Delay and smoke phases on BP motors

[Doug Sams]

Was flying a few yesterday, and, while I've noticed it before, I hadn't thought to discuss it. But I'm inspired to bring it up today.

I have noticed that there are actually two distinct phases in the delay burn. For most of the burn, it's just delay. The smoke only kicks in right before ejection. We don't get smoke for the entire duration of the delay. Is that your observation? Wonder what difference there is in the materials?

I don't know how many times I've had rockets go out of sight briefly, but as long as I keep my eyes aimed at the spot, I can regain the track when the smoke kicks in. And that's usually only a second or so before ejection. That is, I don't have smoke the entire coast phase.

How's that jibe with your experience? Should we modify the cutaway drawing to include two phases of delay? :D

Doug

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[MKP]

Now that you mention it, that does seem to be the case. I launched my Red Max on an A8-3 on Saturday, and that diffidently seem s to be the case.

[tbzep]

During my "manufacturing" of 1/4A3 and 1/2A3 and A8 boosters, I noticed a small amount of BP grains imbedded in the top 1/16" of the delay slug, especially around the edges. That's most likely where it's coming from. In the last fraction of a second before the ejection charge hits hard, you can see and hear more gas escaping through the nozzle than during the bulk of the delay run. If you do it on a test stand, it's easy to see.

[Carl@Semroc]

I always thought that was a function of the velocity. Spreading smoke at 200 MPH vs. spreading smoke at 10 MPH would leave different densities in the trail. If you static test them, there is some difference, but not too much on the old engines. Newer engines do not produce as much smoke from my observations. The newer stuff definately does not mix with Johnson's Baby Powder to provide the "unique" 60's smell.

As the nozzle and case cool, it is possible that more smoke is generated. Heat kills most smoke, so much so that most ozidizers burn way too hot to use in many smoke compositions.

In any case, this is an interesting effect that needs more discussion.

[Shreadvector]

He is describing Estes motors. Modern Estes motors. They have changed over time.

Centuri motors made in PHX had lots of smoke in the entire delay. Estes motors had a bit of smoke during the delay. The Estes smoke disappeared many years ago and annoyed many of us. There was almost no smoke at all period.

Then Quest came along with massive smoke throughout the delay. We talked about it on r.m.r. and on web forums. Estes was lurking. We lauded it on web forums as the years went by and smoke was definitely gone from Estes delays. Estes was lurking. And listening. They then added smoke back in, but only near the end of the delay. I have no idea how the machines load the chemicals and if they are pre-mixed or have several "rams" but it is certainly the case that the smoke is back but only for the last second or two of the delay.

Quest continues to have lots of smoke, even on the Chinese motors.

[Doug Sams]

I always thought that was a function of the velocity. Spreading smoke at 200 MPH vs. spreading smoke at 10 MPH would leave different densities in the trail. If you static test them, there is some difference, but not too much on the old engines. Newer engines do not produce as much smoke from my observations. The newer stuff definately does not mix with Johnson's Baby Powder to provide the "unique" 60's smell.

As the nozzle and case cool, it is possible that more smoke is generated. Heat kills most smoke, so much so that most ozidizers burn way too hot to use in many smoke compositions.

In any case, this is an interesting effect that needs more discussion. Good points, Carl.

I've wondered about the speed effect on smoke density. If the smoke didn't seem to come on so strong all at once, I'd be more inclined toward that, but it sure seems more like a step function than a gradual event.

However, I can see where the combination of post-burn cooling and slowing may have a more abrupt effect (when viewed from 500 feet below).

Your ideas about the test stand are where the proof is. What's that old saying? "One test is worth a thousand expert opinions." :D

But I'm kinda cheap when it comes to doing that sort of thing :) I did burn a B6-0 in the yard Saturday. Its bore was noticeably shallow, and I didn't want to risk it in a rocket. It turned out to burn just fine without any sort of anomalies, but in this case I'd rather not take the risk in a rocket.

Doug


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[Doug Sams]

Quest continues to have lots of smoke, even on the Chinese motors.But ejection charges are another matter :D (J/K in reference to a thread elsewhere.)

Doug

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[Doug Sams]

Quest continues to have lots of smoke...I've accumulated a good stash of Quest A-B-C's, but haven't burned many. Maybe I can kill two birds with one stone this week and take some observations. In fact, I might even take some video to back me up. Just some simple single stagers comparing A8-3/5's with A6-4's.

