Level 3 Project Talk

[bandman444]

Hello again,

I have been doing a lot of work lately on designing my Level Three project that I plan to complete in less than a year from now. (April 2012)

I will be building a 5x Upscale Madcow Squat. Well, that’s he plan right now, you’ll read why in a second.

5x means 20” diameter and just over 11 feet tall.

This project will include a few unique designs and some techniques that are new to me that you may have some experience with.

Points of this project:

Utilize Sonotube as the main airframe tubing

Fiberglass the main frame in two layers of glass

Include custom made nose cone by using body tube Sonotube

Use centering rings inside nose cone to hold shape and provide form (See post here)

Foam the cutouts from the nosecone with 2-part expanding foam

Fiberglass nosecone

All centering rings, bulkheads, and fins will be made from 1/2” Birch Ply


That covers the basic construction bits.

If you would like more details on the above, just post and I will let you know more.

Attached is a RockSim file of the proposed plan.

But I need some help from you guys!

The biggest thing I need are weights.

My goal for this project is 100pounds or less, dry. (Or I will have to bump down the diameter a bit)

I have to use RockSim’s estimations on weight because I honestly can’t predict what the weights of some of the objects are.

My thinking is 60pound booster (I guess it’s not really a booster, maybe a fin can) with a 40pound nosecone.

If you can help give your opinion on what you would estimate some of the pieces will weigh that could prove to be very helpful.


One design part that is still up in the air is the motor situation.

With such a large aft end I feel that one motor is a waste. So I want to open the doors to clustering.

I have talked with a few people already about what size and how many, and I have heard answers all over the board.

One small trend is the central motor, basically 4”, 6”, 8”. Most I’v talked to suggest a 6” mount because “you can’t adapt up”

I agree, but I’m not convinced I would ever fly an “O” or “P”, especially when I’m 18 or 19. (That’s assuming it flies )

Then I want to put 4-54mm so that I have a good selection of motors to pick from when I want to air start motors.


Once I get most of these questions answered and I nail down weights I will contact local TAPs and L3CCs and talk with them about their opinions and/or concerns regarding this project.


Then construction will commence! And you all here at TRF will be the first to know.


Thanks guys,

Bryce


Oh BTW if you have a Madcow Squat kit lying around that you have not built, half built, damaged slightly, built but don’t fly, if the price is right I may be interested. Please Pm me.

View attachment 20inch Squat.rkt

 

[mikec]

I will be building a 5x Upscale Madcow Squat.

Well, that's ambitious and amusing. I have seen dozens of unstable Squat flights, and my own, even after several stable flights, went unstable and crashed on a G64. So I can think of many more forgiving designs to base an upscale on. Just make sure that you have at least 2 calibers of stability.

I don't think you attached the Rocksim file.

 

[edwinshap1]

oh yeah, i remember hearing about this at nsl. that will be a very ambitious way to create a nose cone, especially because sonotube is a lot thicker and harder to bend than your average pvc or carbon fiber.

but if you are able to get it bent without crimping the bend point, then all you have to do is put in the CRs and wrap the tube in something non stick, then pour the foam. it'll seal everything without having to pour the epoxy

 

[UPscaler]

oh yeah, i remember hearing about this at nsl. that will be a very ambitious way to create a nose cone, especially because sonotube is a lot thicker and harder to bend than your average pvc or carbon fiber.

Edwin,
Have you ever seen real carbon fiber? It is not the least bit easy to bend.


trust me, you'll bend sonotube WAY before you bend carbon fiber tubing.


Braden

 

[MClark]

You need to put a central motor mount in it even if you have the 54s. Clusters are not allowed for cert flights.
You would be lucky to get it in at 100 lbs, locally for a club project we made a 16" V2 that was 100 on the pad and another member made a 16 Diablo that was around 100. A 20" rocket is way bigger than a 16.
Even at 100 +20 for a motor another +15 for recovery it will need 3000 N off the pad, limits you motor selection.

All that said if you keep in mind it may come in at 150- 175 on the pad and plan ahead to use something like an Aero Tech N4800T it will work.

Mark

 

[bandman444]

Thanks guy for the comments so far.

Stability is absolutely a fine line that project needs to be on the right side of.
2 calibers is not truly an option. Thats 40" from Cp to Cg and puts the Cg 17" into the Nosecone...so whatever

Jared and Braden: I honestly haven't worked with Sonotube yet, so I don't know what the bend-ability of t will be. That being said I will be making more triangle cuts so that the pieces are smaller and be easier to conform.

Mark: Yes there was no intention of not putting in a central mmt, but the question was as to the size of it. I also know that I can't do airstarts or clusters on cert flights. I just wanted to leave the option open for later flights. Also I was thoroughly impressed with the 16" Diablo and I can't recall how tall it was but this one will only be 12' tall.

N5800 C-Star anyone?

Getting ahead of myself

 

[edwinshap1]

Edwin,
Have you ever seen real carbon fiber? It is not the least bit easy to bend.


trust me, you'll bend sonotube WAY before you bend carbon fiber tubing.


Braden

ask tominator, our drag race consisted of my glass rocket, and his CF rocket. granted his was a one layer thick sleeve, but regardless the process works better the thinner the material.

 

[GRIFFIN]

N5800 was the motor I was thinking. If any motor will push it......It's that one.

