98mm Model Rocket Suggestions.

Hello, i am looking at building a 98mm (4.0") model rocket. I plan to launch it on F & G motors (29mm). Does anyone have any suggestions or things to consider? I am just now moving into Medium range power model rockets and want to get NAR certified in the fall.
Thanks for any help you can provide!

Justin

Aerotech G-Force is a good Rocket to start with.

you don't want to overbuild and have a heavy bird, 31 oz. makes for low flights. 3"(76mm) is easier to keep the weight down. one could look at what Estes has for parts and see if they have anything you like. https://www.estesrockets.com/rockets/pro-series/parts?p=1 note they don't seem to carry tube couplers for 4" (or unslotted 4" tube).
Rex

A LOC IV is the first one that comes to mind. If you really want to use it as a L1 cert bird, I'd stay away from aerotech as their rockets really aren't nearly as strong.

Be careful and choose the high thrust F's though

Ive already purchased 2 of apogee's 4" x 34" LOC body tubes, a connector and a 4"x 19.5" nose cone from a different website. I also bought a 29mm motor mount for the 4" tube.
Does anyone know any videos an how to paper the balsa fins?

Also, does anyone know any articles/videos about thru the wall fins? or if I should even fool with doing this to my Mid Power Rocket?

jcaswell94 said:

Ive already purchased 2 of apogee's 4" x 34" LOC body tubes, a connector and a 4"x 19.5" nose cone from a different website. I also bought a 29mm motor mount for the 4" tube.
Does anyone know any videos an how to paper the balsa fins?

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I would say best to forget about balsa fins, go with plywood at least!

that is going to be a heavy rocket.
Rex

jcaswell94 said:

Ive already purchased 2 of apogee's 4" x 34" LOC body tubes, a connector and a 4"x 19.5" nose cone from a different website. I also bought a 29mm motor mount for the 4" tube.
Does anyone know any videos an how to paper the balsa fins?

Click to expand...

Sounds like you are building an impressive rocket. 4 inch diameter, and 80 or so inches long?

That might be too large to fly on F or G motors. By the time you add fins, recovery, and motor, you might be over the 3.3 lbs class 1 limit.

The Aerotech G force is under $65 at Hobbylinc, and comes with everything you need except the motor and launch equipment. The G Force or other similar rockets are about as big as you can go without certification.

I did a rough rocksim on it and it comes in at about 4.0 lb if you build light. Sims to about 700 ft on a G80.

should i look at saving this rocket for after i get lev 1 certified? I have a rocket i built recently (pics will be posted when i paint it) that is a BT-70 body tube just over 5' tall. it has a 24mm motor mount. maybe i could save the 4" one for a 38mm engine?
Justin

It is more of an L1 rocket then a midpower one. It would be an ideal one to get your L1 cert on after you get some midpower experience on your smaller design. As far as 29 mm versus 38 mm that is up to you. When I got my L1 I flew 29 mm for quite a while. You can get most of the aerotech 29 mm reloads without hazmat shipping and it can be simpler not to have use a motor mount adapter to adapt down from 38mm to 29mm. My rough rocksim file gives about 2500 ft on an 29 mm I200W, so it depends on how high you want to fly and how much you want spend on reloads (and if you have an on site vendor).

terryg said:

It is more of an L1 rocket then a midpower one. It would be an ideal one to get your L1 cert on after you get some midpower experience on your smaller design. As far as 29 mm versus 38 mm that is up to you. When I got my L1 I flew 29 mm for quite a while. You can get most of the aerotech 29 mm reloads without hazmat shipping and it can be simpler not to have use a motor mount adapter to adapt down from 38mm to 29mm. My rough rocksim file gives about 2500 ft on an 29 mm I200W, so it depends on how high you want to fly and how much you want spend on reloads (and if you have an on site vendor).

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If you are really looking for a 4" rocket to fly MPR with, I did that a lot of years with a Binder Design Thug. I'ts half nosecone and half BT. Gets close to 500 ft on an F52T and near 1000 ft with Hobbyline G motors.

As for 38mm MMT, if you are going to build the rocket for L1 flights, my advice is go with the 38mm. You can only get to baby I motors in 29mm, with the 38mm you can get into the baby J motors. It can handle the full range of L1.