We bought the family a little video cam a while back, and I've spent about 0 time with it until recently. It records digitally on tape, but has a memory card option, which would allow easy computer uploads. We've taken it out on a couple launches but don't have anything worth posting...yet. Lots of smoke-only pad shots along with seemingly hours of shots of the ground and my daughter's feet :D

I doubt I'll ever risk strapping it in a rocket, but I did see some video from Scott Cook's L motor flight (upscale Der Red Max) at LDRS last week. He used a stock Aiptek from Target that he gave $120 for. Mem card extra. Scott said it sat on the pad recording for 30 minutes prior to launch and was still recording many minutes after the flight when they were searching for it. So no hacking was required, no on-off switch triggering, etc. Sounds like my kinda (no-brainer) setup.

Doug

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[Solomoriah]

I noticed yesterday while launching rockets using C6-7's that there was, at most, about two seconds of actual smoke. It's much more noticeable with the long delay. And I doubt that it's a velocity issue, as I clearly saw the smoke suddenly pouring out about two seconds before deployment.

[shockwaveriderz]

Itsmay be due to the fact that the initial delay surface burns at engine chamber pressures that are rapidly dropping to near ambient ie 14.7 psi down from say 200 psi....

As far as I am aware the delay train/smoke charge is a homogeneous mixture.... it may produce smoke differnelt depending on buring pressure and burn rate.... higher pressure, greater burn rate and vice versa, lower burn rate with less pressure....

From the slo mo videos I have seen there appears to be a "transition" zone between burn out and the beginning of the delay/smoke train .

EDIT

There also may be some effect from pressing the BP propellant slug at one pressure and the delay train at another pressure in addition the dleay is a different particle size.

Have you seen some of the closeup super slow speed videos on youtube and other sites of estes motors.... theres also a lot of flame in that smoke entrail..... you just can't see it because the rocket is so far away from your field of view.

http://www.truveo.com/1200fps-Estes-A83-Rocket-Motor-Test-Fire-2/id/2963037244

http://www.truveo.com/1200fps-Estes-A83-Rocket-Motor-Test-Fire/id/901794525

also do a search on youtube for D12 slow motion




terry dean

[PaulK]

Interesting stuff. I'd have to agree that I've observed this with Estes motors, though can't offer any quantitative data. The C11-7 motors I've used recently clearly exhibit the most smoke during the latter part of the coast phase, I'll have to time it next time.

The chinese Quest A6-4 motors I flew last weekend seemed to smoke all the way up.

[Royatl]

Itsmay be due to the fact that the initial delay surface burns at engine chamber pressures that are rapidly dropping to near ambient ie 14.7 psi down from say 200 psi....

...

Have you seen some of the closeup super slow speed videos on youtube and other sites of estes motors.... theres also a lot of flame in that smoke entrail..... you just can't see it because the rocket is so far away from your field of view.

http://www.truveo.com/1200fps-Estes-A83-Rocket-Motor-Test-Fire-2/id/2963037244

http://www.truveo.com/1200fps-Estes-A83-Rocket-Motor-Test-Fire/id/901794525

also do a search on youtube for D12 slow motion




terry dean


That first A8-3 video pretty much bears out Carl's theory...

Notice whenever a flame is being ejected during delay, there is no smoke. Occasionally it goes out, and you see more smoke. Then the flame will flicker on, and the smoke is greatly reduced. It cycles like this for awhile. Eventually, as the motor cools, the flame goes out for good, and the smoke is thickest.

[Carl@Semroc]

Thanks for the videos Terry!

From the color of the smoke and the flame, it is a modern A8-3, not the old version.

A timeline of the critical times on the second burn yields the following:

0:04 ignition
0:28 burnout rampdown starts and transition to delay begins
0:32 burnout ends
1:46 max smoke (after flame dies down)
2:42 ejection starts
2:44 ejection charge ends and rest of delay continues to burn
3:17 delay burn (hibatchi effect) ends

Assuming .73 sec burn from NAR site and Estes site:

Max smoke begins at 1.85 sec after burnout
Ejection is at 3.25 sec after burnout
Ejection lasts about 50 ms
Hibatchi effect (burning out of the top of the engine) lasts 1.8 sec after ejection.

I am still amazed that the A8 is called that, because from the NAR S&T site, it has an average thrust of 3.18 Newtons. Must be a marketing decision since it would also be an A3-x, but without the 'T'. But then, since the A3-xT is only 2.2 Newtons average thrust, it should be called an A2-xT. Looks like the engine designations don't have to match the measured performance any more! :D

[ghrocketman]

As usual, Carl is making good sense about his comments regarding engine designations.

