PS, sand tube also before tacking with CA.
Any reason you use CA glue to tack rather than the epoxy, is it just faster? With a 14”x0.2” fin root I don’t know if I would want to give up that epoxy surface area.
Tony
PS, sand tube also before tacking with CA.
I’ve not flown to Mach yet but am about to start a project that will go Mach 2+. My question is, with the loctite epoxy having a temperature range of 300 degrees, is that temperature that it can withstand or curing temperatures. I ask because I’ve read a lot about fin and nose cone temperatures far exceeding that temperature at Mach 2-3+ flights. I will add that I don’t think there’s anything wrong with pushing boundaries as long as you have an experienced mentor to guide you thru the process. I like it.That is an awesome thread, thank you! Have you used hysol loctite ea e-120hp epoxy in the past?
-Tony
I’ve not flown to Mach yet but am about to start a project that will go Mach 2+. My question is, with the loctite epoxy having a temperature range of 300 degrees, is that temperature that it can withstand or curing temperatures. I ask because I’ve read a lot about fin and nose cone temperatures far exceeding that temperature at Mach 2-3+ flights. I will add that I don’t think there’s anything wrong with pushing boundaries as long as you have an experienced mentor to guide you thru the process. I like it.
What I was saying is that 4 fins allow you to make each fin smaller. There's not much point on adding a 4th fin to a 3 fin optimised design.
Any reason you use CA glue to tack rather than the epoxy, is it just faster?
I think "4 fins is more stable" for extreme flight profiles is a misnomer. 4 fins make a symmetric side profile of the rocket, reduces roll induced by sideslip, and can decrease the possibilities of fecal turbine interactions in the middle of a flight where there are other factors attempting to rekit your rocket at the same time.
Additionally you don't flood the whole root with CA, just a couple minute dabs will hold it (held still, not held tight. Don't flick it for no reason)
For the CA glue "tacking" do you apply epoxy along most of the root around the tacking dots of CA glue so you get the best of both worlds? What I have done in the past is used a layer or 2 of tape on the fins to make a snug fit with the fin alignment guides (If needed) and then use epoxy on the full length of the root with a very small "fillet" on the sides just to make sure the whole root is covered. I will then go back later and add the full fillets.
Faster, use zip kicker. You can always epoxy it on and just use the CA on the ends to hold while epoxy dries.Any reason you use CA glue to tack rather than the epoxy, is it just faster? With a 14”x0.2” fin root I don’t know if I would want to give up that epoxy surface area.
Tony
This is ultimately a preference and process thing. Folks prefer superglue so they can get rid of the fin guides quicker. If your timeline allows you to leave the guides on for tacking epoxy to set, there's no reason why not.
Hey, it's rocketry. When stating you'll do something one way, you'll immediately be provided 3 other often contradictory ways to accomplish the same thing which must be discussed at length before the thread returns to baseline
Great project, I hope it works well! I've got my own plans for the O34k that are a little different, but this should be real good
Before I found out about zip kicker, I just sat and watched them dry
I would have to go back and look, but are you using Wildman's tubing? I thought his guides were sized for his tubing???
Question for the group, is the CTI boattail compatible with the O3400 reload? My understanding from their literature is that the O3400 uses an XL nozzle and the boattail is compatible with the XL nozzle. Thanks again.
It's compatible, as long as you use a Gen1 casing (integral thrust ring). The newer Gen2 casings have a finer thread pitch and I haven't seen a tail cone yet for those.
Reinhard
From what I've been told (by CTI), the current boat tail that is offered is compatible with the gen 2 hardware but you need the adapter ring to make it work (part P98-AR)Thank you. I was told the Gen2 hardware would be back in stock around next month so hopefully the Gen2 boat tail will soon follow.
Tony
Thank you!From what I've been told (by CTI), the current boat tail that is offered is compatible with the gen 2 hardware but you need the adapter ring to make it work (part P98-AR)
I think "4 fins is more stable" for extreme flight profiles is a misnomer. 4 fins make a symmetric side profile of the rocket, reduces roll induced by sideslip, and can decrease the possibilities of fecal turbine interactions in the middle of a flight where there are other factors attempting to rekit your rocket at the same time.
