PML's Small Endeavor, featuring the Quantum Tube

Assembly, Quantum Tube Tests, Finishing, Launch

Public Missiles is now offering the new Quantum body tubes in several of their kits. The tubes are gray in color and made from a special blended polymer. PML claims you can drop it, squeeze it, even throw it, without damage. We shall see. They also claim most epoxies and paint will work just fine on the new tubes. 

The Quantum tube does have one thing missing, the spiral groove! For me, the Quantum tube had to be an improvement over Phenolic body tubes which I avoid using. I chose the Little Endeavor kit (Fig-1), a 2.6" diameter, 38mm motor rocket for this review. The kit features fiberglass fins, a heavy duty nose cone, 1" shock cords, a quality 30" parachute, piston assembly, and decals. 

With a few exceptions I built the Small Endeavor following the instructions carefully. I found the instructions to be about average for a high power rocket kit. They had not been updated for the new Quantum body tube; an orange insert explains the use of epoxies and paint on the tube. 

The lower nylon shock cord mounts through the upper centering ring and is epoxied to the motor mount tube (Fig-2). I usually add a section of fiberglass cloth over the shock cord/motor mount just to be sure. I also added a pair of #6-32 blind T-nuts to the lower centering ring for motor retention (Fig-3). Just add two spacers, two fender washers and #6-32 screws, and your motor will stay where it belongs. 

Before proceeding to step 3 - mounting the motor mount tube assembly into the body - thoroughly rough up the inside of the Quantum tube with 60-80 grit sandpaper. This is only mentioned on the orange instruction insert. I cemented the sandpaper to the end of a 38mm tube to allow sanding the whole area where the fins and centering rings must adhere to the inside of the body. Also sand the area around the fin slots on the outside of the body tube. 

At this point I performed an epoxy adhesion test on one of these sanded areas; I tried three different epoxies from 6 to 30 minute cure times. When completely dry, I used an exacto knife to remove the little test blobs. All three were removable, but I was satisfied with the quality of the bond. 

Be sure you do not epoxy the lower centering ring at this point in the assembly, it needs to be removed later. 

I used 6 minute epoxy and a homemade alignment jig for the initial fin assembly. I clamped the upper and lower fins together to keep them perfectly aligned (Fig-4). Let each fin dry thoroughly before moving on to the next set. 

Now it’s time to remove the lower centering ring; I just installed #6-32 screws into my blind nuts to gently pull it out. I’m not sure how you would get it out without the screws. 

At this point, the instructions have you apply epoxy fillets to the areas where the fins contact the motor mount tube and at the inside of the body tube. I decided to try something a little different: I cut 12 pieces of fiberglass cloth about 1" x 3"; one at a time and soaked them with epoxy. With the help of a long stick, I was able to work each piece into those same areas of contact inside the body tube, after completing all 12 areas of the upper fins, I repeated the process on the lower fins. I believe this method will be much stronger than an epoxy filet. The exterior epoxy filets were done in the usual manor; I like to pour the epoxy out of a small paper cup with a "V" folded on the edge. 

The kit included one 4" brass launch lug, but the instructions called for two 2" lugs. I guess you have your choice. I decided to cut the lug, and mount it per the instructions. After the epoxy had set, I added some fiberglass cloth around the lugs and to the body tube for added strength. I have seen several brass launch lugs still on the launch rod after a launch attempt. 

The piston assembly and shock cord setup were installed without any modifications. 

Before I painted the rocket, I wanted to see for myself if you could really abuse the Quantum tube. I placed a sock over the nose cone and took the almost completed Endeavor outside and gave it a toss -- I was attempting to get it to stick in the ground like a lawn dart. On the first two or three tries, I did not get enough zip or arch on my tosses, and the rocket just bounced when it hit the ground, without any damage. Finally I gave it a throw with enough on it for the rocket to stick (Fig-5): again there was no damage. I was not finished. I put the Small Endeavor in the freezer for two hours and then repeated the test: I was not able to damage the Quantum tube. 

I wanted the Small Endeavor to look good with a minimum of time spent on finishing. The orange instruction sheet has you give the body tube a light sanding with 320 or 400 grit sandpaper, I used 400 grit on the whole rocket. I used an inexpensive gray primer, followed by Rustolium metallic charcoal paint. I applied the included decals, and then sprayed inexpensive gloss clear paint over the entire rocket and decals: this gives the decals the same sheen as the paint while making the whole finish more durable (Fig-6). 

I compared the weight of the Small Endeavor to my Rocket R&D Ibis which is the same diameter, slightly longer and was modified to include a piston and 38mm mount. I weighed both rockets with the same PML 30" chute, the Endeavor came in at 31 ounces compared to 25 ounces for the cardboard Ibis. 

I planned to launch the Small Endeavor on either a G-64W or H-73J on it’s initial flight. Because of strong winds, I chose the G-64W with a medium delay. The boost was as straight as possible for the weather conditions. It was the longest medium delay I have encountered to date; I started thinking I would be able to report on what happened after it penciled in. Finally the chute deployed with a jolt that surely would have zippered a phenolic rocket. After the flight I could not even find a mark on the end of the body tube. 

As of now, the Quantum tube is available in diameters up to 4", and it is a bit more expensive than phenolic or cardboard tubes. I would like to see the Quantum offered in the larger sizes, or maybe some new sizes like 3.5" or 4.75". This is a great new product I highly recommend. 