BP SU Engine designations have not been even reasonably close to actual performance for probably over two decades !
I'd much rather have the actual average stamped on the motor and in the designator than the marketing-related garbage numbers that are used.
Labeling a A3-x an A8-x makes about as much sense as claiming a particular car engine has 300 horsepower when it really only has 130.
Totally moronic crock of dawg excrement !

[shockwaveriderz]

I think (notice that I said think) hapened is the A8-x motor that we know to day was originally an A8.x where .8 lbf is equal to 3.6 netons. SO when Estes changed from the english to metric system, they also had the A5, which I think was actually an A3 or A4 and if they labeled the A.8 as an A3 or A4 they would have two and the consumer would not be able to tell what the difference between the two were or Estes would not be able to explsin adequately the differnce between the two.

This may be completely wrong but I think its close. Somebody would have to look at an old A5 thrust curve to see what it actually was... and off the top of my head I don't know if the 5 in the A5 was english or metric notation.

The same thing applies to the T size A10 and A3... they are both basically about an A2 or A3.... although there is a noticeable difference in their respective performances because of the difference in nozzle dimensions.

The actual verus labeled values mean nothing to the typical end user consumer who purchases starter kits for a quickie intro and then exit to the hobby; it only matters to us that know the differences and those that do competition or heavy duty sport flying.


terry dean


terry dean

[ghrocketman]

Whether it means anything or not to "beginners" means zip to me....quite frankly the way they are labeled could be argued as FALSE ADVERTISING if someone called them (most BP SU makers) out. Most are no way within +/-10% of actual average, which is what they are supposed to be.
Actually, I blame NAR S&T for allowing this to continue....don't gimme any garbage about those being the "traditional names" either...it is flat out inaccurate/WRONG and should be changed. :mad:

MPR and HPR composites tend to be true or at least close to their label; for example an F39 and an H128 are pretty close to their designation if one examines the thrust curves.

[barone]

...............Actually, I blame NAR S&T for allowing this to continue....don't gimme any garbage about those being the "traditional names" either...it is flat out inaccurate/WRONG and should be changed. :mad:

Actually, I don't beleive Standards and Testing has anything to do with how the manufacturer labels their motor. If it's an A, it's an A. If it's a B, it's a B. They provide the test data on the NAR site for the user to choose which motor is best suited for their application. Think about it......why provide test info for people who are going to read the label of a rocket kit and then buy the motors that are suggested? Those users don't care. But the true hobbyist will look for the data knowing that the motor markings are giving them an idication of the motor performance but the data shows the motor performance.......at least for those motors that were sampled. Gnaw on this some while I go check the NAR site and see if I can get a description of the responsibilites of the S&T....

[Carl@Semroc]

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.

[shockwaveriderz]

I think both the NAr and the NFPA regulations have soem sayso on how motors are labeled.

But what is the either the NAR or a consumer to do?

The NAR could and I suppose an argument could be made that its their responsibility to ensure that a motor is labeled correctly or they could without certification. By withholding certificatuion, that essentially means the motor could not be sold. But is it realistic? I would say no. How many A8-3 are already sitting out there in the pipeline? The NAR certainly couldn't force Estes to recall their product and I dont even know if they have the authority to do so. Motors are only supposed to be decertfied due to safety reaaons. Is mislabling a safety reason? I don't think so, but then the NAR for years has decertified motors for reasons other than safety anyway ie OOP.

Do we really want the NAR playing "chicken" with Estes over this issue? Estes is big and powerful enough to tel the NAR to go take a hike on this. I don't think this is a fight eithyer the NAR or Estes wants.

On the othe rhand, there is also labeling requirements within NFPA 1125 which applies to the manufacturers: i'll levae it to those that have an interest to gogot www.nfpa.org and look it up. But agin, who's gonna enforce NFPA 1125? Only the local or state fire marshal. So who's gonna call their State fire marshal and drop a dime on Estes? Do you think your state fire marshal would even care? I doubt it.

CPSC also has some labeling requirements but again theres no real enforcement mechinism for mislabeling. And again, who's gonna make the call to complain to the CPSC?


Basically what all this goes to show is how unneccary the NFPA regulations are and how little actual power the NAR has in the marketplace to enfoce anything concerning motors.

The genesis of motor certfication originally started out as the motors being "safety certfied" by the NAR to give marketing cover to the early motor manufacturers to say, hey look, these are safe!... they aren't fireworks...you can buy them legally! The NAR then introduced contest certfication (not in NFPA) for NAR competition in 1959.

I can see where back then a safety certfication program was needed: but its obvious to anybody that knows our history that the NAR saying motors are safe, was a massive conflict of interest as NAR S&T back then was G. Harry Stine; you know, the guy that started MMI; so he was basically using his NAR to certifiy his companies motors so they would sell.

terry dean

[shockwaveriderz]

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.

