G10/12 at Mach 2?

[Walldiver7]

At what speed should I switch over to carbon fiber fins? I have a design that will be above Mach 2 for as much as 8 seconds. I have no experience above Mach 2, so comments from the experienced would be very helpful. Thanks.

 

[djs]

I can't answer your question, but I'm curious as to the rocket/motor combo that will hit Mach 2 for 8 seconds.

 

[blackjack2564]

It depends on what diameter airframe, and fin shape & thickness.

Flutter is the enemy, and stiff fins are your friend.

Also if T-T you can use 1/16 or 3/32 and cover with 2-3 layers of carbon.

Why don't you give some details.........

 

[blackjack2564]

I can't answer your question, but I'm curious as to the rocket/motor combo that will hit Mach 2 for 8 seconds.

3in. minimum diameter rocket with 6xl CTI Green M ............ M-2.1 for 10 sec.



NC was orange.

 

[ksaves2]

Yeah, similar to something Robert DeHate posted some years ago. Said rocket was at >Mach 2 for 28 seconds. Paint was gone and the laminated cloth was burned away on the fin
leading edges. Nothing like trying to take carbon fiber back to elemental carbon! :lol: Kurt

 

[blackjack2564]

To prevent that [delaminating] I used carbon plate 3/16, probably overkill...1/8 would have been fine for that flight.
However I do plan on using this for an upper stage 4in to 3in. where the 3/16 will be needed.

Fins were just surface mounted and fillets added. No tip-tip. Hysol epoxy used for attachment & fillets.

Dragon plate if I remember. Yes I used about 100.00 in plate for 4 fins, but the amount of time,labor and prepping it saves it worth it. No way I could have come close to replicating it.

 

[tfish]

At what speed should I switch over to carbon fiber fins? I have a design that will be above Mach 2 for as much as 8 seconds. I have no experience above Mach 2, so comments from the experienced would be very helpful. Thanks.

Switching from G10 to Carbon is more of a fin shape (flutter issue) or wanting thinner fins, then a speed issue in my opinion. The fastest I've been is mach 2.7 On that flight it looked like I started having fin delaminating issues. This was in the actual G10 material. I've been over mach 2 lots of times with no issues. At most bubbled paint and melted rail guides. I do simple tip to tip with "boat' epoxies System Three T-88 or Raka. I feel you don't need to over thinking thins until your above mach 2.5 +.

Tony

 

[Walldiver7]

Thanks everybody for responding. The PLAN is a 3" MD (I will try attach the OR file), 3 fins w near 14" roots, and the overall length coming in just under 98". OR estimates the top speed, on a CTI M2245 at M 2.67. The fins will be cut from 3/16" G10/12. BlackJack2564 Jim, is the Hysol epoxy any better than AeroPoxy? I am unfamiliar with Hysol. The fins will be surface mounted,... but I was thinking of cutting short lengths of intermittent slots for the fins to "keyhole" into. ... with the hope that this would improve strength for that joint. I have no plans at the moment to glass tip to tip.

 

[Walldiver7]

Switching from G10 to Carbon is more of a fin shape (flutter issue) or wanting thinner fins, then a speed issue in my opinion. The fastest I've been is mach 2.7 On that flight it looked like I started having fin delaminating issues. This was in the actual G10 material. I've been over mach 2 lots of times with no issues. At most bubbled paint and melted rail guides. I do simple tip to tip with "boat' epoxies System Three T-88 or Raka. I feel you don't need to over thinking thins until your above mach 2.5 +.

Tony

Was the delaminating problem due to stress or heat?

 

[Walldiver7]

To prevent that [delaminating] I used carbon plate 3/16, probably overkill...1/8 would have been fine for that flight.
However I do plan on using this for an upper stage 4in to 3in. where the 3/16 will be needed.

Fins were just surface mounted and fillets added. No tip-tip. Hysol epoxy used for attachment & fillets.

Dragon plate if I remember. Yes I used about 100.00 in plate for 4 fins, but the amount of time,labor and prepping it saves it worth it. No way I could have come close to replicating it.

Jim, are you beveling the CF fins or is someone doing this for you? If so, who is it?

 

[TRFfan]

Thanks everybody for responding. The PLAN is a 3" MD (I will try attach the OR file), 3 fins w near 14" roots, and the overall length coming in just under 98". OR estimates the top speed, on a CTI M2245 at M 2.67. The fins will be cut from 3/16" G10/12. BlackJack2564 Jim, is the Hysol epoxy any better than AeroPoxy? I am unfamiliar with Hysol. The fins will be surface mounted,... but I was thinking of cutting short lengths of intermittent slots for the fins to "keyhole" into. ... with the hope that this would improve strength for that joint. I have no plans at the moment to glass tip to tip.

