The line between certified and EX?

[Borderline Sci]

I know if I put my EX fuel grains in a certified reusable motor case that it is now an EX motor but dose any other modifications to the existing components to a fully certified motor change it to EX?

In reading an article in this months HP magazine (TRA publication) on improving EX motors by bringing the nozzle L/D to 0.40.
My question is if I modify the nozzle throat length of a certified motor to make its L/D 0.40 (do not change the throat diameter!) have I made the motor an EX? From what I understand from the article this dose not change the camber pressure, it improves the trust on the divergent side of the nozzle. So you are getting more trust but not changing any internal factors of the motor.

Any comments from the real rocket scientist would be appreciated.

 

[rstaff3]

As TRA defines it, EX refers to making your own propellant.

 

[edwardw]

In the TRA EX Safety Code 9.5 and 9.5.1 say this:

9.5 Modification of Commercially-manufactured Motors

9.5.1 Modifying a commercially manufactured motor in any way shall not make said motor an experimental motor.

Also 3.2.6 says this,

Experimental Motor. Any non-certified, non-commercial motor made by individuals for their own personal non-commercial use.

I don't know if making the L/D ratio on the throat makes the motor non-certified in the same way the plugging a BP motor makes it non-certified.

Here is a link to the TRA EX Safety Code.

https://www.tripoli.org/documents/ex_safety_code.pdf

Edward

 

[bobkrech]

Two comments.

If you modify a certified motor, it is no longer certified. That's means you can't fly it at a sanction launch. However doesn't make it EX, so you can't fly it at an EX launch either.

I have not read the article, however you can not get more thrust out of a rocket motor by changing the throat L/D without changing the chamber operating pressure. The nozzle throat is the mass control point of the rocket engine. If you modify the throat, you will change the cd, or discharge coefficient, of the nozzle. This will change the thrust, chamber pressure and the Isp of the motor. If you increase the throat cd by reducing throat drag, you will increase the mass flow at a given pressure and therefore reduced the chamber pressure since you have not changed the grain burning area, and you will have reduced the thrust because you have reduced the Isp.

If you reduce the cd by increasing the drag in the throat, you will reduce the mass flow at a given pressure, and thus the presure must increase since you not reduced the grain's burning area. Since you have increased the chamber pressure without changing the mass flow you will increase the Isp and slightly increase the thrust. This can be dangerous if the chamber pressure increases substantially.

You typically get the best performance by optimizing the nozzle area ratio to prevent over or under expansion. The PROPEC code will perform these calculations for you.

Bob Krech

 

[Chuck Rudy]

Originally posted by bobkrech
Two comments.

If you modify a certified motor, it is no longer certified. That's means you can't fly it at a sanction launch. However doesn't make it EX, so you can't fly it at an EX launch either.


Bob Krech

However, isn't a flyer permitted to fly an altered previously certified motor if it is clustered around a central EX motor or staged or air started in combination with an EX motor? That might be one way to burn up that motor you made changes to.

Chuck

 

[Borderline Sci]

Maybe I need to read it again???
The article intended to make you think when designing you EX nozzles but it mentioned that most commerce motors did not have an L/D of 0.40. So my little mind went to work on a simple hand tool to correct this. However you are only getting 3-8% more trust by having the L/D at this ratio.

So I guess the real question here should be am I raising the camber pressure sufficiently to case the commercial motor to Cato?
Guess it's time to do some math….

 

[Borderline Sci]

Originally posted by Chuck Rudy
However, isn't a flyer permitted to fly an altered previously certified motor if it is clustered around a central EX motor or staged or air started in combination with an EX motor? That might be one way to burn up that motor you made changes to.

Chuck

I have not made any mods yet.

BTW I like the way you made an Incredibles symbol with a rocket powered single bladed chopper wing thingy.

 

[DynaSoar]

Originally posted by Chuck Rudy
However, isn't a flyer permitted to fly an altered previously certified motor if it is clustered around a central EX motor or staged or air started in combination with an EX motor? That might be one way to burn up that motor you made changes to.

Chuck

It makes it an uncertified motor, not matter what else is packed around it. TRA rules, on which their insurance either pays or refuses to pay, say experimental only means just that.

On the other hand, there's always ARSA.

 

[Borderline Sci]

I have reread this article and it said that the chamber presser is not changed. That the L/D of 0.40 makes that nozzle more efficient up to 8% so we are talking only very small changes to the rockets flight. May be one to two hundred more feet in elevation of the rocket. Not worth my time to mess with a commercial motor but well worth my time when designing my EX motors.
I have several acres of land out in the Arizona desert were I test my EX projects. Also I am a member of ASRA (member number 329) but it is a longer drive to their launch site than it is to the TRA site. (Four hours verses two and a half.)

