Thrust Plates: When and Why?

[Banzai88]

This spring I'll be launching 75mm motors in a legacy MadCow DX3 XL (4" fiberglass with a 75mm motor mount), and will probably be venturing into one of Wildman's 5" or 6" offerings by this fall and I got to thinking about thrust plates.

I've never used one before, never felt that the materials used and assembly techniques in 54mm motor powered rockets (cardboard or fiberglass) weren't going to be up to the task of even the hardest hitting of motors, but I have no experience with 75s+.

When do you consider that a thrust plate is unnecessary, a good idea, or mandatory?

I see that MAC makes some, and Apogee sells SC Precision. I'm guessing from the dearth of offerings that they're not that big of a 'thing'?

Please educate me with your thoughts.

 

[BDB]

I’ve been thinking about the exact same question this week. I just purchased a 4” X-Celerator from Mad Cow, and I’m thinking about upgrading it to 75 mm and reinforcing the fins with tip-to-tip CF.

The kits I’ve built from Binder Design came with a plywood thrust plate, and I saw that Mach 1 sells a 4”-54mm FG thrust plate. I also kicked around the idea of 3D printing one from a durable material like Nylon.

At present, I‘m leaning towards the aluminum plates from SC Precision, but I’d like to hear what others have to say.

 

[Banzai88]

I’ve been thinking about the exact same question this week. I just purchased a 4” X-Celerator from Mad Cow, and I’m thinking about upgrading it to 75 mm and reinforcing the fins with tip-to-tip CF.

The kits I’ve built from Binder Design came with a plywood thrust plate, and I saw that Mach 1 sells a 4”-54mm FG thrust plate. I also kicked around the idea of 3D printing one from a durable material like Nylon.

At present, I‘m leaning towards the aluminum plates from SC Precision, but I’d like to hear what others have to say.

I've built several MAC kits (3" and 4") where the aft plywood centering ring is a thrust plate. It works well, no issues, but one has to account for the further aft position of the motor with the retainer overhang when planning and building a sim file.

 

[Titan II]

This is my Wildman 5" Shapeshifter. It is like adding an appearance option to a new car. Necessary? Absolutely not. Nice to have? Yes. One nice feature is that it has 12 drilled and tapped holes that match the Aero Pack 75mm flanged retainer.

 

[rfjustin]

This is my Wildman 5" Shapeshifter. It is like adding an appearance option to a new car. Necessary? Absolutely not. Nice to have? Yes. One nice feature is that it has 12 drilled and tapped holes that match the Aero Pack 75mm flanged retainer.
View attachment 558052

That about nails it. Not necessary, but trick.

 

[cwbullet]

This is my Wildman 5" Shapeshifter. It is like adding an appearance option to a new car. Necessary? Absolutely not. Nice to have? Yes. One nice feature is that it has 12 drilled and tapped holes that match the Aero Pack 75mm flanged retainer.
View attachment 558052

Concur. The benefit on bigger rockets is looks and you can use the same motor retainer on multiple rockets. I would rather just buy another retainer.

 

[jsdemar]

If the motor mount has no thrust surface, just a tube or spars to center the motor, a thrust plate is necessary. Otherwise, the motor would go through the rocket. Even if there’s an epoxied aft centering ring, it may not be strong enough to withstand the motor’s thrust. A metal plate distributes the force into the airframe and the fin tabs. This is the real purpose and definition of a thrust plate.

Otherwise, it’s just decorative or at least protects the more flammable materials at the aft end.

 

[jmasterj]

If the motor mount has no thrust surface, just a tube or spars to center the motor, a thrust plate is necessary. Otherwise, the motor would go through the rocket. Even if there’s an epoxied aft centering ring, it may not be strong enough to withstand the motor’s thrust. A metal plate distributes the force into the airframe and the fin tabs. This is the real purpose and definition of a thrust plate.

Otherwise, it’s just decorative or at least protects the more flammable materials at the aft end.