I'd have to do some digging but there's a NASA paper out there regarding optimal fin numbers from a stability/drag perspective. IIRC the sweet spot was 6 fins but I could be wrong.I agree, there are certainly advantages, all of the missiles we employ (AMRAAM, AIM-9) are 4 finned and while a lot of that most likely is due to guidance requirements stability is also a huge concern. The roll aspect is also something I have thought a lot about. My biggest concern would be a rapid roll rate combined with come asymmetry in the mass distribution along the longitudinal axis causing procession (I think that is the right term) and the rocket developing a large angle of attack as a result. My current thought on mitigating this is to be as precise as possible in attaching the fins straight.
From my understanding heat soak from the motor case is a complete non-issue as to be certified the exterior of a casing has to stay below 200 deg? I feel like Mark Clark had some relevant comment on this in the past but I can't find it. Regardless, from my understanding case heating is a complete non-issue.I was part of a discussion on another thread that talked about heat soaking the aft portion of the airframe due to motor case/nozzle heating. That is certainly a valid concern and so I would not want an epoxy with only a 100 degree temp rating but I would think 300 deg would be sufficient and if you aren't doing MD then that wouldn't be a concern at all.
-Tony
By the way I personally would never drill holes or rough up my bond areas to the extreme on an Xtreme rocket. Properly using aero-space glues is all that's needed... CTI flew one with fins just glued on...no T-T with Hysol that went over M-5. BUT u must really know what U are doing to achieve this.
I certainly won’t argue with NASA… From a hobby practical perspective though I think it would be more difficult to properly attach and align 6 fins. I wonder too what Mach range the trade off occurs to where you simply would need the span to be smaller and so more than 4 fins would be needed.I'd have to do some digging but there's a NASA paper out there regarding optimal fin numbers from a stability/drag perspective. IIRC the sweet spot was 6 fins but I could be wrong.
Anecdotally if 3 fin configurations were better for high speed low altitude unguided rockets when compared to 4 fins I expect NASA's Sounding Rocket Program would be flying 3 fin rockets. Yet from what I can see the entire NASA SRP fleet are 4 finned vehicles.
From my understanding heat soak from the motor case is a complete non-issue as to be certified the exterior of a casing has to stay below 200 deg? I feel like Mark Clark had some relevant comment on this in the past but I can't find it. Regardless, from my understanding case heating is a complete non-issue.
Have you thought about slotting the airframe and inserting the fins into the slots? That's how I do mine. You could choose to alternate between in the slot and on the surface if you like, something like I did on the Nike Apache. It helped set the fin depth in the airframe in my case.
https://forum.ausrocketry.com/viewtopic.php?f=6&t=5019&start=45View attachment 458595
That would get you actual tensile and compressive strength of the epoxy working in your favour, rather than just peel.
Consider that my fincans are in tension, due to taking the motor thrust to the frame at the forward end, so any weakening of the hoop strength at the aft end is of no concern.
“If it looks right then it flies right” can’t argue with that!I like the way 4 fins look better than three. Therefore I avoid unneeded aerodynamic analysis to determine if 3 or 4 are better since I already know the answer.
That is how I always build. The length of the airframe in compression is shorter. According to Mr Euler a shorter column is much more difficult to break, and the law is a square law (1/L^2). So having only half the length of the rocket in compression means that section can support roughly 4x the loads before buckling.Do you always keep your fincans in tension, if so what do you see as the benefits as opposed to having the motor case seat against the aft end of the airfram?
So the increase in buckling strength for the airframe forward of the motor mount makes sense to me, have you seen many rockets fail due to CF buckling?That is how I always build. The length of the airframe in compression is shorter. According to Mr Euler a shorter column is much more difficult to break, and the law is a square law (1/L^2). So having only half the length of the rocket in compression means that section can support roughly 4x the loads before buckling.
https://en.wikipedia.org/wiki/Euler's_critical_load
This also keeps the back end of the rocket in tension, which is where composites have better properties .
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