Houdini - A 3" Minimum Diameter Project for LDRS 34

I'd rather make a mistake and find out it on my computer than find out on the field.

Going to use Bondo polyester-based FG resin to T-to-T fins. It has a heat rating up to 180 degrees, but I think I could augment the leading edges with JB Weld for a little more protection. I've used it before and it holds incredibly well. Of course I haven't taxed the heat resistance as much.

EeebeeE said:

Going to use Bondo polyester-based FG resin to T-to-T fins. It has a heat rating up to 180 degrees, but I think I could augment the leading edges with JB Weld for a little more protection. I've used it before and it holds incredibly well. Of course I haven't taxed the heat resistance as much.

Click to expand...

Majority on here would recommend epoxy. I have not used polyester, but I have heard its inferior to epoxy. I would also recommend epoxy.

Looked at some other discussion threads. I will need to rethink this.

JB weld all the way!!! Rocketpoxy Also works great.

Rocketpoxy seems to be too thick for this. I picked up some West Systems G-Flex

EeebeeE said:

Going to use Bondo polyester-based FG resin to T-to-T fins. It has a heat rating up to 180 degrees, but I think I could augment the leading edges with JB Weld for a little more protection. I've used it before and it holds incredibly well. Of course I haven't taxed the heat resistance as much.

Click to expand...

You don't need layups for this project in the first place - reference my various threads of flying large MD projects without layups as background on why I say this with certainty - but if you're going to do layups anyway, using polyester resin would seem to defeat the purpose. Why use a material with a low temp rating and augment it with JB Weld instead of just using something like Aeropoxy or Proset that's better suited to the application?

BTW, you won't break the waiver at Potter with a 3" min dia on a 4800/4 grain/whatever CTI calls it. Flew a trimodal 7:1 blue 5500ns motor in my 3" min dia (with no layups) there a few years ago before I moved out west - one alt said 19,999' and the other said 20,841'.

-Steve

[video=youtube;TMR0KMU3cqE]https://www.youtube.com/watch?v=TMR0KMU3cqE[/video]

The flutter analysis suggested the fins would break at about Mach 1.3. This is going to hit Mach 2. Potter's waiver is 15K with a call-ahead to 22.5K.

Sims say this will reach 22.5 on a CTI L1350 (3-grain), which is about 80% of an L, but OR is usually about 10% too high. I thought about a 4-grain, but the booster needs to be longer. I have a 4-grain case and I could use the 7" section of airframe I cut off the payload section to increase the length enough to accomodate a 4-grain motor.

Besides most every sim of a 4-grain L is >24K feet. Even if I back it back 10% I am dangerously close to the waiver.

By the way ...

This is Houdini before fillets, painting, and a lot of other stuff.

It's nasty stuff: steer clear of it!
I tried it once... IT's good if you are building FG boats using FG mat compared to cloth.
The hardener can be tricky as it's about 100:2 resin to hardener ratio.

The chemicals are even worse than epoxy.

JD

SinfulDarkLord said:

Majority on here would recommend epoxy. I have not used polyester, but I have heard its inferior to epoxy. I would also recommend it.

Click to expand...

Tip to Tip Fiberglassing. My first ever attempt. I made a cradle out of some scrap wood. The fillets were done with RocketPoxy, Leading Edges done with JB Weld. Remainder done with G-Flex. That way I have strong mounting to the airframe. Heat resistance on the fin leading edges, and a flexibility for the the rest of the fin to get through the transonic region. Looks like adherence went well. The fin surfaces were smooth although the airframe will need some sanding.

There is a whole lot of nope going on there.

So, let me try to recreate this.

1. Mix and apply RocketPoxy fillets.
2. Mix and apply JB Weld to leading edges.
3. Apply fiberglass cloth
4. Paint with other epoxy to saturate.
5. Clamp. Let everything cure.

If that's what you did, I think you're kinda bastardizing all of the various components.

1. By not allowing the fillets to cure before laying up (as evidenced by the creep of the RocketPoxy up the fun and onto the tube) you have very little benefit of an actual fillet.

