PT-20 Build – The Wings

The plans say this wing will build itself – that’s closer to true than I might have imagined! It quite literally took more time to pop the die-cut ribs out of their sheets and clean them up along with the leading and trailing edges than it did to build BOTH halves of this wing.

PT-20 Wing - removing from plans

PT-20 Wing – removing from plans

In the picture above you can see the construction is very straightforward… once you get the center spar pinned down and the rib webbing pressed into it, the ribs just slide into the notches in the web. Next, press fit the top spar onto the web, trapping the ribs. Align the trailing edge and ribs, glue. Repeat for the leading edge. Just make sure you keep everything flat as you go! Got it all lined up? CA does the rest.

PT-20 Wing Centerline Mating Surfaces

PT-20 Wing Centerline Mating Surfaces

Because I am building the “B” sport wing, I used the dihedral gauge to mark the proper angle and then used a razor saw to cut the LE, TE and Center spars/webbing along that mark – keeping in mind that the cut (front to back) needed to be 90 degrees to these parts. You’ll need to get this correct the first time because you don’t get much of a 2nd chance with it. You can see, I got pretty close – hopefully some careful sanding will get these closer to perfect.

PT-20 Wing - mock join

PT-20 Wing – before joining

PT-20 Build – The Fuselage

Fuselage Right 3/4

Fuselage Right 3/4

Construction of the fuselage has been straight forward for the most part. The only things that presented difficulties were the aforementioned warped parts (which I cut replacements for) that needed to be sanded and shaped a bit to get a good fit. The instructions ask that you drill 3/16″ holes in some of the bulkheads/formers so that they can have the pushrod guide tubes passed through them.

Pushrod guide tubes

Pushrod guide tubes

Some of these bulkheads were plywood and were easy to drill the holes in, some of them, however, were balsa and did not take a drill bit very well. As a result, one of these broke and I ended up cutting a replacement from plywood – just to save the grief of breaking another one.

Bottom view of Fuselage

Bottom view of Fuselage

Fuselage Interior & Servo Tray

Fuselage Interior & Servo Tray

So far, I am pleased with the results  and have just a few more items to complete on the fuselage before moving on to the wing assembly. This project is moving along well and I will be posting the wing build and photos soon.

PT-20 Build – Horizontal / Vertical Control Surfaces

The first steps in this project are building the horizontal and vertical tail surfaces. This is a simple process; only requiring gluing two pre-cut balsa sheets together to form the horizontal and vertical stabilizers. I sanded smooth, rounded leading edges on the stabilizers. In the photos of the horizontal assembly, you can see that I have hinged (but not glued) the elevator on to the stabilizer.

Horizontal Stab and Elevator

Horizontal Stab and Elevator

Horizontal and Vertical Tail Surfaces

Horizontal and Vertical Tail Surfaces

These assemblies have been set aside and I will begin construction of the fuselage next. I’ll post some updates and pictures of it soon.

PT-20 Build – Intro

PT-20 Build - Box Art

PT-20 Build – Box Art

The subject of this build is the Great Planes PT-20 Kit. I haven’t built a kit in a couple of years – so this seemed a simple enough subject to get back to building with. I intend to convert this from glow to electric during the build and will elect to assemble with the sport ‘B’ wing option from the plans.

This kit has been in my possession for quite some time – it moved to Arizona with me about 5 years ago and had been in storage back in Georgia for a while too. Like many who enjoy building kits, I bought this one knowing that I didn’t have time for it ‘right now’ but that – someday – it would eventually get built. Because it had been in storage for so long, I did find some of the die-cut sheets bowed or warped in the box (shame on me.) Those that could be straightened were, and the few parts that were twisted just a bit too much, I made replacements cut from balsa stock so the build could proceed.

I do not intend to get into a lot of detail – regurgitating the assembly manual – but I will post progress photos and any technical issues I encounter and how I resolved them.

Flying soon at an airfield near you.

