School Me

[moocrew]

Alright this is my first attempt at a mid powered rocket.
I've done some reasearch come up with some good ideas but i don't know what to use and how to go about constructing this rocket.

before I start asking questions I'll give some background on what I'm doing.
This rocket is being made mainly for show but still being prepared to be launched..eventually. I would prefer to keep it as low flying as possible and have a nice finish paint job on it that is...well...nice looking. (duh :wink: )

so here are my questions...
1. What size engine should I use?
2. What would be the best material to use for the fins?
3. Should I reinforce the fins?...If so whats the best way?
4. How should I prep-sand-finish this rocket?

Also I read this post https://www.rocketryforum.com/showthread.php?s=&threadid=6855&highlight=fin+reinforcement

I really like the way he mounted his wings its ingenious.
Is this something I should consider trying?
What about glassing and reinforcing the wings?
This also gives some info about what engine size i should use, and how should i mount it with that type of construction?

This pic should also help with what type of feat im tryin to accomplish here...
Specs:
9ft tall
Bottom section is 2" wide
top is standard estses BT-55 tubing. Same for nose cone.
Fins range from 2 ft in length to 6" wide
to 3 in x 2 in.
The weight w/o chute engines or anything is 1.75 lbs.

I hope that I have been clear in my questions and explanations if not i apologize. If I haven't explained something or it is unclear please ask me and I will try to explain it better.

All help is much appreciated and thanks inadvance.

 

[BlueNinja]

Something like that would rock on a G motor. Just for safety with your design, I'd ise a high thrust motor like a G64(reload) or a G80. Also, if you have a LEUP, I would recommend the G75. This need a different case than the G64, the 29/180. The g64 needs a 29/40-120.

 

[moocrew]

i need to get better with this pic posting thing.....heres the blue print....

 

[ghp3]

My first midpower was somewhat similar, 6ft tall with a 2.25" main airframe transitioning to a BT60 then a BT55. You're proposing more fin area than mine has (mine has 3 swept delta fins with an 8" root, extending about 4" from the airframe), but I used a simple 1/8" basswood fin mounted through the wall and it has worked out fine. No glassing or other reinforcement other than epoxy fillets. After doing some research in this forum and other sources, I was comfortable using basswood on MPR level rockets as long as it is mounted TTW with some decent fillets. Much lighter than plywood. Mine weighs in at about 1.25 lb w/o engine and flies very nicely to 1500' on G35 econojets.

Be sure to check the CP of your design as you seem to have a fair amount of fin area above the CG. Given the length of the rocket it'll probably be fine, but it doesn't hurt to check.

Have fun!

George
Pittsburgh, PA
NAR 83277

 

[BlueNinja]

That's an awesome rocket. What I woulkd be concerned about, is the fins on the upper portion of the model. On this tall roc, it may not matter, but thoise fins will make it less stable. I think that as long as teh fins are behind the CG and CP, the rocket is good and stable. Ahead of them, i think it ruins the stability though. As i said, it may not matter on this model but it is something to look out for.


Blue

 

[teflonrocketry1]

Put the upper fins on pivots about their leading edges (that's what pop rivets are for) and they won't affect the CP much. This type of design will be prone to weathercock. I would suggest only flying it on windless days, unless you make the forward fins non-steering as I suggested.

Bruce S. Levison, NAR #69055

 

[rocketkid88]

just one question... where do you get the weight calculation? i would *think* that a rocket this size would weigh more than 1.75lbs..., especially wiht all those fins and the resulting epoxy. My 'first' mpr rocket was 7.5 ft long, 3" OD (aprox) and SpaceCAD said that it would weigh just over 1lb... it weighs about 5, and isn't finished to this day. i don't think it could handle an HPR motor, so utill i get around to lopping a few feet off its jsut a show peice
good luck tho, its a kewl design!

 

[moocrew]

The wieght calc is space cad work ....of course i know it will be heavier..but its a rough estimate.