I think i heard somewhere that cutting slots in MD rockets for fins to go into will weaken the body tube alot.

 

[ksaves2]

Was the delaminating problem due to stress or heat?

Most likely it's the heat that softens the laminating epoxy and the leading edge ablates off. The paint is first to go though. Kurt

 

[Walldiver7]

I think i heard somewhere that cutting slots in MD rockets for fins to go into will weaken the body tube alot.

I was thinking of 1.5" unsloted areas between 2" slots. Maybe that would be the best of both worlds?

 

[TRFfan]

I was thinking of 1.5" unsloted areas between 2" slots. Maybe that would be the best of both worlds?

Even cutting a little slot will weaken it structurally. 1.5" unsloted areas between 2" slots is going to hurt the body tube alot structurally. You would be better off with using a strong epoxy and large fillets.

 

[Incongruent]

So how will the tube fail and is there anything that will fail before the it?

 

[blackjack2564]

" G10/12. BlackJack2564 Jim, is the Hysol epoxy any better than AeroPoxy? I am unfamiliar with Hysol. The fins will be surface mounted,... but I was thinking of cutting short lengths of intermittent slots for the fins to "keyhole" into. ... with the hope that this would improve strength for that joint. I have no plans at the moment to glass tip to tip.

Jim, are you beveling the CF fins or is someone doing this for you? If so, who is it?

Charlie at Carolina Composites made the tube from Carbon Uni-Prepreg.
Fins ...he cut & beveled for me.
For an extra 20 some bucks, he will make you 2 fin guides for your build. They come set up for either 3 fins or 4 fins on same guide. Just tell him how thick your fins are....or better yet, let him cut /bevel them for you.

He has a special beveling jig that can cut bevels at various degree...first ones were sharp as razor..lliterally! Just touching or brushing up on them would slice ya quick. I dulled them with some 120 & from then on requested something a bit more mundane on future fins....LOL
Yes the bevels are a great profile.







I just did all the assembly . He also made me a "double" thick wall coupler/NC shoulder, with a 3in vent band to house all my electronics. The metal tip was replaced with a turned phenolic one that CC made. It served 2 purposes.... Transparency for GPS antenna in NC which went inside the tip...Hole drilled through core & heat insulation. Coupler was done in plain fiberglass for signal transparency. There was a TeleMega & Missleworks GPS units inside, as well as plain GPS in NC tip, for a total of 3 GPS and 3 Altimeters in NC [RRC3...Telemega.....Stratologger]







Hysol was recommended by Jeroen, CTI used it to hold fins on the Mach-5 flight of a Hybrid they flew years ago. Their's were aluminum. Hysol was all that held them on, even with the fins suspended between 2 wedges with 500 lbs pressure exerted on them.

Just filleted with it, nothing more. Tack one fin on with super glue, just a drop or 2. This fin holds the guide firmly in place. Then butter bottom of other 3 fins with Hysol to tack them on. when cured remove guide......break fin off off airframe, clean up the joint.
Replace fin guide & tack/fillet the rest of fins...



This rocket is just long enough for motor... Dual deploy is all in cone. Rocket is 62 in. long

..........................................................................................................................................

They usually fail at the coupler/airframe joint... motor supports frame, the small gap between motor and coupler is weak spot...then the couple itself.......why my coupler is double wall.

No need to dado the slot when using good fin guides. Just tack/CA one fin first, so the guide cannot move during fin installation, like I mention above.

PS 3M makes a comparable epoxy also.

 

[tfish]

Was the delaminating problem due to stress or heat?

My issue was do to heat. Stress issues will happen before or at motor burn out. Usually the rocket make a hard turn and fins will rain down from above. I've never seen stress damaged fins. Normally it's complete failure.

I saw above that some people feel slotting for fins on a min dia rocket weakens the body tube. I don't feel it does. I'm currently building a 2.6 min dia rocket and plan on slotting the body tube for the fins and will be going with just rocket poxy fillets for fin attachment. I plan on flying it on some 75% L motors.

Tony

 

[Incongruent]

CJ, your anecdote (is that the right term?) on the fin bevels reminds me of something I read about the Lockheed F-104 Starfighter. The leading edges of the fins were so sharp (1/2mm or so IIRC) technicians had to put guards on them to avoid injuring themselves.

