Materials question...

[T-Rex]

I am plying with Open Rocket designing what may very well be my L1 cert vehicle. It is essentially a 4" diameter Estes Hornet, though not intentionally upscaled, just turned out that way.

Here is my conundrum, I want to use 3/16 plywood fins, but have been unable to locate 3/16 plywood locally. If I layer 3 sheets of 1/16, turning the center sheet's grain 90degrees, using wood glue or epoxy, would that be durable enough for an H-motor?

I do not want to use 1/4" due to weight. I want to be able to test flight with a large G before I load an H into this thing. 1/8" may be durable enough, but I am also trying to limit its range, until I can set it up for DD in the future.

I am concerned about quality and shipping costs if I order online.

I'm probably being paranoid & over thinking this, I know that.

[MarkII]

I am plying with Open Rocket designing what may very well be my L1 cert vehicle. It is essentially a 4" diameter Estes Hornet, though not intentionally upscaled, just turned out that way.

Here is my conundrum, I want to use 3/16 plywood fins, but have been unable to locate 3/16 plywood locally. If I layer 3 sheets of 1/16, turning the center sheet's grain 90degrees, using wood glue or epoxy, would that be durable enough for an H-motor?

I do not want to use 1/4" due to weight. I want to be able to test flight with a large G before I load an H into this thing. 1/8" may be durable enough, but I am also trying to limit its range, until I can set it up for DD in the future.

I am concerned about quality and shipping costs if I order online.

I'm probably being paranoid & over thinking this, I know that.

I sandwiched 1/8" plywood between two sheets of 1/32" plywood for the 3/16" thick fins of my Javelin XL (Level 1 rocket). The fin thickness was more for looks than for strength; 1/8" thick fins would have been fine. I heat-cured them after laminating the plywood layers; that made them rock-hard. My rocket is 2.34" in diameter. I, too, have my rocket set up so that I can use DD in the future. My rocket, which is much less burly than yours sounds like it will be, reached 2100 feet on an H165R for its certification flight. Motor-initiated deployment at apogee and descent on a Top Flight Recovery 36" chute were nominal, and despite the gusty conditions, the rocket landed just about 1/3 of a mile down range. Don't fear a 2,000 foot flight for your certification; it's manageable.

[T-Rex]

Thanx Mark!

Hadn't considered 1/8 layered with 1/32... will have to take a calculator when next I can get to the LHS. I found 3/16 Midwest on fleabay.

Right now it sims to about 1500ft on an H123, I am comfortable with that.

Might just buy a kit of some sort & get past certification. I'm only doing it because I think certification is important to the hobby as a whole. Since I am 3 hours away from the nearest club launches, my L1 flights will be rare.

Sorry if I am babbling, it's night 2 of night-shift & I am whooped

[troj]

You'll actually get better reinforcement if you take one of those layers of 1/16 and turn it 45 degrees -- the plies are already 90 degrees to each other.

The biggest challenge you'll face will be finding somewhere flat enough to keep things where they belong, while the epoxy cures.

Find that, and your plan should work just fine.

-Kevin

[T-Rex]

You'll actually get better reinforcement if you take one of those layers of 1/16 and turn it 45 degrees -- the plies are already 90 degrees to each other.

The biggest challenge you'll face will be finding somewhere flat enough to keep things where they belong, while the epoxy cures.

Find that, and your plan should work just fine.

-Kevin

No, I think the bigger challenge might be finding a big flat weight. The concrete garage floor should work for the bottom side, might have to see if I can score a piece of plate steel from the scrap bin...

makes sense that the plys are are 90, so I need to go 45, Thanx

[troj]

Before you assume the garage is flat, put a level on it - mine isn't flat enough. I use the kitchen table with heavy plastic (and an understanding wife)

[GregGleason]

No, I think the bigger challenge might be finding a big flat weight. The concrete garage floor should work for the bottom side, might have to see if I can score a piece of plate steel from the scrap bin...

makes sense that the plys are are 90, so I need to go 45, Thanx

You might see if you can get the sink cut-outs from granite counter tops. They are flat and heavy.

I read that suggestion somewhere, but I haven't tried it.

Greg

[bjphoenix]

Here is my conundrum, I want to use 3/16 plywood fins, but have been unable to locate 3/16 plywood locally. If I layer 3 sheets of 1/16, turning the center sheet's grain 90degrees, using wood glue or epoxy, would that be durable enough for an H-motor?

I think this would be plenty strong for a 4" rocket with H motors. I did my L1 with a 4" rocket and H motor, and I think I used 1/8" plywood.

From an engineering standpoint three layers of 1/16" plywood would probably not be quite the strength of 1 layer of 3/16", and I'm talking about strength in bending. It actually depends on how the different pieces of plywood are constructed. I would expect that 3/16" plywood would have thicker outer plies than the 1/16" plywood, and thus slightly more bending strength. Again, depending on the individual material, 1/16" is probably 3-ply with each ply about 0.020" thick, 3/16" might be 5-ply with each ply about 0.038" thick. If you layer 3 layers of 1/16" plywood the orientation of the center layer really doesn't have much affect on the bending strength of the composite piece. (I can do the math if someone really wants to know the difference.) For tension or shear strength the orientation would matter.

[T-Rex]

Before you assume the garage is flat, put a level on it - mine isn't flat enough. I use the kitchen table with heavy plastic (and an understanding wife)

There ya go bursting the bubble.... Maybe that is why I make a lot of scrap, too many assumptions. (Couldn't possibly be my lack of skill and craftsmanship)

[T-Rex]

You might see if you can get the sink cut-outs from granite counter tops. They are flat and heavy.