Sukhoi SU26M Flight Notes

Sukhoi

Sukhoi

This Sukhoi SU-26M is from Value hobby and it saw it’s first flight at Sierra Vista’s Bollin Airfield on Friday Feb 15, 2013.

The Value hobby website recommended build out indicates using the G25 sized motor but the instruction manual that came with with the plane specs out the GForce 15, which I  used, along with an 8×10 prop,  achieving an overall excellent result.

I re-purposed a Great Planes SS45 ESC from an old plane I had.  Servos are all Hitec HS-5065 for the aileron and elevator and a HS-5245 for the rudder.  The battery was a Turnigy nano-tech 3S 5,000mAh.

I don’t have specifics written down, but the plane weighed ~4-4.5lb AUW. The power combo made ~550watts at approximately 40AMPS.

I am impressed with the build of the plane and its handling in the air so far.  There are only  two complaints at this point:

  1. The wings did not line up easily when being attached to the fuselage.  It’s not a big deal, and once lined up properly, they do fasten securely.
  2. The default attachment method for the main wheels has a tendency to self tighten over time.  This can lead to an inadvertent braking action that could cause problems. I am looking at replacing the main gear (which is fairly flimsy) with something more rigid and that will allow the use of true axles and collars for attaching the wheels.

The Sukhoi only has 2 flights on it to date and those consisted solely of basic flight testing and trimming.  A better arrangement for anchoring the battery down needs to be installed so the plane will be ready for some more unusual flight attitudes.

AeroWorks ProX260 Test Flight (29 Oct 2012)

Living in Arizona has a few benefits and one of those is great flying weather almost all year! Today we took advantage of that and headed out after work to perform a second round of test flights on the new AeroWorks Prox260.

I had originally installed a digital, high speed, metal geared micro servo (much like the Hitec 65MG) and quickly found out the engine vibration was simply too much for it. The servo would arbitrarily freeze up and lock the throttle into position.  I built a side mount ply/bass servo box, painted it, and installed a Hitec 5625MG. The weight was not a concern since the ProX is still  tail heavy even after moving the chunky XYZ 20cc motor forward an inch. I added 2 1/4 oz of weight to the top of the nose in an attempt to gain some rudder and elevator stability. I really don’t like adding weight to an airplane so I may remove the engine and rebuild the nose section since some modifications are needed to adjust thrust angle (more later).

A quick note about the XYZ 20, out of the box it ran perfectly with no adjustments. This little engine comes with two Champion CM 6 spark plugs and a real Walbro carburetor. Power is excellent, smooth idle, and it sips fuel. I will be buying more of these.

On the radio side, I increased expo from 15% on low rates to 25% on the elevator, reduced expo on ailerons from 30% to 20%, increased expo on the rudder from 30% to 50%, tightened the fuel tank (again), and gave her a try. The high and 3D rates remain the same as the manual suggested.

The first test maneuvers were “The Wall” (full up elevator from horizontal flight) and “The Parachute” (full up elevator from a vertical dive). With each maneuver, the aircraft dropped the right wing in a very harsh manner, sometimes into a spin.  The correct for this, I added a small amount of sub trim to channel 6 (right aileron) to adjust the control surface down. This gives you a little more lift on the problem wing to delay the stall.

After implementing this fix, the two previous maneuvers became flat and smooth. Next, I went on to evaluate the performance during a Knife Edge. I added 6 percent left aileron to right rudder and 6 percent right aileron to left rudder. Once I was satisfied with the results, I added 5 percent up elevator to rudder for both orientations.

Then I moved on to some hovering experiments. After all the adjustment, radio mixing, adding weight to the nose, and expo adjustment, hovering became a little more predictable. After several runs, I determined the aircraft wanted to nose down out of the hover.  Therefore, I need to remove the engine and reposition it so it will generate a little up thrust.

Lastly, upon landing, I observed a lot of right rudder trim was necessary to counteract the left turning tendencies. I will add some right thrust when I work to reposition the motor. I am hoping these changes will allow me to control some of the torque roll versus her wanting to snap out of the hover. More to come…

Steve