Motors and Motor Development

[Initiator001]

Mike,

When I worked at Enertek for Lee Piester in 1987-88, I discovered a box of random rocket motors in the office closet.

One of the motors was a bare fiberglass casing with graphite nozzle. It was labeled "Dorffler G Motor".

All I have been able to find out about it was that it was made in the mid/late 1970s and that it might have used leftover Enerjet motor components.

I was wondering if you could provide me with some history about this motor.

Thank you.

Bob Sanford

[MDorffler]

Mike,

When I worked at Enertek for Lee Piester in 1987-88, I discovered a box of random rocket motors in the office closet.

One of the motors was a bare fiberglass casing with graphite nozzle. It was labeled "Dorffler G Motor".

All I have been able to find out about it was that it was made in the mid/late 1970s and that it might have used leftover Enerjet motor components.

I was wondering if you could provide me with some history about this motor.

Thank you.

Bob Sanford

Bob - ya know, the more I read the questions here, I'm beginning to learn where all my missing stuff got to! How in the world did my motor protos end up at Centuri I ask? And then I learn Bob Kaplow has at least one of Ed and my 'Brown-Dorffler' motors. You guys collectively have have more of my stuff than I do! Geeezo.

Anyway, Ed and I never had an approved budget in our earliest work with composite motors. We made motors and propellant from what we could essentially find laying around. After Enerjet ceased operations the remaining casings, nozzles, head enclosures, and other stuff was shipped and stored at the Estes plant. Well, Ed and I made an effort hide most of it so it wouldn't somehow be destroyed. In affect we stole it and moved it to an area where nobody would find it.

We must have had well over 1,000 of both E and F fiberglass casings and more than enough nozzles, both graphite and phenolic, to almost go into motor production.

We started making clones of the Enerjets as the fastest way to get on a learning curve. First we made them in the same way Irv Wait did, then we developed our own techniques. The motor you have is one of many of those learning curve motors we made. Then as we took each part or process as far as we could, we chinked over to another aspect of motor design.

One of the coolest things about one of those Enerjet motors was that they lit up like a flashbulb right at burnout. The propellant was loaded into the casing without a liner, which meant that it came i n direct contact with inside of the casing wall. And because they burned outward from the cenetr core, the flame head contacted the case wall at the end of the burn. And if you got a little careless and didn't get the propellant loaded just right you could end up with a ring of fire on the inside of the casing right at the front of the nozzle face as well as at the head enclosure.

Ed and I worked with many propellants over the years. Loading the double-based motors taught me well not to ignore wearing rubber gloves handling the proellant. On one occasion I got one of the biggest headaches I had ever had because I didn't think holding onto a grain bare-handed for a minute or so would be that big a deal. Wrong.

[Initiator001]

Mike,

Thanks for the information about the motor I found.

A few more motor questions:

1) In 1994, Estes released a new E2X kit called the Manta (Parasite B/G). I bought one and the packaging/box listed C10 motors for use with this model. Also, I heard of a C4 motor around the same time. What happened to these two motors?

2) The 1993 catalog introduces the Pro Series Terrier/Sandhawk and Jayhawk scale models. The motor listings for these two kits refer to E15 & E30 motors. Was this E15 the black powder motor which was released? What about the E30 motor?

3) At several hobby shows in the early 1990s, I saw a sign announcing that Estes would have composite motors. This was many years before North Coast Rocketry and the F62 motor. I have attached a picture of the sign. What is the story behind the product mentioned on the sign?

Thanks for your time and I look forward to your answers.

Bob Sanford

[Jerry Irvine]

The D12 is a detuned D13. The E9 is a detuned E15. The E30 and the D20 I saw fly in person were never released but a bunch of prototypes were made. The detuning of motors are done because BP motors continue to cure after shipping and performance varies quite a bit with temperature and humidity. The D13 had a fairly high failure rate in the west but not so much in the south and east.

I am not subject to Estes NDA. The Pro series ended up being released as clustered 24mm rockets.

The F62 internal geometry was an exact copy of the U. S. Rockets F40/F80. As such, one grain is an E, two an F, and three a shippable G. It appears Estes tried to get CPSC to accept G's, and when not, they were not released even though DOT and NAR certified already.

Jerry

[Royatl]

The D12 is a detuned D13.
...
The D13 had a fairly high failure rate in the west but not so much in the south and east.


Oh, the D13 definitely had a high failure rate in the South too! I have film!

[MDorffler]

The D12 is a detuned D13. The E9 is a detuned E15. The E30 and the D20 I saw fly in person were never released but a bunch of prototypes were made. The detuning of motors are done because BP motors continue to cure after shipping and performance varies quite a bit with temperature and humidity. The D13 had a fairly high failure rate in the west but not so much in the south and east.

I am not subject to Estes NDA. The Pro series ended up being released as clustered 24mm rockets.

The F62 internal geometry was an exact copy of the U. S. Rockets F40/F80. As such, one grain is an E, two an F, and three a shippable G. It appears Estes tried to get CPSC to accept G's, and when not, they were not released even though DOT and NAR certified already.

