Friday, December 30, 2011

The Old Train Still Runs!

For the first time in a few years, I set up my old electric train in the shop. I got this train as a very young boy, Christmas of 1952. My dad and his next door neighbor built the train board layout in 1954. Some of the items, including two more freight cars, were added between then and about 1960.

The engine and tender is a 4-6-4 coal-fired steam locomotive of the type that was used to pull passenger trains on the old New York Central railway. Lionel called this particular engine 2046, and used it in more than one of their train sets. My original set included a silver tank car, silver box car, black gondola car, and a caboose. The yellow barrel car and the red explosives box car got added later.

The first image shows a good close-up of the engine and tender:



The second image shows the whole train board layout. The inner (third) loop of track is something I added about a decade or so ago. The original setup had two concentric loops connected by 4 switches, all 1954-ish vintage track and switches.

Along the way, the two extra freight cars, the crossing equipment, the water tower, and the beacon got added, as Christmas presents, if I remember correctly. My paternal grandmother gave me the gantry crane, which still works. It rotates, moves up and down, and the electromagnet still picks up iron things.

I put some miscellaneous small toy cars into this set-up. I also built the loading ramps out of scrap wood from an old VW bus wooden headliner. My painted-paper landscape simulation from over 20 years ago has deteriorated past repair. I need to replace it, and add some more hand-made buildings. I'll do it, once I retire.



The third image is my finger pointing at the entry in an original 1953 Lionel catalog for the exact set that is my original train: 1505WS, which was $49.95 in 1952-dollars, and still the same price in 1953. My good friend Harry Petersen in Minnesota found that catalog and sent it to me. He, too, is a model railroad enthusiast.




Below I have embedded a video clip taken with my wife's camera of this train running on that train board. It no longer smokes, but the whistle still blows. This thing is 59 years old this year, and it still runs! In spite of all the mistreatment I gave it as a child. Lionel certainly made a good product.

This posting is just for fun. Hope you enjoyed looking at it.

GW

Wednesday, December 28, 2011

Latest Production Version of the Kactus Kicker

Update 7-30-15:  The new website is fully operational.  It has all the information,  photos,  and videos anyone could ever need.  It is a turnkey site for selecting,  customizing,  and purchasing a production tool.  Shipping is available,  so sales of plans have been discontinued.  Some additional parts and labor have been farmed out to appropriate vendors,  to adjust to higher production rates,  so prices posted previously are now obsolete.  Go to http://www.killyourcactusnow.com

For those of you wanting to know about my cactus tools, here are some pictures of the latest production model with the tougher snout and bigger barge front. These are from my wife's computer, file number 2010-04-25. I believe they were taken after construction of serial numbers 047 and 048.

This is a "machine" with no moving parts, towed on a simple chain bridle behind any tractor with a drawbar. It kills prickly pear cactus "in situ", without pick-up and disposal of the debris, and without chemicals. It's just driving-a-tractor work. You do it several times, for a full eradication. See http://www.txideafarm.com and go to the cactus eradication sub-page for a good description of how it really works.


photo 040 How to Hitch-Up

It really is just that simple. Flip the loop in the tow bridle over a trailer ball on your towbar. If you do this with a 3-point rig, be sure it is braced for sideways loads over 1000 pounds per tool (you can tow more than one at a time). You will incur forces like that when you turn.


photo 041 What the Bridle Looks Like All Hitched-Up and Ready to Tow

Be sure the bridle is not in the lift configuration, pinned up with a bolt over the tool's center of gravity. It needs to make a big Vee, you tow from the corners of the deck. The snout just stabilizes it like a gigantic, super-tough sled runner out front. The chain through the snout braces just limits up/down and side-side travel on really rough ground. It should be slack, otherwise.


photo 042 How-To Pry-Up the Tool to Get at What's Underneath, or Store It

Back up the tractor and slack the chain, then un-hitch it. You will need about a 6-foot prybar and a 2-foot piece of small angle iron. Use the prybar as the photo shows to get leverage to lift the tool up onto its rear edge, then prop it in place with the angle iron under one of the skids. The "tongue load" on the snout is just too high to do this without a good prybar.