Carl, thanks for that exhaustive research! I could have done most of it myself, but I had to get up really early to goto the hospital for some tests and I was just too tired to.

terry dean

[barone]

Okay....from the NAR site concerning S&T.....

"Model rocket engines are tested according to criteria found in National Fire Protection Association (NFPA) Codes 1122 (for model rocket motors) and 1127 (for high-power rocket motors). These include accurate total impulse and time delay; sensitivity to shock, temperature, and other environmental considerations; adequacy of safety instructions; and gross operational correctness. "

As I said in the earlier post, they're looking at total impulse as opposed to average thrust.

[shockwaveriderz]

NAR S&T has a testing procedure manual(?) but I don't know what it says about marking and labeling.

I thought I had a 1st draft of this document but I can't find it. I'm sure if you emailed NAR S7T they would provide you with their policy on marking and labeling.

Here's what NFPA 1125 says about marking and labeling:

7.12 Rocket Motor Instruction Requirements.

7.12.3 The instructions shall also contain the following information:
(2) Performance data on the rocket motor or motorreloading
kit that include propellant weight, total impulse,
average thrust, time delay, and representative
thrust-time curve



Chapter 8 Testing and Certification
8.1 Certification of Model Rocket Motors, Motor-Reloading
Kits, and Components

8.1.3 Model rocket motors, motor-reloading kits, and components
offered for sale, exposed for sale, sold, used, or made
available to the public shall be examined and tested to determine
whether they comply with the standards and requirements
detailed in 8.1.7.

8.1.7 Before granting such certification, samples of a motor
or reloadable motor system shall be examined as follows:

(1) Static testing, conducted at or corrected to sea level and
20°C ± 5°C (68°F ± 9°F), of a minimum of 10 samples to
determine that total impulse, average thrust, and delay
time comply with the following requirements:

(c) Average thrust shall be within 20 percent (or 1 N,
whichever is greater) of the average thrust that is
computed by dividing the mean total impulse measured
during propellant burn time by the mean propellant
burn time.

(5) Examination of the packaging, marking, and instructions
to verify compliance with all provisions of 7.12 through
7.14


7.13 Rocket Motor Marking.
7.13.1 A rocket motor or motor-reloading kit shall have imprinted
on its external surface, casing, or wrapper, a recognized
code indicating the nominal performance parameters
— for example, “C6-5” [for a model rocket motor having a
total impulse of 5.01 to 10.0 N-sec (1.1 to 2.2 pound-seconds),
an average thrust of 6 N and a time delay of 5 seconds] or
“5-second time delay module” (for a time delay module having
a time delay of 5 seconds) — and the date of manufacture or
equivalent coding.



7.13.2* Rocket motors, motor-reloading kits, and pyrotechnic
components shall be marked with information complying with
the Federal Hazardous Substances Act, 16 CFR 1500.

[ghrocketman]

Based on the information we now have regarding the genesis of the Estes A8 engine, can ANYBODY tell me why the numbskulls at Estes changed the "real A8" to the "mis-labeled A8" that is actually an A3 ?
I can probably already guess that it has some mamby-pamby manufacturing safety baloney/garbage behind it, but I thought I'd ask if anybody has the real scoop....and NO I'm not going to call Estes (for the one guy that invariably suggests such ANNOYING things).

Why any manufacturer reduces the existing average thrust of an already produced engine to enable it to lift actually LESS is beyond me....I can see ADDING long burn engines, but not replacing existing engines with those.
One can ALWAYS use short duration-high thrust engines in light rockets, but the converse of using low thrust long duration motors in heavy rockets does not work.

I'd venture to say that for every one decent decision/change made by Estes in the last 15 years they have made at least TEN idiotic decisions or changes.

What would change my attitude about Estes ?
The idiot owner would sell it to someone that would turn it back into the company it was in the glory days, say circa 1971, with all the engines offered back then.
I could live without them ever producing an "E" engine if we could get back all the 18mm offerings from then.

[Rocketflyer]

Based on the information we now have regarding the genesis of the Estes A8 engine, can ANYBODY tell me why the numbskulls at Estes changed the "real A8" to the "mis-labeled A8" that is actually an A3 ?

[snip]

I would ask NAR S&T that question. If indeed the A8 acts more , and is like an A3, then something is amiss at S&T.

[snip]

Why any manufacturer reduces the existing average thrust of an already produced engine to enable it to lift actually LESS is beyond me....I can see ADDING long burn engines, but not replacing existing engines with those.
One can ALWAYS use short duration-high thrust engines in light rockets, but the converse of using low thrust long duration motors in heavy rockets does not work.

