Saturday, December 18, 2010

Reviews: Heavenly Hobbies Resistor 224 (and H.H. Simit)

The Resistor 224 Planetary Defense Weapon is the latest offering from Heavenly Hobbies. This futuristic, dual motor, 24mm design features their ‘Amaze’ ejection baffle, laser cut plywood fins, rings and baffles, thick wall tubes, and a single big decal. It has two main fins with winglets at their tip. The configuration is a little reminiscent of the Jayhawk. The kit can be built with front or ‘zipperless’ rear ejection. I opted for the latter to make the build more unique. No parachute is provided, which is fine with me since my stash of nylon chutes are all interchangeable. HH offers suitable ‘chutes should you want one.

The kit includes the latest version of the H. H. Simit simulation software.

My thanks to Jose at Heavenly Hobbies for sponsoring this build!


Parts included:

* One big conical balsa nose cone
* Two thick-walled BT-70 body tubes and matching coupler
* Two screw eyes and one small wood screw
* A bag of BBs for nose weight
* Cotton braided elastic shock cord
* Three laser cut baffle bulkheads
* Two 24mm motor mount tubes
* Two laser cut centering rings
* Three long couplers
* Two engine hooks
* One 1/4" launch lug
* One 3” pre-slotted ring tail
* Two sets of laser cut ring tail pylons, fins and fin tips
* A decal sheet
* Instructions and H.H. Simit on CD

The 18-pages of photo illustrated instructions are included on a .pdf file. I found them easy to follow and I liked the way they handled the ‘housekeeping’ instructions, such as what glue to use (the default is 5-minute epoxy), to fill the spirals before constructions, etc. That is, all this stuff is discussed up front..

The build starts with the 2 x 24mm mount. The motor tubes are connected at one end with a pair of centering rings. Since these tubes will be load bearing, long thick couplers are epoxied in the upper end. A third coupler is provided to help in installation. On dry-fitting, everything fit perfectly. However, the rings are thin at their closest point and I snapped one of them on actual installation. This was only a minor snag but the motor tube assembly no longer fit perfectly and required some sanding. I’ve got clumsy paws, what else can I say? Just be gentle as you work these into place.


To accommodate longer (E9) and RMS motors, the upper tab on the pair of motor hooks are to be bent upwards. Mine broke off due to metal fatigue. Makes no difference as you can bend the end 1/4” in from the original tab. This will be reflected in future issues if the instructions.

The larger ring tail is supported by two plywood pylons. The roots of these are sanded into a ‘V’ to better mate with the motor tubes. As the pylons set, I made sure they were aligned by sighting down a rafter angle.

The instructions say to install the ring tail at this point. The overall span of the tabs is about 1/4” too wide so they will require trimming. I suggest this be done before installation. However, a Dremel with a diamond cut-off wheel make quick work of the trimming in situ. I was worried about keeping the fin slots at a perfect right angle to the pylons, so I measured the mid-point between the slots and marked a line to use as a guide.

The baffle consists of a coupler and three plywood baffles. Each has three large holes on one end. They are installed so these hole alternately sit on opposite sides of the coupler. The top baffle has a hole pre-drilled for a provided screw eye. This of course should remain on top.

You attach the shock cord to this eye and then glue the baffle assembly on the top of the lower body tube. To keep the rocket rear eject, you affix the nose cone to the upper body tube with the a provided screw. The rocket then separated at the body tube junction as it typical with zipperless HPR designs. Alternatively, you can glue the upper body to the coupler and let the rocket separate at the nose. (But, you don’t want to do that.)

Nose cone prep involves the typical stuff - seal, sand, repeat, install screw eye. I treated the top couple of inches with thin CA. Pointy balsa cones typically don’t stay that way. You also have to drill a 3/8” diameter x 4” deep hole in the cone to embed the nose weight (BBs). I have one suitable bit and did this with a hand drill. I found this challenging since the dull bit wandered all over the place. I went slowly to make sure I didn’t breach the cone’s wall. By the time you get 4” in, it is getting thin. I got the job done but the big gaping hole is a bit funky looking. I used quick set Gorilla Glue to affix the BBs. The photo shows the big hole plugged with some excess SuperFil epoxy clay.

My as-built weight, including an 18” nylon ‘chute, came in at 10.6 oz. Since the ‘chute is user provided, I assume this is nominal.

Finishing:
The kit includes general finish instructions. I decided to generally keep with Heavenly Hobbies scheme. The ring tail and fins are shot with Krylon black with a Titanium Silver over spray. The exposed motor tubes are straight Titanium Silver. The upper body is Metalcast Metallic Purple.

