طائرة من صنع jetset44

user1002 · December 15, 2004, 4:40pm

F/A-18 Hornet Foam Parkflyer

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Here’s my latest project, an original design foam pusher F/A-18 Hornet. It’s still bare foam right now, but I plan on painting it in Blue Angels colors this weekend. I’ve got 5 flights on it so far with about an hour of flying time, and the flight performance is fantastic! This model has a wide speed range and excellent handling characteristics, and looks fantastic in the air. Here are the specs:

Wing area: 275 sq in (effective area, which includes the effect of the wing strakes)
Span: 28.4 in
Length: 41.7 in
Weight RTF: 15.6 oz as shown
Wing loading: 8.2 oz/ft2 (based on effective wing area)
Motor: GWS EPS-350 with “C” gearing
Battery: 11.1V 1200 mAh Lipo
Prop: GWS 8x6 SF
Current draw: 9.7 amps
Power loading: 101 watts/lb
Radio equipment: GWS R-6 receiver, GWS Pico and Hitec HS-55 servos, 10 amp ESC
Flight controls: Wing flaperons, full-flying horizontal stabilizer, twin rudders
Materials used: Either 6mm Depron or BlueCore fan fold foam

The design goals of this model were:

* True parkflyer: I do most of my flying in nearby small school fields, so this model was designed to be a good small field flyer—meaning good slow flight characteristics. This was achieved by keeping the wing loading under 10 oz/ft2, sizing for a high thrust/weight ratio, incorporating wing flaps to allow easy hand launches and slow landings, incorporating rudders to improve control at low speeds/high alpha, and carefully shaping the wing strakes to provide a good vortex roll-up over the wing and tail (just like the real thing!).

* Simple construction: The design features all flat sheet foam construction with minimal carving, which allows it to be built quite quickly. It’s based on a scale outline of the F/A-18 (1/16 scale), but the fuselage and inlets were simplified considerably to make it easier to build. Balsa triangle stock is used at the corners to allow sanding the corners round, which greatly improves appearance. This model was built over a 2 week period working only evenings and weekends, totaling about 30 ساعة building time. However, since this was a first-of-kind model that had much to figure out, I think I could build a second one in half that time.

* Capable of using inexpensive brushed motors: This model was designed to fly well with the GWS EPS-350C geared motor. Brushless motors will provide even better performance, but are not necessary for good performance. The setup recommended above produces 14.4 oz static thrust with a 48 mph pitch speed, which is ample for this model. While this provides slightly less than a 1:1 thrust/weight ratio, the model will climb at 60 degrees indefinitely and cruises at only half throttle—more than enough for flying in small fields. I do plan to test a geared Himaxx 2015-4100 in this model soon (as soon as I can get my hands on a TP 1320 3s pack—everyone is still out of stock!), so I’ll have a point of comparison soon.

After I finishing tweaking the model, I will clean up the plans and post them here!

Steve

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user1002 · December 15, 2004, 4:45pm

This model was built almost entirely from 6 mm Depron, but BlueCore foam would also work well. I chose Depron because it is slightly lighter (saves 0.5 oz overall on this model) and doesn’t have to be peeled (all the fuselage pieces would need to have the film peeled off). The reason the canopy is made of BlueCore is simply because I ran out of Depron.

This model came out nearly 2 oz heavier than I originally estimated (15.6 oz versus 13.5 oz). Probably half of that difference is due to stuff I just missed, but half is because I used 5-minute epoxy for the entire model. I chose epoxy not just for the strength, but mostly because it cures so quickly. However, I realize now that convenience cost me at an ounce of additional weight. In retrospect, ProBond and a little patience would have been a better choice!

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user1002 · December 15, 2004, 4:48pm

Here’s a preview of the build plans as well as some photos taken during construction of the model. These highlight the flat foam construction, the controls installation (the rudder mechanism was particularly tricky to figure out!), and the canopy and strake details (the canopy is removable and is made from 10 sheets of foam laminated together and then carved to shape). The removable canopy provides access to the battery (which is mounted using Velcro to the fuselage floor to allow CG adjustments). A second hatch is installed over the wing to provide access to the receiver, speed control, and rudder servo.

Note the shaping on the wing strakes. It’s very important that these have a rounded upper surface with a sharp edge as shown. The real F/A-18 was carefully designed so that these strakes create a strong vortex at low speeds that passes over the wing to prolong wing stall and passes over the vertical tails to enhance directional stability. This allows the F/A-18 to fly well at extremely high angles of attack and very low speeds. This model has captured these capabilities. I’ve already learned I can fly the model right down onto the deck at low airspeed/high angle of attack, and then at the last minute chop the throttle and pull full back elevator. The result is the nose comes up to 60 degrees alpha, the model goes into deep stall, and then gently sets down on the ground near-vertically with almost zero forward airspeed.

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