Tuesday, October 04, 2011

Review: Zoomie P-51D

Recently, TRF user Daddyisabar posted a thread on his Estes SpaceShipOne to P-40E kit bash.  I am a big fan of the SpaceShipOne as a subject for kit bashing (ref. the Goonball XL5 and SpaceShipSqrt(-1)).  I loved the P-40E and had another SpaceShipOne.  So, I decided to try a P-51D.  Daddyisabar coined the term 'zoomie' for a 'goonie' version of a scale aircraft.  I call mine the Zoomie P-51D. (So original, eh?).


Construction:

The first photo shows the wings and other fin-like objects.  I patterned the general concept after the P-40E and even the Semroc Gee'hod.  I first roughed them out based on drawing of the P-51D that I found on the Web.  I laid these out on a rough profile of the SpaceShipOne's body.  All the components, except the lower 'air intake' are cut from dense 1/8"  balsa and the intake is 1/4" balsa.  The wings are 2-part because I only had 4" wide stock and the whole wing wouldn't fit with the proper grain orientation.  All wing/fin parts were laminated with full page label stock. The edges were treated with thin CA and minor imperfections were filled with Fill'n'Finish.

Based on my prior experience, stubby winged rockets require a good bit of nose weight.  My XL5 is 18mm but requires a D13, D21 or D24.  The SpaceShipSqrt(-1) has a 24mm mount, and can fly on a C11 or D12.  For this latest model, I thought a 24mm mount was the way to go.  I didn't need that nozzle anyway.  The photo to the right shows the motor mount.  I expanded the center holes in the stock centering 'rings' and positioned them per the instructions.  On the front, you can see an I Build Rockets plywood shock cord mount.  This serves as a motor block and and could be the attachment point for a steel leader.  However, I was worried that its proximity to the motor could result in an over pressurization. That is, the mount might be ejected. As a result, I chose to mount a Kevlar leader through the rocket's body adjacent to the launch lug. 

This photo is the in-progress tail cone.  I roughed out the rear opening and sealed the rear gaps with SuperFil epoxy clay.  One thing I learned from the Sqrt(-1) is that 24mm ejection charges are tough on plastic cones.  The upper ring on the SpaceShipOne leaves almost half of the cone exposed - not good.  So, I made a double layer, card stock cone to fit between the inside if the shoulder to the upper ring.  That should keep the hot gasses away from the wimpy plastic.


Here, I have attached the the wings, fins and all related structures.  Along the way, I readjusted the cockpit and intake sections.  They looked OK but sat too far forward (stability issue).  Next, I added some sections of FirstFire tubes under each wing.  Either will work as a launch lug on 3/16" or 1/4" rods.  They look ordinance-like, so they should fit in well enough. Finally, I settled on a 2.125" plywood disk, cut in half, for the wing mounted 'landing gear'.

Finally, I cut the base off the cone to provide a little extra space for the laundry.  For the nose cone weight, I embedded lead shot in epoxy.  I set the weight to provide a margin of 0.9 with a D12-5 loaded. Should get to around 600'.


Finishing: 

I started with a base of Duplicolor Metalcast primer/basecoat.  This has become my favorite silver paint.  Next, I grabbed a Sharpie and highlighted the cockpit, wheels, and tail section.  I also 'painted' the tires with a jumbo-sized Sharpie.  The cockpit is a somewhat mottled sky blue made with a combination of thinned white paint and some blue. Not exactly what I envisioned, but not bad.  The exhausts from the P51-D's Packard V-1650 V-12 were simulated with some Lego components.


The decals were printed on Testor's clear decal sheets (link to my detailed review).  I roughed out the decals in GIMP and then sent them to my other computer so I could make the background transparent.  The decals came out less than perfect but are fine for a first try.  The final trim scheme is a very 'goonie' version, incorporating a V2 rocket girl logo, an MDRA logo, and  numerical designation matching the motor she will fly on.




Flight and Recovery:

I flew the Zoomie P-51-D on the motor whose designation is marked on its fuselage.  I added two pieces of Quest wadding wrapped around a small handful of dog barf and clipped on an 18" Nylon 'chute.  It weather cocked and 'flew' into the prevailing wind.   Ejection was late but it recovered with no damage. Still, a 3 sec. delay would be advised.  For future reference, the plywood motor block/shock cord mount did not come loose.