photo 045 Proper Stowage Without Killing Grass

Once propped up, you can remove any debris accumulated under the tool that makes it ride off the ground. Old barbed wire and certain kinds of vine-like weeds are prone to do this. Just kick or hoe them out from underneath, and you can lower the tool with the prybar, re-hitch, and resume work. This is also a very good way to store the tool in the pasture between treatments, since it cannot kill a whole big patch of grass while tipped up on edge like this. This is how I store mine.


photo 037 How to Pick-Up the Tool with Its Own Bridle

If you pull the tow bridle aft, you can pin it together with the extra 2"L 3/8 UNC bolt, nuts, and washers that I provide with every tool. If you have serial number 047 or 048, you might have to re-rig the snout travel-limiter chain slightly to do this, but I generally already have it rigged for lifting easily, right from the shop (from serial number 049-on). The center of gravity is just between the rear of the snout tube and the front edge of the big ballast bar flat. Pin the bridle together there, and pick it up at the pin point as shown.

The snout travel-limiter picks up the forward load of 3-places, the chain towers being the other two. Be careful, this thing weighs 600-700 pounds. But most tractors now have hydraulic buckets. Just use a tow chain with hooks, and pick the tool up with the bucket, and put it right where you want it (pick-up bed or flat trailer).

GW

Other Related Articles on this Site (date highlighted on this one)


Date.....…title/content
2-9-17....Time Lapse Proof It Works
............watch cactus being crushed and composted
7-30-15......New Cactus Tool Website
...................turnkey site for info,  photos,  videos,  purchases
1-8-15……Kactus Kicker Development
………………production prototype & 1st production article
1-8-14……Kactus Kicker: Recent Progress
…………..….testing a revised wheeled design (experimental)
10-12-13..Construction of the Tool
………………building a “Kactus Kicker” (plain tool)
5-19-13…….Loading Steel Safely
……………….transport and storage of materials
12-19-12…Using the Cactus Tool or Tools
……………...how the tool is employed (applies to any model)
11-1-12….About the Kactus Kicker
..…………….painting and rigging finished tools (plain tool)
12-28-11..Latest Production Version
………………new bigger snout and barge front (plain tool)

Wednesday, December 21, 2011

FTL Neutrinos Update

I posted an update to the faster-than-light neutrinos article. Scroll down to it dated 10-9-11 and titled “Faster-Than-Light Neutrinos? Maybe! Their Meaning? Arguable!”

GW

Wednesday, December 14, 2011

Reusability in Launch Rockets

A group of folks I correspond with (at the forums on NewMars.com) has been discussing reusable launch rocket possibilities. One of the names they use is “big dumb booster”, or BDB. My own opinion is that reusability is incompatible with the low inert mass fractions used in the stages of typical launch rockets today: too light is simply too fragile. I do know from their website that Spacex is interested in reusing the first stage of their Falcon-9 booster, but that their results so far are unsuccessful. So, my analysis results here should be of interest, both to my correspondees, and to Spacex.

Spacex’s Falcon-9 is a two-stage rocket with kerosene-oxygen engines in both stages. It features an interstage ring and a payload shroud (on the satellite version) that I assume both get jettisoned at staging. The same engines are used in both stages, except that the one in the second stage has a longer bell than the nine in the first stage, and the first stage engines see atmospheric backpressure.

Baseline Falcon-9 Performance Estimate

I looked up most of the basic engine and vehicle data from Spacex’s website, for Falcon-9 as a baseline case, and reverse-engineered the rest. Here it is, summarized, in Figure 1:


Figure 1 – Baseline Falcon-9 Data

These performance data were computed with the simple rocket equation, and some experiential “jigger factors” that knock down ideal velocity increments to more realistic values. The other choice for analysis is a real trajectory computer code, either two-dimensional or three-dimensional, which is a complicated thing to set up and to use. I used the simple analysis approach to set up actual computer trajectory analyses, for the Scout launch vehicle at LTV Aerospace, about 4 decades ago.