So true. And how many first timers have had a rocket auger in or not performed? We'll never know, but I bet we lost a few good rocketeers because of it.

[shockwaveriderz]

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.


Carl, and as you pointed out in another earlier thread, the 1995 specs that the NAR provides for the A8 engine don't correspond to what the Estes 1995-2007 catalogs show, as they show a thrust duration of .5 seconds .

terry dean

[CJU]

So true. And how many first timers have had a rocket auger in or not performed? We'll never know, but I bet we lost a few good rocketeers because of it.

I almost lost a clone of a NASA Pegasus on an A8-3 a couple weeks ago - no altitude at all, and ejection probably 30 feet up. The original flew fine on an A8 back in the 80's. Now, it's a minimum of a B6-4 for that bird.

[Carl@Semroc]

Carl, and as you pointed out in another earlier thread, the 1995 specs that the NAR provides for the A8 engine don't correspond to what the Estes 1995-2007 catalogs show, as they show a thrust duration of .5 seconds .

terry deanI was probably trying to keep it too simple! Around 2004, the thrust curve was changed to match the NAR curves from 1995, but the tables still showed the .5 second burn from the A5-x.

[Peartree]

Based on the information we now have regarding the genesis of the Estes A8 engine, can ANYBODY tell me why the numbskulls at Estes changed the "real A8" to the "mis-labeled A8" that is actually an A3 ?


Why any manufacturer reduces the existing average thrust of an already produced engine to enable it to lift actually LESS is beyond me....


Oooh, ooh, ooh This one is easy (but you won't like the answer).

Estes makes LOTS of A8's, maybe more than any other (its at least in the top five if not the top three).




Less thrust = less BP = less $$ to make = more profit.




Simple.




(I *said* you wouldn't like it)

[jetlag]

Oooh, ooh, ooh This one is easy (but you won't like the answer).

Estes makes LOTS of A8's, maybe more than any other (its at least in the top five if not the top three).




Less thrust = less BP = less $$ to make = more profit.




Simple.




(I *said* you wouldn't like it)


Could Estes possibly be so devious?

[Royatl]

Oooh, ooh, ooh This one is easy (but you won't like the answer).

Estes makes LOTS of A8's, maybe more than any other (its at least in the top five if not the top three).

Less thrust = less BP = less $$ to make = more profit.

Simple.

(I *said* you wouldn't like it)

I don't like it because it's wrong!

less thrust does not mean less BP.

Less total impulse means less BP.

--------------------

and I should mention that the usual reason behind total impulses that are below maximum is either manufacturing tolerances (making sure that more than 10% don't go above the maximum), or geometries that prevent the full amount of propellant being used (either smaller casing, or a deep core. and occasionally a less energetic batch of BP)

[Peartree]

I'd still bet that the change made Estes money.

[ghrocketman]

Agree with Peartree here.
I doubt Estes would do anything unless it helps their bottom line.
In fact, those in charge there are so ignorant they (or at least the person at the top) don't do things to satisfy their repeat customer base (note i did not say consumer) that would help the bottom line.
The only organization showing more inept management is the NFL's Detroit Lions !

[shockwaveriderz]

I don't like it because it's wrong!

less thrust does not mean less BP.

Less total impulse means less BP.

--------------------

and I should mention that the usual reason behind total impulses that are below maximum is either manufacturing tolerances (making sure that more than 10% don't go above the maximum), or geometries that prevent the full amount of propellant being used (either smaller casing, or a deep core. and occasionally a less energetic batch of BP)


Roy, of course is correct. Estes manufactures their motors at approx 1 mile above sea level. And they manufacture to 10% of the total impulse at their altitude at Penrose, Colorado.

Therefore when they are used at sea level they are evena lower than total impulse. Vern Estes did numerous experiments in the early days and he found out their was a substanital difference in the performance of the motors that were tested at penrose versus at MIT at sea level.

Ambient pressure at Penrose altitude in in the neighborhood of 12.x psi not 14.7 psi which is what it is at sea level. Therefore when you have a nominal 2.0 expansion nozzle the pressure difference results in a different total impulse. simple physics.

And the A8 nozzle throat dimensions has been changed 3 times down through the years which also obviously would effect the total impulse, average thrust and peak thrust.



In adition the actual black powder used in Estes engines has chnaged at least 3 times in the past 50 years. It was DuPont at first; then in the early 70's the only USA DuPont BP plant blew up and Estes had to purchase Canadian BP from CIL for awhile.

