4" Fiberglass 75mm motor mount recommendations needed

[Banzai88]

I’m at a crossroads for where to go next with my build projects.

I desperately want a 4” fiberglass rocket (WM something), but I’m on the fence with getting it in a 54mm or a 75mm motor mount. I already have several 3” fiberglass rockets with 54mm mounts that I get full J and K fun with, and I’ve run the $$ numbers on 54mm vs. 75mm equivalent-ish reloads, and I’m still in a quandary.

When I want to touch the sky, I launch down at Bayboro with 5 square miles of treeless recovery area and 17.5K waiver, so altitude limitations aren’t really going to be a ‘thing’ for this rocket.

I guess my question for the masters is “At what point did you make the jump from 54 to 75mm motors, and why” and “What would/did you choose to make this step”? Or am I looking at this all wrong and ya’ll went to L3 98mm motors, then stepped back to 75s?

 

[Jay Dub 4009]

75mm is a great choice for having some capability when you want it and push higher and faster, and able to use 54mm if you need to. Recommend getting the 75!

I once got a 3" IRIS with a 38mm mount, and now wish I would have gotten a 54! Same thing here.

 

[Theory]

You make the jump when you want to fly L motors and above. To that end, 75mm all the way!!!

Can easily adapt down to a 54mm when you want to fly those.

I did it when I wanted to have the option to fly L motors and also the K1000. IDK, just something about that motor...

 

[heada]

Always go with the bigger motor mount. You can adapt down but you can't easily adapt up.

 

[rocketgeek101]

Agree with others. Go 75mm and adapt down if needed. If one is unsure, I always recommend going with the biggest motor mount that is practical to put in the rocket. I have some rockets that have only ever flown on motors smaller than their motor mount diameter (with an adaptor obviously) but it is nice to have the option of going bigger. A standard 4" FG rocket will be somewhat stymied to a low-n-slow flyer with a 54mm mount so 75mm is a no-brainer here IMO.

 

[mtnmanak]

I love all of Wildman's Extreme series and own a few of them. Great 4" rockets with 75mm mounts.

But, my favorite 4" rocket with 75mm mount is the Monster Mamba from Mach 1:

https://www.mach1rocketry.com/product-page/monster-mamba-98
The problem with Wildman's Extreme series is that they are too extreme - they are pretty light, so it is difficult to put any kind of 75mm motor in them on a small field (Love them at a big field, though - you can really get some altitude with WM Extremes!). The Monster Mamba adds a solid 2 feet in length (it has a full sized payload bay) which lets you fly some decent 75mm motors without breaking the ceiling at the small field. When you want to crank it up on a big field, throw an L or M in 'er and let it rip!

 

[JackC]

Go with 75mm and adapt down if you need to do it. So, if you want to kind of fly low, use a 54 mm L motor. If you want to fly much higher, use a 75mm L motor. For economy’s sakes, having the 54 mm option is nice but when you have the itch to go high, having a 75mm motor is great and relatively inexpensive compared to 98 mm motors.

 

[FMarvinS]

Hi- I agree with the previous responders. In particular, WM 4 inch to 6 inch rockets are exceptional. I fly in S.C.(IBM club) and when I can, less frequently in Bayboro too. the use of rockets like a 4 inch Dark Star or Drago 4XL look just as great on 75 or 54 mm motors. I vote with the 4 inch versions given the inherent greater versatility. By the way (independent of GPS tracker use), it is often easier to spot a 4 inch 6 to 8 foot tall rocket descending under its main chute than most 3 inch rockets and at Bayboro, that potential added visibility can make a difference.

Fred,L2
ICBM/Bayboro
KG4YGP

 

[jimzcatz]

My recommendation is DON'T DOIT!!!!

But I'm an altitude weenie. If I can't see it its a waste of a perfectly good motor!!

Good luck irregardless!!

 

[rfjustin]

https://wildmanrocketry.com/collections/wildman-4-inch-kits/products/motor-eater

 

[James Kobel]

https://wildmanrocketry.com/collections/wildman-4-inch-kits/products/motor-eater

I second this

 

[kramer714]

Yes..... but.......

