Tip to Tip or not

[rocketman4h]

This is the tail section of my Mad Cow 38mm mongoose. This is a beautiful carbon fiber rocket. It looks likes its going mach one standing still. with is being a min dia kit. the fins are surface mounted with High temp JB weld. with te biggest engine I can put in it it sims to mach 1.9. Talk about punching a hole in the sky! carbon mat is way to thick to lay a tip to tip. and 2oz fiberglass tip to tip will also screw up the look. going that fast would the glass peel off? do I need to go tip to tip?

 

[OverTheTop]

Surface mounted or into slots?

If you use automotive two-pack paint you won't even get Mach rash.

If fins are slotted in you probably don't need tip to tip. If they are surface mounted it would likely benefit from that.

The fiberglass will not likely peel at those speeds. The leading edge is within the Mach cone so airflow normal to the edge is subsonic, giving a low stagnation temperature there.

 

[rocketman4h]

Good points. This is a min diameter rocket. to no fin slots. also managing a groove in carbon would take tooling I can't do (yet)
I have that 2oz fiberglass coming in. that may be thin enough to be somewhat transparent when whetted out. That is what I shall use. I will post a few more pics to this thread on that procedure.

 

[OverTheTop]

Check out this for comparison.
https://forum.ausrocketry.com/viewtopic.php?f=6&t=4758
If I did this again I would just use West Systems 105/206 next time instead of JB.

 

[David Schwantz]

Just finished a MC Tomach. I slotted the tube to mount the fins. I slid in 54mm motor and used that as the spacing tool inside. Alittle touch with sandpaper is all it took to get the motors to slide in and out freely. I also did not want to ruin the look of the CF, so I did not do tip to tip. Yours looks great. Good luck.

 

[kzimmerman]

Why don't you tip to tip with carbon cloth? It's not that expensive for the little bit you'll need, and it comes in all kinds of weights.

 

[JohnCoker]

It's unlikely you'd need tip-to-tip reinforcement as long as you bonded properly. Of course, overbuilding is our thing so I wouldn't want to discourage you from trying something new.

 

[rocketman4h]

I did lay up 6" wide carbon cloth, I believe it's the 3k variety, but way thick and not a smooth layup. For the resin I am using Fiberglast system 2000 epoxy laminating resin. I do have some nice 2oz fiberglass coming in for another build ( bashed Mean Machine). I think that glass will look good and give that extra bond to the body tube.

 

[ksaves2]

Depends upon how large of a motor one intends to use. If one is going to stuff the biggest one that can fit (eventually) sometimes T to T is good insurance against fin flutter. On larger projects, layer the glass cloth or other medium in the manner of 1/3, 2/3rds and full span up the root of the fin is helpful as is rotating the cloth on the 2nd 2/3rds layup so the weave is at 45 degrees.
This is not necessary with your 38mm project. I'm with Mr. Coker. If you used a good product to surface mount the fins first, you are likely in good shape as long as you scuffed both surfaces before initial bonding. ie. Used a good epoxy for initially mounting the fin to the tube and not "tack" mounting it with CA and then building the fillets on the fins. That technique is fine with modrocs but not with more substantial higher power.
As built, you could fly your rocket on lower impulse motors. Test out your tracking system to make sure it works nominally for recovery and mull over in your mind whether you want to do tip to tip. Would only take 3 pieces of cloth to do.
You could do it just to start to get experience with the process.
I will tell you that the 1/3, 2/3rds and full span layup technique is
"BORING"!!!! Twelve pieces of cloth to do a 4 finned rocket. Have to put down one layer and wait for it to cure over night. With 12 pieces to lay, it takes quite a bit of time to get the process done and try to mix up just enough epoxy to lay down one sheet without too much waste is a learning experience in and of itself.
As I mentioned, that is overkill with your 38mm rocket.
Whether you glass or not, best of luck with flying the rocket.
Kurt Savegnago

 

[David Schwantz]

You might also think of flying as is and can always sand off clear and do tip to tip later if you feel it needs it.

 

[G_T]

If you are using carbon fabric with an open weave, start with the fabric on another surface and hard roll with a wallpaper seam roller to close up the weave.

You don't need tip to top, regardless! The extra fabric at the tips just adds weight and thickness to no benefit, and can in some cases reduce the flutter speed by putting mass where you don't want it. Having fabric over the fillet though is not a bad idea at all, and should extend at least far enough on the fin to adhere well to it.

