Friday, January 28, 2011

Review: Loki 38mm Motor System

This is a review of Loki's 38mm line, circa mid-2005.

Loki Research has been manufacturing EX hardware since 2001 and has had a hand in some of the largest projects flown over the past few years. Well, I am happy to say that as of December 2004, Loki has started offering reloads for their 38/240, 38/480, and 38/740 casings. The initial offerings are the H144, I405, and J528, all based on Loki White propellant.

The Loki hardware should already be familiar to many high-power fliers. Each motor includes the following components: a blue anodized casing with pre-installed stainless steel thrust ring, a graphite nozzle, a delay bulkhead with charge well, two snap rings, one stainless steel nozzle washer, and two O-rings. (The nozzle and closure come installed in the casing.) The lengths of the three casings are 7”, 11.5”, and 16”, respectively.

Each of the reload kits includes the following parts: propellant grains, a Kraft-Phenolic liner, a delay element, six delay O-rings, two main O-rings, ejection charge, and cap. The H144 uses four grains, the I405 uses eight, and the J528 uses six. That is not a typo—the grains in the H and I motors are shorter than a true Bates grain, which has one big benefit: these two motors are shippable via USPS with no HAZMAT fees. These are cost-effective motors, and this helps keep them that way. The prices without tax, title, and license are $19.99 for the H144; $29.99 for the I405; and $39.99 for the J528, as of 12/2004. 

The ease of assembly falls in the middle range of high-power motors. There are more parts than some, and fewer than others (you all know whom I am talking about). The number of unique components is minimal, and there should be little confusion about what goes where. Since the motors use snap rings, you will need a pair of snap-ring pliers. The thrust ring is pre-installed but can be removed with a screwdriver if necessary. (Note: Eye protection should be used whenever using snap-rings.)

The delay design is simple and is one of the major attributes. All these motors use the same element, which is adjusted over a wide range (XS ~ 5 sec., S ~ 8 sec., M ~ 10 sec., L ~ 13 sec., XL ~ 17 sec.). You will never be stuck with the wrong delay with Loki. To adjust the delay, you use the Loki DAT tool. This is the CTI DAT, but with an alternate calibration label. Once the DAT is set, you put in the assembled forward closure and drill the delay to the chosen depth.

The rest is simple: grease and install the main O-rings, install the nozzle, insert the steel washer, install the bottom snap ring, load the slugs into the liner and put this into the motor, add the forward closure, and snap in the top ring. At launch time, you pour the powder into the charge well, add some wadding, and slip the cap over the top. The motors do not come with igniters.

Flight Report
I have only flown the H144 and the I405. [When this was written.] I was going to get the 'J', but my Chief Financial Officer objected. Assembly went without a hitch, and the simplicity of the design more than made up for any minor fumbling with the snap rings. As noted earlier, you supply your own igniter and, per the instructions, first insert the igniter all the way, then back it out 1/2 inch. So far, I have successfully used home-dipped Magnelite, QuickBurst Slim Gem, and Aerotech FirstFire igniters.

I was happy with the performance of the H144, but the I405 really rocks! With an initial spike of almost 800-N (180 lb.), I can tell you this motor really gives a 3.5-pound rocket a kick and will be great for your heavier projects. Both motors emit a large amount of thick white smoke. The one potential issue is that the delay, especially on the I405, appeared to run a little long. These motors, however, have a regressive thrust profile, and I found it difficult to get a good measurement without a stopwatch. Still, I currently recommend you pick the delay that is just below the nominal optimal value.

One final issue is compatibility with Aero Pack and Giant Leap Slimline retainers. I can’t speak for all flavors of these products, but my older Aero Pack and the snap-ring Slimlines are not compatible with this motor. This can be a big issue, or a non-issue, depending on what you are after. (I understand that the newer Aero Pack retainers work with Loki hardware.)

For me, the attractive pricing and the adjustable delays are the two biggest selling points and outweigh all other factors. These motors all give you a good “bang for your buck,” providing the maximum stated total impulse (i.e., the J is a full 740 N-sec.), and are very competitively priced. When you spread the other nonrecurring costs (i.e. tools) and recurring costs (nozzle replacement, igniters) over, say, 20 flights, you only add a couple of bucks a flight.

The next thing I found attractive is that these cases can be used for EX work. Of course, Loki also sells compatible liners, casting tubes, and other accessories. Finally, the word is that more loads are on the way, with different propellants and grain geometries. Pop over to the Loki web site and see what Jeff is cookin’.