2. By not allowing the JB to cure before applying other epoxy you have introduced other compounds that may deter its effectiveness.

3. By not allowing either of the previously mentioned epoxies to cure prior to using your glass saturation epoxy, you are likely to get some wonky curing of that.

Or, you could have discovered something awesome. I don't know.

I am hoping for the awesome. I will probably add more RockePoxy fillets. The JB Weld mixed with the G-Flex although it was completely JBWeld at the leading edges. Everything is seeming to cure appropriately although it is taking a little more time than usual.

I guess we'll see when it flies.

Realistically all you need are the fillets. Everything else is gravy.

That was not what the math was telling me. More work, but a greater chance of success.

EeebeeE said:

That was not what the math was telling me. More work, but a greater chance of success.

Click to expand...

Its not a greater chance of success with all the components mixed together. Chances are you weakened it more. You want to do one at a time and let each one harden. By mixing two epoxies your introducing each epoxie's hardener to each other and that is where it messes up the curing properties.

What you did there might cure, but might not be as strong as you'd imagine it would be.

All three epoxies had a long curing process (about the same time each) so they all cured about the same time. They all also had 1:1 mix ratios.

I know that you can mix some epoxies together without any real problems. That is sometimes how you can speed up curing of G-flex for example. The chemical reaction process is largely the same.

The end result is that everything seems to be very strong...much stronger than before the tip-to-tip. We'll see when it flies. I am going to add more rocketpoxy to the fillets because right now they are fairly small. I am going to be sanding tonight and tomorrow, then applying fillets one more time afterward. More photos after I finish sanding.

EeebeeE said:

All three epoxies had a long curing process (about the same time each) so they all cured about the same time. They all also had 1:1 mix ratios.

I know that you can mix some epoxies together without any real problems. That is sometimes how you can speed up curing of G-flex for example. The chemical reaction process is largely the same.

The end result is that everything seems to be very strong...much stronger than before the tip-to-tip. We'll see when it flies. I am going to add more rocketpoxy to the fillets because right now they are fairly small. I am going to be sanding tonight and tomorrow, then applying fillets one more time afterward. More photos after I finish sanding.

Click to expand...

It has nothing to do with the curing time nor the mix ratio. Each epoxy has their own kind of hardener that gives it its strength. Because you mixed some together you may have changed some of its properties. Not only just strength, but glass transition, brittleness, etc.

Im crossing my fingers though that all goes well.

I am going to add more rocketpoxy to the fillets because right now they are fairly small. I am going to be sanding tonight and tomorrow, then applying fillets one more time afterward. More photos after I finish sanding.

Click to expand...

Fillets over T2T?? Correct me if I'm wrong but I don't think that will add much strength only weight.

They are mainly to fill a couple gaps where there were some minor ripples. This is what it looks like after rough sanding. Still a lot more sanding to go.
The epoxies did blend together, but I think overall the process was pretty effective. Of course a Mach 2 flight will let me know for sure.

Entire Airframe


T-to-T fins

Easy to follow build with a flight that should be spectacular.

Your Geneseo and Potter N.Y. launches are always exciting to watch and this one
to 4 miles will be a treat.

Subscribed to your youtube channel for the video.

Tom C.

I am in sanding mode right now. Lots of sanding so instead of posting boring photos of me with sandpaper, I thought I would show you what I hope my onboard video cameras capture at 20,000+ feet. These are screen grabs from Google Earth, and I have identified some key points of interest in Western NY and the Finger Lakes Region. HD views would be excellent.

The views are starting from North and rotating counterclockwise if looking down.

Starting the AV Bay. I spaced the two threaded rods as far apart as possible to give me more room toward the center of the bay.

I cut a sheet of G10 to be used for the sled. If you can envision this, the two stratologger altimeters will be horizontally mounted at the top of the AV Bay. On the other side of the sled I will mount the MT-4 Timer. I will cut a hole in the center of the sled for the horizontally mounted video camera. Still trying to figure out how to mount the vertical camera (facing aft). Then on the aft end of the sled I will mount the batteries in some sort of subcompartment to prevent them from crashing into the electronics if they come loose.