The closest LOC kit is the HYperLOC 835 at 60 oz. = 3.75 pounds unloaded, minimum motor G. You could do middle split with optional half tubing length version for smaller motors.

Do any of you know anything about the threw the wall fins? or if i should use them on this rocket?

You should definitely use through-the-wall fins if possible! They lead to a minor increase in weight on most designs, but a huge difference in strength.

Check out the fin sets on my website. I could upscale a design to 4" for you if you like one. Or email me an OpenRocket file of what you want.

jcaswell94 said:

Do any of you know anything about the threw the wall fins? or if i should use them on this rocket?

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Through the wall fins makes the fin can, and thus the rocket, much stronger.

Apogee has a series of videos on building a high power rocket. I believe the rocket in this series is a 4" Madcow Torrent. The video showing the fin installation is here:

https://www.apogeerockets.com/Advanced_Construction_Videos/Rocketry_Video_63

The other videos in the series would probably help get you going in the right direction. Poke around in the video subject list and you'll find more info you might need.

I would used 1/4 inch plywood fins (cut from material from Michaels). Rocksim or Open Rocket can calculate the tap depth for you and print out fin templates. The tab goes thru the body tube and is glued to the motor mount tube. Front and rear edges of the fins are glued in between the centering rings. Attached picture is for a 29mm motor mount.

Does anyone know of any website that sells thrust plates for the bottom my 4" tube. I plan on using a 38mm motor but cant find anyone who has them.
Thank you
Justin

jcaswell94 said:

Does anyone know of any website that sells thrust plates for the bottom my 4" tube. I plan on using a 38mm motor but cant find anyone who has them.
Thank you
Justin

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https://scpconcepts.com/rocket-accesories.html?m

the smallest plate they have is 54mm. i need one for a 38mm.

I think we are dealing with a difference in terminology here. A thrust plate is typically a machined plate used for high performance motor mounts (often clusters). There is no need for that in the mid to L1 power you are planning here. A centering ring mounted flush with the end of the body tube is all that is needed. The structure created by the centering rings and the thru the wall fins is not going anywhere. You do need to provide motor retention, which can be done with motor clips or with aeropack or equivalent retainers. I like the aeropack since it has a really nice system to adapt down to smaller diameter motors. If you are referring to thrust rings that are glued into the motor mount tube in low power rockets, they are not used in high power since the motors are of different lengths. Reload cases have a flange on the front that prevents the motor from flying up thru the rocket.

https://www.wildmanrocketry.com/ProductDetail.aspx?product=1649

Awesome! i wasnt sure if i needed the plate for a L1 rocket or not. How long of a motor tube would you all suggest? I am going to use a 38mm motor.

For long rockets I usually use 17" (half of a LOC 34 inch motor mount tube length). There is no hard and fast rule about this. The motor can project beyond the end of the tube. It also depends on how much volume you want to pressurize for parachute ejection.

Also check out the videos at https://jcrocket.com/

A little update on the L1 build.
I am in the process of waiting on the motor mount to dry . I have Began on the fins and cutting the fin slots. Im using 3/16 Birch wood for the fins and centering ring. I think i might only use 1 of the 4" x 34" body tubes for now. I've been tossing the idea around about saving the 2nd tude for later and maybe using it to add dual deployment to the rocket after I get L1 certified. What are you guys thik about this? Good idea or Bad?

jcaswell94 said:

Also, does anyone know any articles/videos about thru the wall fins? or if I should even fool with doing this to my Mid Power Rocket?

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My certify level 1 video has info about TTW fins (and shows building a LOC IV kit).

You can do both if you want to. You can build it to be dual deploy capable if you use an ebay kit instead of a coupler:

https://shop.locprecision.com/product.sc?productId=55&categoryId=39

You do not glue in the ebay, but use screws to attach it to the the upper body tube and when you fly with motor eject it seperates in the middle and the parachute deploys from the lower section. You can also fly it with just the lower section and a nose cone. However because it is shorter it will balance out differently and you might need to add nose weight depending on the size of the fins.

Estes Pro Series Der Mega Red Max.

4" diameter.

Flies quite nice on G motors.

Not super light and not stupidly heavy.