Which flys higher, a 1/4A or an MMX in Min-Diameter

[Art Upton]

I think the 1/4A in BT5 flys just slightly higher then a 6.5mm MMX rocket [not using plastic]

I think the idea when they came out If I recall correctly was the plastic parts of the Quest rockets tended to keep it under 50 feet in your backyard. [I still have a Little Joe II Set, I had 4 of them but sold the rest] I also remember MiniBrutes made of plastic in the early 70's I could keep in my front yard; like the X15

I still have MMX motors and ignitors, but I would think BT5 is easier to work with; your experienced comments welcome.

 

[kuririn]

MicroMaxx motors are 1/8A.

 

[Art Upton]

MicroMaxx motors are 1/8A.

Yes but that is not what I asked.

"Which flys higher, a 1/4A or an MMX [1/8a] in Min-Diameter

Edit: FYI the question is not trying to see how high you fly but how low you can fly between one over the other as an Almost in your back yard rocket

 

[GlenP]

really depends on weight. You could make either heavy enough to keep the apogee under control, up to a point, but if the speed at the end of the rod is not fast enough then the fins won’t be effective yet for a stable flight, but any rocket sim can help you figure that out.

 

[mh9162013]

1/4A 13mm engines in a BT-20 sized rocket would be pretty good for keeping a low altitude. The problem is the ejection delay. If your rocket isn't getting above 50 feet, 3 seconds probably means no time for a parachute or streamer to start working.

Of course, if you just want tumble or nose-blow recovery, this may not be an issue...

 

[lakeroadster]

I think the 1/4A in BT5 flys just slightly higher then a 6.5mm MMX rocket [not using plastic]

I think the idea when they came out If I recall correctly was the plastic parts of the Quest rockets tended to keep it under 50 feet in your backyard. [I still have a Little Joe II Set, I had 4 of them but sold the rest] I also remember MiniBrutes made of plastic in the early 70's I could keep in my front yard; like the X15

I still have MMX motors and ignitors, but I would think BT5 is easier to work with; your experienced comments welcome.

In Open Rocket I started with the example "A Simple Model Rocket".
I scaled it down to fit a 1/4A2 and ran the simulation, apogee = 277 ft.
I then scaled that down for a MMX, apogee 131 ft.

 

[GlenP]

In Open Rocket I started with the example "A Simple Model Rocket".
I scaled it down to fit a 1/4A2 and ran the simulation, apogee = 277 ft.
I then scaled that down for a MMX, apogee 131 ft.
View attachment 580644
View attachment 580642

Great sim results! If you add some nose weight, how much can you add so that speed off the rod stays above 30 mph, then what are the altitudes?

As an alternative to adding weight, you can add drag to slow it down, like a base spool or saucer type of fin, but that alters the rocket appearance and then it won’t look like a traditional 4FNC if that is what the OP is going for.

 

[cls]

Theoretically, MMX are about 1/8A total thrust.

The best thing about MMX is the super violent ejection charge, which can double the altitude of some parts of my rocket!

 

[lakeroadster]

Great sim results! If you add some nose weight, how much can you add so that speed off the rod stays above 30 mph, then what are the altitudes?

I checked.... and adding nose weight decreases the altitude.

 

[GlenP]

I checked.... and adding nose weight decreases the altitude.

Cool. I cant run OpenRocket due to java errors on my Mac. Does it get the altitude down to 50'? could you post a similar screen shot for those of us who are OR challenged?



Good points about recovery deployment when that low, almost need a 0-sec delay, and then the nose cone may get another 25' or 50' due to the ejection charge if the shock cord breaks!

There are always odd-rocket options like saucer, spinning (GyROC), monocopter, and Sputnik rockets that don't require traditional recovery deployment and use drag/tumble recovery that are good for 0-delay low altitude flights.

Has anyone made an MMX GyROC style rocket?

 

[neil_w]

Cool. I cant run OpenRocket due to java errors on my Mac.