And about the stability its around 6 calipers. I know thats high...and not very good but if I ever did launch this rocket it would be in, near or perfect weather.

And as far as the upper fins being above the center of grav...the center point is somewhere around the 4 ft mark.....way behind the fins

 

[Hospital_Rocket]

This almost looks like a superroc project, I would be concerned about a ligtweight body made out of paper tube flexing as it left the pad. Somehow th Moment of Inertia on this thid kinda worries me. On a slow liftoff this better be on a rail as it would stand a good chance of rod whip.

 

[powderburner]

I am not sure that I can agree with teflonrocketry's suggestion to let the fwd fins pivot on pop-rivet axles. Yes, this would aerodynamically unload the fwd fins and make the overall rocket more stable. However, it appears that moocrew has the situation well in hand, and that the design is already analyzed to be stable with the fwd fins rigidly attached.
The potential risk/problem with mounting free-floating fins on pivots is that you could also design a flutter situation into your pivoting fins. Placing the center of mass of the fin BEHIND the axis of rotation will excite and amplify any potential fin deflection. You will have a very high probability of flutter to failure.
Hospital Rocket also makes a very good point, that is, you will have to use something like a 1/4 inch rod, or a rail, to support this thing. A 1/8 inch rod will be a disaster.

 

[moocrew]

do i need to reinforce the wings in any way or will just attaching with through the wall ,CA glue and epxoy ?

And about the engine...i know that i will eventually want to launch and ill look into this more on my own but Blue_Ninja mentioned G engines...what brands and what would I need to make this a SS roc? ...just for curiostiy

 

[moocrew]

concerning engines....
are any of these alright?
https://www.redarrowhobbies.com/aerotech-rms.htm
and should I use a reloadable?
Whats the best way to go with this?
And if i use a reloadable...is it still possible to mount TTW and attach to the engine tube?

 

[BlueNinja]

Sure, those motors will work. Just don't be too skimpy on thrust .

The 29/40-120 reload casing is the same diameter and length as the other 29mm G's.It goes in the motor tube just the same, so you can use it in any rocket. Yes, you can construct it the same.

If you use a reloadable, remember that even though it costs like 50 bucks for the casing, you cna use it over and over again and the reload kits are cheap so you are saving money over time.

EDIT:

I should add that the bare minimum motor of those reloads I would use with that rocket is the F40.

 

[moocrew]

I don't mean to be repetitive or make any mad but im still having a hard time understanding this whole reloadable thing.
is the construction for these any different from say..reg. estes mounts?
mabey pics or a list of the needed materials would help im having a hard time finding either....
Any light on this is way beyond appreication...
Thnx

 

[BlueNinja]

Alright... Ill try to explain it a little better.

A reloadable casing can fit into a standard MMT. This means that, say, you had an Estes Blue Ninja. It has a 24mm motor mount x inches long. A single use Estes D or Aerotech E will fit, as will a 24mm reloadable casing.

The casing aft closure is wider than the rest of the casing. This is because in HPR, there is usually no thrust ring to accomodate varying motor lengths. It acts as a thrust ring, transferring the thrust to the aft of the motor tube. I will try to get a pic tomorrow at the launch.

The casing is loaded with little chunks of propellant. For this rocket, there will probably be one grain unles oyu get into the HPR reloads. The case is loaded with the delay first. The propellant and liner is then inserted into the casing, and the nozzle is then inserted. After that, a few O-rings are inserted into the casing to seal off the gases from blowing through the forward closure (blow-by) and torching your rocket.

Any more questions, just ask. You're not making anyone mad.

Blue

 

[moocrew]

Thnx that helped alot...
the reason i ask is because im starting construction and i need to know if i have to wait till i get the motor mount to attach the TTW fins to. But according to your explaniation all i need to do is mount a reg estes D tube and attach the wings to that then i can insert the motor at a later time....im still tryin to decided if reloadable is the way to go..or if i should just get a composite mounted inside a single use tube.....

