Rev 8pm 7/15/08

Our newest laser cut semi-kit, the

Rocketeer A

It's full size at 42" span, 314 square inches. Power can be just about any engine from .15 to .23, diesel or spark ignition, and the model can be flown Free Flight or RC. The plane in the picture is set up for Free Flight and the engine is a Russian replica Elfin 2.49 cc / .15 cu inch. You get CAD drawn plans plus laser cut wing ribs, curved tip parts and a ply firewall.

Prices: Plans US $9.00; Laser cut parts $33.00; Plans and parts $42.00. Please include 15% for packing and Priority postage in the US. 

For overseas shipment, please see the "Overseas Postage" lines at the top of the M~Z page of the AALmps

Master List and Photo Finder

where you can place your US or Overseas order via PayPal.

 

This is the 3rd Rocketeer that I've built. The first was a good flying scale down to 29" span /  .020 Replica size that I did in the mid-70s for Model Aviation magazine. Sometime later, the Rocketeer was scaled down even more to 19" and became one of the mini-old timers semi-kits offered by AALmps.

Here's a "how-to" that will tell you more about the new Rocketeer. [click on a small picture to see it full size]

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The body is built by beginning with a crutch, so named because it looks like a medical crutch. The crutch is assembled over the top view. In the picture, the crutch has been moved with its front end overhanging the building board and table so the firewall can be glued in place. Note that the landing gear has been attached to the firewall with strong thread plus glue. You can't clearly see them, but the blind nuts for the firewall mount have also been installed. The plan also shows how you can use hardwood beam mounts if desired.

In this view, note that the lower formers, the subcrutch, and the lower stringer have also been installed. The metal blocks help keep things solidly to the board and are called 1,2,3 blocks, being 1" X 2" X 3". They are intended for machinists to use in various machine setups. ENCO sells them at about US $8 per pair. These are very handy for many model building chores. You may have access to scraps of 1" or 2" square steel rods that would work as well.

Do a Google search for ENCO.

 

www.aalmps.com/rock/cabin2a.jpg (63045 bytes)

With the crutch completed, it's time to build the cabin. Note the 1,2,3 blocks securing the top square to the board and the guide strip that makes sure that the cabin uprights are cut to the exact length required.

With one side glued in place, flip the plan over and make the other side pieces to match.

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The AALmps guard cats [Molly in the foreground; Phoenix sleeping] make sure the model is not disturbed between working sessions.

This view also shows the body essentially done with the cabin in place and the upper rear formers and stringers in place.

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A family member contributed the Maltese Falcon which Phoenix seems quite fond of.

The stabilizer lays upon the body here. Note that the stab is built with a 1/4" X 1/2" spar that is tapered before building. The stab ribs are 3/32" sheet X 1/2" rectangles that are sanded to an airfoil shape after being installed.

 

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The firewall on my model is drilled to match the holes of a plastic radial mount that fits an O&R .23. What you see here, however, is an Elfin mounted to a cubical box made of 1/8" ply. The rear face of the box matches that plastic mount hole layout and a large hole in the front of the box allows screws to be installed to secure the box to the plane. The front face of the box has 4 holes for the Elfin which are fitted with blind nuts.

The arrangement of the Elfin with its bottom intake, needle valve plus the need for a fuel shutoff and a tank caused some head scratching here. You can hardly see the shutoff where it's mounted on a piece of aluminum angle held on with the engine's left side mounting screws. There is a small rectangular tank attached to the bottom of the box and there are 2 tubing vents for filling just at the right side of the crankcase.

 

 

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Wanting to clear the blind nuts' threads after paint, I made a tap stretcher from a piece of 5/32" brass tube with its end formed to a square opening for the tap.

If I was to build this model again, believe I'd make the cowl removable which would really simplify working with an Elfin or an Arden. You can, of course, add another firewall forward of the existing one for an Arden or an Elfin and this would allow for a smaller removable cowl.

If you'll be using an O&R .23 sideport, or an engine with a more common rotary valve up top, you should have much fewer difficulties!

Similarly, building the model with hardwood beam mounts also simplifies things as the screws will be easier to reach.

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This view shows the Free Flight rudder adjusting screws. They are 2-56 nylon screws threaded into 1/8 X 1/4" spruce - hard balsa will work as well.

You can tap threads into wood using a real tap or just a screw with a taper filed into the end about 1/4" long. Start screwing the tap into the wood, back it out every turn or so and resume. When you get through, back out the tap and harden the threads with thin or medium CA glue. When that sets, run the tap through again and you're done.

 

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In this picture, you can see the stab's hold down rubber bands. My model has a Texas Timer MAX I timer that shuts off the engine and serves as a dethermalizer timer. Look for the timer's wire lead [plastic coated fishing leader] that goes through a piece of 1/16" OD hard plastic tubing under the bamboo hold down. That tubing also serves as the stop for the wire, thus limiting the angle at which the tail pops up - approx. 45 deg.

