Tip to Tip Is it worth the weight?

[AlexBruccoleri]

Thanks for sharing. Certainly with the motor out it is clear. I cannot tell with the motor in but definitely taking your word for it. Anyway clear evidence that stiffening the airframe between the fins has value for flight.

 

[SolarYellow]

I'm not sure I agree that material over the body tube is wasted. It's my belief that part of what keeps surface-mounted fins from failing is to keep the underlying tube round (i.e., don't allow the tube to go out of round when force is applied to the fins). I think material over the tube helps to accomplish this, and it turns the fins and associated tube into a single unit from a stength perspective.

Jim

Never thought of this before, but what about internally sleeving the fin can section of a cardboard tube with glass or c.f.? Like make an external mandrel to contain the geometry, then slide the sleeve in over an inflatable mandrel, and inflate it to expand the sleeve against the tube and external mandrel. Thinking TTW fins so the whole thing would be slotted, but you could add a ton of stiffness to the tube just in the fin can area without affecting the external aerodynamics/geometry.

 

[JimJarvis50]

Never thought of this before, but what about internally sleeving the fin can section of a cardboard tube with glass or c.f.? Like make an external mandrel to contain the geometry, then slide the sleeve in over an inflatable mandrel, and inflate it to expand the sleeve against the tube and external mandrel. Thinking TTW fins so the whole thing would be slotted, but you could add a ton of stiffness to the tube just in the fin can area without affecting the external aerodynamics/geometry.

There are several things you can do to increase the strength of the tube. I would say, though, that having slots in the tube for TTW fins is not one of those things. It's just my preference, but I would not slot a composite tube that is 5" or less in diameter. 6" is a tweener. Why take a strong tube and weaken it with slots? Cardboard or blue tube is a different matter, and I suppose that TTW for composite tubes would be OK if one wished to avoid larger external fillets and/or tip to tip for the purpose of appearance.

Jim

 

[charrington]

So I have a different point of view from what others have said here and I want to preface this by saying that I have by no means any scientifically conducted research based evidence to back up what i'm going to say. Its all going to be anecdotal evidence.

I am not a fan of T2T on very high performance rockets and think that the place where T2T really shines is moderate performing rockets that you want to be able to launch over and over again. If you want your rocket to be a tank that can slam against playa and concrete without batting an eye, by all means t2t.

The issue I have with t2t composited on high performance rockets (altitude records) is: Most of these are only launched one time and the t2t layup needs to be perfect. @watheyak 's L record has great photos of what shockwaves at mach 3.5 will do. Also, if your composite work is subpar you may see delamination at high speeds which will cause an increase in drag which may cause a structural failure on its own at high speeds.
If you can do composite layups perfectly or you want to work towards that then by all means become a composite master! t2t looks amazing and if you are really good at it then its a great way to turn your rocket into a tank.

This rocket from jurvetsons youtube channel went to about Mach 5, experienced a shred due to the nosecone collapsing in on itself. This rocket shredded at mach 5 and the fins survived. I want to say that this rocket did not have t2t and it was just a big fillet of a strong epoxy. I could definitely see the argument that they may have a short strip of carbon reinforcing the roots between fins but its kind of hard to see in this photo. Either way, its a far cry from going full t2t.

Heres the video and some photos:
*Note: they used a carbon fiber fin can ontop of the aluminum motor tube which may make it appear to be t2t but I do not think that it actually is. Looks like a large fillet of epoxy that has been sanded smooth to me.

Actually in this photo I think it is pretty clear that there isnt t2t since you can see the thick white epoxy fillets

Here is the recovered rocket with the fins still attached!

 

[Bill Owens]

This is a great conversation - Thanks for all of the expertise being contributed!

I am new to T2T and planning to do it on several minimum diameter projects. I'm interested in guidance for how to size the FG layers. I've been thinking about airframe, fin height/area, expected velocity....but are there metrics for the number of layers x weight of fabric?

In my case I'm thinking about fiberglass body tube and fins, 38 to 75 mm body tubes, maxV in the range of mach 2, and Tony's 1/4 - 1/2 - 3/4 approach. I suspect there's a real risk for the inexperienced to over-engineer it.

 

[airforcetp1991]

Built with perfect gradients? No. This started from a different thread where someone suggested tip to tip.

I attempted that theory of mass distribution with my 98mm MD. Unfortunately it shredded (NC I think) but the fins held through the Mach 3.5 shred and ground impact.

Discussion about stiffening the tube is interesting. I’ll have to look into that for the eventual rebuild. Would be simpler than T2T for sure.

 

[user 30299]

I do tip to tip..actually ...1/4 - 1/2 - 3/4 on all of my real min dia rockets. I did rocket poxy on one 98mm min dia and have slowly had to replace those filets with tip to tip..because off cracking.

I use .097 G10 and layer like Handeman shows in his original post. I've perposly have done some extreme flights with no issues. I've also had some ...non normal flights that have ended well because of the tip to tip..

