HPR Thrust Ring Standards?

What is the standard length of the thrust rings for standard sized motors.

I know that 29mm Aerotech Single Use Motor thrust rings are .25" long. I'm presuming their reloadable systems are the same for 29mm motors. But what about other popular motor diameters? I seem to remember that one manufacturer's thrust rings may be a little longer than most others, and thus a slimline motor retainer might not be able to be used with that company's motors.

Thanks!
Jim

I don't know if there is a standard, since IIRC most HPR rockets use the bottom of the airframe as the part that transmits motor thrust.

That said, the thrust ring needs to be strong enough to hold whatever thrust that's being applied. My guess is that 1/4" plywood is good enough for 99% of 29mm motors. Perhaps 54mm motors would be an 1".

That said, you need enough surface area on the ring for the adhesive (wood glue, epoxy, etc.) to have an adequate bond to resist the sheer stress at the joint.

:2:

Greg

I think he is talking about thrust RINGS, not plates.

If he means centering rings, all that is required is that they need to hold to hold the motor to the center and be of adequate strength. You could go as low as 1/8" thick plywood for CR's for 29mm motors.

Greg

AT and CTI publish the external dimensions of their motors on their web pages:.
https://www.aerotech-rocketry.com/resources.aspx?id=7
https://www.pro38.com/drawings.php

It's my understanding, that all commercial retainers are compatible with these dimensions.

Snap ring casings are a bit different. You need to check them on a case by case basis (not sure if pun intended).

Reinhard

The AT 38mm DMS motors barely work with the GLR snap-ring retainers, never had any issues with CTI hardware. Screw-type retainers are adjustable, and they're easier to use too.

Reinhard said:

Snap ring casings are a bit different. You need to check them on a case by case basis (not sure if pun intended).
Reinhard

Click to expand...

I'll ++1 this. Encountered it when I glued the snap ring retainer of my boys' Wildman 2.1" V2 using a CTI Pro29 casing. Then tried to put in an Estes branded Aerotech single use. Luckily, the difference is sandable.

GregGleason said:

If he means centering rings, all that is required is that they need to hold to hold the motor to the center and be of adequate strength. You could go as low as 1/8" thick plywood for CR's for 29mm motors.

Greg

Click to expand...

I meant thrust rings.



So from what I'm understanding is that there isn't a single convention that could be charted like:

Motor Diameter Thrust Ring Length
29mm ............... .25 inches
38mm ............... .XX inches
54mm ............... .YY inches

The chart would need to include manufacturer and motor size (e.g. Aerotech HP29/360)

Reinhard said:

AT and CTI publish the external dimensions of their motors on their web pages:.
https://www.aerotech-rocketry.com/resources.aspx?id=7
https://www.pro38.com/drawings.php

It's my understanding, that all commercial retainers are compatible with these dimensions.

Snap ring casings are a bit different. You need to check them on a case by case basis (not sure if pun intended).

Reinhard

Click to expand...

Thanks for the links Reinhard

That's the kind of info I was looking for.

There are no standard lengths, thicknesses or diameters for thrust rings. It is totally up to the manufacturer. There are no standards for motor retainers either, nor are there standards for airframes and/or motor mounts.

While there are no dimensional standards, new components that do not conform to existing design conventions do not do well. The hobby is small and competitive. Manufacturers tend to make their new components compatible with existing dimensional conventions so they can sell their products to this community. Most new motors and motor retention components are designed to be compatible and used with existing designs. When they are not, they do not stay on the market very long. The most recent example was the 20 mm Quest BP motors. They were excellent Chinese motors but they did not conform to existing US design conventions and required motor mount modification to be used in existing rockets. They were not commercially successful and are no longer available. The same would be true for any motor casing or motor retention hardware designs that do not conform to existing design conventions.

Bob

K'Tesh said:

I meant thrust rings.

So from what I'm understanding is that there isn't a single convention that could be charted like:

Motor Diameter Thrust Ring Length
29mm ............... .25 inches
38mm ............... .XX inches
54mm ............... .YY inches

The chart would need to include manufacturer and motor size (e.g. Aerotech HP29/360)

Click to expand...

Check the mfgr website. As a previous poster mentioned, AT and CTI post their drawings, with dimensions. Note however (as I've found out the hard way) that the AT 29/40-120 case thrust ring has different height than the other AT 29mm RMS cases.

-e

And the 24/40 has a different thrust ring length than the 24/60. Found that out the hard way!