Why Engines Codes Are Often Wrong

[shockie]

The A8 is actually more like an A3. It was originally the A.8 (as in 0.8) when thrust was expressed in pounds.

The Estes A3 and Estes A10 are more like A2s, but the A10T has more peak thrust.

The C5 is descended from the old Centuri C5 and B8 family. They shared a nozzle design that allowed them to deliver more peak thrust over their stablemates in the B-C range. The C5 restarted production a couple of years ago and is only available as a C5-3. It's marketed as the "Super C5" on the packaging that boasts of its 50% increase in max thrust over standard C6 engines. I think the motor wrap has a "Super C" emblem as well.

Why this was allowed in the first place will likely continue to be the subject of much finger pointing, but the combination of more easily differentiated products, thrust figures useful enough to figure out what to load them in, and readily available product use suggestions is likely what allows it to continue.

It's marketing BS. The current C5 is a wimp compared to the original. The new C5 has less BP, a different thrust-time curve, ie lower maximum thrust,etc No where near the original. Estes should be ashamed of their selves .

 

[shockie]

Prior to 1969 the NAR and manufacturers used English units. From 69 onwards they used metric units. In 62 you would have bought an A.8 (the decimal is important) implying 0.8 lb-wt average thrust (roughly an A3 or A4 in metric).

I have a NAR S&T listing from 1965 so certification has been in effect since at least then. Curiously that list includes both the manufacturer assigned code and the NAR assigned code and they weren't always the same.

At some point in time a policy decision was made to include only the manufacturer code and the manufacturer assigned total impulse in the S&T listing. In the mid-70s members of the MIT RocSoc became interested in the discrepancies and began their own testing and publishing the results. Quite interesting as there were a few engines that not only had incorrect average thrusts, but were not even in their labeled letter class (Ds that were really Cs etc).

gary

Yeah Trip Barber had a great Rant about how the FSI fireworks should be banned from use in one of the MIT Journals.

 

[smstachwick]

It's marketing BS. The current C5 is a wimp compared to the original. The new C5 has less BP, a different thrust-time curve, ie lower maximum thrust,etc No where near the original. Estes should be ashamed of their selves .

I suppose that’s a valid take, but I’m just glad that we have them now. They kind of bridge the gap in form and application between the C6-3 and C11-3.

 

[shockie]

And here's

the information about the transition of the A.8 to the A8....Carl from SEMROC makes some fascinating discoveries

.https://www.oldrocketforum.com/printthread.php?t=3847&pp=40

compare the new C5 thrust time curve to the original Estes C5

The attached .pdf was done for me by Doug Sams, who also is in this thread, he actually starts it. RIP Doug.

 

[BEC]

@shockie thanks for that. Interesting stuff....and as you say Carl (RIP) had lots of good clear analysis. I may actually necro that thread over there after I look a little more at old Estes catalogs and compare the 1st and 7th editions of the Handbook of Model Rocketry to better understand the transition between the English- and metric-unit-based total impulse classifications. Then maybe I can say something more about flying that 55-year-old motor yesterday beyond "Wow, that worked way better than I expected!"

I want to see if I can come up with a valid way to create overlaid comparison time-thrust curves for at least the old A.8 and current "A8" Estes motors. But just this one bit Carl posted tells us a lot. Quote from the YORF thread linked to above, posted by Carl McLawhorn, on 9-10-2008:

The original A.8 was actually 3.1 N-sec before the A impulse max levell was dropped to 2.5 N-sec. Estes then reduced the A.8 to 2.5 N-sec and called it an A5. It was still in the early (thick-walled) tubes


1964 A.8-x 3.1 N-sec .90 sec 3.44N avg (today it would be .6B3-x) (thick walled .406ID Mabel I tube)
1969 A5-x 2.5 N-sec .50 sec 5.0 N avg (thick-walled .406 ID Mabel I tube)
1969 A8-x 2.5 N-sec .32 sec 7.8 N avg (thin-walled .500 ID Mabel II tube)
1995 A8-x 2.5 N-sec .73 sec 3.4 N avg (thin-walled .500 ID Mabel II tube)

I thought I had some Centuri A5-x engines around here in the Mabel II tube that were similar to today's Estes A8-x in performance and construction. Maybe I imagined it, but I am still looking.

As the A8-x has gone from the original A8 (actual) to A3 (real), the maximum recommended liftoff weight has also changed from 4 oz to 3 oz. It is not my imagination that an A8 will not lift what it used to! That is probably why the A8-0 booster was dropped.

 

[smstachwick]

@shockie thanks for that. Interesting stuff....and as you say Carl (RIP) had lots of good clear analysis. I may actually necro that thread over there after I look a little more at old Estes catalogs and compare the 1st and 7th editions of the Handbook of Model Rocketry to better understand the transition between the English- and metric-unit-based total impulse classifications. Then maybe I can say something more about flying that 55-year-old motor yesterday beyond "Wow, that worked way better than I expected!"

I want to see if I can come up with a valid way to create overlaid comparison time-thrust curves for at least the old A.8 and current "A8" Estes motors. But just this one bit Carl posted tells us a lot. Quote from the YORF thread linked to above, posted by Carl McLawhorn, on 9-10-2008:

And now the A8-0 is revived. I’ve flown three.

I don’t know how many people will want to try flying one directly off the pad as I did, but it did the job fine in my Mongoose-by-way-of-Generic E2X two-stage conversion and my Super Hi-Flier.

