To tip-to-tip or not? Madcow 2.6" Tomach w/54mm mmt.

I recently acquired a thin-wall fiberglass 2.6" tomach with the 54mm motor mount, and I plan to push it pretty hard. Unfortunately it comes with 1/16" thick G10 fins, which in my opinion would likely flutter right off the rocket around mach 1.5. Considering that this rocket can do nearly mach 2, I'm not overly comfortable with attaching these fins conventionally (tiny little TTW slots and big external fillets).

So do I do tip to tip to add some thickness and hold the fins to the rocket better? I've never done any tip-to-tip, so it would be a learning experience.

I could also add a layer of carbon to each side of the fins before attaching them to just add thickness, which might stop any flutter. With my available "facilities" this would be a bit easier, but would it add enough improvement?

Also, what might be the speed limit of these 1/16" fins. Is my mach 1.5 estimate alright?

I am open to any and all suggestions and TRF wisdom from y'all!

That fin shape looks to be quite stable with a long root.

so long as they are on dead straight on all axies(sp?) I would bet that a good fillet would be all that’s needed to keep em on

fly it high n’ fast!

I would go the simple safe route: carbon fiber sandwich the fins, open slot a bit to fit.
Glue them in and all will be happy in rocket land. No need for T-T unless ya got some huge honking 54 L made of unubtainium. {or Loki M}
Other alternative recut fins from 1/8 in stock G-10 plate.

Anything else is pretty much overkill for this size project.
Yes 1/16 is on the dangerous edge of failure...I know from personal experience "buzzing" mine a few times when pushing high thrust 38's motors. Would not even try with 54mm motors over 2-3 grain size.

I have a 2.6" DX3 DD. Basically the same rocket, just a slight difference in the fin shape. It's flown many times. Its flown once maxed-out on a 6XL CTI L730 white. If you can see my signature the stats are there. 16K+ft and Mach 1.5.

Fins were attached with rocketpoxy. Double buttered attachment to the MMT and external rocketpoxy fillets pulled with 1/2" PVC. It came back from Mach 1.5 unscathed. Not a crack in the fillet or in the paint.

The fins feel flexible when they're not attached to anything. Once you get them epoxied and filleted in they're quite sturdy and don't budge mutch.

ETA: Huh. I actually disagreed with a CJ post. Never thought that would happen.

Rocketpoxy is good stuff in sub to super M1.7 range. Beyond that I don’t trust it thermally just my own opinion. Also have done university projects multistage L1 stuff with narrower span 1/16 fiberglass to M1.69 in 29mm format.

CJ is probably playing it conservative to prolong lifespan of rocket. Just cause it can do an L flight doesn’t mean it should always do L for every flight.
If you want an alternate approach list the root, tip, fin span, body tube diameter, fin sweep, and fin thickness in inches, and I can chunk it in finsim and let the NACA complain some more. Trying to finish an L2 cert though.

There was one sandhawk kit I had where the sim complained it flutters on I motors. I wanted a K motor in it. Then I kinda went crazy with a dremel then sold it off outta panic lol. Then I bought a Mac Hyper 54 which safely does like M2.4.
(and has a cool fincan all aluminum)

There’s also been fliers on here who’ve pushed kits beyond what finsim said they’d fail at so take that with a grain of salt too. I’d say if you want to Tip to Tip it for the learning experience it sure wouldn’t hurt. Biggest factors of flutter usually are fin span followed by fin thickness assuming material is up to snuff.

A lot of vendors and fliers got real good at judging what certain fins withstand too. Not just theoretical but practical from experience. I think Wildman was bragging how one of his fiberglass kits got radar tested by military at pretty high Mach numbers. It also has fiberglass fins if I’m not mistaken.

Went to MC site. If you get the fin upgrade for 54 mount [click button says out of stock] what thickness are they?
I would think they would be 1/8th. Just can't imagine 1/16th comes with 54 mount.

Andrew_ASC said:

I think Wildman was bragging how one of his fiberglass kits got radar tested by military at pretty high Mach numbers. It also has fiberglass fins if I’m not mistaken.

Click to expand...

It has, those fins are 1/8th G-10.

Exactimator said:

ETA: Huh. I actually disagreed with a CJ post. Never thought that would happen.

Click to expand...

Hey it happens, I even don't agree with my self.....sometimes! LOL
Do me a favor and check the fin thickness, unless you are sure they are 1/16th. I thought going 54 they upgrade to 1/8?

If they are 1/16th then I stand corrected, you have proven they will work fine.

I flew my 2.6" Screech at LDRS on a Loki L1400. Arrow straight, no damage. 16k. I had about 1" between the forward closure eyebolt and the aft bulkhead for the coupler/av bay.

Planning on flying it on a L1040 next time I'm out at Argonia...

Edit: 1/16" fins, no additional reinforcement other than the usual injected fillets as well as ~1/4" radius fillets.

blackjack2564 said:

Went to MC site. If you get the fin upgrade for 54 mount [click button says out of stock] what thickness are they?
I would think they would be 1/8th. Just can't imagine 1/16th comes with 54 mount.

Click to expand...

My screech came with 1/16" fins with the 54mm upgrade. I imagine it'd be similar across their 2.6" line.

Also, I would be more concerned about recovery.. You have more mass in your motor section with a larger motor in it. If it lands just right, it will most likely snap a fin. I used a 52" parachute for my 2.6" Screech. Nice, slow descent. Landed in a tree, though. Easily retrievable, though.

The fins are 1/16".

I had a few conversations with mikec about launching on an L. Like you CJ, he has more experience with high performance flights than I. He had the same concerns you mentioned above. We ultimately decided it had a good chance of survival and I launched it successfully. He even did a post flight inspection with a magnifying glass and didn't see any issues.

Great rocket. I’ve flown mine twice on an L1000 and once on an L935, video link below. Nothing special on the fins on mine, no tip-to-tip, just good fillets. About 15 flights overall on mine, zero fin issues.

The video caption says it’s an L935 Vmax, which is wrong, it is an L935 IMAX.

The Tomach is a great kit. Got over mach 1.5 with no issues. Replaced it with a Screech when it lawn darted from 7000' (find were still intact). Screech has survived at least a K....without looking at my log.

As said above, good fillets.