Saturday, January 01, 2011

Review: Public Missiles - Small Endeavour

The Small Endeavour is a simple single stage rocket designed for G - I motors. It is based on PML's Quantum Tube, has a 38mm motor mount, uses piston ejection, and sports a cool split-fin design.


Construction:

Parts list:
1 - Pre-slotted Quantum Tube airframe
1 - Nose Cone
3 - Lower G-10 fins
3 - Upper G-10 fins
1 - Piston subassembly, including
1 - Phenolic piston body
1 - Nylon piston strap (~4 ft)
1 - Slotted plywood bulk plate
1 - Metal D-ring
1 - 30" ripstop nylon conical parachute
1 - 38mm x 10" phenolic motor tube
2 - 3/16" plywood centering rings
1 - Heavy elastic shock cord (~ 9 ft)
1 - 1/4" brass launch lug

The Small Endeavour came packaged in a plastic bag. I immediately checked that all the parts were present and reviewed the instructions. What struck me first was the mirror-smooth finish on the Quantum Tube. It almost looks too good to paint!

As in many HPR kits, the instructions are brief. In addition to the main instruction sheet, there were individual instructions for the piston subassembly, preparation of the Quantum Tube, and the chute. The piston instructions included an important discussion on the amount of black powder that should be used as an ejection charge. On the down side, the instructions should have addressed the fit (snugness) of the piston. I have to point out that PML provides a lot of additional information on their WEB site (FAQs, specs, motor selection charts, RockSim files) and has a support representative who monitors the r.m.r. newsgroup. Anyone with web access can get answers to any construction or flight question. I promptly got an answer to my piston question and have since learned that the PML kits now include more info from the FAQ and identify the web address.

Out of the bag, the nose cone and piston did not fit into the Quantum Tube. I sanded the inner edge of the tube and they then fit snugly. The CRs and fins fit perfectly.

I constructed the MMT as noted in the instructions except for the following two tweaks. I recessed the front CR by 1" vs. the 0.25" noted in the instructions. This way the leading edge of the front fin tab rests against this CR. On the rear CR, I added some small T-nuts for motor retention.

As noted in the instructions, I sanded all areas that had to be glued, including the inner and outer fin fillets. I then installed the MMT and fins pretty much per the instructions. To ensure their alignment, I installed the upper and lower fins at the same time. I clamped the pairs of fins together using a plastic ruler and two 3/8" binder clips. The T-nuts provided an easy way to remove the rear CR, which was not glued in until after the fins (including inner fillets) are completed.

As mentioned earlier the fit of the piston body was very snug. PML recommends that their pistons "should slide easily in or out with just a little push or pull". I sanded the piston until I thought it met PML's criteria. However, the only way to know if I sanded it enough is to try it.

I installed Blacksky rail guides in place of the provided brass lug. One of the rail guides is installed immediately above the rear CR and the other is immediately below the forward CR.

I decided to keep the strap elastic shock cord. It is stronger than the average elastic, it should not come in contact with the ejection gas, and the rocket is not very heavy. I looped the elastic over on itself about two inches and sewed it.

The 30" conical panel chute is made of heavy rip-stop nylon and has a large (5") spill-hole. It appears to be of above average quality for this size chute. I added an eyebolt to the nose cone and used quick-links to connect the shock cord to the nose cone and piston. Finally, I used a heavy duty swivel that I obtained from Giant Leap to connect the chute to the shock cord. The added weight should not be an issue on this rocket and the recovery components are now removable. 


Finishing:
While thinking about painting, I noticed there were no decals in my kit. The PML web site claimed that there should have been so I shot an email off. Evidently, my kit was produced before the decals were provided. No problem - three days later they were here.

In preparation for finishing, I wiped the QT with rubbing alcohol, lightly sanded it, and wiped it down a second time. I also filled the nosecone seams and the flaws in my fillets with SuperFil from Shadow Composites. SuperFil is a light epoxy filler that is very easy to sand. I used 3 coats of Krylon white primer, sanding between each coat, and two cans of Testors Burgundy Purple Metal Flake applied in four thin coats.

The self adhesive decals were not easy to install. In order to fit the flames and the "Small Endeavour" text as shown on the PML web site, I had to cut out the clear decal material from between the outer legs of the flame. These outer legs had to overlap the fillets. Also, these decals really grab hold (this is probably a good thing in the long run). I didn't get the last section where I wanted it. However, it wasn't too bad and since I was scared it would lift the paint, I left it where it was.


Flight/Recovery:
I couldn't use the commercial motor clips that I already had because there is not enough room between the motor mount and body tubes. Instead, I fashioned a clip from coat hanger wire and some electrical bayonet-style terminal lugs. I place the end of the wire through the barrel of the lug and bend a 1/8" section at a 90 degree angle. I then bend the foot of the lug the opposite direction, make the proper bends so the wire conforms to my Giant Leap 29mm - 38mm adapter with a SU G80 installed, and repeat the termination procedure at the other end. The adapter had the same shoulder dimensions as a RMS casing. This way the retainer holds both a RMS casing and a SU motor in the adapter. This procedure doesn't always result in the prettiest retainer, but is easy and has worked for me.

The maiden flight was on 3/10/2001 in Middletown, MD at the NARHAMS launch (my thanks to the hosts!). It was quite windy so I opted for a G35-7 to keep the flight low. My home-made Igniterman igniter worked perfectly. The Small Endeavour arched into the wind and because of the trajectory, the ejection was quite late. However, the recovery was perfect and there wasn't a scratch on the rocket. The piston worked fine despite my worries. 

The Small Endeavour has logged 22 more flights on the following motors:
AMW RMS G69-7, AT EconoJet G35-7, AT RMS G64-5, AT RMS G64-7, AT RMS G67-7, AT RMS G77-6, AT RMS G79-6, AT RMS H123-10, AT SU G75-7, AT SU G80-7