to back. Once you have all your measurements, cut the necessary foam from the parts.

After the plane is fully assembled, check to see that the area where the depron disc will glue to is completely straight and level. These jets do not require you to add any thrust angles on the motor due to the fact they are in a pusher configuration aft of the CG. Next, glue the ply mount to the depron disc with hot glue. After the glue sets, place the motor cross mount on the ply and mark the screw holes, then tap the holes. Then mount the motor.

Normally you can glue the mount in with the motor already attached, and the prop installed. If you can do this, then that is the preferred method. If not, you will need to mount the motor without the prop attached. Use hot glue to secure the motor mount to the plane, making sure you "build up" some glue at all the joints.

The biggest problem with the motor mounts is that they tend to break loose after a while due to prop strikes on the ground. It helps to inspect the mount on a regular basis. Hot glue stays slightly flexible, and is not as susceptible to vibration as epoxy is.

Pat
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Old May 20, 2009, 02:49 PM
DreamArcher's Avatar
Joined Apr 2008
1,979 Posts
Quote:
Originally Posted by crxmanpat
...I'll use the glue that GWS includes with their kits (I always have several tubes lying around).
Hi. The GWS glue seems like typical plastic model glue. i.e. Testors. The smell, texture, dry time. Do you think it's the same?

Great thread. Thanks.
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Old May 20, 2009, 03:15 PM
Pusher jets rule!
crxmanpat's Avatar
Mesa, AZ
Joined Jan 2006
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Hinging your control surfaces

Most people hinge their control surfaces using packing tape. I used this method for quite a while, but finally got tired of the tape peeling up on me as I live in a very hot summertime climate (it can get to over 120 in my garage in the summer), and I finally switched to 3M Blenderm (same thing as Parkflyer Hinge Tape sold in hobby stores by DuBro). Here's how you do it:

1. Cut a 45 angle on the leading edge of the control surface.
2. Add a strip of Blenderm (or packing tape) to the top leading edge of the control surface.
3. Place the control surface against the trailing edge of the plane so that it is angled down at 45, then smoothly attach the tape to the plane.
4. Flip the plane over, then fold the control surface back until the 45 angle is lined up even with the trailing edge of the body and add another piece of tape.

This will cut down on slop in the control surface.

For control horns, I've used everything from old GWS horns, to laser cut ply horns, to homemade horns from 1/32" lite ply, to plastic scrap. Any of these work fine. I will cut a slit in the foam for the horn, then cover the back side with scotch tape. I'll then use hot glue and fill the slot and insert the horn.

Pat
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Old May 20, 2009, 03:19 PM
Pusher jets rule!
crxmanpat's Avatar
Mesa, AZ
Joined Jan 2006
17,203 Posts
Quote:
Originally Posted by DreamArcher
Hi. The GWS glue seems like typical plastic model glue. i.e. Testors. The smell, texture, dry time. Do you think it's the same?

Great thread. Thanks.
I think they are similar, but not the same. I think the Testors glue is specially formulated for styrene plastic that models are made from (I've emptied my share of tubes in the past!). If you want to use Testors glue on foam, I'd try it on a test piece first. But I think Testors would probably melt foam.

Thanks for the accolades!

Pat
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Old May 20, 2009, 03:35 PM
Pusher jets rule!
crxmanpat's Avatar
Mesa, AZ
Joined Jan 2006
17,203 Posts
Ailerons and Tailerons on the same servo

Most of these plans call for the control surfaces to be taileron only (aileron/elevator mixed on the same surfaces). But I've found that cutting in ailerons separately gives you much better control response throughout the flight envelope, especially at slower speeds. Here is my method for hooking the ailerons and tailerons up on the same servo so that you still only need two servos total instead of four.

On the servo arm, use something like a DuBro E/Z Connector on the outermost hole of the arm. Use the same thing on the taileron control horn. Then run .047 gauge wire from each E/Z Connector to the control horn on the aileron. Use a z bend on the wire at the aileron horn. You can then adjust the wires on the ends so that both surfaces are trimmed level.

Alternately, you can install two control rods on the servo arm, one running to aileron and one to elevator. In this case, use the z-bends at the servo arm, and the DuBro connectors on both control horns so that you can adjust each surface as needed without using sub-trim on your radio, or having to use mechanical adjustments.

Pat
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Old May 20, 2009, 03:53 PM
Pusher jets rule!
crxmanpat's Avatar
Mesa, AZ
Joined Jan 2006
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Power System and electronics

This post deals with the typical pusher jets in the 13-20oz AUW range.

Because of the limited size of the prop canyon, the biggest prop you can use is 7", and in some cases 6" is as big as you can go. Unfortuntely, that limits the choice of motors you can use. However, you do have options.

My absolute favorite setup is a Welgard/Suppo 2212-6 motor, a 30amp ESC and an APC 6X4E prop. This setup will give you unlimited vertical on a typical profile jet, and when used with a 1300-1500 lipo will give a flight of about 5 minutes of very spirited flying. Here are some places to get these motors:

Nico Hobbies - You can get a motor/ESC combo for $28.

Grayson Hobby - This is the combo deal with the 30A ESC included and is $40.

BP Hobbies - You can get this with a 30A ESC for $36.

RC Hot Deals - The A2212/6 2200kv motor is the one you want, and the combo with a 30A ESC is $30.

Model Aero

RC Timer - Listed as a 2826-6, but is pretty much the same as the 2212-6.

HobbyKing - Same motor that RC Timer sells as a 2826-6 2200kv. Also comparable to the 2212-6 motor.

If your model ends up heavier than the typical 15 to 20oz, you can step up to either the Grayson Super Mega Jet motor, or the BP Hobbies Ultimate outrunner. These should give you about 32oz of thrust.