I read that suggestion somewhere, but I haven't tried it.

Greg

Was noting that in another thread earlier today. Will look into it when I get to go home....

[T-Rex]

I think this would be plenty strong for a 4" rocket with H motors. I did my L1 with a 4" rocket and H motor, and I think I used 1/8" plywood.

From an engineering standpoint three layers of 1/16" plywood would probably not be quite the strength of 1 layer of 3/16", and I'm talking about strength in bending. It actually depends on how the different pieces of plywood are constructed. I would expect that 3/16" plywood would have thicker outer plies than the 1/16" plywood, and thus slightly more bending strength. Again, depending on the individual material, 1/16" is probably 3-ply with each ply about 0.020" thick, 3/16" might be 5-ply with each ply about 0.038" thick. If you layer 3 layers of 1/16" plywood the orientation of the center layer really doesn't have much affect on the bending strength of the composite piece. (I can do the math if someone really wants to know the difference.) For tension or shear strength the orientation would matter.

OK, will keep that in mind. Right now it's all a dream (nightmare?). The final outcome will be decided by price tags and my wallet. I'm thankful that I have a job in today's times, but I still have to watch what I spend.

[cbrarick]

Got a Woodcrafter's near you? you can also shop on-line http://www.woodcraft.com/Family/2004113/Plywood.aspx
because you might just spend more trying to make it....

[T-Rex]

Got a Woodcrafter's near you? you can also shop on-line http://www.woodcraft.com/Family/2004113/Plywood.aspx
because you might just spend more trying to make it....

Looks like there is one 2 hours away in Houston.

I am leaning toward just ordering it online and just taking the chance that I get good pieces.

http://www.hobbylinc.com/htm/mid/mid5125.htm

I appreciate all of the responses. You all have given me things to consider on this and future projects.

Added the OR file. The name comes from all the 4s involved: 4 fins, 4ft tall, 4" tube, and a fin span of 16" (4squared)

[MarkII]

Before you assume the garage is flat, put a level on it - mine isn't flat enough. I use the kitchen table with heavy plastic (and an understanding wife)

I used the kitchen counter, wax paper, and a stack of computer textbooks. (Might as well get some use out of them. ) I cut out rectangles that were just larger than the fins, and laminated each one separately. Then I traced and cut out a fin on each one. The 1/32" stock seemed to flex easier in one direction, so I oriented the skins so that this flex pattern was perpendicular to the surface grain of the 1/8" stock. The fins are as stiff as a granite slab.

[dixontj93060]

Before you assume the garage is flat, put a level on it - mine isn't flat enough. I use the kitchen table with heavy plastic (and an understanding wife)

I use 12"x12" or 18"x18" simulated marble tile (depending on fin size) with four or so clamps distributed around the perimeter. Another thing that works well if you need dimensions greater than 18" in length is shelving material (shown in use here on my L3 build). Both the above have been working very well for me for years now.

[chadrog]

Looks like there is one 2 hours away in Houston.

I am leaning toward just ordering it online and just taking the chance that I get good pieces.

http://www.hobbylinc.com/htm/mid/mid5125.htm

I appreciate all of the responses. You all have given me things to consider on this and future projects.

Added the OR file. The name comes from all the 4s involved: 4 fins, 4ft tall, 4" tube, and a fin span of 16" (4squared)

I've used this exact plywood from Hobbylinc, it actually measured .205". Didn't matter for what I needed it for, it might make a difference to you. It is quite nice, and they do occasionally put it on sale.

[UPscaler]

Looks like there is one 2 hours away in Houston.

I am leaning toward just ordering it online and just taking the chance that I get good pieces.

http://www.hobbylinc.com/htm/mid/mid5125.htm

I appreciate all of the responses. You all have given me things to consider on this and future projects.

Added the OR file. The name comes from all the 4s involved: 4 fins, 4ft tall, 4" tube, and a fin span of 16" (4squared)

I suppose if you really need wood from the woodcraft store my dad and I could pick it up and ship it to you, might be a little costly, but it's only 11 min. from us.



Braden

[edwinshap1]

For my level 1 i used 1/8" ply with a layer of 5oz glass on both sides. the things don't bend at all

However i did go about 550mph on my L1, i wouldn't expect that you'd need more than 1/8" with 1/32" sandwiching. It'll also make a great looking veneer if you want to leave them unpainted

[T-Rex]

I suppose if you really need wood from the woodcraft store my dad and I could pick it up and ship it to you, might be a little costly, but it's only 11 min. from us.



Braden

Thanx for the offer, Braden, but if I do decide to get it from there, I will probably just add it to other excuses to make the drive. My daughter really likes visiting the Houston SPCA to see the horses....
Or possibly combine it with a trip to a launch in Herne or NASA

[UPscaler]

Thanx for the offer, Braden, but if I do decide to get it from there, I will probably just add it to other excuses to make the drive. My daughter really likes visiting the Houston SPCA to see the horses....
Or possibly combine it with a trip to a launch in Herne or NASA

You must be south of Houston? We're 20 minutes north, and Hearne is still a 2 hr. drive. Have been to JSC three times now



Braden

[T-Rex]

Actually I am Northeast, almost due east of you. About 2hrs to NASA Or Bush Intercontinental, 3hrs to Herne