liner length versus compatibility

At XPRS, one fellow tried to use a Cesaroni M3400 in the Aerotech case of matching size, only to find that the liner is too long by an amount too large to compensate for with O rings.

Many of us thought 75mm and 98mm matching case sizes were fully compatible with the lone exception of O rings differing for various reloads. Then Mike of Bay Area Rocketry made a few claims that made us think cross compatibility was no more. I sure hope not!

Does anyone out there know the latest? I am asking about physical compatibility only, of course certification is a different story.

The 98mm CTI reloads with an XL nozzle are not cross compatible. I've seen it mentioned before, but don't see it specifically mentioned on the CTI site. The 98mm product notes shows how the XL nozzle is different, e.g. the nozzle carrier isn't used in the CTI case.

I'm not sure if one of these might be the reason for the assembly problem, but the CTI M3400 is a bit different than the typical CTI Pro89 4G reload.

https://www.pro38.com/pdfs/Pro98_Instructions.pdf

Separate section for using CTI M3400 reload in AT Casing, notes the final grain spacer disk may not fit and if so is not required.

https://www.pro38.com/pdfs/Pro98_notes_V1.6.pdf

Standard Pro98 nozzle carrier is not used as the M3400 nozzle is a Pro98 XL design. Trying to use the nozzle carrier and the XL nozzle would make it appear that the liner was too long.

Bob

I see, the XL nozzle is the reason. Thanks for the explanation, and hopefully all the other motors we wanted to try work fine. Especially, I wanted to run an Aerotech L900 dark matter in the Cesaroni 75mm4G case at an EX launch.

bobkrech said:

I'm not sure if one of these might be the reason for the assembly problem, but the CTI M3400 is a bit different than the typical CTI Pro89 4G reload.

https://www.pro38.com/pdfs/Pro98_Instructions.pdf

Separate section for using CTI M3400 reload in AT Casing, notes the final grain spacer disk may not fit and if so is not required.

https://www.pro38.com/pdfs/Pro98_notes_V1.6.pdf

Standard Pro98 nozzle carrier is not used as the M3400 nozzle is a Pro98 XL design. Trying to use the nozzle carrier and the XL nozzle would make it appear that the liner was too long.

Bob

Click to expand...

Hey guys.
I was the one that tried to fly the M3400 in the 10240 and nope, it does NOT fit.
A couple things-
A. The nozzle carrier is omitted by the fact that the nozzle has a larger "shoulder" area. It doesn't actually change the length of the component.
B. You are NOT allowed to remove the FORWARD SEAL DISK, as you suggest. You ARE allowed to omit the final ORING grain spacer only.

All - I had a long discussion with Mike about it that night. For some reason, CTI is quietly phazing out their compatibility with RMS hardware. Not sure how this is even possible given the hardware hasnt physically changed in dimensions, but maybe it means theyl stop coming with ARKs.
All I know is that when you try and stuff an M3400 into the M1939 tube, this happens.



I was so greatful that Tony was at that launch.... If not this wouldnt have happened -

Frozenferrari said:

A. The nozzle carrier is omitted by the fact that the nozzle has a larger "shoulder" area. It doesn't actually change the length of the component.

Click to expand...

Right, I think A is the key. Since the nozzle holder isn't used for a CTI load in an RMS case, the fact that the XL nozzle effectively fills the same lengthwise dimension as a regular nozzle plus nozzle holder, makes the assembly (XL nozzle + liner + seal disk) too long for the RMS case.

Yep Mark I think you are exactly right. It appears that the RMS hardware geometry does the job of the nozzle holder and retaining ring combined, so therefore if the nozzle has the geometry to exclude the holder, the RMS hardware now has extra geometry. Makes total sense.
So we were all right.

And to sum it up, CTI XL nozzle loads are NOT compatible with RMS. CTI Should really make this more obvious, but should they not heed this, peeps!

Happy flyin!