Which of these motors for Saturn V?

[TahoeGator]

There are lots of threads on motor conversions for the Estes Saturn V. I am posting this to ask for advice because I have a limited set of specific engine options.

Long story short, I am on vacation at my parents with plans to build and launch the Saturn V while here. I want to use larger than the suggested D motor, so I ordered some larger motors with plans to sort it out when I got here. Here are the engines choices I have in my possession:

Aerotech 29mm
F42-4T
F20-7W

Aerotech 24mm
F44-4W
E14-7W
E30-7T

Estes 29mm
F15-8
E16-6

Estes 24 mm
E12-6
E9-6
E9-4

For starters, I need to decide on 29mm vs 24mm mount in order to build it. I could use an adapter, of course, but don’t want to modify the rocket unless 29mm is the better option.

I have never used any of and so do not know the Aerotech motors, and have only modest experience with larger Estes motors, hence needing advice.

Which of the above motors would be best for the Saturn V?

Note: I do realize I will need to add nose weight to get the CG correct. Any suggestions on how much or any other mods to make it fly with the motor you suggest are most welcome.

PS my initial thinking is to leave the recessed engine design as-is regardless which means do not fly with the engine cones on, but if that factors in to your motor suggestion, please express such.

Thank you for any advice and Happy 4th of July!

 

[Rex R]

the big question I have is, which version kit you have? is it catalog #2157? if so the correct response is none of the above, reason the delays are too long. I would stay with the 24mm motor mount and use an E30-4 as suggested in the catalog I have. failing that an E12-4 is the next option listed.
Rex

 

[TahoeGator]

Rex, thank you for your response. Yes, it is the #2157.

I see no mention of an E12-4 in the instructions. Only D12-3.

I get the delay issue — I guess I was hoping those bigger motors could warrant a 6s delay — but what about the F42-4T (29mm) or F44-4W (24mm)? Also, I don’t have an E12-4, only E9-4.

 

[lakeroadster]

I'd suggest running a simulation with Open Rocket to help in determining nose weight and if the delay is in fact an issue.

 

[TahoeGator]

I'd suggest running a simulation with Open Rocket to help in determining nose weight and if the delay is in fact an issue.

Good suggestion. Trying to find a pre-existing file. The only one I can find is a .rkt and the engine tube is off the back.

 

[lakeroadster]

Good suggestion. Trying to find a pre-existing file. The only one I can find is a .rkt and the engine tube is off the back.

If you have the kit it's pretty easy to measure the pieces and input the data. That's the most accurate method.

 

[mikec]

Depends on how high you want to go. Of the motors on your list, the best I'd say would be the F44-4 -- most of the others on your list have delays that are too long. I think the E15-4/E20-4 is about perfect from the one flight I've made so far on mine.

 

[smugglervt]

Good suggestion. Trying to find a pre-existing file. The only one I can find is a .rkt and the engine tube is off the back.

View attachment 356938

Here's my Estes Saturn V ork. file. I haven't done the final overrides for the mass and CG.

 

[Rex R]

your kit likely pre-dates the 2016 catalog(or at least the instructions). the 29mm motors will require nose weight, which increases overall weight, which in turn means you'll need bigger chutes etc. whereas the 24mm motors need only minimal changes(if any). my guess is that you would need a 5 second delay for those Fs*. my rule of thumb; add or subtract one second for each impulse class up or down from your known good engine/delay combo.
*but the extra altitude should help
Rex

 

[afadeev]

Long story short, I am on vacation at my parents with plans to build and launch the Saturn V while here. [...]
For starters, I need to decide on 29mm vs 24mm mount in order to build it. I could use an adapter, of course, but don’t want to modify the rocket unless 29mm is the better option.

Funny you should bring this up, because #2157 SatV is "next inline" in my build queue.
For me, the motor choice is simple.