Fins are often too thick at the tip, and could stand to be thicker at the root. But if made from fiberglass or carbon fiber sheet, it is expensive to properly contour them. So they end up more flexible than ideal at the root and way stiffer than needed at the tips. For low mach numbers it is unlikely to matter.

Gerald

 

[ksaves2]

If you are using carbon fabric with an open weave, start with the fabric on another surface and hard roll with a wallpaper seam roller to close up the weave.

You don't need tip to top, regardless! The extra fabric at the tips just adds weight and thickness to no benefit, and can in some cases reduce the flutter speed by putting mass where you don't want it. Having fabric over the fillet though is not a bad idea at all, and should extend at least far enough on the fin to adhere well to it.

Fins are often too thick at the tip, and could stand to be thicker at the root. But if made from fiberglass or carbon fiber sheet, it is expensive to properly contour them. So they end up more flexible than ideal at the root and way stiffer than needed at the tips. For low mach numbers it is unlikely to matter.

Gerald

Agreed,

That is where the 1/3, 2/3rds full span laminating comes in. Just like you say, more mass at the fin base and thinner at the tips. For a 38mm rocket not needed at all. I think care must be exercised more with larger rockets that are going to fly with big motors at high speed. Flutter can happen as I'm sure a lot of us have witnessed a small high speed rocket's fincan disintegrate under the thrust of a K.

Funniest shred I saw was a triangular postal tube rocket made entirely out of a triangular cardboard shipping tube. Had three cardboard fins and a triangular cardboard nosecone. It was glassed with cloth. Flier got 13 nominal flights out of that odd roc on lower impulse motors then decided to fly a K motor one day.

Launched the thing on the K and the rocket didn't shred. It "confettied" on the boost! Nothing but small pieces of "confetti" cardboard coming down that couldn't hurt a flea if the pieces landed on them. Nothing was seen for awhile and we were giving our condolences to the flier in between our laughing. Lo' and behold, much, much later a chute is seen coming down with a bare body tube and the triangular centering rings (that stayed on the tube)! It was such a long time before the remains were seen under the full main the flier had a long face develop and looked dejected. Flier got his chute back and more importantly the costly motor casing. He was happy then. The centering rings stayed attached and probably stabilized the flight. It took a long time before the fully deployed chute was seen and the rocket remains likely had a nominal boost to a high apogee after the skin was shed! Wished someone had videoed it but there wasn't anyone there with a camera. Best shred I've ever seen. Cheap rocket (to build) and flier got the expensive bits back to reuse.

Kurt Savegnago

 

[JBoyson]

That's an absolutely beautiful rocket there my friend.
For doing a tip to tip I've always found it will add thickness around where you do the layup. Though not a lot with 2oz glass. If you plan to paint it then with enough lite sanding you will never see the tip to tip layup in my experience.

 

[watheyak]

The problems created by tip to tip increases as velocity increases. As in getting it to stay stuck becomes more difficult as velocity increases.

 

[cbrarick]

What the heck, tip to tip everything! It's almost never needed in our world (unless you go to the center of the universe, BALLS where people fly really crazy fast stuff really high).
Rocket people love overbuilding. I've had standard loc rockets above mach without any problems. I sorta have a addiction to VMAX and Warp 9..........

seriously, if it makes you feel better, go for it!

 

[Glasspack]

"What the heck, tip to tip everything! It's almost never needed in our world (unless you go to the center of the universe, BALLS where people fly really crazy fast stuff really high).
Rocket people love overbuilding. I've had standard loc rockets above mach without any problems. I sorta have a addiction to VMAX and Warp 9..........

........................................................."


Cbraick,

Was that LOC Cardboard Tube rockets or Glass Tubes .... above MACH ??
I am pretty sure my LVL2 Model has a chance to fly Mach 1 with the right 54mm motor. Its LOC heavy Paper wound Tube ...and Binder Design Cobra parts

Paul

 

[GrouchoDuke]

Like @JohnCoker said, as long as you bonded them properly, there's no need for T2T. You followed this...right? https://www.rocketryforum.com/threa...our-government-doesnt-want-you-to-know.58389/

 

[plugger]

Given your fin trailing edges are swept forward and it's a 38mm MD there's no need for t2t. TBH even at higher speeds (approaching Mach 3) t2t is unneccessary as long as you have good fillets and straight fins.

 

[rfjustin]

No need for it, but good practice!

 

[plugger]

The problems created by tip to tip increases as velocity increases. As in getting it to stay stuck becomes more difficult as velocity increases.

View attachment 471827

Out of curiosity, what epoxy system did you use for this t2t work?

 

[watheyak]

Out of curiosity, what epoxy system did you use for this t2t work?

