Is this crazy for my first scratch build?

TopRamen said:

I don't even use Cellphones.

And come to think of it, what's a PDF????

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Well stated-- thank you very much!

Here's the first frame.


I'm likely being overly optimistic but I built the frame from 1/32 basswood. The perimeter is x1/4 and the braces are x1/8. It is now skinned with 1/32 balsa and will get paper tomorrow. The fin seems a bit fragile right now but the glue is not set. Once the glue sets, they will stiffen some and they still need ribs and paper. If I don't like the results, I can always build another with 1/16 material.

fin flutter??

Screaminhelo said:

Here's the first frame.
View attachment 246714

I'm likely being overly optimistic but I built the frame from 1/32 basswood. The perimeter is x1/4 and the braces are x1/8. It is now skinned with 1/32 balsa and will get paper tomorrow. The fin seems a bit fragile right now but the glue is not set. Once the glue sets, they will stiffen some and they still need ribs and paper. If I don't like the results, I can always build another with 1/16 material.

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cbrarick said:

fin flutter??

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I think that it is addressed in the original design by the fence. I plan to laminate a 1/32x1/4 doubler under the fence and possibly a second at about 2/3 span.

The first fin is completed! It is next to my most recent Flutter-By for a size comparison.

The doublers really stiffened the assembly and papering made it all rock solid. In hindsight, I probably don't need the doublers for rigidity but they may be beneficial for strength in the recovery phase. I went ahead and installed fences since they may help to encourage instability during recovery. It may just be wishful thinking but it makes this beast look more like the original.

When I shoot my latest F-B, we'll call it a small scale test of the effect of the fences. I left them off since papering the fins stiffened them up so much. I don't expect much, if any, noticeable difference at the original scale.

Here is the booster body. 1/32x1/8 basswood strips fit the coupler to the body tube. I have a little research to do before I build the MMT. I will be building it to accept future 24mm reloads so it will be a first for me.


Here is a picture of the upper stage and booster tube with a kit F-B. I am feeling a bit insane at this point but the cows are out of the barn and there is no turning back.


I am hoping to get the booster fins built over the holidays so I can start doing some pre-launch testing.

Screaminhelo said:

Here is the booster body. 1/32x1/8 basswood strips fit the coupler to the body tube. I have a little research to do before I build the MMT. I will be building it to accept future 24mm reloads so it will be a first for me.
View attachment 247634

Here is a picture of the upper stage and booster tube with a kit F-B. I am feeling a bit insane at this point but the cows are out of the barn and there is no turning back.
View attachment 247635

I am hoping to get the booster fins built over the holidays so I can start doing some pre-launch testing.

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Well thank goodness you are actually seeing it through. So many here get all hung up on Sims and Safety that it sucks all the Fun out of Rocketry, and I hate them for it.
Kudos to you for building your Vision!!!

TopRamen said:

Well thank goodness you are actually seeing it through. So many here get all hung up on Sims and Safety that it sucks all the Fun out of Rocketry, and I hate them for it.
Kudos to you for building your Vision!!!

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Thanks to the kudos. Truth is, the naysayers did a lot to encourage me to continue. I have a gut feeling that this will work, it may just require some trial and error.

Booster fins are next on the agenda. They will be a little more fiddly to build but nothing too hard.

One quick question for ya'll. Am I correct in my assumption that the MMT for composite and RMS motors will be built just like a LPR mount without the thrust ring and engine hook? I plan on using fiber rings and epoxy for this so I believe that it should withstand the abuse of the higher thrust motors. I'll be leaving about 1/2" of the tube exposed for future motor retention, I'll start with tape for simplicity and weight savings.

Screaminhelo said:

Here's the first frame.
View attachment 246714

I'm likely being overly optimistic but I built the frame from 1/32 basswood. The perimeter is x1/4 and the braces are x1/8. It is now skinned with 1/32 balsa and will get paper tomorrow. The fin seems a bit fragile right now but the glue is not set. Once the glue sets, they will stiffen some and they still need ribs and paper. If I don't like the results, I can always build another with 1/16 material.

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I've thought about building "hollow" fins on some of my larger rockets--good to see that someone's tried it, and that it works.

O.K. My son dubbed this one the Fatter-By since it the inspiration came from him saying that a Fat Boy sized Flutter-By would be a good thing to have.

The motor mount will need to go in very soon. Having never built anything to accommodate motors other than Estes BP motors, I need guidance. I plan on a 4" motor tube with no hook or engine block. Retention will be friction fit and I plan on tape thrust rings for BP motors. Will this work for everything from BP motors to 24mm RMS cases?

I'll post more pics when the booster is done.