I'm a round up kinda guy, with 75mm giving you more options than a 54mm for motors. I typically go bigger not smaller. Here is the but part..... (and this isn't necessarily addressed to the OP).

Somethings to think about,
1) Weight and CG - 54mm mount is lighter than a 75mm (all at the rear of the rocket)
1a) Weight and CG - a short 75mm motor shifts the CG aft vs a longer 54 mm motor of the same impulse in a 54 mm mount
2) 'hardware' - think about things like shock cord attachment. Using the centering ring and a u bolt gets pretty hard when your centering ring is less than 1/2 inch wide.
2b) your shock cord will be running up against your motor, not a lot of room between them for 'stuffing the laundry'
3) TTW fins will have small internal fillets

None of these are show stoppers just things to think about during your selection and build.

Mike Kramer

 

[Banzai88]

https://wildmanrocketry.com/collections/wildman-4-inch-kits/products/motor-eater

I second this

I've done HED with a Punisher 3, not a fan.

 

[rfjustin]

I've done HED with a Punisher 3, not a fan.

Add a foot of tube....

 

[Neutronium95]

I've done HED with a Punisher 3, not a fan.

What parachute did you use?

I used the Motor Eater for my first attempt at L3, and a 7 foot Rocketman chute was an incredibly tight fit. I ended up using an old 72" Top Flight parachute that packed much smaller and still gave a reasonable descent speed.

 

[Banzai88]

What parachute did you use?

I used the Motor Eater for my first attempt at L3, and a 7 foot Rocketman chute was an incredibly tight fit. I ended up using an old 72" Top Flight parachute that packed much smaller and still gave a reasonable descent
speed.

I used all the same TF chutes recommended by Crazy Jim in the build threads. Worked well enough, no complaints, just not something that I like overall.

 

[MidOH]

Don't you attach the shock cord to a threaded motor closure with an eyelet?

Attaching to the FCR would be semi-permanent, because I can't reach the FCR in a 40"+ booster. Like on a Loc Iris. It's nice being able to reach into a shorter 4" rocket, and connecting the cord with a quick link.

 

[James Kobel]

I've done HED with a Punisher 3, not a fan.

I personally love head end deployment. Takes away some unnecessary space for my rockets. Makes them lighter, and they go faster!

 

[JackC]

Get a Wildman Competitor 4 with a 75mm motor mount and call it a day. It’s an extremely versatile rocket (I think there is a nice review of it on the old EMRR site-it used to be a Performance Rocketry kit before Wildman inherited it).

https://archive.rocketreviews.com/reviews/all/oop_perform_competitor_4.shtml
Then you need to choose if you want an Aeropack retainer and adapter (they won’t work for Loki motors and most snap ring motors) or buy or craft your own Giant Leap rocketry adapter with snap ring and use screen clips or fender washers as your retainer. This option will allow you to use all motors.

 

[NateB]

Then you need to choose if you want an Aeropack retainer and adapter (they won’t work for Loki motors and most snap ring motors) or buy or craft your own Giant Leap rocketry adapter with snap ring and use screen clips or fender washers as your retainer. This option will allow you to use all motor.

My Loki cases have all been purchased in the past 2 or 3 years, but they all fit with my Aeropack retainers and adapters without any issues.

 

[cwbullet]

My Loki cases have all been purchased in the past 2 or 3 years, but they all fit with my Aeropack retainers and adapters without any issues.

View attachment 543465
View attachment 543466

I think they have been compatible for the last 3-5 years.

 

[Rocketjunkie]

https://wildmanrocketry.com/collections/wildman-4-inch-kits/products/motor-eater

This is the original Motoreater (deluxe version), 1999. The standard size (5.5", 54 & 8 29 mounts) has 73 flights from 1990 and is still flying.

 

[heada]

I think they have been compatible for the last 3-5 years.

Longer than that. The only ones that didn't fit were the gen1 ones from 10-ish years ago and you could replace the exterior spiral ring for $1 to make it fit or spend 30 seconds grinding a few thousandths off the ring with a dremel.

 

[JackC]

I think they have been compatible for the last 3-5 years.

