Jet Powered "JexJet" for Youthful Payload Pilots Article & Plans
April 1960 American Modeler

April 1960 American Modeler Table of Contents These pages from vintage modeling magazines like Flying Aces, Air Trails, American Modeler, American Aircraft Modeler, Young Men, Flying Models, Model Airplane News, R/C Modeler, captured the era. All copyrights acknowledged.

It is surprising that today there is no equivalent to the Jetex type motors that provide a simple and safe form of jet propulsion for small airplane models. you can still buy Jetex engines on eBay for not too much money, but the fuel pellets are quite expensive. Over the years, a couple companies have manufactured Jetex-compatible fuel pellets, but all of those are gone now, too. A couple decades have probably passed since Jetex fuel pellets were available. American Modeler and a few other magazines used to run build and fly articles for Jetex powered model airplanes. This April 1960issue included plans for the JexJet, which uses the Jetex 35 or Jetex 50 size engine. A built-up wing (23" wingspan) and horizontal stabilizer helps keep the weight down. If anyone knows of an available Jetex fuel pellet source, including instructions for safely making your own, please send me an e-mail.

Jet Powered "JexJet" for Youthful Payload Pilots Article & Plans

With fine prizes being offered in many meets and comparatively few entries to compete against, one is sure missing out on a lot of fun and prizes by not making one of these fine-flying Jetex powered jobs. This design, made as stable as possible for use by beginners, is almost impossible to loop because of its long tail moment arm.

Adjustment is quite easy. The stabilizer is set at the angle shown, the engine position shifted to obtain the best gliding angle. Then the Jetex engine is permanently fastened and powered flights are a cinch. More about that later.

Interested? Well, stock up on some very soft 1/16" sheets, that is the primary size used. We used Sig "Contest Balsa" in our model. From the full size plans obtain the proper outlines for the fuselage sides and top panel piece. Also cut out all required formers and rudder parts. Cement the side pieces to the nose block; be very careful to line up the sides. Pinning the tail ends of the side pieces together with help. Cement former A in place, then the fuselage top panel, which rests against the back of A and is flush with the upper edges of the side pieces. The formers cement in the places shown on the plans. The bottom sheeting is next-when the cement has dried thoroughly, the sheeting is trimmed flush with the side sheeting.

The roof of the cabin area is cut out of very hard balsa or pine, shaped, and cemented in place. The celluloid windshield and side windows are added. When cementing the rudder to the fuselage dab some cement on along the lower edge before inserting through rudder positioning slot, since we want the lower part of the rudder to be glued to the inside bottom sheeting for maximum strength. Add the rudder fairing piece (curved) to the front of the rudder, then the various stabilizer mount parts.

The little block under the trailing edge of the stabilizer is soft, so it can be easily cut for changing stabilizer incidence during flight tests. Bend and cement de-thermalizing hook in place. The fuselage assembly is sanded and given one coat of clear dope. Re-sand lightly with No, 400 Wet-or-Dry sandpaper.

The leading and trailing edges of the stabilizer are cut from 1/8" sheet and can be pre-shaped somewhat before pinning down to the workbench for assembly. The ribs are cut out as per plan outlines and cemented in place. Tips cut from 1/16" sheet are added. Sand entire stabilizer to a smooth airfoil shape, then cover with light tissue (we used "Airco" thin grade). The front stabilizer hook and de-thermalizing hook are bent and cemented in place. Water-spray assembly lightly. When dry give a single coat of clear dope that is a 50-50 mixture of thinner and standard clear dope. For each ounce of the above "mix," it will be necessary to add three drops of Castor Oil to "plasticize" it so the covering will be less brittle when thoroughly dried out.

The dummy is cut out of 1/16" sheet and "ballasted" with bits of solder to weigh 1/4 ounce. He should be 3/8" deep (front to back) and 3/4," square for the body part, topped off with a 3/8" x 3/8" "head." These are minimum dimensions which may be exceeded, but do not build this character undersize. Note that the "cockpit" is fairly deep front to back - this allows the dummy to ride forward or rearward for minor balancing of the model when flight testing. Wherever the dummy rides, use soft balsa spacer blocks of 1/16" or 1/8" sheet to keep him from shifting position. (With a 3/8" deep dummy in a 3/4" cockpit, a total of 3/8" of scrap will be needed to fill up the empty space.)