 

[Walldiver7]

My issue was do to heat. Stress issues will happen before or at motor burn out. Usually the rocket make a hard turn and fins will rain down from above. I've never seen stress damaged fins. Normally it's complete failure.

I saw above that some people feel slotting for fins on a min dia rocket weakens the body tube. I don't feel it does. I'm currently building a 2.6 min dia rocket and plan on slotting the body tube for the fins and will be going with just rocket poxy fillets for fin attachment. I plan on flying it on some 75% L motors.

Tony

For a while now, I've heard both sides of the argument (regarding airframe integrity) when it comes to slotting them. My idea was to cover both sides with the idea I mentioned above. It complicates the build, but...

 

[Walldiver7]

Charlie at Carolina Composites made the tube from Carbon Uni-Prepreg.
Fins ...he cut & beveled for me.
For an extra 20 some bucks, he will make you 2 fin guides for your build. They come set up for either 3 fins or 4 fins on same guide. Just tell him how thick your fins are....or better yet, let him cut /bevel them for you.

He has a special beveling jig that can cut bevels at various degree...first ones were sharp as razor..lliterally! Just touching or brushing up on them would slice ya quick. I dulled them with some 120 & from then on requested something a bit more mundane on future fins....LOL
Yes the bevels are a great profile.


View attachment 318538 View attachment 318539


View attachment 318540

I just did all the assembly . He also made me a "double" thick wall coupler/NC shoulder, with a 3in vent band to house all my electronics. The metal tip was replaced with a turned phenolic one that CC made. It served 2 purposes.... Transparency for GPS antenna in NC which went inside the tip...Hole drilled through core & heat insulation. Coupler was done in plain fiberglass for signal transparency. There was a TeleMega & Missleworks GPS units inside, as well as plain GPS in NC tip, for a total of 3 GPS and 3 Altimeters in NC [RRC3...Telemega.....Stratologger]

View attachment 318562 View attachment 318563

View attachment 318564



Hysol was recommended by Jeroen, CTI used it to hold fins on the Mach-5 flight of a Hybrid they flew years ago. Their's were aluminum. Hysol was all that held them on, even with the fins suspended between 2 wedges with 500 lbs pressure exerted on them.

Just filleted with it, nothing more. Tack one fin on with super glue, just a drop or 2. This fin holds the guide firmly in place. Then butter bottom of other 3 fins with Hysol to tack them on. when cured remove guide......break fin off off airframe, clean up the joint.
Replace fin guide & tack/fillet the rest of fins...

View attachment 318541 View attachment 318542

This rocket is just long enough for motor... Dual deploy is all in cone. Rocket is 62 in. long

..........................................................................................................................................

They usually fail at the coupler/airframe joint... motor supports frame, the small gap between motor and coupler is weak spot...then the couple itself.......why my coupler is double wall.

No need to dado the slot when using good fin guides. Just tack/CA one fin first, so the guide cannot move during fin installation, like I mention above.

PS 3M makes a comparable epoxy also.

Jim, Thanks for ALL this great information! I had no idea that the coupler would experience the amount of stress that would necessitate the use of a double walled coupler. Also, thanks for the heads-up on Carolina Composites... now that I (we) don't have Rocketry Warehouse to call up for custom work, I was looking for someone to do that type of work. I would really like to shy away from the use of a CF nosecone so that I don't have to go to the trouble you did for RF considerations. Will a standard FW NC survive?

 

[blackjack2564]

Will a standard FW NC survive?

Yes....look at the NC picture above. It's standard fiberglass NC from Ken Allen [Performance Hobbies}...just replaced the metal tip with custom phenolic. Then coated whole thing with epoxy. Sanded smooth on lath.

NC shoulder/coupler 2x's wall...... standard glass.

Just the Vent band carbon on cone.
All of fincan/airframe carbon.

Contact Charlie through his website, leave phone # and brief description of what interested in...he will call back to discuss.

 

[Walldiver7]

Yes....look at the NC picture above. It's standard fiberglass NC from Ken Allen [Performance Hobbies}...just replaced the metal tip with custom phenolic. Then coated whole thing with epoxy. Sanded smooth on lath.

NC shoulder/coupler 2x's wall...... standard glass.

Just the Vent band carbon on cone.
All of fincan/airframe carbon.

Contact Charlie through his website, leave phone # and brief description of what interested in...he will call back to discuss.

Sorry, Jim, I was multi-tasking while reading your post.... I see now the NC question was already answered.

