Tip to Tip Is it worth the weight?

[Handeman]

I've used tip to tip fiberglass on a couple rockets and thought it helped the durability and longevity of the rocket.

I recently read a comment that tip to tip isn't worth it because those that use it don't understand the stress points involved.

Is there a consensus on tip to tip glassing? Does it really help make the fins stronger and more resistant to fin flutter and hard landings? Or is it just adding weight without adding any strength that you don't get with good fillets? Is it only worth it on MD rockets? Is it overkill on TTW mounted fins?

I did tip to tip on one of my rockets. I used three layers, the first small, second larger, and last over the full fin. I thought it added strength and a little air foil to the fin because I thought I remembered that fin flutter started at higher speeds on fins that didn't have a uniform cross section.
The black lines are the outlines of each layer. I use a sharpie to mark the glass cloth when I cut it out.

Of course none of this helped when I catoed an EX motor and blew the whole fin can off the rocket. I only found two fins with all the glass peeled off. There was still some of the tip to tip glass stuck to the BT parts I found.

 

[jderimig]

I like what you did with the layers. The root of the fin sees the highest stress. There is essentially no (bending) stress or flutter deflection at the tips. So adding weight out there is actually counterproductive and probably increases the propensity to flutter. The glass on the airframe between the fins adds nothing but weight.

Strengthening the fin near the root is a good idea. A fiberglass tape bridging the root and part of the airframe will do that nicely. The maximum strain also happens at your approach the root. If you want to dampen fin flutter a small trianglular layer of kelvar would work nicely there, then top with a veil of fg for a nice finish.

A constant stress fin (most efficient use of material) would have the fin thickness maximum at the root and go to zero towards the tip.

 

[Hobie1dog]

I'm not in favor of doing it for all the time it takes to do all of it, and then get all that glass weave smooth.

 

[sharkbait]

I like what you did with the layers. The root of the fin sees the highest stress. There is essentially no (bending) stress or flutter deflection at the tips. So adding weight out there is actually counterproductive and probably increases the propensity to flutter. The glass on the airframe between the fins adds nothing but weight.

Strengthening the fin near the root is a good idea. A fiberglass tape bridging the root and part of the airframe will do that nicely. The maximum strain also happens at your approach the root. If you want to dampen fin flutter a small trianglular layer of kelvar would work nicely there, then top with a veil of fg for a nice finish.

A constant stress fin (most efficient use of material) would have the fin thickness maximum at the root and go to zero towards the tip.

Not going to argue the results Aero fin or Fin Sim but A lot of this depends on your fin shapes and what type of flight profiles you want to achieve. If you are just sport flying for fun then T/T will help you preserve your rocket from travel rash, hard landings, and ripping it down from trees, no fancy calculations but go up on your roof and drop your wooden fin and cardboard rocket onto your driveway and then do the same with one that has T/T and compare the results

 

[Handeman]

Not going to argue the results Aero fin or Fin Sim but A lot of this depends on your fin shapes and what type of flight profiles you want to achieve. If you are just sport flying for fun then T/T will help you preserve your rocket from travel rash, hard landings, and ripping it down from trees, no fancy calculations but go up on your roof and drop your wooden fin and cardboard rocket onto your driveway and then do the same with one that has T/T and compare the results

That's why I said I thought one I did added to the strength and longevity. Mine was once cut off a ±60 ft powerline and bounced 5 ft when it landed with no damage. It was glassed LOC tubing and tip to tip 1/4" ply fins.

 

[rharshberger]

That's why I said I thought one I did added to the strength and longevity. Mine was once cut off a ±60 ft powerline and bounced 5 ft when it landed with no damage. It was glassed LOC tubing and tip to tip 1/4" ply fins.

I have heard from various sources over the years that the style T2T you did, makes a difference in fin flutter since it tapers the fin from root to tip along its weakest axis and it alters the oscillation frequency at various points along the fin which helps reduce flutter. I kind of understand what the sources are saying but not how effective it really is.

 

[jderimig]

I have heard from various sources over the years that the style T2T you did, makes a difference in fin flutter since it tapers the fin from root to tip along its weakest axis and it alters the oscillation frequency at various points along the fin which helps reduce flutter. I kind of understand what the sources are saying but not how effective it really is.