Here, I used a “jigger factor” of 1.10 to knock down the first stage ideal velocity increment, because that stage sees air drag, and flies mostly vertically, so that gravity drag is significant. For the second stage, I used 1.05, reflecting flight in vacuum, mostly but not entirely horizontal. The final summed velocity increment I estimate for Falcon-9 is about 26,900 feet/second, or 8.19 km/second, which is remarkably close to the orbital velocity at low altitudes (about 7.9 km/second). It’s close enough that any simplified design trades made under these assumptions are realistic enough to be useful.

I looked at two potential solutions to the trade-off between extra structural weight for reusability, and reduced payload fraction that increases the price per unit payload delivered to orbit. One was to retain the basic two-stage design, and increase the size of the first stage to compensate for added inert fraction, at constant mass ratio. The other approach was to replace the two-stage design with an equivalent three stage design, keep the top two stages as throwaways, and increase the first stage size to compensate for increased first stage inert weight fractions. Both were done at constant delivered payload weight.

Two Stage Analysis with Heavier Structural Inert Fractions in the 1st Stage
The payload is exactly the same as baseline. I assumed the payload shroud weight to be proportional to the maximum payload weight it contains at 15.18%. There are no changes to the second stage weight statement or performance values. The interstate ring weight I assumed proportional at 0.815% to the weight it carries, in this case the second stage ignition weight. It is the first stage weight statement that varies, but at constant mass ratio, so the propellant weight fraction is the same as baseline in all cases. The equation relating mass ratio MR and propellant weight fraction fprop is:

fprop = (MR – 1)/MR

Now, 1 – fprop is the total of the inert mass fraction and the stage payload mass fraction, where the first stage payload comprises the ready-to-ignite second stage, the interstage ring, and the payload shroud. I looked at the baseline, twice, and three times the first stage inert weight fraction, scaling up the first stage ignition weight to match. The resulting weight statements are given in Figure 2. Bear in mind that the delivered stage performance data are identical to baseline, since the mass fractions are identical to baseline.

Three Stage Analysis with Heavier Structural Inert Fractions in the 1st Stage (Only)

I had to allocate velocity increments among the three stages in some logical fashion. I chose to make the second and third stage mass ratios 5 like the Falcon-9 second stage, and my first stage mass ratio 4, like the Falcon-9 first stage. I used “jigger factors” of 1.10 and 1.05 on my first and third stages, similar to the Falcon-9 first and second stages. I used an intermediate factor of 1.07 for my second stage. My first stage Isp was 289.5 sec, like the Falcon-9 first stage. My second and third stages used Isp = 304 sec, like the Falcon-9 second stage. The corresponding exhaust velocities are 9314.4 and 9780.9 ft/sec.

I computed the sum of the estimated actual velocity increments to be factor 1.5406 too high, so I knocked down each stage’s velocity increment by this factor, and recomputed mass ratios as 2.45935 for my first stage, and 2.84251 in my second and third stages. I ran the design study to the same payload as Falcon-9, with the same shroud weight, and two interstage rings at 0.815% of the stage weights above each ring. I assumed that interstage ring 1-2 and the payload shroud drop off with stage 1, and that interstage ring 2-3 drops off with stage 2.

The payload is exactly the same as baseline at 23,050 lb. I assumed the payload shroud weight to be proportional to the maximum payload weight it contains at 15.18%, for 3500 lb. There are no changes to the second or third stage weight statements or performance values as I changed first stages. The interstate ring 2-3 weight I assumed proportional at 0.815% to the weight it carries (in this case the second stage ignition weight) for 606 lb. Interstage ring 1-2 is 0.815% of stage 2 ignition weight, for 1999 lb. It is the first stage weight statement that varies, but at constant mass ratio, so the propellant weight fraction is the same as baseline in all cases, and so is the performance.

For the “baseline” three-stage inert fractions, I assumed 5% for my first stage, very similar to the multi-engine first stage of Falcon-9. I used the same 4.2% for my third stage as for the single-engine second stage of Falcon-9. My second stage has an intermediate inert fraction of 4.6%, chosen to reflect only a few engines in the second stage. The weight statements for the trade study are given in Figure 3. Bear in mind that all three versions of the three-stage vehicle have exactly the same estimated velocity performance, also shown in the figure.