All BP is not created equal at the standard 75/15/10 formulation. The type of charcoal plays a large role in the potency of the BP.

SO over the past 50 years the A8 has used 3 different nozzle throat diameters, 3 different kinds of BP and 2 different case sizes of inside diameter. As you probably suspected the nozzle diameters of all the Estes engines changed when they started using the thinner wall casings. That's because the Burn Area Ratio (Kn =Ab/At) changed where Ab is the burn diameter area and At is the nozzle throat diameter area.

terry dean

[STRMan]

Roy, of course is correct. Estes manufactures their motors at approx 1 mile above sea level. And they manufacture to 10% of the total impulse at their altitude at Penrose, Colorado.

Therefore when they are used at sea level they are evena lower than total impulse. Vern Estes did numerous experiments in the early days and he found out their was a substanital difference in the performance of the motors that were tested at penrose versus at MIT at sea level.

Ambient pressure at Penrose altitude in in the neighborhood of 12.x psi not 14.7 psi which is what it is at sea level. Therefore when you have a nominal 2.0 expansion nozzle the pressure difference results in a different total impulse. simple physics.

And the A8 nozzle throat dimensions has been changed 3 times down through the years which also obviously would effect the total impulse, average thrust and peak thrust.



In adition the actual black powder used in Estes engines has chnaged at least 3 times in the past 50 years. It was DuPont at first; then in the early 70's the only USA DuPont BP plant blew up and Estes had to purchase Canadian BP from CIL for awhile.

All BP is not created equal at the standard 75/15/10 formulation. The type of charcoal plays a large role in the potency of the BP.

SO over the past 50 years the A8 has used 3 different nozzle throat diameters, 3 different kinds of BP and 2 different case sizes of inside diameter. As you probably suspected the nozzle diameters of all the Estes engines changed when they started using the thinner wall casings. That's because the Burn Area Ratio (Kn =Ab/At) changed where Ab is the burn diameter area and At is the nozzle throat diameter area.

terry dean

Why would the total impulse change depending on the nozzle diameter? It seems the energy in the BP would remain constant irregardless of the nozzle diameter. Am I missing something here?

[tbzep]

Why would the total impulse change depending on the nozzle diameter? It seems the energy in the BP would remain constant irregardless of the nozzle diameter. Am I missing something here?

Different nozzle shapes and diameters affect the efficiency of the solid motor by changing the combustion chamber pressure, and the expansion of the gases as they exit.

All rocket nozzles are compromises. The bell nozzle of a NASA rocket can be optimized for low altitude, mid-altitude, and even vacuum of space. It will perform with greatest efficiency in that altitude range it is optimized for, but it will be less efficient at other altitudes. This is another bonus for multi-staged rockets instead of SSTO. It's also why the aerospike engine is still kicking as a possible solution.

[STRMan]

OK, I get it. I always thought the total impulse of an engine was based upon the total amount of potential energy in the black powder of an engine. I didn't realize that efficiency was taken into account as it was a real measure of the performance of the engine.

This reminds me of how outboard motors used to be rated. In the old days, they were rated at the power head. Some years back, they started rating them at the prop shaft, taking into account the efficiency of the lower unit. Now I know. Thanks.

[Royatl]

SO over the past 50 years the A8 has used 3 different nozzle throat diameters, 3 different kinds of BP and 2 different case sizes of inside diameter. As you probably suspected the nozzle diameters of all the Estes engines changed when they started using the thinner wall casings. That's because the Burn Area Ratio (Kn =Ab/At) changed where Ab is the burn diameter area and At is the nozzle throat diameter area.

terry dean


IIRC, the nozzle size of the oldest A8 and 1/2A6 motors was about, but not quite, the same size as the B6 and C6 motors.

Eventually they expanded to the same size as the B4 motors. I had thought this happened in the early 90's when the igniter plugs came in, but apparently it was much, much earlier than that. I just wasn't paying attention.

Also, about marketing: Estes, having the effective monopoly it does, also has a problem. It can't change "A8-3" to "A4-3" or whatever, because the average unwashed peon typical weekend flyer will see all those older rocket kits that recommend "A8-3" and say, "I guess I can't use this A4-3 motor in it. It won't go as high." Or at least that's what I figure.

[shockwaveriderz]

IIRC, the nozzle size of the oldest A8 and 1/2A6 motors was about, but not quite, the same size as the B6 and C6 motors.

Eventually they expanded to the same size as the B4 motors. I had thought this happened in the early 90's when the igniter plugs came in, but apparently it was much, much earlier than that. I just wasn't paying attention.