 

[powderburner]

I'm not sure that I can recommend one way or the other.

Yeah, some people think composites are more fun so they put up with the foibles and quirks. Single-use composite motors might be worth trying for your first few shots, so you don't have to invest in a reloadable motor system. That way you can learn whether you like to fool with the crapperhead igniters, how easy/difficult it is to obtain the desired composite motors or reloads, and if the 'bang for the buck' is worth it. Be aware, BEFORE you go and purchase a RMS, they are finicky about how much grease you use, how you load the delay grain, and a bunch of other things. Probably best to learn about RMS while under the supervision of an experienced guy in your part of the country?

 

[BlueNinja]

No you don't have to use the estes D tube...that was just an example. I would go with a 29mm tube.

Yeah... I agree with Powder about the reloads. It is better to have someone watch you as you assmeble the motor so in case you make a mistake they can point it out.

Personally, I think composites are fun for SFX, while BP is fun for everyday flying.

Yet another edit ablut the reloads-

You will probably only need help once with it, once you do it by yourself you realize how easy it is.

 

[moocrew]

yes i understand both points and am leaning towards single use comps.
Just to....learn on. And it seems a bit simpler....(less chance for me to mess it up lol.) thnx for all of your advice guys its has helped alot.
-moo

 

[ghp3]

I would definitely go with the 29mm motor mount tube. In your earlier posts you said the rocket would weigh in at 1.75lb which is an awful lot of weight for the 24mm motors that are out there. I have a 12 oz rocket that will only go about 250' on an Estes D and 500' on an Estes E. Double that weight and it's not likely to get off the ground.

With a 29mm mount, you can easily handle all of the mid-power single use motors and the reloadables that are available You can also use a 24mm adaptor which should work on the higher thrust Aerotech Es and the new F21 Econojet.

As for single use v. reloads, I flew about a half dozen single use composites (mainly F & G Econojets) before trying reloads. I managed to get 24/40 and 29/40-120 cases and some reloads. My first try (a D9-7 in a 24/40) didn't work so well (motor didn't seem to generate enough power, the rocket arced over and lawn darted, but soft ground minimized damage. Don't know if it was my fault or the older reload.) However, my second and third tries this last weekend worked fine. I don't yet consider myself an "old hat" at reloads, but I can now put one together in about 20 minutes and (when you can find them), they are about 1/3 less cost than single use.

Good luck!

George
NAR # 83277
Tripoli Pittsburgh
Pittsburgh Space Command

 

[moocrew]

alright so 29mm sounds the way to go...
now, w/o launching this thing to the moon and w/o using reloads what are some of my basic choices...
Aerotech?
apogee?
others?

 

[BlueNinja]

Well... Aerotech is recovering from a fire and was just purchased by ISP (wasn't it?) but they are the leader in MPR so they would be the place to look. Apogee carries their F motor line, i believe they have the F20 right now which is AWESOME if you're looking for noise.

Apogee makes a sweet little motor called the F10... It burns for 8 seconds! I wouldn't use it in this rocket however, as it has a low thrust for that 8 seconds.

 

[ghp3]

now, w/o launching this thing to the moon and w/o using reloads what are some of my basic choices...Aerotech? Apogee? others?

Your choices are pretty straightforward, but be aware of the weight of your rocket. (That will keep it from the moon, but you should be able to easily bust the 1000' mark.) Aerotech has the most selection of single use mid-power motors including the F20 econojet, F25, F50, G35 Econojet, G40 and G80. Blue Ninja in an earlier post recommended the higher thrust motors which would be the F50 and G80. I think a G35-7 Econojet would also work fine.

The Apogee motors are low thrust but very long burn. They might not do so well for a 1.75 lb rocket, and are currently out-of-stock anyway. (They are actually made by Aerotech for Apogee, so are impacted by Aerotech's recovery from its fire and restructuring as well.)