Figure 2 – Weight Statements for the Two-Stage Reusability Trade Study


Figure 3 – Weight Statements for the Three-Stage Reusability Trade Study

Note that in both Figure 2 and Figure 3, I have included the overall payload weight fraction, computed as payload weight delivered to orbit Wpay, divided by the stage 1 ignition weight, which is the launch weight WL. (In the context of this analysis, the term “weight” really refers to mass.) In both trade studies, payload fraction decreases as stage 1 inert weight increases, exactly as expected. I was surprised and pleased to see that the baseline throwaway 3-stage option had a slightly higher payload fraction than the corresponding baseline throwaway 2-stage option. This and the slopes of the trends did seriously impact the final conclusions.

Trajectory Comparison

The final trajectories are compared in Figure 4. Both the 2-stage and 3-stage vehicles follow similar paths to the same orbital insertion conditions, at the same altitude (in the vicinity of 200-300 miles, or 300-500 km, up). Only potential re-use of the first stage was considered, for either configuration. A first stage fallback is indicated for each. Reentry velocity is simply assumed the same as the first stage burnout velocity. They would be comparable, in any event. Noting that reentry gets really challenging much above 10,000 feet/second (near Mach 10), I see little point to trying to make the second stage of the 3-stage vehicle reusable. It simply comes back too fast to be readily survivable.


Figure 4 – Comparison of Trajectories for 2-Stage and 3-Stage Vehicles


Figure 5 – Comparison of 2-Stage and 3-Stage Results


Payload Fraction Results Comparison

The payload fraction vs first stage inert fraction data are plotted in Figure 5 for both the 2-stage and 3-stage vehicles. The trends are reasonably linear-looking over the ranges computed, but at different slopes. As expected, the 3-stage vehicle design is less sensitive to first stage inert fraction than the 2-stage design (3-stage having the shallower slope). I did not really expect to see the baseline 3-stage vehicle to have a slightly-higher payload fraction at the baseline throwaway inert value, but it did.

Between the higher baseline throwaway payload fraction, and the shallower slope with first stage inerts, it appears that at 10% inerts in the first stage, the 3 stage vehicle has a payload fraction near 2.8%, while the 2-stage vehicle is down near 2.2% at the same 10% inerts. 10% inerts in the first stage is of enormous interest, because that is close to the inert fraction of the Space Shuttle solid booster motors, which actually were reusable most (but not all) of the time. That’s about the level where your tankage becomes strong enough to be pressure vessel-capable, as well as survivable for ocean impact on parachutes. Tankage that is pressure vessel-capable might as well be used as a pressure-feed system, eliminating the weight, cost, and reliability risks of turbopump machinery.

Conclusions

It is clear the 3-stage option is more tolerant of higher inert weights in the first stage. Combine this with a lower first stage fall-back speed, and reusability seems more certain at 10% inerts, and with a higher payload fraction (nearly 3% 3-stage vs only a bit over 2% 2-stage).

Accordingly, 3 stages is a better option than 2 stages, if the first stage is to be reused. The drop from 2-stage non-reusable payload fraction is actually quite small (3.1% to about 2.8%). This is because the all-throwaway 3-stage vehicle actually has a better baseline throwaway payload fraction than the 2-stage (3.3% at 5% inerts, vs 3.1% at 4% inerts).

This does raise the question of whether 4 stages might allow first stage reusability at even better payload fraction, or else allow the same payload fraction with both first and second-stage reusability. I leave that for others to investigate.

The main lesson here is that you really do have to do something different in order to get a different result. Reusability will require a greater inert weight fraction to cover recovery gear, and to confer the strength to survive better. Practical reusability simply cannot happen in the 4-8% inert range.

This study points toward 10% inerts in the first stage, at the very least. The more first stage inerts you have to “cover”, the more stages you need to use, to be tolerant of lowered mass ratio in each stage.

But at least we know the job really can be done, and here is one well-proven way to do it (more stages).