I think this is the answer. I've used them (made from the same material as the centering rings) on multiple tube fin rockets because there are no TTW structures to anchor the motor mount to the airframe besides the centering rings.

 

[mrwalsh85]

A thrust plate, stepped to accommodate the body tube ID/OD would be a good idea for rockets with 3D printed centering rings. I've seen it in action. Rocket has flown 3x with no damage to 3D printed CRs.

 

[BDB]

A thrust plate, stepped to accommodate the body tube ID/OD would be a good idea for rockets with 3D printed centering rings. I've seen it in action. Rocket has flown 3x with no damage to 3D printed CRs.

What size of rocket and motor?

I was thinking of printing a thrust plate, but it might only be cosmetic unless I could use it to transfer the thrust to the outer airframe and m fin tabs.

 

[cwbullet]

A thrust plate, stepped to accommodate the body tube ID/OD would be a good idea for rockets with 3D printed centering rings. I've seen it in action. Rocket has flown 3x with no damage to 3D printed CRs.

3D printed centering rings will take what ever force you need in rocketry when teamed with through the wall fins. There is no reason for a thrust plate if this is your only reason.

 

[cwbullet]

I think this is the answer. I've used them (made from the same material as the centering rings) on multiple tube fin rockets because there are no TTW structures to anchor the motor mount to the airframe besides the centering rings.

I missed this but I concur.

 

[mrwalsh85]

The rocket was a 5" rocket flying on a L1150R. Utilized an aluminum thrust plate in conjunction with a flanged AeroPack retainer.

 

[BDB]

Pretty cool to see 3D printed parts on that intense of a project.

 

[thzero]

The rocket was a 5" rocket flying on a L1150R. Utilized an aluminum thrust plate in conjunction with a flanged AeroPack retainer.

What was the point? Was there something that printing 3d centering did that normal materials wouldn't?

 

[BDB]

3D printing is arguably easier than cutting centering rings. Though it would take much longer to make a single ring. That said, nothing beats a CNC.

 

[cbrarick]

they just add weight and slow you down!

 

[K'Tesh]

If the fins are designed in a manner that allows the bottom of the tube to hit first, thrust plates prevent damage (cosmetic or otherwise) to the tube. They also reduce the forces on joints for centering rings, thus reducing the chance of the motor from blowing through the rocket (presuming the rocket is not built TTW (as would be the case for minimum diameter designs)). Now, in the unlikely event of a water landing your thrust plate can act as a flotation device, increasing your chances of recovering the rocket, presuming they are sealed.

Cosmetically, they also hide the inside of the body tube, making it less important for painting that area.

 

[OverTheTop]

In HPR, never. All my HPR rockets get an Aeropack-style minimum diameter retainer in the motor mount. I always position it so the thrust ring at the tail of the motor is just clear of the rear plate when the motor is screwed in onto the retainer at the front. All thrust is taken on the front mount. It keeps the airframe rear of the mount in tension, which is where composites perform best.

I am lucky to have a lathe and mill of my own so I can do this sort of thing.

Here is an example, 4", from my half-scale (8.25" dia) Nike Smoke.


Here is an example of a rear plate on my half-scale Nike Smoke (8.25" diameter). This was fabricated out of multiple plates of aluminium that were offcuts from another job and free for me. It is purely decorative and takes no thrust, Interestingly, people still called it a thrust plate, which it isn't.

https://forum.ausrocketry.com/viewtopic.php?f=6&t=4612&start=28

 

[teepot]

When I started building rockets with 54mm mmt I put a few thrust plates on I made of 1/4" ply. Now I don't. When I start flying K's and L's I might go back to putting a thrust plated on. But that is down the road.

 

[Banzai88]

When I start flying K's and L's.........

That's where I'm at right now with this rocket.

