Going for 100,000 Feet

[Nytrunner]

am hoping that this time I can run flat wires internally to the motor from the AV bay instead of externally as I had to do with Do...

I've seen this technique before, but cant quite place where (Jim? Jim2?). Where do you get your flat wiring?

that will serve as a motor block.

Ahhhhhh, I was wondering how you guys do the "motor as connecting piece" . Am I right in guessing it requires making a flush aft closure?

 

[EeebeeE]

Does this tactic still count for the TRA altitude commercial records? Do I need an L2 to do this or does TRA not view it as a motor mod even at L1? Just a fellow TRA member kinda curious. I would love to do this to a CTI 24mm thrust ring for uh reasons someday. It sure beats machining a new aft closure.

Actually, CTI has tapered closures that will fit inside the airframe for every diameter of case EXCEPT 38mm. I used the 29mm tapered closure the last time.

 

[Andrew_ASC]

Ahhhhhh, I was wondering how you guys do the "motor as connecting piece" . Am I right in guessing it requires making a flush aft closure?

Second SEDS L1 MD multistage I designed and built. Borrowed the flush closure idea from Adrian Adamson after the first interstage on another design imploded in flight at M1.5... the interstage with casing overhang is foolproof as long as you ground test a sideways loading on the casing to prevent wobbles. Wobbles kill multistages.

 

[EeebeeE]

Definitely not. Modifying the motor from its as-certified condition makes it Research by definition, and inelligible for commercial record attempts.

Would it qualify as a research record?

 

[Andrew_ASC]

Actually, CTI has tapered closures that will fit inside the airframe for every diameter of case EXCEPT 38mm. I used the 29mm tapered closure the last time.

Haven’t seen them for 24mm. Have used the 29’s before also.

 

[EeebeeE]

For reference, this was Do, which set a commercial I record. Note the aft closure on the sustainer motor. It was a tapered closure that fit inside The igniter wire from the flatwire on the outside of the airframe (the long copper strip) was shielded magnet wire that you can see on the sustainer in this picture. That wide helped make a very snug fit onto the interstage coupler. The booster on this was powered by a CTI H399. Sustainer was an I204. Flight was friggin' awesome. 15,101' at Mach 1.53.

The problem with the pro 38's is that they do not have aft closures.The aft closure/nozzle is part of the reload, and they do not make versions of motors that do not have thrust rings on the rear nozzle assemblies.

At the end of the day, if I have to switch to Loki, AMW or Aerotech to set a commercial K record, I'll do it. Problem with all of them is that their 900+ NS motors are all fast burners. They will push the rocket to the Mach 2.4 which is still OK for FG rockets, but it won't fly as high. They will still go well into the 37-38K range, but I was really hoping for 40K with this one.

 

[AeroAggie]

Would it qualify as a research record?

Yep, you can go for a research record with commercial motor mod like that.

 

[MClark]

Research records are single motor only.
No clusters or staging

M

 

[EeebeeE]

I just went to the Records section. There is no delineation at all between commercial and research in multi stage records. There is a set of "Research Records," but all those flights are single stage.

 

[MClark]

From Rules......

The purpose of this altitude competition is to obtain the greatest altitude possible for a given total impulse for staged motor configurations. The event is open to all rockets using certified motors. The motor class will be determined based on the total impulse of all motor(s) as tested.

 

[EeebeeE]

From Rules......

The purpose of this altitude competition is to obtain the greatest altitude possible for a given total impulse for staged motor configurations. The event is open to all rockets using certified motors. The motor class will be determined based on the total impulse of all motor(s) as tested.

If that is the case, then there are no altitude records kept for flights using staged research motors. I would have wasted a lot of time pursuing a record that does not exist. If there are any people who certify motors for TRA looking at this, I would ask them what the specific parameters are regarding "certified motors." There is nothing on the TRA web site that describes what is involved. It just says TRA certifies motors. There needs to be more transparency.

In this particular case, I want to use a CTI case. I want to use a 38mm CTI motor, which unlike all their other HPR motors, has a combined aft retainer and nozzle. The aft retainer is used as thrust ring. What I want to do makes no change to the motor case, the forward closure, or the motor nozzle. All I want to do is sand the aft retainer component down so it is flush with the motor case. This is not a structural change at all. I am not altering threads. I am not adding or removing any O rings. What goes inside the motor case is unchanged.

I just want more clarification than a simple "No you can't," especially when the motor certification process appears to be nebulous at best. What would even be better would be a specific rule or clause that addresses this particular issue. I kind of doubt one exists, and we are all making SWAGs.