Think of a pendulum. In the case of fins you do not want to store energy towards the tips, store it near the root.

 

[rharshberger]

Think of a pendulum. In the case of fins you do not want to store energy towards the tips, store it near the root.

It probably also moves the fulcrum point out towards the middle of the fin instead of at the root reducing strain on the root edge as well as reducing the flutter frequency.

 

[tfish]

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!







Tony

 

[Neutronium95]

I'm not a big fan of tip to tip on non minimum diameter rockets. Mounting fins through the wall with good internal and external fillets is a very strong fin mounting method. If you need the fin to be stiffer or stronger, I think it's typically easier to laminate the fins with fiberglass before attaching them to the rocket. That will give the same strength fins as tip to tip, but you just need to lay up the composites on a flat plate instead of on a larger curved surface.

 

[WoShuGui]

I only use tip to tip if fin flutter is a concern. Not based on MD versus TTW other than MD tending towards higher velocity flights making flutter more likely to be a concern. There are TTW rockets that need tip to tip or laminated layers. A stock WM Goblin 5 with those floppy FG fins needs stiffer fins for most L motor flights. This Goblin 5 got three tip to tip layers small to large for the root stiffness reasons described. I did the flutter calculations after fin can was built, so laminated layers was not an option. If I had it to do over, I would go with laminated layers.

Not all MD needs tip to tip. This WM Mach 2 was fine with stock FG fins on an L935IM to M2.3 b/c the fins were designed for that kind of flight profile.

So for me, the need for tip to tip all depends on whether flutter comes into play.

 

[AlexBruccoleri]

I've used tip to tip fiberglass on a couple rockets and thought it helped the durability and longevity of the rocket.

I recently read a comment that tip to tip isn't worth it because those that use it don't understand the stress points involved.

Is there a consensus on tip to tip glassing? Does it really help make the fins stronger and more resistant to fin flutter and hard landings? Or is it just adding weight without adding any strength that you don't get with good fillets? Is it only worth it on MD rockets? Is it overkill on TTW mounted fins?

I did tip to tip on one of my rockets. I used three layers, the first small, second larger, and last over the full fin. I thought it added strength and a little air foil to the fin because I thought I remembered that fin flutter started at higher speeds on fins that didn't have a uniform cross section.
The black lines are the outlines of each layer. I use a sharpie to mark the glass cloth when I cut it out.
View attachment 552746
Of course none of this helped when I catoed an EX motor and blew the whole fin can off the rocket. I only found two fins with all the glass peeled off. There was still some of the tip to tip glass stuck to the BT parts I found.

I second what @jderimig said. The most efficient use of material is to go from zero thickness on the tip to max at the root. A good reference is below: https://www.engineeringtoolbox.com/cantilever-beams-d_1848.html

The way you layered it looks really good and pretty structurally efficient too. There might a little waste in the far tip and middle body tube, but as you and others have pointed out, if handling robustness is your goal, then this makes a lot of sense.

 

[DeeRoc29]

I second what @jderimig said. The most efficient use of material is to go from zero thickness on the tip to max at the root. A good reference is below: https://www.engineeringtoolbox.com/cantilever-beams-d_1848.html

The way you layered it looks really good and pretty structurally efficient too. There might a little waste in the far tip and middle body tube, but as you and others have pointed out, if handling robustness is your goal, then this makes a lot of sense.

Do you have a a pic of a rocket you built like that, Alex?

 

[AlexBruccoleri]

Do you have a a pic of a rocket you built like that, Alex?

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

 

[waltr]

That was me saying LaserLOC 223 and do the tip-to-tip glass that comes with the kit.
Then someone post "tip to tip is not needed.'

Been reading along to hear opinions and facts.

 

[Theory]

IMHO it’s not worth it unless you are really going to push the envelope on a minimum diameter build, and even then, a single layer would likely suffice so long as sound building practices are followed.

As others said, the material on the airframe is only adding weight and adds to finishing time.

 

[Hobie1dog]

15 replies to your question, have you made a decision on what you're going to do?

 

[JimJarvis50]

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

 

[AlexBruccoleri]

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

That is an interesting question. I suspect the motor casing would provide that support in a minimum diameter rocket and the centering rings in a through the wall.

 

[JimJarvis50]

That is an interesting question. I suspect the motor casing would provide that support in a minimum diameter rocket and the centering rings in a through the wall.