Ok, now that you've flown this, do you feel that the coating of epoxy on the NC was necessary? What epoxy did you coat it with and what did you use to thin it with? Would a G10/12 airframe be sufficient? I haven't flown a rocket in (what Wildman refers to as) a HED configuration; The advantages are pretty significant. Was your drogue in the NC?.... I wouldn't think you'd have room in there for a main.. especially with the antennas protruding into this area. I have questions/comments about your Avionics package, but I'll save you the wear and tear 'till I get there. I guess I do need to ask this: What was the length of your coupler?

 

[BDB]

View attachment 318562 View attachment 318563
View attachment 318564

This looks like an amazing flight with a lot of planning and engineering. But did you restrain the batteries with tape only? How about the ejection charges? They look like glove tips that are just dangling from the bulkhead. Am I seeing that correctly? I would have never thought that was possible for a flight this extreme.

 

[Walldiver7]

This looks like an amazing flight with a lot of planning and engineering. But did you restrain the batteries with tape only? How about the ejection charges? They look like glove tips that are just dangling from the bulkhead. Am I seeing that correctly? I would have never thought that was possible for a flight this extreme.

I've been flying with my lipos secured this way for some time now. I had a rocket hit the ground at above 90fps (main hung up inside) and nothing in my Av-bay broke loose... including my taped-on lipos.

 

[blackjack2564]

1. do you feel that the coating of epoxy on the NC was necessary?
2. What epoxy did you coat it with and what did you use to thin it with?
3. Would a G10/12 airframe be sufficient?

4. Was your drogue in the NC?....
5. I wouldn't think you'd have room in there for a main.. especially with the antennas protruding into this area.

6. I guess I do need to ask this: What was the length of your coupler?

1. Necessary ...No. Beneficial......yes. I wanted a perfectly smooth transition from the phenolic tip to the fiberglass cone. Epoxy acting like filler & also smoothing imperfections in the cone. See glare line in pic, perfectly straight, no waves..showing a match in parts with no seam line.



2. West 105/105 No thinning. Applied with folded rag, so it can be "wiped" on thin & lays out smooth. Spun on lathe/sanded with 320-400-600 .

3. You must figure stresses involved with YOUR flights to answer that. Aggressive motors flying in lower atmosphere create a lot of heat . [N-5800]

4. No there is just enough room between top of motor and bottom of coupler/av-bay for shock cord [25ft of 1/4. Kevlar and 18 in. drogue [Spherachute]

5.Main was Fruitychute toroidal 36.in folded in kevlar burrito....15ft 1/4in kevlar cord. Cord in front of cone. Burrito fit easily between antenna's The front BP is recessed in coupler 4inches to replace the lost room in NC tip where the 3rd GPS lived.

You can see GPS av-bay in Nc front..... by black internal fillet line for CR.
1in. ledge glued inside coupler, for front BP to rest on.

Vent holes in carbon band are barely above BP..[1/4 in] these double as arming holes for switches mounted on BP...look at pics of sled [in previous posts above]and you can see the white square boxes on BP. Those are screw switches.
So internally the coupler is half for electronics & half is open for recovery gear. Cone is shear pinned to it. WITH VENT HOLES IN THE NC.....due to nc being used as a payload area.







This flight was to test electronics for a future flight with a P-N 2 stage I'm working on with Charlie Ogino.
Many more details on this bay here:

https://www.rocketryforum.com/showthread.php?132380-Sparrow-HV-Arcus-P-N-project

6. Without measuring....10.5 inches. Front end was tapered to fit deeper into cone. Front BP was recessed inside coupler to front edge of vent band to allow mounting combat robotic screw switch to BP. Actual inside space for av-bay was 6.5

This looks like an amazing flight with a lot of planning and engineering. But did you restrain the batteries with tape only? How about the ejection charges? They look like glove tips that are just dangling from the bulkhead. Am I seeing that correctly? I would have never thought that was possible for a flight this extreme.

Yes, tape only.
Yes on glove tips.
Drogue side has small long charge ''barrels" that have proven best for complete burning of BP at higher altitudes. Powder poured in, Match is on TOP of bp.....Not below.

Main charges will fire at 700 feet.Well below range considered high altitude.
So glove tips are fine and save space inside cone.

 

[Walldiver7]

1. Necessary ...No. Beneficial......yes. I wanted a perfectly smooth transition from the phenolic tip to the fiberglass cone. Epoxy acting like filler & also smoothing imperfections in the cone. See glare line in pic, perfectly straight, no waves..showing a match in parts with no seam line.

