Old School Model Works Comet

The Comet flies well and the author chose to install an optional working rudder. He found it to be mildly effective and its performance was improved with additional throw.

Written by Greg Gimlick A 1950s design with modern construction Product Review As seen in the April 2019 issue of Model Aviation.

Bonus Video

At A Glance

Specifications

Model type: Sport delta wing

Skill level: Intermediate to expert

Wingspan: 39.5 inches

Wing area: 470 square inches

Airfoil: Symmetrical

Length: 32 inches

Weight: 3 to 3.5 pounds

Power system: Electric: 25-size brushless motor; 60-amp ESC; 3S LiPo battery; .19 to .30 glow engine; 4-ounce tank

Radio: Four-channel system (with elevon mixing); three 40 to 70 inch-ounce servos for elevons and rudder; one 40 to 70 inch-ounce servo for throttle (if using a glow engine)

Construction: Laser-cut wood kit

Needed to complete: Four-channel radio; three or four servos; power system; covering; wheels; control rods/clevises; adhesive

Price: $119.95

Test-Model Details

Power system: Cobra C-2826/8 1,130 Kv brushless outrunner motor; Cobra 60-amp ESC with 6-amp switching BEC; Turnigy 3S 2,200 mAh 40C LiPo battery

Propeller: Master Airscrew 9 × 7 three-blade

Radio system: Spektrum iX12 transmitter; Spektrum AR620 receiver; three Spektrum A6180 standard metal gear servos

Ready-to-fly weight: 56 ounces

Wing loading: 17.2 ounces per square foot

Flight duration: 5 minutes

Pluses

Illustrated manual with online supplemental photos.
Good quality and parts fit.
Plans rolled and detailed.
Nice flight characteristics.
Designed and manufactured in Ohio.

Minuses

Battery hatch on bottom instead of top.
No room to adjust battery location for CG.

Product Review

When I Opened the box, I was immediately struck with the fact it had rolled plans! (One of my pet peeves is folded plans that I must flatten.) They are nicely detailed and the illustrated manual is a good step-by-step build plan. Everything was bundled and bagged with no visible damage to anything during shipping. The wood quality appeared to be excellent and laser cutting was clean. Everything was clearly labeled for easy identification.

My first impression was good and I was excited to get building!

Construction

Begin by carefully inspecting everything then spend some time reading through the manual and studying the plans. There is a link in the manual for more online photos and those are helpful during the build. Resist the urge to begin removing parts from the carrier sheets and organizing them into groups. Many builders prefer that, but I think it would be a mistake. I removed parts as called for and cleaned up the edges as I went.

During the build, you will flip the airframe back and forth between upright and inverted, but keep track of which side is up! It sounds silly even as I write it, but there were times when I caught myself about to glue something in upside down because I didn’t pay attention to which side I had up. That is especially easy to do on the nose gear mount—ask me how I know.

This isn’t a beginner’s model or build, so I won’t describe it as I would a novice build.

The build begins with the plywood fuselage sides and center wing rib laminations. From here, you’ll work outward on both sides. I found it easy to simultaneously build both sides.

A word of caution as you remove ribs from their carriers: Be aware that small protrusions act to locate trailing edges (TEs), spars, etc., and might be mistaken for the tabs that held them into the balsa carriers. When you’re cleaning them up after removal, don’t clean those off!

Both ends of the ribs have extended tabs that fit into a jig to align and support the wing while framing. If you break one while removing it from the sheet, carefully glue it back in place. Having all of these in place is paramount to success and straight building.

01: The laser-cut kit parts are laid out for inspection.

02: The plans are cut and taped to form a full-size layout.

The choice of glues while framing the wing is a personal thing, but because I am extremely allergic to CA glues, I chose to use Titebond and lots of clamps, pins, etc. This slowed my build time, but it worked well. Some areas lend themselves to using CA for ease and I donned a respirator for those parts.

Assuming that you’ve built kits before, there are no surprises along the way. Standard construction methodology is used with spars, leading edges (LEs), and TEs. Pay attention when doing the sheer webs because the outer two are done differently than the others. LE sheeting is on top and bottom and requires careful fitting/trimming to nicely match the fuselage. After the wing is taken off the board to do the bottom side, it becomes challenging to remember which side is up. You don’t want to confuse that when installing fuselage sheeting and hatches.

