Falcon Mk. VII - 1100mm Interceptor - RC Groups
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May 19, 2015, 06:42 PM
We don't need no stinkin' tail
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Build Log

Falcon Mk. VII - 1100mm Interceptor

After a long series of small tweaks to the falcon 5B and a good deal of research into flying wing lift distributions, I decided that the changes were big enough to constitute a new airframe.
So, I give you the mark 7. Fast as a speeding bullet, strength of a hundred men, hyperbole of a billion pundits.

It is an incremental improvement in a variety of areas. It will have a better spar layup, hopefully increasing stiffness. It will only have elevons in the outboard ~60% of the wing, as elevons in the inboard region are counterproductive in pitch. It will have more washout and better distributed washout for an actually planned out lift distribution and a specific design CL. It will use the 3 mil laminate from the famed Assassin that Meanbaby gave me, so the packing tape is no longer a structural member. This frees up the trim scheme a bit, as you can see in the below picture. It also allows the LE and TE of the elevons to be non-parallel, permitting better optimization. The laminate also provides a good means to secure a fixed TE to the inboard portion of the wing.
It will use more intelligently designed (and effective, therefore smaller) ventilation. I am also using only the Metric system, after becoming thoroughly fed up with the Imperial one (who the heck puts 16 ounces in a pound? what do those words even mean?), so that's a huge improvement.

I will be trying to put in an hour of building each day right after school, to get it running by the time the Warwick Fun Fly rolls around next month.
The plans are drawn, the parts are ordered, and the glue gun's hot.
Ladies and gentlemen, THE BUILD IS ON.

5/19: Wing cores are drawn out and cut free.

5/20: Elevons are drawn and cut, formers are drawn, cut, and laid up. Still need the new graphlite to arrive to finish them.
The parts arrived, the graphlite is cut to size and glued into the shear webbing.

5/21: Wingtip blanks are drawn, cut, and laminated. Need to get the wing cores foldable before they can be sanded.
TE blanks have been sanded and laminated. The laminate allows for them to be sanded in a straight taper (instead of only tapering the trailing-most 1/2, resulting in a bump in the airfoil) while maintaining rigidity, and for a constant and tighter ~1mm blunt TE, very close to the optimal thickness for this scale (note - the optimal is not zero, the flow on the top/bottom of the wing are at different speeds, so if they meet flush with each other the plane will start shedding large vorticies. A small blunt TE creates a buffer of separated flow).

5/22: The LE of the wing cores have been fiberglass taped, and the upper surfaces have been pre-curved.
The spars are glued into the lower wing surface, the center spar has been compiled and mounted.
Electronics have been mounted (servos, Rx, ESC).
The wing cores have been joined at the root and their TE's beveled to accept the upper surface.
Fins have been drawn, cut, sanded with a much shallower TE bevel, laminated, and taped with red trim.
Once I cut the battery tray out, the wing cores will be ready to be folded

5/25: The battery tray is cut out, the twisting jig is assembled and the wing cores are folded over.
The wingtips are attached to the wing cores, and they are laminated over as a single unit.
The elevons are hinged with glass tape and laminate, and the inboard TE's have been glued on and secured with laminate.
The fins have been inserted into the wingtips, secured with a dab of hot glue and the seams have been laminated.
The battery hatch has been gut out, as well as access hatches for the servos should they be needed.

5/26: The motor mount plate has been machined and its foam tetrahedron has been assembled. The mount has been secured to the plane and the motor mounted, with the balance point 190mm behind the nose (It was 175mm on the mark 5, which probably had less loaded tips, and with the elliptical distribution the mark 7 should have the optimal CG is 200mm. Nose heavy flied poorly, tail heavy flies once).

5/27: The main landing skid has been drawn, cut, glued together, laminated and mounted.

5/28: Trim scheme on the bottom has been taped in.

5/30: Trim scheme on the top has been taped in.
Control horns have been fabricated and the linkages have been set up.
A plastic acetate strip has been glued to the ventral skid to withstand asphalt landings.
Ventilation holes have been cut, and the newly exposed foam laminated over.

Th-th-th-th-that's it, folks. The mark 7 is ready to go (record time! 11days!), maiden flight will be no later than Warwick (6/20)

6/21: Maiden was this Saturday, and hot diggety is this a great plane. Despite my fears about the higher pitch prop, the climb rate is as good as, if not better than the mark 5. It seems that the prop makes it faster indeed, which means that there is lower parasitic drag. And it loses even less speed in turns, which means that the Culver twist works and there is lower induced drag. Which all makes this bird handle like a hotliner. (Not as good as an actual hotliner, just similar. maybe it's a hotliner's little brother. )
Maneuverability and especially energy retention are better than the mark 5, so it's really good at power off loops and turns. But what's really fun is starting up high or fast, cutting power and doing gliding low passes, zooming past the pits in ground effect. This bird does not want to slow down. And I didn't notice until I was the only one flying, but as it passes by it makes a hollow, ghostly whistling sound. This is most awesome at higher speeds and when entering a turn from high speed. The sound is still present at low speed, it's just toned down to a whisper.
All in all, this is thespecially new best plane yet.

Status: awesome
Last edited by RPM314; Sep 09, 2017 at 04:11 PM.
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