I have previously suggested adding a centering ring or two in the area of the fins for 98mm motors in 5" tubes or 75mm motors in 4" tubes, etc.

Jim

 

[user 30299]

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

Jim,

On the strength perspective, which forces (bending, tension, compression, torsional, etc.) do you feel, or know, to be
the main reason for the distortion of the body tube? I agree that its distortion can lead to assorted failures.

I have a 5.5" dia. rocket, cardboard, that I decided to sleeve its inside with long lengths of coupler tubing
vs. applying fiberglass to the whole body. I took this approach as a way to 1) increase the overall strength
of the body tube, 2) have a possible weight-saving method compared to glassing the whole thing, and
3) maybe see if it's an easier method than glassing the whole thing.

I used West System epoxy on the sleeves.

 

[rfjustin]

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

100% accurate as always.

I have a fiberglass sport two stager on the bench right now and the booster is 54mm minimum diameter with surface mounted fins with no tip to tip. If I grab the fins and flex them a bit, the fiberglass tube does in fact go out of round. Granted yes the 1706 motors will help hold the shape, but no doubt tip to tip would add rigidity to the fin can and lessen any flex. This particular build does not need to tip to tip on the booster or sustainer, but when necessary, its absolutely worth the weight.

Oh and if other readers in this thread have not done tip to tip yet, buy a LOC 4" Goblin for practice and have at it. The kit does not break the bank, and the experience is worth the cost of admission.

 

[AlexBruccoleri]

100% accurate as always.

I have a fiberglass sport two stager on the bench right now and the booster is 54mm minimum diameter with surface mounted fins with no tip to tip. If I grab the fins and flex them a bit, the fiberglass tube does in fact go out of round. Granted yes the 1706 motors will help hold the shape, but no doubt tip to tip would add rigidity to the fin can and lessen any flex. This particular build does not need to tip to tip on the booster or sustainer, but when necessary, its absolutely worth the weight.

Oh and if other readers in this thread have not done tip to tip yet, buy a LOC 4" Goblin for practice and have at it. The kit does not break the bank, and the experience is worth the cost of admission.

How well does the case help hold rigidity in your rocket? A quick hand test would be great if you are comfortable doing it.

 

[tjsnakez]

I’m a fan of doing carbon t2t when needed in performance applications (MD and near MD). It doesn’t add much weight and I like the extra insurance of tying everything together and reducing flex as Jim mentioned. Obviously it’s been proven to not be necessary with proper fin thickness and adhesion - but I still think there is a benefit.

If it’s a less extreme rocket and I want more durability for hard landings or beefing up a kit with thin fins, I’ll lean toward glassing the fins by themself’s before assembly.

 

[JimJarvis50]

Jim,

On the strength perspective, which forces (bending, tension, compression, torsional, etc.) do you feel, or know, to be
the main reason for the distortion of the body tube? I agree that its distortion can lead to assorted failures.

I have a 5.5" dia. rocket, cardboard, that I decided to sleeve its inside with long lengths of coupler tubing
vs. applying fiberglass to the whole body. I took this approach as a way to 1) increase the overall strength
of the body tube, 2) have a possible weight-saving method compared to glassing the whole thing, and
3) maybe see if it's an easier method than glassing the whole thing.

I used West System epoxy on the sleeves.

A coupler tube on the inside is another way to reinforce the tube. I also reinforce zipperless couplers so they stay round. I might put 3 bulkheads or centering rings in them so that they don't go out of round. I stopped having coupler tube failures when I started doing this.

Jim

 

[rfjustin]

How well does the case help hold rigidity in your rocket? A quick hand test would be great if you are comfortable doing it.

I'll grab some pics tonight and post later. The tube does still deflect a bit, even with a motor case in it. Granted the motor case is not shimmed with tape tight, hopefully the pics will show some of this tube flex.

I ended up splitting a coupler length wise and double wall coupling the inner stage. I didn't want any tube flex of the portion that goes up into the sustainer.

 

[rfjustin]

Two stage as it sits.... then no stress on the fin can...

 

[rfjustin]

Stress added, picture stinks but can you see how how its out of round a bit?

 

[rfjustin]

Motor installed, no stress...

 

[rfjustin]

Stress added with motor in...