Landing gear mounts and radio bays are built in the usual fashion and are fitted to your particular equipment. The nose cowling is a process of laminating parts around a crutch assembly. At first glance, this looks as though it will be quite an exercise in alignment and carving, but it goes quickly.

I suggest using wood glue as you laminate the sections to make it easier for final shaping. I used a stationary sander for the rough shaping and finished it with sanding blocks. Go slowly, and trial-fit it several times to ensure that you don’t go too far. Finish-sanding is crucial because you’ll be covering it with UltraCote and it will show any imperfection. I broke off the mounting tabs several times in the process of fitting it, but in the end, it came out well.

Power System and Radio

I used standard-size servos because that’s what the plans called for, but any size with enough power can be used. Because the wing servos are behind the center of gravity (CG), that would be one area where a lightweight servo might be handy if you have difficulty attaining the proper CG. My receiver choice was the new Spektrum AR620 model without an antenna and it has been flawless.

The recommended motor is a 25-size outrunner. I chose to go with a similar motor with a slightly higher Kv and threeblade propeller. Propeller clearance and my grass field predicated this decision. The Cobra C-2826/8 1,130 Kv motor worked well paired with a 9 × 7 three-blade propeller. The power is roughly 100 watts per pound.

Control Throws and CG

I installed everything in the recommended positions within the fuselage and found that my CG came out roughly 1/4 inch ahead of the recommended location. Because there isn’t room to adjust the battery, I left it at that for the test flights and decided that it is fine there.

Be sure to measure from the front edge of the firewall and not from the wing’s LE! Errors here would drastically alter the location. With my CG located where it is, the Comet is fully aerobatic and will fly inverted with some help on the elevator.

The controls were set to the values listed in the manual. They "looked" as though they would be sporty, so I set up triple rates on the Spektrum iX12 transmitter to offer 100%, 75%, and 50% just in case, but I left them at 100% and am perfectly comfortable there. I set 30% exponential on all of the surfaces.

03: The laminated cowling is laid up and clamped according to the instructions.

04: The Cobra motor is test-fitted to the firewall and the Cobra 60-amp ESC programmed with the programming card. The only change was disabling the brake.

Flying

The test-flights were made on a sunny, 48° day with light wind at roughly 8 to 10 mph. Despite a slight crosswind, the Comet lifted off and tracked nicely with little input required. Rushing it off the ground is something you’ll want to avoid because it can get your attention. I did that once and it recovered by lowering the nose and applying more throttle.

Now I let it run until it wants to come up by itself. I’ve dialed in a slight amount of reflex on the elevons and that might be mostly because of my slightly forward CG.

The Comet climbed out nicely and performed quick axial rolls when commanded. It’s sporty but not twitchy, and it doesn’t seem overly sensitive in either pitch or roll. Rudder is optional according to the manual and I chose to install it. My rudder throw is slightly more than suggested, but I like it and it is mildly effective. I don’t think it will be a big deal should you opt not to use one.

Delta wings are different when performing loops, but this one doesn’t do anything scary and will pull through with power. It turns on a dime and although knife-edge flight isn’t in its repertoire, the rudder was effective enough to do some nice photo runs tipped up on one wing.

05: Everything was connected and checked before covering. This provides a good opportunity to see what is involved in building the Comet.

06: The equipment fit snugly, but everything fit where suggested and the CG came out roughly 1/4 inch ahead of the recommended location.

I took the Comet to altitude and attempted several stalls. I refer to "attempted" because it never really broke. It mushed along with full elevator and began a descent in a high-alpha attitude. The closest thing to a tip stall I encountered was when I pulled it off the ground before it was ready. I don’t think you’ll find any surprises if you set this machine up the way it’s designed.

Conclusion

I enjoyed building this kit and the result certainly didn’t disappoint. There’s something about flying an airplane you’ve built yourself that adds to the overall enjoyment of flying. The Comet is well designed and engineered, and Old School Model Works has simplified the process of building symmetrical wings. If you’re looking for something a little different and a project that builds quickly, I highly recommend that you consider the Comet.

By Greg Gimlick | maelectrics@gimlick.com Photos by the author