So this is how the electronics sled will look. I decided to vertically mount the altimeters. A little more room that way. They will be in the aft end of the bay. The batteries will be zip-tied into place with two ties. One on each side of the sled. The timer will be on the opposite side of the altimeters. The camera is an HD Wing Cam from Hobby King. I still need to figure out how to put the other one in place. I haven't bought it yet. Anyone know of a video setup where the camera and the recording unit are separate?

EeebeeE said:

If these do flutter, at least under thrust they will punch through transonic in less than half a second. Coming out of Mach they will be transonic for about 2 seconds and that could be an issue.

Click to expand...

Definitely watching for your results, with a similar project of mine on the horizon.

I tend to pack my rockets fairly tight. No reason for wasted space.

Click to expand...

Love it! My Nuke Pro with a 38mm5G and full electronics feels like a little brick.

Not sure I understand, though, are you saying that you are getting 75mm3G motors for less than 54mm6G ones?

watermelonman said:

Not sure I understand, though, are you saying that you are getting 75mm3G motors for less than 54mm6G ones?

Click to expand...

2 grain 75 [133.00] which most are equal to or greater Ns than a 54 6xl [173.00]are significantly less cost.





3 grain 75 [189.00]is only a few bucks more, and WAY more punch for the buck.





So 2 G 75's are much better value than the largest 54's and 40.00 cheaper.
Old timers are well aware of this....lots of comparisons in the motor world reveal better value for flying larger motors cheaper. This is one of the best.


He's figured it out.:grin:

watermelonman said:

Love it! My Nuke Pro with a 38mm5G and full electronics feels like a little brick.

Click to expand...

I had a Nuke Pro Maxx and certified L2 with it with a J270. 8,458' up. It landed a mile and a half away. So I took it to LDRS 31. I upped the ante with a CTI J530. The sims showed 13,000' and Mach 1.5. At 3,700' just about peak speed, it crushed like a beer can. Pieces rained all over the range. It was glorious.

blackjack2564 said:

Old timers are well aware of this....lots of comparisons in the motor world reveal better value for flying larger motors cheaper. This is one of the best.
He's figured it out.:grin:

Click to expand...

I kind of am an oldtimer. oint:

I priced the CTI L1350 (4,280 NS) at Wildman Rocketry for $170.96. The 54MM CTI L935 (3,076 NS) is $179.99. Both are Wildman Club prices. So in addition to saving $9.03 I get 1,204 more NS (a full J more power), can fly 6,000' higher, and 280 MPH faster. Seemed like a no-brainer to me.

EeebeeE said:

I had a Nuke Pro Maxx and certified L2 with it with a J270. 8,458' up. It landed a mile and a half away. So I took it to LDRS 31. I upped the ante with a CTI J530. The sims showed 13,000' and Mach 1.5. At 3,700' just about peak speed, it crushed like a beer can. Pieces rained all over the range. It was glorious.

Click to expand...

Yes! I only hit 7800 feet on a J290; funny enough the J270 was exactly what I wanted but the vendor was out that day. I am going to do fiberglass reinforcement on mine so I do not have to think twice about the 5G reloads. If you got 6XL in there you must have been making even better use of your space. Consider me impressed!

blackjack2564 said:

2 grain 75 [133.00] which most are equal to or greater Ns than a 54 6xl [173.00]are significantly less cost.

Click to expand...

Oh, I was taking the 6G as literal and those are in a little lower class, no L options. The 6XL ones certainly do get expensive fast, especially the ones I want! Well, definitely more food for thought after the current build and fly rounds are completed.

watermelonman said:

If you got 6XL in there you must have been making even better use of your space. Consider me impressed!

Click to expand...

It was a challenge, but I squeezed it in. I moved the coupler tube forward and moved the motor mount about .375" aft. Then I did not put a nut on the loop part of the eyebolt so I could bury it into the bulkhead. Had to wrap the shock cord around the motor casing to get it to fit. Next time I will glass the airframe.


This is a photo of it taking off with the J530. It almost made it. The shred was way up there.