 

[blackjack2564]

If you want CTI-38 closure flush to airframe/MMount, ya can stick it in a lathe and turn it down like this one, Even has a slight taper for a faux tail cone...every bit helps It will not be perfectly round as the "grabbers" on the nozzle to help turn them are below diameter of airframe.
They show as slight depressions around it.
This will get ya into I/S coupler!

 

[AeroAggie]

If that is the case, then there are no altitude records kept for flights using staged research motors. I would have wasted a lot of time pursuing a record that does not exist. If there are any people who certify motors for TRA looking at this, I would ask them what the specific parameters are regarding "certified motors." There is nothing on the TRA web site that describes what is involved. It just says TRA certifies motors. There needs to be more transparency.

In this particular case, I want to use a CTI case. I want to use a 38mm CTI motor, which unlike all their other HPR motors, has a combined aft retainer and nozzle. The aft retainer is used as thrust ring. What I want to do makes no change to the motor case, the forward closure, or the motor nozzle. All I want to do is sand the aft retainer component down so it is flush with the motor case. This is not a structural change at all. I am not altering threads. I am not adding or removing any O rings. What goes inside the motor case is unchanged.

I just want more clarification than a simple "No you can't," especially when the motor certification process appears to be nebulous at best. What would even be better would be a specific rule or clause that addresses this particular issue. I kind of doubt one exists, and we are all making SWAGs.

I feel your pain. I traded a lot of emails with the TRA records committee regarding certified motors and modifications. In my case, I was asking about simply exchanging one Loki forward bulkhead for another Loki forward bulkhead (extended, more tracking smoke, no change to the propellant or case) - both are certified, but on different motors. They said, flat out, NO. It has to be the exact combination of hardware without modification that was tested during the cert process to qualify for a commercial record.

It's not nebulous at all. They test a specific hardware and propellant combination, it passes, that's the only combination that is "certified", regardless of any strength equivalency of other hardware. Their argument is that you can do whatever you want to the motors and fly them till the cows come home under TRA research rules, but if you want to qualify for a commercial record, the rules are very strict. As an engineer who makes a living analyzing aircraft structures and certifying by analytically demonstrating equivalency to a certification basis, this bothers me a little bit. But I understand their position. The rules are necessarily strict to reduce ambiguity, level the playing field, and reduce the burden on the committee to adjudicate what meets cert minimums. If you want your name by an impulse record, gotta play by their rules.

 

[MClark]

There are no records for staged or clustered research motors.
TMT will not certify motors for an individual, motors must be made by a real manufacture.
If you want to know if a motor is certified contact TMT not Records Committee or a forum.

 

[EeebeeE]

There are no records for staged or clustered research motors.
TMT will not certify motors for an individual, motors must be made by a real manufacture.
If you want to know if a motor is certified contact TMT not Records Committee or a forum.

That isn't the issue here. I know the motor is certified.

 

[JimJarvis50]

I haven't reviewed this entire thread in detail, so forgive me if I miss something here.

The obvious way to solve your problem (Plan A) is to use an air frame sleeve around the extended motor section, and then design your interstage coupler to accept the larger tube. I have three interstage couplers that go to a larger booster that are designed that way, and I just roll a tube around an air frame mandrel for use in the interstage coupler. In another case, I rolled the booster air frame itself on an air frame mandrell so that it would accept a sleeved motor. I don't know if this ship has sailed for you on this project, but it would work.

I suspect that the motor modification you are asking about would not be approaved. However, I am not sure that this is a slam dunk. I went through this discussion with the powers-that-be back in 2009 regarding the use of a CTI 98mm motor without the integral thrust ring. In that particular case, it was decided that if CTI made a case for me without the ring (the rings were always there on the Gen 1 cases at the time), that it would be considered certified. Some of the discussion points that came up during that time were that CTI would need to make the modification, that they would need to be willing to stand by their commercial warranty, and that CTI and CAR both agreed that the modification didn't affect the performance or safety of the motor. I doubt that removing the plastic that constitutes the thrust ring would affect the motor, so in theory, you might be able to follow a similar path. Plan A would be a lot easier though.

Jim

 

[EeebeeE]

I feel your pain. I traded a lot of emails with the TRA records committee regarding certified motors and modifications. In my case, I was asking about simply exchanging one Loki forward bulkhead for another Loki forward bulkhead (extended, more tracking smoke, no change to the propellant or case) - both are certified, but on different motors. They said, flat out, NO. It has to be the exact combination of hardware without modification that was tested during the cert process to qualify for a commercial record.