There is no reason this should be the case with the packaged installer. Please PM me to sort this out.

 

[Art Upton]

I checked.... and adding nose weight decreases the altitude.

Thanks, I Added 5grams to the nose, using 1/4A-3 with a BT-20 tube and does 125 feet perfect delay time.

 

[GlenP]

https://www.rocketryforum.com/threads/estes-astron-gyroc-k-24-or-1224-gallery.19885/

 

[lakeroadster]

Cool. I cant run OpenRocket due to java errors on my Mac. Does it get the altitude down to 50'? could you post a similar screen shot for those of us who are OR challenged?

Add 0.75 ounces to the 1/4A2-2 and it apogee's at 50 feet, and the delay of 2 seconds is ok.

​

Add 0.16 ounces to the MMX and it apogee's at 51.7 feet, but it's still ejecting the chute way too early.

​

I suggest you take Neils advice and work with him to get Open Rocket working on your Mac. It's fun for stuff like this... and for anything else you can dream up.

 

[GlenP]

Add 0.75 ounces to the 1/4A2-2 and it apogee's at 50 feet, and the delay of 2 seconds is ok.

View attachment 580732​

Add 0.16 ounces to the MMX and it apogee's at 51.7 feet, but it's still ejecting the chute way too early.

View attachment 580733
​

I suggest you take Neils advice and work with him to get Open Rocket working on your Mac. It's fun for stuff like this... and for anything else you can dream up.

A very handy tool, this is a great example of what you can do with it. Basic stability is easy enough to do with a cardboard cutout and a swing test, but speed off the rod, you can estimate only very crudely without it, but this kind of trade study to tweak the model for a particular apogee is pretty handy. Thanks for working that up and sharing your sims here!

I did recently update my macOS version, so maybe I should download and try OR again one of these days. I tend to just use mid-sim and make slight variations to proven designs, nothing really out of the box for my cardstock downscales. But I stick to 13mm for those, I have not really gotten into MMX size yet to have enough of a mind-sim developed for those.

 

[Art Upton]

Add 0.75 ounces to the 1/4A2-2 and it apogee's at 50 feet, and the delay of 2 seconds is ok.

View attachment 580732​

Add 0.16 ounces to the MMX and it apogee's at 51.7 feet, but it's still ejecting the chute way too early.

View attachment 580733
​

I suggest you take Neils advice and work with him to get Open Rocket working on your Mac. It's fun for stuff like this... and for anything else you can dream up.

I'm not seeing a 1/4A-2 , only the -3 being sold. I also have 1/2A-4T in-stock, those bulk packs. If I add the .75oz in the nose of the BT20 Version it also flys 133 feet but on a motor I already have and the delay is fine for it.

 

[BABAR]

In Open Rocket I started with the example "A Simple Model Rocket".
I scaled it down to fit a 1/4A2 and ran the simulation, apogee = 277 ft.
I then scaled that down for a MMX, apogee 131 ft.
View attachment 580644
View attachment 580642

never mind, should have read ALL the threads.

 

[SolarYellow]

If I was working on this problem, I'd look at the 1/2A3-2T motors for the short delay and build the rocket for the motor. It would be very lightly constructed to get off the rod at a decent speed, and kinda big and draggy (maybe even BT-50, but probably cardstock) to keep the apogee low. That would also limit its descent before ejection.

https://www.apogeerockets.com/Building_Supplies/Nose_Cones/Low_Mid_Power_Nose_Cones/VFNC_24B_2_pk

 

[Art Upton]

If I was working on this problem, I'd look at the 1/2A3-2T motors for the short delay and build the rocket for the motor. It would be very lightly constructed to get off the rod at a decent speed, and kinda big and draggy (maybe even BT-50, but probably cardstock) to keep the apogee low. That would also limit its descent before ejection.

I did that with a Mini Fatboy sim today. 83 feet ; I have this rocket in stock a few but need to order the motors. I will check with the local hobby store , Hobby Town and see if they have it. Hobby Lobby only sells the 1/2A-4