As far as servos are concerned, any regular old 9g servo will do. I personally prefer HXT900s from Hobby King. I've beat the tar out of these and they keep on trucking. I've also used the cheap TowerPro or TP servos that you can get from Hobby King or RC Hot Deals, but they have a higher failure rate than the HXT900. I like these servos so much that I carry them in my webstore, even though none of my mini kits use 9g servos. That's how popular they are!

Pat
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Old Jun 04, 2009, 09:17 AM
If it flies, its cool
bondohead's Avatar
Atlanta
Joined Apr 2007
1,114 Posts
I Like The Guys At Grayson And Rc Powers But Doesnt Look Like Thay Even Sell It With Out The Esc. What Kind Of Quality Are The Grayson Escs?
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Old Jun 04, 2009, 12:15 PM
Pusher jets rule!
crxmanpat's Avatar
Mesa, AZ
Joined Jan 2006
17,203 Posts
Quote:
Originally Posted by bondohead
I Like The Guys At Grayson And Rc Powers But Doesnt Look Like Thay Even Sell It With Out The Esc. What Kind Of Quality Are The Grayson Escs?
You can buy both the Park Jet and Super Mega Jet motors separate from the motor/ESC combo packages:

2212-06 Park Jet V2

Super Mega Jet motor

As far as the ESCs that come with these motors, I have had several and not had the first issue with any of them. The only problems I've ever had with any of these power combos was magnets coming loose in the older V1 motors. But that has been address with the V2 models and I've not had any issues with those.

Pat
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Old Jun 04, 2009, 01:06 PM
Pusher jets rule!
crxmanpat's Avatar
Mesa, AZ
Joined Jan 2006
17,203 Posts
Painting/Finishing/Decals

There are some people who seem to have trouble finding the right paints for foam. In the years I've been doing this, I've used Testors rattle can spray paints more than anything else. I've used it on everything from beer cooler foam (EPS, like on GWS planes) to depron, to Elapor (EPP or EPO, like on Multiplex planes). And it works on blue and pink foams as well. Some people also use Krylon H2O, but I've never seen a need to buy any myself (as I do mostly military scale models and need the colors Testors sells).

The trick with using spray paint is to spray at least 12" away from the surface, and to use light coats. It's not the paint itself that eats the foam, it's the propellant used in some spray paints that is the problem. By staying 12" away, most of the propellant will evaporate before it reaches the foam.

Another good paint is the water-based acrylic craft paints that you can find at places like Michael's (Apple Barrell brand), Jo-Ann's (DecoArt Americana brand), or the craft section at Wal-Mart. Any brand will work well, as long as it's water-based acrylic paint. And even though they don't carry true military colors, you can find just about any shade you require. These can be applied by hand with a brush, or thinned and used in an airbrush.

Most of my planes get water-slide decals applied to them for the scale markings. I use 8.5"x11" sheets of decal paper that I purchased from www.beldecal.com. You can get sheets made for both Laserjet and Inkjet printers, and clear paper as well as white paper (white paper is good for decals that have white in them, such as USAF stars and bars, as printers don't print "white" ). If you have access to a color laserjet, this is the preferred method for printing decals. Because with inkjet, you have to also apply a protective coating after printing to keep the ink from running. Laserjet printers are just much easier to work with.

Most of my decal sheets are made up of Word documents that I create by taking images from the web and the "post scale decals for downloading" thread in the Scale Electric Planes forum, and then sizing them as needed in Paint and pasting on the Word doc. And since I do a lot of USAF builds, I downloaded a font called "AmarilloUSAF" from the internet. This font will allow you to type words and numbers that match the USAF block type font.

Here's a decal application instruction guide that I have on my website:

http://www.nicohobbies.com/store/fre...structions.pdf

Pat
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Old Jun 04, 2009, 11:09 PM
I just want to fly
justwanttofly's Avatar
USA, IN, Jeffersonville
Joined Aug 2008
690 Posts
this thread need to be a sticky!!!

Hey Pat thanks so much for this thread.this is exactly what i have been needing i love to build planes I'm just now starting to get a little more complex with my builds incorporating wood and foam together.I want to scratch build but i have a few questions that i be lot of us just starting want and needing answers to.is there a link or maybe you can help or others can chime in on this. Is there a formula to use when i need to know how big my wingspan needs to be to carry the load..lets say i want to build a prop jet 40 inches long how do i know how much wing i need?

And how tall should my v-stabs be i have too many new ideas in my head but I've tried to use sketchup and I end up with part of the plane on different axis.But anyways I've also wondered when you guys say 1to1 thrust are you saying if my plane weighs 20 oz I need at least 20oz of thrust to fly and how much watts per pound should a jet have.i had a whole bunch more questions but I can't remember them so when I do I'll chime back in..

Again I want to say thanks sooo much for this thread..

Happy
Flying!!
Mike BeMiller
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Old Jun 05, 2009, 08:58 AM
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jhtitan's Avatar
Washington MO
Joined Jul 2008
567 Posts
Quote:
Originally Posted by crxmanpat
Most of these plans call for the control surfaces to be taileron (aileron/elevator) only. But I've found that cutting in ailerons separately gives you much better control response throughout the flight envelope, especially at slower speeds. Here is my method for hooking the ailerons and tailerons up on the same servo so that you still only need two servos total instead of four.

On the servo arm, use something like a DuBro E/Z Connector on the outermost hole of the arm. Use the same thing on the taileron control horn. Then run .047 gauge wire from each E/Z Connector to the control horn on the aileron. Use a z bend on the wire at the aileron horn. You can then adjust the wires on the ends so that both surfaces are trimmed level.

(pics to be added later)

Pat
Any pics of this yet? would love to see your set up.
Thanks
jon
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