That's too bad if it is the case in this situation. I am not changing bulkheads or adding new delay charges. I am just asking if I can sand off part of the case to make it fit. Also, by the logic you described, we should also not be able to remove preset ejection charges or drill delays because to do either one would not make it the "exact combination." Another "modification" of hardware opposite of what I want to do is wrapping masking tape around the case for a more snug fit.

To make sure I am completely clear, what I want to do is sand off the segment of the aft thrust ring beyond the red line in this photo so that an airframe will fit around it. That's all. Note that CTI does allow a 1/16" gap in that area so the only physical purpose it serves is to be a thrust ring. I am substituting a thrust ring with a motor block and an internal motor retention system. This part has no integral contribution to the structural integrity of the motor.




I have an e-mail into the motor certification committee, and whatever they say goes. If push comes to shove, I'll use a Loki without the thrust ring ... unless the motors were certified using the removable thrust ring.

 

[Nytrunner]

Sincerely wishing you good luck on that email endeavor!

Also, I don't think you mentioned what kind of flat-wire you use to run down the outside of the motor?

 

[EeebeeE]

I haven't reviewed this entire thread in detail, so forgive me if I miss something here.

The obvious way to solve your problem (Plan A) is to use an air frame sleeve around the extended motor section, and then design your interstage coupler to accept the larger tube. I have three interstage couplers that go to a larger booster that are designed that way, and I just roll a tube around an air frame mandrel for use in the interstage coupler. In another case, I rolled the booster air frame itself on an air frame mandrell so that it would accept a sleeved motor. I don't know if this ship has sailed for you on this project, but it would work.

I suspect that the motor modification you are asking about would not be approaved. However, I am not sure that this is a slam dunk. I went through this discussion with the powers-that-be back in 2009 regarding the use of a CTI 98mm motor without the integral thrust ring. In that particular case, it was decided that if CTI made a case for me without the ring (the rings were always there on the Gen 1 cases at the time), that it would be considered certified. Some of the discussion points that came up during that time were that CTI would need to make the modification, that they would need to be willing to stand by their commercial warranty, and that CTI and CAR both agreed that the modification didn't affect the performance or safety of the motor. I doubt that removing the plastic that constitutes the thrust ring would affect the motor, so in theory, you might be able to follow a similar path. Plan A would be a lot easier though.

Jim

I had thought about a sleeve as well, but the issue with the 38mm motors in particular is that this ring extends even beyond the diameter of the motor tube. A sleeve would also have to account for the 0.5-1.0mm additional width. That would create a significant wiggle issue so in my mind it would be better and far safer to use a different motor manufacturer altogether.

 

[EeebeeE]

Sincerely wishing you good luck on that email endeavor!

Also, I don't think you mentioned what kind of flat-wire you use to run down the outside of the motor?

Sorry about that ... I can't remember if I got this on Amazon or e-bay. The strips are 0.5mm thick and about 6mm wide. IN my 29mm airframe I could get the motor in with two strips, but three was not possible. Since I was running both separation and ignition cables to them, I needed three flat cables (common ground). WIth my 38mm airframe being larger and the separation charges being triggered from the booster, I am hoping the wire will now fit. THis was a roll of 30 feet for about $29 or so.

 

[Nytrunner]

Fantastic! thanks. Those look really familiar from my brother's audio phase in the 90s

I assume you must solder a connection to the ends of each piece?

Interesting. It looks like those are two isolated parallel strips, but from your description that sounds incorrect. I'd have imagined running hot and ground down one strip for the charge, and down another for the igniter.

 

[EeebeeE]

Fantastic! thanks. Those look really familiar from my brother's audio phase in the 90s

I assume you must solder a connection to the ends of each piece?

Interesting. It looks like those are two isolated parallel strips, but from your description that sounds incorrect. I'd have imagined running hot and ground down one strip for the charge, and down another for the igniter.

My plan was to have a common ground be one of these wires. The other wire in the pair would be for booster ignition. I would then cut away one wire from another section of flat wire to add a third wire for booster separation. Three wires however was too snug for the motor case to fit through, and I only had two days before the launch to come up with a solution.

I ended up running three wires out the AV Bay bulkhead. I soldered wires to the forward end of the flat wires through the airfame. I then loosely twisted the wires to those coming out the bulkhead and then covered them with layer of electrical tape to prevent short circuits. I wanted good electrical connections that could easily pull apart at apogee separation.

On the aft end, I soldered shielded magnet wire and cut 3 small notches into the airframe so they could slide back inside the airframe and connect to the igniter and separation charge. The shielded wire was soldered to the flat wire witrh a half-inch long section of copper plumbing solder so that I wouldn't pull out the connection to the igniter wire after booster separation.