 

[FlyBy01]

If the fins are designed in a manner that allows the bottom of the tube to hit first, thrust plates prevent damage (cosmetic or otherwise) to the tube. They also reduce the forces on joints for centering rings, thus reducing the chance of the motor from blowing through the rocket (presuming the rocket is not built TTW (as would be the case for minimum diameter designs)). In the unlikely event of a water landing they can help act as a flotation device, increasing your chances of recovering the rocket, presuming they are sealed.

Cosmetically, they also hide the inside of the body tube, making it less important for painting that area.

The water landing part is too funny, thought I was on a commercial flight for a moment.

 

[K'Tesh]

The water landing part is too funny, thought I was on a commercial flight for a moment.

Close, but no cigar.... It's a commercial, based on a train... (0:53)



[EDIT] Confession... I did after your comment, watched the commercial I mentioned, and altered the text to more closely align with the ad.

 

[JohnCoker]

Plywood is an amazing composite material. However, I generally like to finish off the aft end of the rocket so it is tempting to use something. Recently I printed a curved transition that fits around a Slimline 75mm retainer. (The nose is stubby so this matches.)

 

[jmasterj]

Plywood is an amazing composite material. However, I generally like to finish off the aft end of the rocket so it is tempting to use something. Recently I printed a curved transition that fits around a Slimline 75mm retainer. (The nose is stubby so this matches.)

View attachment 558292

A print-your-own tailcone retainer! I'm sure it's simple, but I'd be interested in seeing the design file.

 

[rharshberger]

A print-your-own tailcone retainer! I'm sure it's simple, but I'd be interested in seeing the design file.

That would be easy to design, as its a "sleeve" for a COTS retainer. Nice work John!

 

[thzero]

A print-your-own tailcone retainer! I'm sure it's simple, but I'd be interested in seeing the design file.

I've done that for some 2.63" rockets as a tail cone. Not sure I'd use it on bigger rockets.

https://www.rocketryforum.com/threa...ling-tube-printed-rocket.164180/#post-2093936

 

[cautery]

In HPR, never. All my HPR rockets get an Aeropack-style minimum diameter retainer in the motor mount. I always position it so the thrust ring at the tail of the motor is just clear of it when the motor is screwed in onto the retainer at the front. All thrust is taken there. It keeps the airframe rear of the mount in tension, which is where composites perform best.

I am lucky to have a lathe and mill of my own so I can do this sort of thing.

Here is an example, 4", from my half-scale (8.25" dia) Nike Smoke.
View attachment 558236

Here is an example of a rear plate on my half-scale Nike Smoke (8.25" diameter). This was fabricated out of multiple plates of aluminium that were offcuts from another job and free for me. It is purely decorative and takes no thrust, Interestingly, people still called it a thrust plate, which it isn't.
View attachment 558235
https://forum.ausrocketry.com/viewtopic.php?f=6&t=4612&start=28

Beautiful work! Right up my alley. Wish I had a shop to put mills and lathes in.... I will have to be satisfied with what I have.
I miss having an entire Aviation Maintenance operation (almost depot level) at my disposal...

 

[BDB]

FYI...for anyone considering a 75 mm MMT right now, like @Banzai88 and me, flanged 75 mm Aeropacks are nearly impossible to find. Madcow, Chris' Rocket Supplies, and Wildman are all out. And Giant Leap and LOC don't carry Aeropack. The only places I could find them were at AMW and Mac Performace.

 

[Banzai88]

FYI...for anyone considering a 75 mm MMT right now, like @Banzai88 and me, flanged 75 mm Aeropacks are nearly impossible to find. Madcow, Chris' Rocket Supplies, and Wildman are all out. And Giant Leap and LOC don't carry Aeropack. The only places I could find them were at AMW and Mac Performace.

Pssst: Check here!

https://www.apogeerockets.com/Build...w-On_Retainers/75mm_AeroPack_Retainer_Flanged
https://www.apogeerockets.com/Build...ners_75mm/75mm_AeroPack_Retainer_Body_flanged