Also, about marketing: Estes, having the effective monopoly it does, also has a problem. It can't change "A8-3" to "A4-3" or whatever, because the average unwashed peon typical weekend flyer will see all those older rocket kits that recommend "A8-3" and say, "I guess I can't use this A4-3 motor in it. It won't go as high." Or at least that's what I figure.

Roy, your recollections or correct as far as I know. ANd your marketing hypothesis sounds pretty good to me too.


terry dean

[Doug Sams]

Why would the total impulse change depending on the nozzle diameter? It seems the energy in the BP would remain constant irregardless of the nozzle diameter. Am I missing something here?To add to Tim's answer...your instincts are correct to a first order approximation. That is, we can make an approximate relationship between the mass of propellant and the total impulse, independent of nozzle size and shape, grain geometry, etc. For example, BP motors tend to have about 0.8Ns per gram of BP. The Estes B6 is listed at 4.33Ns and 5.6g of propellant which amounts to 0.77Ns/g (or ~79secs of Isp).

A typical Isp for APCP is 200secs, but it can vary widely with different formulations. For example, an AT F42T works out to 1.96Ns/g for an Isp of 199.9secs but the old F23's numbers were 1.65Ns/g and 168secs.

Unlike BP, APCP's burn rate is pressure sensitive, so the nozzle shape will affect the thrust and burn time, which will affect the efficiency and hence the Isp.

Anyway, your assessment is a good rule of thumb but not a law.

Doug

.

[Doug Sams]

OK, I get it. I always thought the total impulse of an engine was based upon the total amount of potential energy in the black powder of an engine. I didn't realize that efficiency was taken into account as it was a real measure of the performance of the engine.Interestingly enough, they don't consider the total efficiency of the motor system. They ignore the mass of the motor case, for example. Higher pressure motors need stronger and hence heavier cases. So if someone developed a propellant that was twice as efficient as anything else before, but the motor case had to be twice as heavy to contain it, then some of the propellant's new efficieny would be lost when considering the entire motor system. A good case of that is the hybrid. The N20 and plastic which comprise the oxidizer and propellant appear to have pretty good Isp, but the big @$$ tank needed to confine the N20 mitigates that efficiency when you look at the bigger picture.

Doug

.

[Doug Sams]

This reminds me of how outboard motors used to be rated. In the old days, they were rated at the power head. Some years back, they started rating them at the prop shaft, taking into account the efficiency of the lower unit. Now I know. Thanks.Detroit did something similar around 1970. They went from rating the motor sans accessories (alternator, water pump, etc) to rating them with all these necessities in place. But I'm not sure if that's when they included the drive train losses, or if that happened at a later date.

But I do recall that between them changing the rating methods and going to lower compression with unleaded fuels, horsepower numbers fell by more than 50% in only a few years :(

Fortunately, with computer controlled fuel delivery systems, horespower is back. So I got myself an Impala SS with 18mpg just in time so see gas go up to 4 bucks a gallon. :eek:

Doug

.

[Doug Sams]

IIRC, the nozzle size of the oldest A8 and 1/2A6 motors was about, but not quite, the same size as the B6 and C6 motors.

Eventually they expanded to the same size as the B4 motors. I agree. I just prepped an old A8-0 the other night, and the B4's yellow plug wouldn't fit NFW. The pink B6 plug was much closer, but still too tight. I think I ended up using the orange A3 plug.

Doug

.

[Shreadvector]

I agree. I just prepped an old A8-0 the other night, and the B4's yellow plug wouldn't fit NFW. The pink B6 plug was much closer, but still too tight. I think I ended up using the orange A3 plug.

Doug

.

YES. i did exactly the same thing with old motors from the early 1970's.

And for modern motors, nozzles may be identical, but the centerbore can be slightly different on different motors.

For Estes:
C11 and E9 have same nozzle but slightly different bores.

D12, and D11 have same nozle and slightly different bores.

B6 and C6 have the same nozzle and used to have identical bores, but I will swear that the latest B6 motors have a shorter bore.

[tbzep]

To add to Tim's answer...your instincts are correct to a first order approximation. That is, we can make an approximate relationship between the mass of propellant and the total impulse, independent of nozzle size and shape, grain geometry, etc. For example, BP motors tend to have about 0.8Ns per gram of BP. The Estes B6 is listed at 4.33Ns and 5.6g of propellant which amounts to 0.77Ns/g (or ~79secs of Isp).

A typical Isp for APCP is 200secs, but it can vary widely with different formulations. For example, an AT F42T works out to 1.96Ns/g for an Isp of 199.9secs but the old F23's numbers were 1.65Ns/g and 168secs.