 

[dave carver]

The only problem with this L\D discussion is that the real ratio that you need to worry about is throat-to-exit diameter. as it stands right now most aerotech nozzles are very much underexpanded. research into clamp on nozzle lengthener/diameter increaser optomized to, let's say, mid-burn altitude, would greatly increase altitude. you see, i measured the nozzle from a I-435 and found the best place to launch it would be Death Valley, Cali. just think of how high an optomized K-250 would do at Hartsel, Colo.

 

[Austin]

Originally posted by Chuck Rudy
However, isn't a flyer permitted to fly an altered previously certified motor if it is clustered around a central EX motor or staged or air started in combination with an EX motor? That might be one way to burn up that motor you made changes to.

Chuck

Chuck,

Dynosaur is correct. Any modification to the certified motor makes it decertified and it does not matter what other cluster motors are included, the motor itself is still de-certed and not usable at TRA EX launches.

Carl

 

[Chuck Rudy]

Well then I stand corrected.......and my statement will remain in the thread. ;-)

 

[rstaff3]

This is a point of confusion because IMO what is allowed varies from place to place. i.e. I have seen reports of uncertified old motors being used along side EX motors at EX launches. I for one tend to forget the TRA EX rules as MDRA doesn't fly under those rules.

 

[Chuck Rudy]

Originally posted by rstaff3
This is a point of confusion because IMO what is allowed varies from place to place. i.e. I have seen reports of uncertified old motors being used along side EX motors at EX launches. I for one tend to forget the TRA EX rules as MDRA doesn't fly under those rules.

Same here, MDRA is an oasis in the madness. Or common sense in the real world. I've heard tell of a really wild motor which may make itself known in another two months. But that will be another thread.

Chuck

 

[rstaff3]

I'll be looking for that thread...

 

[hybridfreak]

I know if I put my EX fuel grains in a certified reusable motor case that it is now an EX motor but dose any other modifications to the existing components to a fully certified motor change it to EX?

In reading an article in this months HP magazine (TRA publication) on improving EX motors by bringing the nozzle L/D to 0.40.
My question is if I modify the nozzle throat length of a certified motor to make its L/D 0.40 (do not change the throat diameter!) have I made the motor an EX? From what I understand from the article this dose not change the camber pressure, it improves the trust on the divergent side of the nozzle. So you are getting more trust but not changing any internal factors of the motor.

Any comments from the real rocket scientist would be appreciated.

I'm digging up a really old thread here I guess but I've read said article and now I can't find it anymore! Does anyone have a link to it?

Thanks!

 

[jsdemar]

I'm digging up a really old thread here I guess but I've read said article and now I can't find it anymore! Does anyone have a link to it?

Thanks!

https://www.rasaero.com/dl_solid_motor.htm

 

[hybridfreak]

https://www.rasaero.com/dl_solid_motor.htm

Awesome, thanks!

 

[Rschub]

I don't want to open a can of worms here but if I buy propellant grains from ACS and load them into a case with a custom Kn and a drilled-out nozzle, where is that in the TRA rule book? Seems like up the creek from reading this, albeit old information.

 

[Handeman]

I don't want to open a can of worms here but if I buy propellant grains from ACS and load them into a case with a custom Kn and a drilled-out nozzle, where is that in the TRA rule book? Seems like up the creek from reading this, albeit old information.

That is an EX motor. It's pretty simple. If it's not a commercially available motor reload that is assembled exactly as it was certified by the manufacturer, it's EX.

The club I fly with is Tripoli and we are setup with distances and safety code for EX for all of our launches, so it doesn't matter much to us as long as you are L2. You really need to ask the NAR guys what they think about it, it's a big deal to them.

 

[jsdemar]

Let's update this thread by including a link to the current Tripoli Unified Safety Code:
https://tripoli.org/content.aspx?page_id=22&club_id=795696&module_id=520420

 

[Rschub]

Thanks for the link, I am Tripoli and level 2, just now dipping my toe into the EX motor side of it. Found the answer in the definitions section.

 

[SolarYellow]

I think it's just a typo, so should be easy enough to fix:

Research Motor: A Rocket Motor, made by a Tripoli member or team of Tripoli members or a Certified Motor which has been intentionally modified by a Tripoli member of team of Tripoli members for their own use at a Tripoli launch.

Pretty sure that should be "or."

 

[Art Upton]

Interesting. I was a TRA and NAR member well before 2005 when this thread started. Why in 2005 would TRA forbid the flying of a modified motor as an EX motor?

Post #23 is what I remember it to be.