The wing ribs are cut out - don't forget notches for the spar. The center section is pinned down and cemented together first, then the tip panels. Tip spars are omitted until the assembled tip panels are propped up for dihedral. Then the tip spars may be added ... Less work fitting them to the dihedral angle this way. The false ribs are added to the center section and "recess" made for the wing key. This "key" is merely a rectangular piece of 1/16" sheet that fits a corresponding recess in the wing bottom to position the wing exactly the same for all flights. Use scrap balsa under the spar in the center section where the "recess" is made, so it is flush with the rib bottom edges for covering. Apply covering after sanding smooth the assembled wing. Wing covering is similar to that described for the stabilizer. Do the bottom of the center section first, then the top. Tip panels are done last. If a good sprayer or atomizer is not handy for water-spraying, a small piece of folded tissue dipped in water will do the job. Be very careful in "brushing" on the water with it, as the moistened covering tissue is very weak. Keeping the water used to a minimum is one way of not poking holes in the tissue covering, and usually results in less warps.

Colored trim is okay if you use colored tissue to do it with. Colored dope weighs too darned much for these lightweights, so it is o-u-t ... OUT. Ditto for doping - the one coat of clear, throughout, is all that is allowable.

The balance point shown on the plans should be marked on the model before any flight-testing is attempted. For the first few glide-tests, strap the Jetex unit in approximate position atop the cockpit with rubber bands ... just enough to hold it during glide-tests. If your wing and stabilizer are quite warp-free, you should get reasonably good gliding angles on the first attempts, providing that the wing and stabilizer incidences match those on the plans closely. Minor adjusting can be made by sliding the Jetex forward or aft. Once satisfied with the glide, fasten the Jetex to the cockpit roof area - position it as straight as you can. The Jetex charge should be omitted throughout all glide-tests.

Power flying should be a snap. Load the Jetex as per manufacturer's instructions, then light the fuse with the model held in a steep 90 degree bank. This avoids sparks falling onto the wing as would be the case when the model is held level. Once you hear (and feel) the increase in thrust, you can launch the model. A slight nose-up attitude is best, with a moderate "heave." But not like a hand-launched glider, lest you "fold" your wing. Watch the entire flight to see if climb, glide, and circling (if any) are satisfactory. If the power flight is alright and model glides straight, tilt the stabilizer (without changing the incidence) to achieve some circling in the glide. The glide circle should be in the opposite direction to the power circle. This balance of circling directions steepens the climb to the maximum attainable without looping. A swooping turn during power climb is desired - if the model turns too tight, loosen the Jetex unit and re-screw like you would offset in an engine. Once really satisfied after continued testing, a small fillet of cement can be added around the base of the Jetex mount for additional strength. The Jetex mounting does not get too hot to do this, but don't touch the Jetex unit after a charge has burned - it gets HOT. If you desire, you may. add a little aluminum foil to the wing center section as protection against flying sparks. A piece about 3" long, about 1" or 2" wide in front and 3" or 4" wide at the back will protect the fan-shaped area of the wing center most susceptible to the sparks. Just light gluing around the perimeter of the aluminum foil will do - weight is all-important in a model of this size.

Remember these main adjusting hints: Power turns adjusted with the Jetex. Gliding turns through stabilizer tilting. Rudder always left alone (dead straight). Above all, follow the instructions about cleaning out the jet motor. And that means every flight. The same goes for use of de-thermalizing cord - this model has real soaring capabilities, so avoid losing it by lighting that dethermalizer on every flight.

If dear old Dad has helped in flight adjustments, let him get his kicks with a few flights. But be sure you get to know your own flight adjustments - nothing looks worse at contests than having Dad carry the model, light the fuse, make the adjustments, launch it, and retrieve it. Under those conditions, it isn't really entered in the Junior event, is it?

Full size construction plans for "JexJet" are on Group Plan #460 from Hobby Helpers, 770 Hunts Point Avenue, New York 59, N. Y. ($1.10).

JexJet Plans

Posted February 27, 2021