Written and submitted by Al Casper for Rocketry Online -- Copyright 1996-1999 
 

A couple of months ago, Charlie, the owner of HobbyTown USA in Brea, CA told me he was bringing in PML kits I started getting excited. I told him to hold on to a Pterodactyl Jr. for me (See Kerry's review of the kit). When they came in, I opened the shipping box for Charlie and pulled out the Pterry (sorry Kerry). I found the kit easy to build and very sturdy. I liked it so much I went out and bought a PML Small Endeavor kit.

The Small Endeavor is also a straight forward PML kit. If you have ever built a kit by this company you will know what I mean. It features six precut G10 fins, pre-slotted Quantum tubing, a very sturdy 38mm engine mount, piston ejection, tubular nylon shock cord, and a 30 inch ripstop nylon chute with spill hole. ( I can personally attest to the strength of these kits as last week the Pterry forgot her ejection charge and tried to drill for water in the nearby dry riverbed. The only damage was a ruined paint job and a loose fin).

First thing I did, after checking to make sure that all parts were there, was to sand the entire Quantum tube inside and out in the fin can area to make sure the epoxy would adhere properly. I then test fit the Motor mount and fins to make sure everything fit together well. I built the motor mount/ shock cord assembly per the instructions, with no modifications. (To protect the shock cord from ejection, I will put a bit of wadding on top of the motor tube before loading the piston). Make sure you don't glue the rear centering ring on at this time.  At this point, I installed the "T" nuts for the motor retention system. I used 6/32 threads as this is standard for most of my high power models. I have two sets of the Giant Leap retention systems and I share them amongst the different models. By installing the nuts now, I can screw in the cap screws now, this makes pulling the ring out much easier later when reinforcing the fin joints on the inside of the tube and on the motor tube.

Before epoxying the fins in place you need to prepare them. First, sand the root edge area to making sure it is clean, smooth and straight. Make sure you wipe any dust off. Rough up the area were the fin will contact the main airframe too. G10 fins are very thin, some people will sand a leading edge, but I just rounded the leading and trailing edges. Again, before epoxying, make sure ALL areas are dust free. I have discovered that Epoxy, fiberglass and plastic shavings and dust LOVE to stick to surfaces due to static. A damp towel usually will dissipate the static charge and clean the dust off.

With the motor mount and forward centering ring epoxied in place, and the aft ring in place but not glued, it is time to epoxy the fins in place. I cut a jig out of thin card board (see the illustration). I glued each fin in place one at a time using 5 minute epoxy, making sure the jig is holding the fin perfectly straight.  After the epoxy had set, I pulled the rear ring out and applied generous Fillets on the motor tube fin joint and the inside airframe fin joint using 30 minute epoxy. Finally, I epoxied the rear ring in place making sure the retention screws did not line up with the fins.

One of the biggest changes was in the Piston assembly, I have heard about short pistons jamming so I replaced the 2 inch piston sleeve with a 4 inch sleeve. (As you can see in the picture, you may also notice the rear centering ring with "T" nuts and screws ready to be installed. The fin jig sits to one side.)

After installing the recovery harness, in is time to prepare for Paint. I sanded the entire model with extra fine sand paper first, then two coats of Krylon Gray Sandable Primer sanding in between. I like to give my projects nicknames from good books and this one is named "Rainbow Six" so each of the six fins would be a different color of the rainbow. I gave the entire airframe a coat of Gloss White Krylon, wet sanded then another coat of white. Finally, each fin received a different color. After a quick buff, I put on the stickers and three coats of clear and she's ready to go.

I'm going to put her up a 29mm reload the first time, we'll see how she does.

I wonder if I can talk Kerry into a Drag Race of "bullet proof" Pterodactyls, then our Small Endeavors?

Brief:
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.

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.

Construction Rating: 4 out of 5

Flight:
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 always 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.

I plan to fly it on a G80 next and then, hopefully, a new H242 "Redeye" reload (turning blue while holding my breath). Watch for updates in the flight logs.

Recovery:
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.

As I said earlier, the ejection on the first flight was late. Although it was quite windy, the spill-hole in the chute kept the drift down. It appeared that a larger chute should be used, especially if the terrain is rough.

Flight Rating: 5 out of 5

Summary:
Overall this rocket went together easily. The QT and piston took a bit more work than the other simple HPR kits that I've built, but that isn't necessarily a bad thing. The question is whether these items were worth the effort. The bottom line is that I don't think I have enough experience to pass final judgment. The QT provided a great finish, but I don't know how it will hold up over time. The piston worked for me, but I've only lit one motor in it. Nevertheless, here are the PRO's and CON's of this kit based on my experience to date:

PRO's:
The kit used high quality components (sturdy NC, G10-fins, QT airframe). The QT provided a great finish. Although the instructions themselves could have been better, the excellent online data and support more than made up for them. No wadding needed, easy flight prep.

CON's (all minor issues):
Decals were missing, but they were easily obtained from PML. Piston instructions were unclear. Although the online FAQ provides guidance, it is not perfectly clear as to how snug the fit should be. The elastic shock cord - however, this is a common issue with every entry-level HPR kit I've built.

Overall Rating: 5 out of 5