 

[dixontj93060]

Bryce,

From your description it looks like a fun and challenging project. I would make sure I had the issues/considerations around stubby rocket stability down cold. Here are a few links to get you started:

Stability of Short Stubby Rockets

TRF Archive discussion

Rocket Dungeon resource

Also, given you don't yet have a grasp on the weight of your materials, I would highly encourage you to do an intermediate, scale-up project of similar design. As an example, you could do an 8" or 10" Sonotube (readily available at HD) project using your nosecone build technique and fly it on a K/L-class motor a few times. You then would have a reference point for the material weights, any associated construction techniques, and potential flight profile issues with a large stubby rocket before embarking on the L3 build.

-Tim

 

[mikec]

Stability is absolutely a fine line that project needs to be on the right side of.
2 calibers is not truly an option. Thats 40" from Cp to Cg and puts the Cg 17" into the Nosecone...so whatever

An L3 attempt is the wrong time to be thinking about stability as a "fine line", IMHO. You want lots of margin. If I were your L3CC, I would require you to have at least 1 caliber stability. Stability has been seen with the Squat at 1/2 caliber, but it's not guaranteed.
I'll be interested to hear what your committee says.

 

[troj]

Mark has a good handle on the final weight of something like this.

Something else to consider is what folks have said regarding this being a design that's already borderline in terms of stability.

Not a good choice for a cert rocket, in my opinion. Especially when you consider that your rocket is going to be heavy, which means a bigger motor, which is adding weight exactly where you don't want it on an already borderline design.

Of course, end of the day, it's up to you and your TAPs and/or L3CC.

-Kevin

 

[bandman444]

Thanks guys for the responses.

Stability (Safety) is by far the number one consern for this project.

Thank you very much Tim for posting those links those and a couple other sources are what leads me to believe that under 1 caliber is safe and do-able, but not recomended. Obviously there is no reason to build a rocket inheritly unstable, but with solid construction and building techniques I think that it will work. (Before I get shunned for that statement) It is clear that a rocket CAN fly straight on as little a .2 caliber, but I do not intend to fly it as such. 1 Caliber would be a strong goal to keep and if achieved will be very good.

The rocket has a 5foot tall airframe with a 6foot tall nosecone with huge fins (It spans over 70").

Also as Tim suggested, I do plan on making a 1/2 scale version 10" diameter 6feet tall. It will be the test bed (as with some micro-scale)

Kevin (Or anyone else)? Can you confirm or deny the claim made in post #3 about not being able to bend cut sonotube?

Bryce

 

[MClark]

20" sonotube is quite thick and unless it is wet it will be difficult to bend. And it is likely to come out looking bad.
I would suggest one of the stacked foam methods, they work well.

As for stability for short rockets if it has a margin of 10% of the length it will be OK. So if you have 1.1 foot it will be fine. This also goes for long rockets. A long for diameter rocket (say 1" dia and 40" long) will need more than a 1 caliber margin of stability, 4 would be fine. The Rule of thumb of using 1 caliber comes from a lot of the Estes/Centari kites being about 10x as long as diameter.

Mark

 

[troj]

I agree with Mark in regards to bending sonotube. At that diameter it's 1/4" thick.

Also you may well have to step up to 24" or down a bit to get a size that's not special order.

-Kevin

 

[bandman444]

Kevin, As far as I knew it was a regular size.

20" was good because it comes in 12' lengths and utilized all of it.

 

[troj]

Kevin, As far as I knew it was a regular size.

20" was good because it comes in 12' lengths and utilized all of it.

Is it a size that they normally stock? That's the important question to ask.

Locally, I can buy anything from 4" to 48" in varying increments (2" or 4", depending on the size)....the trick is what sizes they stock. Here, 20" isn't a standard stocked size, so it would incur about a $150 fee, on top of the cost of the tubing.

-Kevin

 

[bobkrech]

This is a classic article on Wind Caused Instability by the late Bob Dahlquist TRA #3032 https://www.apogeerockets.com/education/instability.asp

A complementary article by Robert Galejs "Wind Instability What Barrowman Left Out" is attached.

Your NC idea is not practical. It's much easier to make a male plug from foam insulation board, glass over it, and dissolve out the foam with acetone afterwards. Alternately make a wood frame cage, cover with thin foam or screen and fiberglass over it. Both alternitives are lighter and easier to make.

Bob

View attachment sentinel39-galejs.pdf

 

[bandman444]

Your NC idea is not practical. It's much easier to make a male plug from foam insulation board, glass over it, and dissolve out the foam with acetone afterwards. Alternately make a wood frame cage, cover with thin foam or screen and fiberglass over it. Both alternitives are lighter and easier to make.

Bob

Sorry I don't want to sound rude, but what part of my method is "not practicable". I ask that as I respect your opinion but don't see where that's coming from.

Thanks

Bryce

 

[rokit]

What about a modular motor mount, where you use something like a 12" tube for the motor mount, and then build different "cannisters" that you can swap between. The cannisters could be for single motors, or different cluster configurations. I though I remember someone doing this, or at least proposing it, but can't remember where I saw it.

If it turns out that bending the sonotube for the nosecone doesn't work out, this is an alternative:

https://www.rocstock.org/wizards/bignose.pdf

Mike