I filled the nose early in the build but didn’t do so on the fins. This was a mistake as the fancy fins are harder to work around than those on a 3/4FNC design. I also painted the rocket before permanently attaching the motor mount assembly to the lower body section. This was a good idea and made painting easier (less masking).

The decal is a peel-and-apply. This makes it easy to get on but the clear background stands out a bit.

A couple of silver vinyl stripes and an MDRA logo competed the finishing.



Flight:
Because of the baffle, prep was simple. Attach a 'chute, slide in two motors, etc. I used the low end of the recommended chute size (18") due to the prevailing wind. If you don’t use a motor with a built in thrust ring you will have to add your own. The instructions recommend you glue on a thin strip of BT-50, but I’d rather just use masking tape. Ignition was handled with Quest Q2-G2 igniters.

Two C11-2’s are a bit underpowered for my liking and ejection was early. This motor is great for small fields.

Two D12-5, however, were perfect. Great boost and ejection at apogee.

Recovery:
The early ejection on the C11 flight fouled the ‘chute, but that’s also common for regular nose ejection. The rocket landed on mowed grass under the resulting ‘streamer’ and suffered no damage. By the time I flew it on the D12’s, the wind had picked up. The combination of a fast descent and high lateral velocity resulted in a hard landing. An 18” 'chute is a little small. I expected a winglet to pop off, but it didn’t. One wing suffered a cracked fillet, which was repaired with thin CA.

Summary:
IMO, this is a pretty nice looking rocket. The parts fit is good and thick walled tubes, plywood fins, and reinforcing stuffer tubes make it pretty tough. Although it flies on C11’s, it should be hefty enough to handle a pair of 24mm reloads (but, plan on a long walk). The baffle and rear eject option makes field prep a cinch and it is easy to get in the air. This is a great feature and I’d like to see it on other kits. Rear ejection also protects the cone from ‘Estes dings’. The only cons are the required trimming of the pylons and the difficulty of boring the nose cone. The latter will, of course, vary depending on what tools the builder has on hand.

H.H. Simit
H. H. Simit is the simulation spreadsheet that Heavenly Hobbies distributes for free with their kits. I thought I’d take the time to do a quick review even though it is not separately available.

Simit consists of an Excel spreadsheet and an accompanying instructions file in .pdf format. I initially tried loading this is OpenOffice, but it was not compatible. It works properly in Excel 2003.



The Simit spreadsheet is a pretty basic simulator but should be a great help if you don’t have access to a more robust program or don’t want to take the time to enter the design. It can handle up to two stages with multiple motors in each stage. The program includes data for 10 motors, including the ones that would be most commonly used in the Heavenly Hobbies kits. The rocket parameters includes mass values and dimensions for the major components. It comes pre-coded for the Resistor 224, Backdraft and Brutus 2.6 kits. While the motor and kit data seems limited, the instructions describe how to add your own. After using the program and studying the results, you should be able to use it for just about any design. And ThrustCurve has the motor data you'd need. Even though you may select English or Metric values on the input screen, results are provided for both. It appears the factory entered motors use metric units but the designs use English. The units setting needs to match these.

The input screen includes the summary results (don’t forget to hit ‘F9’ if automatic calculations aren’t enabled). In addition, detailed tabular and graphical data are provided for acceleration, velocity and altitude. The instructions do a good job of showing how to interpret the results, based on the Backdraft. For that design, interpreting the results are especially important as you have to select the ignition delay for the retro motor.


OK, I just couldn’t leave well enough along, so I entered the Resistor 224 into RockSim 9 just to see how its results compare to Simit. I adjusted Simit to reflect my Resistor 224’s actual as-built weight. Noting that Simit only provides acceleration and velocity at tenth-second intervals, these results are remarkably similar.

For 2 C11-3s:
Max Acceleration Max Velocity Max Altitude Optimal Delay
Simit 362 131 241 N/A
RockSim 358 129 250 3.3
For 2 D12-5’s:
Max Acceleration Max Velocity Max Altitude Optimal Delay
Simit 407 214 584 N/A
RockSim 481 215 581 4.5
 
It is not fair to compare this spreadsheet to products such as RockSim, SpaceCAD, or OpenRocket. It it however useful for Heavenly Hobbies' kits and is really easy to use. This is especially true for their Backdraft with its retro motor. I wish I had a quick and dirty altimeter like Apogee's AltimeterOne so I could critique its accuracy...and that of RockSim-9 for that matter.