Unlike BP, APCP's burn rate is pressure sensitive, so the nozzle shape will affect the thrust and burn time, which will affect the efficiency and hence the Isp.

Anyway, your assessment is a good rule of thumb but not a law.

Doug

.

As an example, a sparky motor type propellant often has an ISP down around 180 give or take a little based on actual formula, chamber pressure, nozzle erosion, etc. Pretty much all of the special color or other effects will lower the ISP somewhat because the materials used to make those colors or sparks are taking up space that could be used for more efficient fuels and oxidizers.

Standard APCP hobby motors are usually around 200 like Doug said, but if you like to fool with PBAN and tweak your formula, nozzle shape, chamber pressure etc. it can get up considerably higher in decent home made EX motors. IIRC, the PBAN based Shuttle SRB's have an ISP around 235.

It's been a long time since I've fooled with EX so don't quote me on any numbers. :rolleyes:

[moonzero2]

Wouldn't this difference of the labeled A8 and actual numbers come up during NAR Cetrification Testing Process and it noted somewhere by NAR that this A8 is really an A3?

[ghrocketman]

Detroit changed to SAE "Net" Horsepower from SAE "gross" horsepower the same year all manufacturers lowered compression ratios for highly leaded fuel to low lead fuel.
The year of this dread is 1972.
While one could get engines with compression as high as 11.5:1 factory-installed in 1971, in 1972 there were virtually no automotive engines with compression over 9.5:1, with most right around 8.5:1; some such as the Pontiac 350 were dropped to a PATHETIC 7.6:1 !
Each point of compression is worth 4% in overall horsepower as a "General" rule for Auto engines.
One can see that all being equal but compression ratio, an engine that goes from 11.5:1 to 8.5:1 would lose 12% in real horsepower.
Changing to the "Net" SAE rating system with all accessories installed (including A/C) and operating with measurement at the back of transmission instead of flywheel caused another 20% horsepower loss, although this was a paper "non-real" loss.
Stricter emission controls such as retarding camshaft timing and the introduction of EGR caused another 10-15% loss in 1972.
Many engines lost over 45% of their rated horsepower from 1971 to 1972, but the actual loss was closer to 25-30% due to the emission control change and lowered compresssion; the rest was a "paper loss" due to the Net rating method.
For example the 7.0 litre Ford 429 V8 went from 360hp in 1971 down to 212hp in 1972 from lowering compression from 11.0:1 to 8.0:1 and changing to the net rating method. This engine did not even have any emission changes until 1973.

Conversely if a modern engine is rated at say 500hp such as the 2008 Chevy Corvette Z06, if one was to translate into "pre 1972" flywheel horsepower, you are talking about around 675hp !!!
The good old days for horsepower really are RIGHT NOW, but the spectre of $4+/gal premium unleaded sure is ugly.
I want the 110 octane LEADED pump gas of yesteryear for $0.75/gal with today's horsepower.
Quite frankly I don't care what it would take to get our govt to do it either.

[Shreadvector]

Wouldn't this difference of the labeled A8 and actual numbers come up during NAR Cetrification Testing Process and it noted somewhere by NAR that this A8 is really an A3?

it's a long and winding thread....

http://forums.rocketshoppe.com/showpost.php?p=47615&postcount=21

[Royatl]

Wouldn't this difference of the labeled A8 and actual numbers come up during NAR Cetrification Testing Process and it noted somewhere by NAR that this A8 is really an A3?

And indeed it is... http://www.nar.org/SandT/pdf/Estes/A8.pdf

[Bazookadale]

In adition the actual black powder used in Estes engines has chnaged at least 3 times in the past 50 years. It was DuPont at first; then in the early 70's the only USA DuPont BP plant blew up and Estes had to purchase Canadian BP from CIL for awhile.

All BP is not created equal at the standard 75/15/10 formulation. The type of charcoal plays a large role in the potency of the BP.


terry dean

I've been told by people close to the fireworks industry that no one makes high energy BP anymore because the small market for it doesn't justify the increased liability

[billspad]

And indeed it is... http://www.nar.org/SandT/pdf/Estes/A8.pdf

I think the average thrust thing has been covered but for anyone interested in the procedures and policies S & T goes by take a look here:

http://www.nar.org/SandT/docs/index.html

The first link is the important one. That and 1125 are what we go buy.

Always refer to the official Engine Data Sheets. They contain real data from the testing. On most of the sheets if you go to the last page you'll find the list of points you need for Wrasp and other simulation programs. Some of the newer sheets like the one for the D5 contain data from the certification firings on the second or third page which is interesting if you want to see how much they varied.