 

[BEC]

Yes, A8-0s came back a few years after Carl posted that on YORF (I have some on hand with April, 2011 date codes). I have used a few. The current Sterling Silver/Epic II minimum diameter two-stager works well A8-0 to A8-5. (Epic II is the Hobby Lobby version — the models have identical parts, just different livery. There are a few other small two-stagers from times past for which it is still a good choice, going back to the Apogee II.

 

[shockie]

@shockie thanks for that. Interesting stuff....and as you say Carl (RIP) had lots of good clear analysis. I may actually necro that thread over there after I look a little more at old Estes catalogs and compare the 1st and 7th editions of the Handbook of Model Rocketry to better understand the transition between the English- and metric-unit-based total impulse classifications. Then maybe I can say something more about flying that 55-year-old motor yesterday beyond "Wow, that worked way better than I expected!"

I want to see if I can come up with a valid way to create overlaid comparison time-thrust curves for at least the old A.8 and current "A8" Estes motors. But just this one bit Carl posted tells us a lot. Quote from the YORF thread linked to above, posted by Carl McLawhorn, on 9-10-2008:

Both the 63 and 64 Estes catalogs have A.8-3 drawings and thrust time curves. Compare and contrast to current A8-3.
The 68,69 Estes catalogs show the 1st A8-x.

The Estes A8.-0 dates to 59-60 and was produced till 1967. CENTURI sold it from 62 to 68.Centuri also sold A8-x from 69 to 84. Of course all were made by Estes.

The A.8-x series were based on the original Carlisle A4.

Bernard, superimpose the A8.-, the 1st A8-X, the current A8-3, and the A5 . That would be instructive.

 

[ghughes1138]

Please scan and post that 1965 NAR listing.

Will do if it survived the purge and hasn't been packaged away. Could take a while.

It was published in Frank Zaic's Model Aeronautics Yearbook for 1965, along with an overview article by G. Harry Stine.

gary

 

[ghughes1138]

Yeah Trip Barber had a great Rant about how the FSI fireworks should be banned from use in one of the MIT Journals.

I remember that. Some of the FSI engines had serious deviations from the manufacturer published data, even to the class in some cases (Ds that were really Cs, Fs that were Es).

Still, they were a lot of fun to fly.

gary

 

[BEC]

Both the 63 and 64 Estes catalogs have A.8-3 drawings and thrust time curves. Compare and contrast to current A8-3.
The 68,69 Estes catalogs show the 1st A8-x.

The Estes A8.-0 dates to 59-60 and was produced till 1967. CENTURI sold it from 62 to 68.Centuri also sold A8-x from 69 to 84. Of course all were made by Estes.

The A.8-x series were based on the original Carlisle A4.

Bernard, superimpose the A8.-, the 1st A8-X, the current A8-3, and the A5 . That would be instructive.

That sounds like a good plan. I just need to get all the data in one spot so I can overlay curves. I have a 66 catalog as well as 68-72.

I do have FS Mini data for the A.8-3 flight from Saturday as well as a couple of A8-3 flights in an Alpha III (though not the same one) so I can overlay altitude and also total acceleration curves. The latter make a pretty good proxy for time-thrust curves, at least in their shapes.

The original A.8 would've been an A4 when metricized, based on just converting the average thrust value, then rounding to the nearest whole Newton....

 

[shockie]

That sounds like a good plan. I just need to get all the data in one spot so I can overlay curves. I have a 66 catalog as well as 68-72.

I do have FS Mini data for the A.8-3 flight from Saturday as well as a couple of A8-3 flights in an Alpha III (though not the same one) so I can overlay altitude and also total acceleration curves. The latter make a pretty good proxy for time-thrust curves, at least in their shapes.

The original A.8 would've been an A4 when metricized, based on just converting the average thrust value, then rounding to the nearest whole Newton....

 

[MJ D]

Here's an excerpt of an article I wrote for publication. I have recently realized that it won't be published, so I'm posting some portions of that article here. I hope you find it enlightening or at least interesting.


Why Are the A8-3 and A10-3T Estes Engine Codes “Wrong?”

Marketing and existing DOT authorizations are the primary reasons, not science or NFPA rules. The old A was an A0.8 as in 0.8lb average thrust which is more like 4N. The B14 used to be a B3 as in 3lb average. The D11-P was a D12-0 with a clay plug, called D11 simply to differentiate it from the D12.

The sales volume to savvy rocketeers that know or care about such things doesn't even register on the radar. The company's primary goal is to pump out as much profitable product into the retail market as possible, not appease NAR rocketeers.

Also, it stands to reason that if your hobby motor production increases to where you are cranking out 25,000+ motors a day, there would be much more profit in running the major cost ingredient at somewhere under the allowable limits?? Not to mention loose production tolerances won't bump any production examples into the next motor class. As a similar example, a local manufacturer of cookies (a client of ours in my day gig) for a very popular trendy coffee chain recently reduced the average number of chocolate chunks on their big choc chip cookies from 12 to 11. Their annual revenue immediately increased by about $100k.

Different BP formulation? I love these theories lol. Just like someone who once posited that perhaps they blend the BP sizes to control the burn rate. Mmm, no they don't.. it's dead pressed into a solid grain at about 10,000 psi. No, they bring in several tons at a time of one grade of bulk powder, run some ballistic checks on test press made motors to see if all is well, then into production motors it goes. You'll get subtle variation but on average pretty close.