That's a great Name for it!:clap:

Screaminhelo said:

O.K. My son dubbed this one the Fatter-By since it the inspiration came from him saying that a Fat Boy sized Flutter-By would be a good thing to have.

The motor mount will need to go in very soon. Having never built anything to accommodate motors other than Estes BP motors, I need guidance. I plan on a 4" motor tube with no hook or engine block. Retention will be friction fit and I plan on tape thrust rings for BP motors. Will this work for everything from BP motors to 24mm RMS cases?

I'll post more pics when the booster is done.

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I've successfully friction fit motors up to 29mm G class. I always add two or three wraps around the end of the motor tube and motor. Here's a picture of a 24mm reload in an Estes Mean Machine to give you a better idea.

The conclusion that I am drawing is that as long as the motor tube is long enough to stabilize the longest motor that would be used. I figure that the FWD centering ring should be near the end of an RMS case if I want to include that as an option. I will be leaving 1/2" of tube exposed on the AFT end to accommodate a retainer later.

Holler if you see any problems with the plan.

Here is the Fatter-By next to its little brother


The BT-50 MMT is the same size as the main body tube on the original! Initial finger balancing indicates that the CG is further aft than OR predicted and that is without a motor. This thing is going to require some weight in the nose to work. I'll play around with it this weekend and see what it's going to require. I have one question regarding this part. When using the cardboard cutout for CP estimation, should I just go with the balance point or is the actual CP consistently off one direction or the other? Since this is a bit on the heavy side for its size, I am aiming for a CP margin of less than one caliber and wanted to know how close to 1/2 I could get away with.

I'm thinking of going to with the original silver and red paint scheme or maybe trying to find a metallic blue to pay homage to the Fat Boy. I hope to enlarge the kit decals and maybe incorporate the Fat Boy font for the FAT in Fatter-By.

If anyone has suggestions for ground testing, I am all ears. I am just going with basics here, so the experience of the forum will be of great benefit to me.

Well, I am at it again. Work, Christmas craziness and a minor back injury had me away from the bench for a while but I am finally back in the looney bin.

Swing testing has shown marginal results for the largest motor that I would stuff in but removing 5g from the dummy motor produces consistent results with my limited experience. Since I plan on limiting this to 1k and below, I am happy with the margin. I'll focus more on optimizing stability in a future build and retain the option of stuffing in an F35 if I get access to a field with a little more soft surface.

I haven't found much on for lift capabilities for different motors so I am using Thrust Curve data to extrapolate information, basically getting a picture of relative thrust to weight for various combinations. Current empty weight is 193 grams with no fill or finish. Thrust Curve tells me that it will hit 68 ft/s off of a 6 foot rod and make it to about 475 ft. on a D15. I figure that this gives me some room for finishing if all is well with initial trials. Since I plan on a 24/40 case, I am also looking at an E28. It is pushing the altitude limit for my local field but, at 83 ft/s off the rod, it provides a bigger fudge factor. I guess my question here is "Am I wrong in thinking that the D15 will work just fine here?" If anyone has data for total liftoff weight for these motors, it would be helpful. The information may be on the Aerotech web site but I haven't found it yet.

I am not ruling out single use motors. I just figure that starting out with reloads will simplify the process in the end.

I found what I needed right here on TRF. The right search terms on Google did the trick. See post #23 in the following link for a handy spreadsheet.

Greg Gleason's ChartEng utility

I can see this being a handy reference in the future. I haven't played with it to try and import files yet but it meets my current needs quite well as is. It contains a native utility for importing .eng files so if you encounter engines that are not already included, you can add them.

I just re-read this entire thread because I missed a few postings, but did you say how much this FB weighs unloaded?

Gary Byrum said:

I just re-read this entire thread because I missed a few postings, but did you say how much this FB weighs unloaded?

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I had intended to but seem to have left out the fact that it weighs in at 193g unloaded and unfinished. It will gain some weight with finishing but it appears that my motors of choice have enough power to handle the increase.

Screaminhelo said:

I had intended to but seem to have left out the fact that it weighs in at 193g unloaded and unfinished. It will gain some weight with finishing but it appears that my motors of choice have enough power to handle the increase.

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Here's my thinking for a low powered test flight. We all know a D12 BP motor is barely enough to power the early version Saturn V, which weighed in at 9.9 oz, so with your FB in at 6.8 oz, you could get about a 200' flight in a smaller launch area using that motor.

I decided on the D15 simply because every method that I that I have used to estimate performance indicates that there will only be about 50-75 ft difference in altitude but the D15 will be faster off the rod by about 10 fps. This my not be a significant difference though since the D12, at just under 60 fps, should be more than adequate. Maybe it will come down to what is available.