The below is a 3" min dia rocket with 42" of propellant ...It lost one side of the nozzles exit cone . 750 feet 1200mph and it stayed together. I think the tip to tip and the 1.1 calibers fin simi span all helped..

It can't hurt!



View attachment 552788

View attachment 552789

Tony

Tony,
Do you think the rocket poxy fillets started cracking because of the forces exerted on the fins?
A flexing (flexible) fin working against a solid (inflexible) fillet?

If the fin had a higher "stiffness" to it would the fillets have held up better?

 

[tfish]

Tony,
Do you think the rocket poxy fillets started cracking because of the forces exerted on the fins?
A flexing (flexible) fin working against a solid (inflexible) fillet?

If the fin had a higher "stiffness" to it would the fillets have held up better?

I'm not really sure. I would guess it might be a combination of factors.

Tony

 

[charrington]

I'm not really sure. I would guess it might be a combination of factors.

Tony

Most definitely a combination of factors. I have always wanted to scientifically test fin bonding. Isolating variables to see where most fin failure is caused and repeating the test until there is a statistical relationship. I feel that a lot of knowledge in the amateur sector has not been tested in this manner. Maybe a good summer project for myself or someone else...

 

[jFlds]

I stopped doing any tip to tip a decade ago. Used to do it on all paper or phenolic airframes for strength and durability to maximize flight counts more so than to stop any fin flutter. As I have aged and do mainly fiberglass or canvas frames now they hold up just fine without it, not that I am Mach busting or doing minimum diameter flights. I still build some paper tube LOC kits but don't glass them anymore and use very little epoxy in their assemblies, paper airframes.

 

[JimJarvis50]

One thing to keep in mind here is that tip-to-tip doesn't really need to add much weight. When I do this, I have a final fin thickness in mind, and the tip-to-tip is part of that thickness. So, the tip-to-tip adds a lot of strength but not really much weight.

Regarding the comment that tip-to-tip is somehow not suitable for record flights, I've had 5 Tripoli records (still have 2), all done with rockets having tip-to-tip applications.

Jim

 

[wsume99]

One thing to keep in mind here is that tip-to-tip doesn't really need to add much weight. When I do this, I have a final fin thickness in mind, and the tip-to-tip is part of that thickness. So, the tip-to-tip adds a lot of strength but not really much weight.

Regarding the comment that tip-to-tip is somehow not suitable for record flights, I've had 5 Tripoli records (still have 2), all done with rockets having tip-to-tip applications.

Jim

...mic drop

 

[AlexBruccoleri]

One thing to keep in mind here is that tip-to-tip doesn't really need to add much weight. When I do this, I have a final fin thickness in mind, and the tip-to-tip is part of that thickness. So, the tip-to-tip adds a lot of strength but not really much weight.

Regarding the comment that tip-to-tip is somehow not suitable for record flights, I've had 5 Tripoli records (still have 2), all done with rockets having tip-to-tip applications.

Jim

I am not sure why some one said that either. You can definitely do tip-to-tip and it’s not that sub optimal. You will do a little better tapering off to the edge of the fin where the bending forces diminish. The OP looks pretty close and getting it perfect would be very hard, and the exact forces are not easy to calculate either.

 

[SolarYellow]

Something that's been bugging me for awhile. Why does fiber composite fin/fillet/can reinforcement (seemingly, in the hive mind of this forum) have to be either not at all or tip to tip? Why not just laminate an "L bracket" on each side of the fin along the root, and then fillet that? Or maybe laminate the corner, lay down a fillet, then laminate over the fillet, possibly extending a little farther. Or a small fillet to keep the first lamination from being too sharp a bend, a first lamination, a bigger fillet, and then another lamination. Concentrate the material where the leverage of the bending moment is greatest, rather than all the way out to the tip where it doesn't really do much.

Is it just because of the difficulty of getting the edge of the lamination smooth? Reluctance to have stepwise reduction in thickness? (Not sure the latter really matters for performance.)

 

[robopup]

Something that's been bugging me for awhile. Why does fiber composite fin/fillet/can reinforcement (seemingly, in the hive mind of this forum) have to be either not at all or tip to tip? Why not just laminate an "L bracket" on each side of the fin along the root, and then fillet that? Or maybe laminate the corner, lay down a fillet, then laminate over the fillet, possibly extending a little farther. Or a small fillet to keep the first lamination from being too sharp a bend, a first lamination, a bigger fillet, and then another lamination. Concentrate the material where the leverage of the bending moment is greatest, rather than all the way out to the tip where it doesn't really do much.

Is it just because of the difficulty of getting the edge of the lamination smooth? Reluctance to have stepwise reduction in thickness? (Not sure the latter really matters for performance.)

I've done partial shapes/"L's" on several rockets which have survived just fine - if you poke around there are actually many projects which do partial coverage on both the tubing and fins.

Having said that, I'm still not convinced it's actually doing much structurally, is still liable (although less so) to all the typical problems with poor quality tip to tip lay ups and is still kind of a pain to do. Accordingly, I don't do either a full or partial tip to tip.