It all worked almost completely flawlessly, except that the electrical tape I put over the soldered ends on the aft end, came loose slightly and created some unnecessary drag. Do flew to 15,101' on 630 NS of power. I was only about 3,500' short of the complex J record. It simmed closer to 17,000, and I think the drag, combined with some real stiff winds above 10,000' is what caused it to fall short.

 

[JimJarvis50]

I had thought about a sleeve as well, but the issue with the 38mm motors in particular is that this ring extends even beyond the diameter of the motor tube. A sleeve would also have to account for the 0.5-1.0mm additional width. That would create a significant wiggle issue so in my mind it would be better and far safer to use a different motor manufacturer altogether.

Yep, a different motor with no thrust ring is a good option too. However, by my measurements, with a typical air frame tube (0.07" thick), the closure does not extend beyond the OD of the air frame tube. This would work with a sleeved motor.

I'm not sure what you mean by wiggle? Yes, you have to roll a tube as the mating tube in the interstage coupler. However, it can be rolled to the exact diameter that you want using the motor tube as a mandrel. Wires would go under the sleeve. Fine if you want to take a different path, but this would work.

Jim

PS - Taperwire 424 (Taperwire.com) comes in at less than 0.4mm. 4 conductor, 1" wide.

 

[boatgeek]

You might have some luck using the approach that Crazy Jim did for his eyebolt in the touch hole solution with CTI. He basically got an email from CTI that said that this was an approved modification (just like removing BP to plug, adjusting delays, etc.). With that email in hand, it becomes not a research motor when you make that mod (please correct me if I'm wrong on details, here).

If you follow that approach, you might be able to get CTI to tell you that removing the outer perimeter of the aft closure is OK as long as it's only to the OD of the MMT. They would know that any extra material there is just that. With that in hand, you should be able to convince TRA that this isn't research.

That said, getting that email may be difficult. I don't know who would handle that kind of thing at CTI these days.

 

[EeebeeE]

You might have some luck using the approach that Crazy Jim did for his eyebolt in the touch hole solution with CTI. He basically got an email from CTI that said that this was an approved modification (just like removing BP to plug, adjusting delays, etc.). With that email in hand, it becomes not a research motor when you make that mod (please correct me if I'm wrong on details, here).

If you follow that approach, you might be able to get CTI to tell you that removing the outer perimeter of the aft closure is OK as long as it's only to the OD of the MMT. They would know that any extra material there is just that. With that in hand, you should be able to convince TRA that this isn't research.

That said, getting that email may be difficult. I don't know who would handle that kind of thing at CTI these days.

I submitted a query. They make tapered closures for 29mm and 54mm cases.

 

[blackjack2564]

See post 372... they already did. It was Ok'd to do safety wise, no mention of approval for record attempt, didn't ask,
That's standard closure turned down..many years ago. I asked about a 38 tapered and was told no way a mold would be done for limited use, just taper one flush. It had been done before.
only reason knob is there, for easy of screwing into place by hand.

PS to be clear approval for the eyebolt in closure was verbal not written.

 

[EeebeeE]

See post 372... they already did. It was Ok'd to do safety wise, no mention of approval for record attempt, didn't ask,
That's standard closure turned down..many years ago. I asked about a 38 tapered and was told no way a mold would be done for limited use, just taper one flush. It had been done before.
only reason knob is there, for easy of screwing into place by hand.

PS to be clear approval for the eyebolt in closure was verbal not written.

Without a charge and with a bulkhead/motor block, friction fitting would be OK. I just wanted to be safe and have an active retention system.

 

[EeebeeE]

See post 372... they already did. It was Ok'd to do safety wise, no mention of approval for record attempt, didn't ask,
That's standard closure turned down..many years ago. I asked about a 38 tapered and was told no way a mold would be done for limited use, just taper one flush. It had been done before.
only reason knob is there, for easy of screwing into place by hand.

PS to be clear approval for the eyebolt in closure was verbal not written.

I did not read that post as "official permission." I did ask the records committee. They asked for a photo to see what I was talking about, but the response sounded positive. Crossing fingers. If not, I will use a Loki motor.

 

[EeebeeE]

The Records board has said this mod is OK. I am not modifying the engine. Plus it is necessary for a MD rocket. Crisis averted. On to the next one.

 

[Nytrunner]

The Records board has said this mod is OK. I am not modifying the engine. Plus it is necessary for a MD rocket. Crisis averted. On to the next one.

Excellent! Reason prevails