Jerry

Sorry Jerry, as the primary designer of the F62 I can tell you most assuradly I did not copy any U.S. Rockets motors, or any one else's for that matter. The internal ballistics of the 'Smokey Sam' propellant dicatated the internal grain geometry just as all propellants do.

[shockwaveriderz]

Mike. what do you think of a BP re-loadable.

I understand that there would be at least 1 initial detriments:

CPSC would not recognize this as a model rocket because of the metal casing; therefore only adults could purchase and use. Ok so Estes makes a product for adult only.


It sems to me that Estes could use its current investemnet in its Mabel technologies:

you just press a propellant grain/delay/smoke train/ejection charge/clay containg cap into a smaller length and diameter paper casing.

Using a metal casing would allow you to burn the BP propellant at much higher chamber pressures resulting in much higher Isp's.

Nozzles could be single use or multi-use perhaps and replaceable.

looking forward to your responses.

terry dean



what advantages/disadvantages pros/cons do you see to such a product?

[MDorffler]

Mike. what do you think of a BP re-loadable.

I understand that there would be at least 1 initial detriments:

CPSC would not recognize this as a model rocket because of the metal casing; therefore only adults could purchase and use. Ok so Estes makes a product for adult only.


It sems to me that Estes could use its current investemnet in its Mabel technologies:

you just press a propellant grain/delay/smoke train/ejection charge/clay containg cap into a smaller length and diameter paper casing.

Using a metal casing would allow you to burn the BP propellant at much higher chamber pressures resulting in much higher Isp's.

Nozzles could be single use or multi-use perhaps and replaceable.

looking forward to your responses.



terry dean



what advantages/disadvantages pros/cons do you see to such a product?

Terry - first of all pressed black powder only increases a couple clicks in ISP by increasing the chamber pressure to as much as 1,000 psi.. You might get lucky to get ~95 out of it at those pressures. Estes BP motors run typcally down around ~80 ISP at 50psi. Black powder as a propellant for re-loadables simply does not merit the effort. This was the whole purpose for introducing the composites with ISPs typically in the ~180 range into model rocketery.

Then there is the problem of pressing the re-loadable BP grains. It would be a mess. You would either press into a very thin tube to act as the exterior inhibiror, or press into a solid un-inhibeted grain. The latter is going to burn on all surfaces making it a high thrust short burn motor. The inhibeted grain will be an end-burner with either one or both ends burning. Remember, BP burns right at 1" per second no matter the chanber pressure, so you can get out your calculator to see that the options you have for grain design versus burn time is very limited. And then consider having these solid grains of BP rolling around in your flight box. A 1" diameter uninhibited grain is going to totally burn in .5 second if you accidently light it up. A typical AP composite grain will burn at .25" per second with the exterior almost always inhibeted. You'll have a far greater time getting out of the way of a burning composite grain than the BP grain. Give that some thought.

Next, I would estimate that to press re-loadable BP grains would end up to be very nearly the same cost as pressing an entire motor. And then you need to now purchase and maintain the re-loadable metallic casings to drop them into. Black powder is a terrible corrosive burning propellant. Have you noticed how nasty and ugly your blast delector gets from using BP motors? That's what it will do to the inside of your metallics. And the exhaust is also very abrasive. While a black powder motor is running, the internal gas flow is chewing out the paper just in front of the clay nozzle. That's what will happen over time in a re-loadable casing unless you also drop in a heavy liner.

Terry - there are in my opinion simply no pros in opting for a re-loadable BP motor. There are far more design and manufacturing issues than with the composites. Sorry.

[shockwaveriderz]

ok fair enough. Mike. Do you or Can you foresee a day when the majority of Estes engines are made with composite propellants?


terry dean

[Bazookadale]

Sorry Jerry, as the primary designer of the F62 I can tell you most assuradly I did not copy any U.S. Rockets motors, or any one else's for that matter. The internal ballistics of the 'Smokey Sam' propellant dicatated the internal grain geometry just as all propellants do.


Mike - the world needs F62 Darkstars! - OK I need F62 Darkstars! It is the finest model rocket motor ever, you need to find someway of bringing it back.

[Initiator001]

Mike,

What's the history for the G70 Darkstar motors?

Why did they never go into full production?

As always, thanks for taking the time to answer my question.

Bob Sanford

[MDorffler]

Mike,

What's the history for the G70 Darkstar motors?

Why did they never go into full production?

As always, thanks for taking the time to answer my question.

Bob Sanford

Hey Bob,

Both the F62 and G70 motors fell victum to a serious accounting error which ended their short lives. Composite motor mterials and construction costs are already severe with any motor maker and their retail prices reflect this. It can be a struggle. If the costs are not tracked or are not correctly controlled, the actual price to produce a motor may leave no room for any profit. This problem appeared during F62 production which then rolled over to bringing the G70 online. Estes simply didn't make enough profit on the F62 to continue with either motor.