That wire lead goes a bit farther under the stab's leading edge and then goes into another piece of the hard tubing that curves around leading the wire to the rear. A loop at its end hooks to the rudder/stab.

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Here's the rest of the DT wire and the timer. The spring is used to make sure the stab stays put before DTing takes place.

 

RC Installation:

For a diesel powered model, there's plenty of room in the body for RC equipment. I'd suggest that everything can be placed on a platform at the top of the crutch. Three small servos will fit comfortably at the rear, just forward of the wing's trailing edge. The receiver can go up front and the battery can be moved around for balance. Leaving the covering off the cabin top will allow excellent access.

If you're building an RC spark ignition model, then some consideration needs to be given to separating the coil + spark battery from the RC equipment. In this case, locate spark parts way forward and RC parts way aft. Even if you have very small hands, it looks like it would be necessary to install some hatches to access the batteries for both systems.

If you have a new 2.4 system, then spark interference shouldn't be a problem and you'll have much more latitude on where you can put equipment.

Weight:

Per SAM rules at 341 square inches/ 2.181 sq ft:

~ a FF Rocketeer A must weigh 8 ounces/sq ft or 17.45 ounces

~ an RC model must weigh 10 ounces/sq ft or 21.81 ounces.

My FF diesel powered model weighs in at just under 17 ounces with an ounce at the tail end for balance. Perhaps some of those old wooden wheels might be lighter than the light foam wheels I used and require less tail ballast? A little extra lead will be necessary at the balance point. The only intentional extra weight in the structure is a spruce wing spar which may help keep things together when the model dethermalizes. A spruce spar is also a good idea with RC due to the possibility of inadvertent extreme flight loads.

Note that a spark ignition model with its required 3-5 ounces of coil and battery would be difficult to build at the required weight for FF. Perhaps a 300-500 mah high discharge Lipoly single cell can be used to power the coil for little weight? I'm not sure just what is needed to keep from discharging a cell below the safe voltage level, however. One should plan on using Larry Davidson's new lightweight coil in any case. 

Diesel plus RC is very practical at the required weight.

 

rock3a.jpg (62702 bytes)

The wing and tail are covered with polyspan which offers a tough, light covering that is quite durable. The body was done with K&S silk, using just 2 pieces - one per side, wrapped up and over the cabin and top stringer area.

Clear, regular nitrate dope [CPC brand, from California] was applied - about 5 coats on the silk and 3 on the polyspan surfaces. Floral spray "Holiday Red" [rattle can stuff, solvent based, don't get the water based one; from Michael's craft store] was used for the trim after masking off with 3M automotive 1/4" trim tape - go to an auto paint store for this.

Polyspan will act a bit 'funny' even if you've covered with it correctly by putting the fuzzy side down - from Larry Davidson, the fuzzy side is down on the rolls that he sells. If you're not sure, gently rub the surface with your fingers - you should be able to tell fuzzy from smooth. If still not sure, cut off a scrap, mark it as to outside or inside from the roll and give the scrap a coat of dope on both sides. Dope will raise the fibers on the fuzzy side, and you do not want that on the outside of your model! Anyhow, after doping, polyspan needs a bit of 600 paper applied to knock down roughness. On my model, that roughness also happened after applying the red trim.

Diesel fuel will eat nitrate dope and it really does bad things to unprotected Floral Spray, so my model received 2 coats of Minwax polyurethane rattle can varnish which also needed some 600 paper applied. The resulting finish looks pretty good and the effect of the Holiday Red looks like red Japanese tissue was used for trim.

 

Final Thoughts

Check the balance! If you have used an Elfin, your model may be nose heavy as mine was. One ounce of lead was installed inside the aft end of the crutch below the stab. If you're building for spark ignition, then the batteries should be installed where they need to be for proper balance. For RC, you have more latitude on locating the necessary bits to get proper balance.

Check for warps and take out any that you find. A very small amount of washin [LE up] is probably a good idea to keep the left wing up in the FF's left climb [cabin models usually climb to the left]. Test glide the FF model, shimming under the front or rear of the stab as needed. The rudder should receive a bit of offset to the right - for now, just enough so that you can see a tendency to turn right in the hand glides.

FF test flights should start low and slow. Watch for very tight turns to either side and if you see that, carefully examine the model looking for warps that you've missed or maybe the whole stab/rudder is pointing wrong.

An RC Rocketeer can have the CG a bit farther back. You probably should do a low power test flight so you'll know just what the model wants to do. The nicest setup would be to have a small amount of downthrust and right thrust so that the climb is just about automatic - at a steep angle, without turning.

 

Enjoy your Rocketeer A !

Copyright 2008 AALmps

Contact AL at:

AALmps@aol.com

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