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Monday, January 2, 2012

Art-Tech Pitts Special + Super Tigre .10 = Atlas V Rocket

Update: Coming Soon - AS3X Head-to-Head comparison.

Yes, I admit it, I knew from the start that my easy-hovering gyro-enhanced Cessna 150 Aerobat might not have been the best AS3X comparison platform for the recent E-Flite UMX Pitts M12 w/AS3X review--not because of a lack of aerobatic prowess (the Cessna is surprisingly capable)--but because the high wing 150 comes from a different Phylum, Genus, and Species of the aircraft Kingdom. 

The Art-Tech S2B Pitts Special was the longstanding, official Z8RC All-Time Favorite overall RC airplane until the 51" Great Planes Yak-55M unseated it with authority, fairly recently. Granted, the little $75 S2B benefited from a--then $18 after typical discounts--Super Tigre .10 stashed under the hood.  The resulting combo pumped out a leisurely 1.5:1 T:W with a few carbon stiffeners to match to the power.  But even as shipped, it was hard to beat the F:P (Fun:Price) ratio of this fantastic little bipe!

The trivial set-up and easy success of my Cessna's twin gyros (installation time: < 5 minutes) inspired me to investigate other AS3X alternatives for the same or less than the $196 E-Flite Ultra Micro Model 12 when packaged as a BNF.  So with $196 as a self-imposed ceiling, the Art-Tech Pitts Special bipe seemed like a good starting starting point even though the S2B is historically a bit 3D-challenged.  So I'm going to modify a brand new AT Pitts S2B from Hobby King (my beloved AT Pitts Special in Banana Hobby colors was destroyed by a dropped link from my Spektrum DX8 radio) with a few budget, after market gyros, just to see what happens in a price-constant head-to-head showdown with AS3X.  Coming soon...

My original, January 2010 AT Pitts Special mod article follows:

The AT Pitts is just about the most fun you can have RC flying.  It putters along carving perfectly lazy lines on a Sunday afternoon, relaxed as can be.  Most of us will never get tired of such an enjoyable sportster, but that never stopped us from going hog wild before.

Enter z8rc's favorite little motor, the Super Tigre .10 (no affiliation).  At only $20, this motor dominates its class, pumping out well over twice the motor-Thrust-to-Weight ratio of the next best technology.   With a sleek cowl wrapped around it and an 11" GWS DD/HD prop, the ST .10 peaks somewhere around 22:1 motor-T:W.  Compare to a pricey Power 10 in a similar installation at 11:1, or Turnigy 3536 at around 8:1.

The motor only weighs 2.2 ounces due to its steel bell-type design, as opposed to the more bulky, aluminum front and rear casing that houses most motors.  Although the engine is a feather weight, making it ideal for lighter-end.10 installations demanding monster pull, the copper coils are only slightly smaller than those in overall larger .10 size motors as shown in a previous head-to-head:

In fact, the light weight of this motor is likely to be your biggest problem--a great problem to have.  The ST motor so dominates motor-thrust:weight in its class, that most .10-class models don't really allow for the possibility of such a light motor.  Their CGs are inherently too far back, in anticipation of the usual chunk of lead in the nose that it is difficult to install an ST .10 with a rational CG.  That means installing the motor, and then fashioning a creative way to shove the battery and other components farther forward or into the cowling.

This little Pitts makes for a pretty cooperative light engine conversion.  There are two battery bays, the front one allows you to insert an 1800 mAh battery vertically, right behind the firewall.  That config will be too nose heavy with most engines, but it works well with an ST .10 up front.  If you want to run a 2200 mAh--handling in the air is only slightly degraded--just heat up a soldering iron and bore a hole in the front corner of the rear battery bay, then slip a longer battery in diagonally toward the nose so the end of the battery is against the back-top of the firewall.  Pretty simple.

One thing the Pitts lacks in stock form is any sort of cooling airflow for the engine and ESC.  The firewall is almost completely solid and the cowling is vented with about as much area as a soda straw.  Oddly, the fuselage is vented behind the bottom wing attach point, to allow air to escape, but there is no way for air to enter.  So to make it all cool off, I drilled three 1/2" holes in the firewall, not too close to the engine mount, opened the bottom cowl vent with a Dremel sanding drum, and slightly increased the size of the cowl intakes with a Dremel mini sanding drum.  The Super Tiger .10 mounting mod is shown using a 4mm prop shaft adapter, for a ripping 1.5:1 aircraft Thrust to Weight ratio.

It is hard to imagine more fun for under $180 as an RTF, including the 10-size motor upgrade with a bundled 1800 mAh Lipo, 6 ch RX, and a 8-AA 2.4Ghz 4ch radio TX.

Construction Tips: 
  • Wire the wing box and horizontal stabilizer
  • Wire the rear line of the landing gear fairings for strength (make a triangle)
  • Add a wire connecting the inner wheel hubs to make the gear itself into a triangle
  • Reinforce the top wing with wooden or carbon spar underneath, or the ST .10 will fold it (flight tested)
  • Tape all leading edges with clear mailing tape for strength and durability
  • Tape the landing gear fairings with on both sides, to prevent cracks from a bounce
  •  Replace the nylon top wing bolts with 4" x 1/8" metal bolts into anchors embedded in the fuse
  • Increase the number and size of the cowling intakes to keep your ST .10 monster running ice cold.  Also vent the firewall to let air escape through the fuse vents already present on the underside


Newer version photos:

Not shown - I Guerrilla Glued a square carbon fiber beam along the inside of each side of the fuselage before attaching the bottom wing.  Also put two carbon fiber X braces inside the fuselage, in front of and behind the bottom wing, so the foam fuselage doesn't "roll" side to side.

Overall, these carbon fiber mods make the plane extremely rigid.  Let the G-Glue dry overnight and watch it for the first few hours to make sure it doesn't expand into unwanted places--it will try.









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