The thrustiest 24mm motor on your list is F44, which has 42 Ns of total impulse. Using my .ork file (similar to Jim's), I get 589 feet of maximum altitude and 85 ft/s velocity off rod. That will work, but that's as good as it gets.
Estes E9's and E12's are unsafe (too slow off rod, too low). I don't have E14 motor profile, but E30 might work (464 feet, 49 ft/s off rail).

29mm tube size offers far more motor options, including reusable motors that cost way less than single-use F44.
You can always adopt down to 24mm.
I will build using 29mm motor tube.

Which of the above motors would be best for the Saturn V?

Note: I do realize I will need to add nose weight to get the CG correct. Any suggestions on how much or any other mods to make it fly with the motor you suggest are most welcome.

You will need to add upwards of 100+g of ballast to the nose cone for 29mm F and G motors. 150+g for H and above.

Experiment with the .ork file, and you will see!

HTH,
a

P.S.: Even with 24mm motors, my sim required 50+g of nose ballast to attain 1+ calibers of stability
P.P.S.: Don't forget - just "no" motor hooks, "yes" to motor retainers.

 

[mikec]

For me, the motor choice is simple...
I will build using 29mm motor tube.

If you want to go higher than about 800 feet with this rocket, yes.

I built mine stock with a 24mm MMT because that altitude limit was OK with me, and the E15/E20/F44/F35 motor choices were all acceptable.

If you build for 29mm, at some point you may want to strengthen the MMT and centering rings. I'd recommend moving the upper centering ring down so you have more space for chutes, since an AT motor will happily pressurize the increased volume.

 

[TahoeGator]

P.P.S.: Don't forget - just "no" motor hooks, "yes" to motor retainers.

Not sure I understand. Bad idea to use the metal engine hook per instructions? If so, why so?

 

[afadeev]

Not sure I understand. Bad idea to use the metal engine hook per instructions? If so, why so?

Multiple reasons:
1). Estes hooks work OK for smaller Estes engines, but fail to properly retain single-use or reusable Aerotech motors. AT motors have an aft retaining ring that has a wider diameter then Estes black-powder motors, and Estes hooks don't always grab them securely enough to retain them during ejection charge firing. BTDT, lost one motor case this way - never again!
2). Estes "thrust ring" and forward bend of the hook can interfere with Aerotech motors ejection charge caps, and thus they may not fit into the metal hook+"thrust ring" contraption at all.
3). The combination of Estes hooks and thrust rings assumes that you will always fly a fixed length motor. That doesn't work well even for Estes's own lineup of 24mm motors, with some being 2.75 inch long, others 3.75" long. You can try stuffing "filler" tubes to make things work for Estes motors, but see #1 and #2 for issues with Aerotech, CTI, and all other motors.
4). To work with a wide variety and length of motors, it's far more flexible and more secure to retain the motors their aft thrust rings. Even Estes, themselves, sell proper (plastic) motor retainers:
https://www.estesrockets.com/009750-estesr-24-mm-motor-retainer-set

Another source of motor retainers is one of these:
https://www.rocketarium.com/Build/Motor-Retainers

Lastly, you can just leave a motor to stick out from the aft end of the motor tube, and use masking tape to secure it in place.
Alas, in case of Saturn V with motor tube recessed into the airframe, this will be really inconvenient.

Hope this helps,
a

 

[TahoeGator]

Maiden flight today on the F44-4 worked perfectly well. OpenRocket predicted ~600 feet and that seemed about right. I did add a nose weight: my son built me a lunar lander out of his heat-activated clay that went just below the capsule per the pic below. Unknown weight of the lander, but the COG ended up being ~22” from top. All chutes opened with plenty of altitude to spare. My only complaint is that the F44 really boogied off the pad. Way faster than needed. Next time I think I will try a slower/longer burning engine.

Launch & recovery video:


Slo-mo launch video:
https://instagram.com/p/Bk-_07Hj6ad/

 

[RocketRoll]

I'm planning on using an E15W-4. Nice plume of white smoke at liftoff. I'm using a 6' launch rail to get more stability... other members of my club warned me not to use launch lugs for this one.