Ellis Mountain makes a long burn G35 that I haven't used yet, it's allegedly tempremental to ignite but performs well.

I don't think the Estes Black Powder D and E motors can effectively lift a 1.75 lb rocket, so you might stay away.

As was mentioned previously, finding these motors is the biggest challenge. Aerotech is back in production but supply still is very hit and miss. Check your local hobby shop and the online vendors frequently and order when they have stock available. I've had good luck with Al's Hobby Shop, Great Lakes Hobbies, Commonweath and Red Arrow.

Good Luck!

George
NAR #83277
Tripoli Pittsburgh
Pittsburgh Space Command

 

[ghp3]

You might want to download the Wrasp rocket altitude simulator. It's available free from https://www.wrasp.com/ and can give you an estimate of your altitude on various motor combinations. It's also great for selecting delay times as it estimates the time to apogee as well as total altitude. I entered in your general specs (1.75 lb weight, 2.25" main airframe, 0.75 drag coefficient.) and got altitudes from 600' to 1400' on the various mid power motors.

For what it's worth, an Estes D12 will lift it to an altitude of 19' 5", so best to stay away.

George

 

[moocrew]

im thinking of going with the F25-w from aerotech...its only a 200 m launch but thats fine with me. or mabey a G-40 which gets around 300-400. does that sound alright? it accelerates alright too so i think those will probably do.?

 

[ghp3]

Your choices should work fine, although remember that with the amount of fin area you have, you will have a lot of drag on the rocket. An F50 might be a better choice than the F25. The G40 should work fine.

George

 

[loopy]

Originally posted by ghp3
Your choices should work fine, although remember that with the amount of fin area you have, you will have a lot of drag on the rocket. An F50 might be a better choice than the F25. The G40 should work fine.

George

I agree - skip the F25, especially if there's even a hint of a breeze in the air. The lower thrust won't give it great velocity off the pad, but on a windless day, it might be all right. Still, I think I'd opt for the F50 or the G40.

Loopy

 

[moocrew]

the G40 is looking better and better all the time.....

 

[moocrew]

alright...im getting things and ideas together to start construction.....
the only thing im concerned at all with it the MM and MMT.
the fins i feel and im sure everyone else will agree should be TTW? mounted to the MMT.
For centering rings what should I use? thick balsa?..basswood?
what about the actual MMT?
is there anything i should be especially careful with?
and i will proabaly be opting for the the G40 in this bird...mabey a little larger...

the length of a G40 is 124mm....
can i make that MT that long then put a regular block in like usual and extend the tube farther? up to cut down on the volume inside the body?
Is it mabey even possible to put the MMT inside another larger tube?..for later bigger better engines????

 

[BlueNinja]

Fins- Yes should be TTW.

CRs- light plywood or basswood, for this design with big motors balsa probably won't cut it.

A MMT, you can buy tubes from LOC. More on this. You would want a 38mm tube if you want to be able to use motors larger than a G. That is not totally true, though. There are a few 29mm H motors. 38mm has G's (Cesaroni makes them for 38mm) all the way up to a J570. Pretty high range of motors for this rocket if ya ask me. If you fly it on the larger motors (I-J) then you would probably want to fiberglass it. i think this would be a cool rocket for a cert attempt.

Yes, you can put a big MMT in it then use adapters to go down. An adapter is simply a tube with centering rings on the outside of it that fit the normal MMT. Check out www.giantleaprocketry.com for these.

Also, for cutting down body volume you can just have the upper 6' or so of your rocket be a payload section and have a small (1ft or so) parachute section above the motor.


As far as motor blocks go, I wouldnt use one in this rocket if possible. Reloadable motors have one built into them and you can easily put one in a single use motor by wrapping tape around the nozzle end of the motor until it is thick. Use masking tape.