My real challenge here is doing my own math and estimating flight parameters using thrust curves. Right now, I am using Thrust Curve for altitude and velocity data and trying to correlate my own estimations with the information there. In the long run, I want to do it the other way around and use Thrust Curve etc. to confirm my own work.

I guess I just don't understand all the math you're doing on a LPR flight. When I started figuring MPR into my scenario, I too, used the online tools trying to figure the same things you are, because I was so unfamiliar with all of it. Now that I have some MPR experience under my belt, I see those motors as "advanced LPR."

For what it's worth, I often show up at a launch with 4-5 new models getting their maiden flights. Since I have nowhere to do a test launch, I usually just show up with them and give a heads up on anything I have even the slightest doubt about. I'm not tootin" my horn here, but I'm pretty confident about my design skills.You, are going to fly an upscale of a proven design. You must have some serious past experience building and flying if you are doing up-scales, eh? Don't let the software rob you of a good gut instinct. Big deal if it doesn't give you 100% the first time. That happens sometimes. Just take a look at what I thought was a dead on given. Granted, this doesn't happen to me often, but even the guys flying HPR that did all the math, have worse case scenarios. This was the maiden flight of my Whizzler rocket, that I was just wrong about. A little nose weight made all the difference 2nd time around.

https://s343.photobucket.com/user/glbyrum/media/Wizzler_zpscd26fd93.mp4.html?sort=2&o=12

My Meow-Mixer is a 2.6" Build that weighs in at a hefty 11.75 with a D12-3 Loaded, and it flies just fine.
https://www.rocketryforum.com/showthread.php?68414-Meow-Mixer-24mm-Scratch-Build

I'de definitely start with a D12-3 for your 6.8 oz. Rocket without hesitation.

Looks like it was an interesting flight Gary!

I am certainly no rocket surgeon but building and aerodynamics make sense to me. That, along with a respect for safety and little fear of failure, tells me that I can't succeed if I don't try. I could have just come up with my own 3FNC design but I would have still been using basic building techniques. When the idea of and upscale FB came to mind, I knew that I would have the opportunity to expand my abilities with a small safety net provided by using an existing, proven design that I had already built more than once. Good counsel from TRF members helps to keep me headed in the right direction and introduces me to better methods.

As for the math, that is just a result of fixing and crewing helicopters for 20 years. I am used to having to learn the hard way so that I can understand how the easy way works. I kind of stumbled into it while looking for liftoff weight info any way. Now that I have some good ready references the math isn't necessary, just interesting. With time the motor choice will become more intuitive.

I have thought about the D12 and realized that I could use my MM. Maybe still get the D15 and keep it in reserve for flying after I get any bugs worked out.

Well, whatever you do, make sure you eventually actually launch the Rocket.
You see, around here a lot of stuff gets built and then fades into obscurity do to second guessing, opinions, simulations and lack of willingness to take even the slightest of chances.

TopRamen said:

Well, whatever you do, make sure you eventually actually launch the Rocket.
You see, around here a lot of stuff gets built and then fades into obscurity do to second guessing, opinions, simulations and lack of willingness to take even the slightest of chances.

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It's going to fly for sure. I'm just a slow builder with lots of irons in the fire. I'm grabbing some BP motors today and plan on getting a primer finish on it by the weekend. I'm having to work it in with Pinewood Derby season though. Rocket work is going in drips and drabs right now but it is still going.

I didn't realize it had been so long!

The Fatter-By is ready for its maiden launch today and it will go up on a D12. Unfortunately, I don't have pictures to post at the moment but I will take a couple before it launches.

Screaminhelo said:

I didn't realize it had been so long!

The Fatter-By is ready for its maiden launch today and it will go up on a D12. Unfortunately, I don't have pictures to post at the moment but I will take a couple before it launches.

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Awesome! Looking forward to hearing how it goes. Best of luck.

Well, its just a cell phone video but you can see a successful launch! I left the launch base at the house but since I had the 1/4" rod with me, I was able to set as stable platform and get it in the air. It went up on a D12-5 today since that is what I had for the Mean Machine and the delay was a bit long, it dropped about 75' before separation but the featherweight recovery performed well and it was recovered with no damage. I'll try a -3 next time and then E power.

[video=youtube;qeah2C-49dA]https://www.youtube.com/watch?v=qeah2C-49dA[/video]

I'm wishing that I hadn't put the effort into the finish that I did. After seeing the launch, I have some ideas that I want to incorporate that may mean rebuilding the fins

OR didn't like it and ThrustCurve said it was too slow off the rod for the D12 but the swing test turned out well and pad weight was below total weight for the motor. Besides, it looked like it would work.

Congrats!!!