Those rockets were Aeropoxy. Even post cured per their specs.The result was awesome and embarrassing all rolled into one. Back when I made these I had posted about them a bit and even had the disclaimer that the T2T was purely cosmetic. And somewhere deep down I kinda wanted some serious Mach rash. Mine hangs on the wall in my rocket shop

A few folks in this thread have pointed out that tip to tip is a good educational practice. That’s definitely what these rockets were. Not my first tip to tip, but first at above M2.7. I learned a lot and subsequent versions were successful at even higher speeds.

 

[Theory]

A few folks in this thread have pointed out that tip to tip is a good educational practice. That’s definitely what these rockets were.

definitely all about practice and new techniques. thats 62.3%* of what this hobby is about.

*percentage is purely theoretical and may change without notice ; - )

 

[plugger]

Those rockets were Aeropoxy. Even post cured per their specs.The result was awesome and embarrassing all rolled into one. Back when I made these I had posted about them a bit and even had the disclaimer that the T2T was purely cosmetic. And somewhere deep down I kinda wanted some serious Mach rash. Mine hangs on the wall in my rocket shop

That's really interesting. Looking at that photo without context I would have said the epoxy system wasn't sutable for the purpose as you t2t layup came undone and yet your underlying FG fins didn't appear to have any heating effects. On the other hand I thought Aeropoxy would have been able to handle that level of performance.

 

[watheyak]

That's really interesting. Looking at that photo without context I would have said the epoxy system wasn't sutable for the purpose as you t2t layup came undone and yet your underlying FG fins didn't appear to have any heating effects. On the other hand I thought Aeropoxy would have been able to handle that level of performance.

I noticed the same thing about the G10 cores, which led me to a couple realizations.

Hobby epoxy such as Aeropoxy, West Systems and similar aren’t appropriate for speeds above ~M2.6. High temperature materials and epoxy are required.

I also realized that tip to tip to tip, it it’s usual implementation is prone to failure at the leading edge. This is nothing new, but people keep doing it, including me.

G10, is tough stuff. While lacking the “cool factor” that tip to tip has, simple G10 fins (without any tip to tip) and a toughened, high temp epoxy (even JB Weld) is more appropriate for flights above M2.7.

Then there is the insanity of recessing the tip to tip into your G12 fin cores. Only weirdos do that.

 

[plugger]

I noticed the same thing about the G10 cores, which led me to a couple realizations.

Hobby epoxy such as Aeropoxy, West Systems and similar aren’t appropriate for speeds above ~M2.6. High temperature materials and epoxy are required.

Yea, I agree. West Systems is not suitable for Mach 2+ but I naively assumed Aeropoxy would have been better. That said last time I looked at Aeropoxy systems the options were a bit dizzying. I use Araldite K3600 and it's definitely superior to West.

I also realized that tip to tip to tip, it it’s usual implementation is prone to failure at the leading edge. This is nothing new, but people keep doing it, including me.

Agreed. Yet another reason why the classic t2t isn't really necessary and when it is it's potentially a liability/point of failure.

G10, is tough stuff. While lacking the “cool factor” that tip to tip has, simple G10 fins (without any tip to tip) and a toughened, high temp epoxy (even JB Weld) is more appropriate for flights above M2.7.

I think that depends. I've been in this area for 2 flights, one successful, one not. My fins were vac infused quasi-isotropic cf made by Mike Passaretti. I can't recall what system he uses (other than it's not West or Aeropoxy) and they survived to M2.67 and ~M3 with no t2t, leading edge treatment, etc; just fillets. In the M3 flight the airframe buckled between the front of the motor casing and the base of the fwfg coupler holding the NC on and yet the lower 2/3rds (~) or the rocket just kept going despite losing the NC. Those fins held in so far that even though the rocket broke in two at the end of the boost the casing+airframe+fins just keep on trucking. That taught me two things.

1) t2t is unnecessary up to M3 if your fins and fillets are appropriately designed.
2) unreinforced hand wound airframes need internal stiffening if they're expected to hold up to M3 flights.

Then there is the insanity of recessing the tip to tip into your G12 fin cores. Only weirdos do that.

LOL

 

[OverTheTop]

Yea, I agree. West Systems is not suitable for Mach 2+

The correct answer is "it depends". It has been done. By me. Apache booster to M2.14. CF plate skins over G10 isgogrid core.

 

[plugger]

The correct answer is "it depends". It has been done. By me. Apache booster to M2.14. CF plate skins over G10 isgogrid core.

I'd consider that pushing it to the limits OTT!