That’s good to know! I still have some old motor cases so those may not fit. Thanks!

 

[JackC]

Longer than that. The only ones that didn't fit were the gen1 ones from 10-ish years ago and you could replace the exterior spiral ring for $1 to make it fit or spend 30 seconds grinding a few thousandths off the ring with a dremel.

I’ll try that! Thanks!

 

[Ian A Dalton]

I love all of Wildman's Extreme series and own a few of them. Great 4" rockets with 75mm mounts.

But, my favorite 4" rocket with 75mm mount is the Monster Mamba from Mach 1:

https://www.mach1rocketry.com/product-page/monster-mamba-98
The problem with Wildman's Extreme series is that they are too extreme - they are pretty light, so it is difficult to put any kind of 75mm motor in them on a small field (Love them at a big field, though - you can really get some altitude with WM Extremes!). The Monster Mamba adds a solid 2 feet in length (it has a full sized payload bay) which lets you fly some decent 75mm motors without breaking the ceiling at the small field. When you want to crank it up on a big field, throw an L or M in 'er and let it rip!

Be carful with the Monster Momba and other long rockets from Mach 1. I’ve had the thin glass spiral fracture on me because the motor mount tube is a little too short for the kit. It really needs another 4-6 inches with another centering ring. This happened to my 3” Daedalus and BT60 Starlight. A couple of my friends report the same issue. The extreme length can cause some intense stress points on the airframe when it lands due to fulcrum effects. I have in flight video of it happening when the rocket came down under chute at 22fps. Not pretty, but I’m glad I got video to see what happened. This is a something to think about will all rockets that are really long, regardless the material.

Unfortunately, I left the company before I could make the required changes to the kits so they could withstand better landings. Other than that, it’s a beautiful rocket!

 

[kramer714]

I've done HED with a Punisher 3, not a fan.

Head end deploy works well, one trick is to use a compact av bay, dont have the av bay run the full length of the coupler to give some more room in the nose. The red piece in the picture is a short piece of coupler cut like a letter C so it can be fit inside the coupler, bonded in place. The OD of the bulkheads was the ID of the coupler so they fit inside. The av bay lives in the center of the coupler, with room above for chute in the nose and below, in my case it was to fit a longer motor into the rocket. Total height of the av bay 1.5 inches in a 6: long piece of coupler tube.

 

[Chris_H]

My recommendation is DON'T DOIT!!!!

But I'm an altitude weenie. If I can't see it its a waste of a perfectly good motor!!

Good luck irregardless!!

Jim Catz is a low flying weenie!!!! Sorry Jim, but if you had not crapped all over my initial L1 and L2 flight plans, recommending to stay nearest the Earth, with the smallest, simplest designs, maybe I would not rib you. Remember, you said that my redundant dual deploy L1 flight was ridiculous? I do not recall youur exact words, but they were more harsh than that!!!! Well, it was a perfect flight! This was all well previous to your public disclosure of apology for being a dick to so many folks. I was one of them. What you recommend worked for you. So glad that humanity is not afraid to push boundaries, even when not even really pushing boundaries. 'Drone' life is boring. You want to be in the middle of average? Build where you are comfortable. Some people like to live life in the 'drone' lane. Not me.
If you are building a 4" airframe, definitely design for 75mm, even if you never fly there. You might want to.

 

[sharkbait]

Get a Wildman Competitor 4 with a 75mm motor mount and call it a day. It’s an extremely versatile rocket (I think there is a nice review of it on the old EMRR site-it used to be a Performance Rocketry kit before Wildman inherited it).

https://archive.rocketreviews.com/reviews/all/oop_perform_competitor_4.shtml
Then you need to choose if you want an Aeropack retainer and adapter (they won’t work for Loki motors and most snap ring motors) or buy or craft your own Giant Leap rocketry adapter with snap ring and use screen clips or fender washers as your retainer. This option will allow you to use all motor.

Comp 4 is an excellent choice, burn both 54’s and 75’s in mine, for economic comparison, 2g 75’s are about the same price as 5g 54’s, and cheaper than 6g & 6xl 54’s, more Ns and less issues than with longer L/D 54’s