View attachment 318571

2. West 105/105 No thinning. Applied with folded rag, so it can be "wiped" on thin & lays out smooth. Spun on lathe/sanded with 320-400-600 .

3. You must figure stresses involved with YOUR flights to answer that. Aggressive motors flying in lower atmosphere create a lot of heat . [N-5800]

4. No there is just enough room between top of motor and bottom of coupler/av-bay for shock cord [25ft of 1/4. Kevlar and 18 in. drogue [Spherachute]

5.Main was Fruitychute toroidal 36.in folded in kevlar burrito....15ft 1/4in kevlar cord. Cord in front of cone. Burrito fit easily between antenna's The front BP is recessed in coupler 4inches to replace the lost room in NC tip where the 3rd GPS lived.

You can see GPS av-bay in Nc front..... by black internal fillet line for CR.
1in. ledge glued inside coupler, for front BP to rest on.

Vent holes in carbon band are barely above BP..[1/4 in] these double as arming holes for switches mounted on BP...look at pics of sled [in previous posts above]and you can see the white square boxes on BP. Those are screw switches.
So internally the coupler is half for electronics & half is open for recovery gear. Cone is shear pinned to it. WITH VENT HOLES IN THE NC.....due to nc being used as a payload area.

View attachment 318573 View attachment 318574


View attachment 318575


This flight was to test electronics for a future flight with a P-N 2 stage I'm working on. Many more details on this bay here:

https://www.rocketryforum.com/showthread.php?132380-Sparrow-HV-Arcus-P-N-project

6. Without measuring....10.5 inches. Front end was tapered to fit deeper into cone. Front BP was recessed inside coupler to front edge of vent band to allow mounting combat robotic screw switch to BP. Actual inside space for av-bay was 6.5





Yes, tape only.
Yes on glove tips.
Drogue side has small long charge ''barrels" that have proven best for complete burning of BP at higher altitudes. Powder poured in, Match is on TOP of bp.....Not below.

Main charges will fire at 700 feet.Well below range considered high altitude.
So glove tips are fine and save space inside cone.

Impressive.. your design and craftsmanship are excellent. And now I must quit talking (now that you have answered all the pertinent questions) and get to work. Jim, your experiences were/are very much appreciated, Thanks. I will be studying the post you provided the link to, shortly. Patrick

 

[boatgeek]

For a while now, I've heard both sides of the argument (regarding airframe integrity) when it comes to slotting them. My idea was to cover both sides with the idea I mentioned above. It complicates the build, but...

I do not have experience in high-performance flights, but I do a lot of engineering. I'm having real trouble seeing a failure scenario where the first thing that broke was a slotted body tube, especially if it's filled with epoxy from gluing in the fin. The body tube is really well supported there by the MMT even though the stresses are somewhat higher due to fins. I would worry a lot more about fin attachment, couplers, flutter, and stability/coning (not necessarily in that order) before the slotted body tube.

Of course, my two cents are severely devalued by lack of experience, so I'm open to correction.

 

[TRFfan]

So how will the tube fail and is there anything that will fail before the it?

Well if the tube is weak around the fin area, can't you see how the fins might tear off??

 

[Walldiver7]

I do not have experience in high-performance flights, but I do a lot of engineering. I'm having real trouble seeing a failure scenario where the first thing that broke was a slotted body tube, especially if it's filled with epoxy from gluing in the fin. The body tube is really well supported there by the MMT even though the stresses are somewhat higher due to fins. I would worry a lot more about fin attachment, couplers, flutter, and stability/coning (not necessarily in that order) before the slotted body tube.

Of course, my two cents are severely devalued by lack of experience, so I'm open to correction.

And, I too, don't have any experience with Mach2+ flights, but I tend to agree with your assessment regarding slotted airframes.... when it's the traditional airframe-MMT build (that includes internal fillets). The build I'm discussing here is an MD (minimal diameter) design where there will be no MMT. I've build many low/mid power MD rockets, but never a MD that will top out at M2.67 ... so, I thought I'd get on here (TRF) and get some differing viewpoints.

 

[boatgeek]

And, I too, don't have any experience with Mach2+ flights, but I tend to agree with your assessment regarding slotted airframes.... when it's the traditional airframe-MMT build (that includes internal fillets). The build I'm discussing here is an MD (minimal diameter) design where there will be no MMT. I've build many low/mid power MD rockets, but never a MD that will top out at M2.67 ... so, I thought I'd get on here (TRF) and get some differing viewpoints.

You're right--MMT was the wrong term. I was thinking of the motor casing and just put the wrong letters in. I'm all over asking for more info from people who have experience, too.