FlisKits: Tres

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Jan 17, 2009
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Didn't know where to put this but since there isn't a review on the Tres yet, I thought I'd put it in here :)

In another thread it was mentioned that the Tres had an odd behaviour at MaxQ. The note is quoted here:

Originally posted by cls
Don, the Tres willl keep you off the streets for a while - enjoy the building!

I've seen three fly, and they all exhibit the same thing: they start corkscrewing at some certain speed. one fellow's does it really bad, right at launch; mine does it a little, consistently at maxq (3x C6-5s) right before burnout; another one does it about half way through boost. I have no idea why it happens.

Having built 2 of these kits, I have never seen this happen and I fly it mostly on C motors. Has anyone else seen this? I suspect that the problem may be with the attachment of the upper fins or, perhaps, with an asymetrical airfoil (if one was applied) to the upper fins.

Another thought would be a twisted motor mount, but that should affect the entire flight, not just at MaxQ...

thoughts? Comments?
Hmmm this also happens on my Estes BlueNinja at MaxQ. Just before burnout it spins like CRAZY!:confused:
Ahh , maybe up there the wind is stronger , and catching all the fins on the Tres , and just spinning it around ! This could be possible as the BlueNinja is extremely light for it's size , and the wind could easily throw it around!
I haven't had any problems with mine, including 2 flights with only 2 of the 3 engines lighting. All the flights have been in moderate to zero winds, so I can't really speak to the handling in gusty conditions.

As for the review, I sent one in to EMRR a few months ago, but it hasn't posted yet. Seems I even sent a copy to you, Jim, of the webform-generated e-mail documenting its submission. I was just under the impression that EMRR hadn't had a chance to get it formatted and posted yet.

I noticed that my 24mm Deuce's Goblin spun a but (but not bad) on the way up at NSL. I double checked the alignment of everything with a laser sight I have for work, and everthing seems to be in order. So I began hypothesizing, and the only thing I came up with may be what causes that spinning on the Tres.

BTW, Jim, I thought I noticed a little spin/waggle on yours when you flew it Sunday at NSL. Once again, not bad, and nothing to make you take pause and worry or anything - but perhaps I'm not remembering correctly.

Anyway - my only theory on my Goblin that makes any sense to me is attributed to slight inconsistencies between the two E9-8 motors used. Although they are directly opposing each other in the horizontal direction, a slightly inconsistent burn/thrust-curve between the two motors might cause "one side" to thrust a tad higher than the other at finite moments during the motor burn. This is probably amplified a bit with the higher thrust of the 24mm engine and the longer burn of the E's. Perhaps a phenomenon like this caused just enough non-vertical force to be applied by the engines to cause a slight spinning effect (with the aerodymic stability of the rocket itself in flight keeping her going straight up overall)

If this motor inconsistency theory can possibly be applied to the Tres: Sure, you have three canted motors whose horizontal thrust vectors cancel each other out when the thrust is equal. However, if there are finite inconsistencies in the individual thrust curves of the three motors in question (more possible with three than two as well) then you could have a somewhat oscilating net horizontal thrust vector during the motor burn, possibly in three different directions (rather than just two in the Deuce case.) This could be a cause.

I've not modelled the Tres on RockSim to find the static margin of the rocket - increasing the static margin might fix the waggle if it's an oscillating horizontal thrust vector (enough overstability in the aerodynamic stability to overcome it.)

This seems to be the case in the Deuce design - as I've never seen one waggle or spin (unless the spin was imparted on purpose.) The other helping hand on the stock Deuce design is that it only uses 2 motors, 18mm in size (a manageable amount of thrust and duration in this case) and the possibilities of horizontal thrust vectors due to inconsistent or non-exact engines is not as great with only two motors directly opposing each other.

Actually, after thinking a bit more about the Tres case, this oscillating thrust vector would not necessarily be limited to three directions, it could oscillate a full 360 degrees to the opposing angles and the possible differences in the thrust curves. And also, this dynamic horizontal vector has the greatest possibility to be largest at MaxQ.

**Disclaimer - I'm no rocket engineer, but this hypothesis makes sense to me. Any of you "real" rocket scientists want to chime in?
When I have a problem with a digital or electronic control I call it UEP


Yea...that's it...a UEP!:rolleyes:


In other words...I don't know...

Maybe it's magic?

Well, one thing is for certain. You won't see Carl or RocketJunkie's upscaled 38mm/54mm versions twirling! Perhaps the errant flights could be attributed to light weight vs. strong winds?
Yeah, Sand...it IS magic! Maybe we should drink some "Happily Ever After" potion and fix all the problems! j/k j/k

An easy way to test this might be to used the Tres' MMT in a standard 3FNC rocket instead of the Tres' "Fins-all-over-the-place" design. See, my thought is that if the motors not igniting simultaneously is causing this effect, but there's not enough speed to get it to spin until "MaxQ" because of the drag of the fins, maybe using a low-drag design would solve this problem.

The other obvious solution is that the motors are twisted a bit. Unlikely, but IMHO, the MMT on the Tres is a bit "unstable," meaning that it has a tendency to wiggle around a bit as you insert it in the main body. Some small balsa wood strakes from the intersection points of the motor tubes to the ID of the BT-60 would fix this quite easily.

I ain't no gosh-darned rokit siintis iither, but I have done did some rokits over at that gosh-diddly-darned place.

:D :D :D

Oh yeah...I forgot to mention.

Those of you with the problems of corkscrewing might want to try adding some noseweight to it. This might work. Either that, or as Eugene said, it might be light weigth vs. strong winds.

Originally posted by wwattles
As for the review, I sent one in to EMRR a few months ago, but it hasn't posted yet. Seems I even sent a copy to you, Jim, of the webform-generated e-mail documenting its submission. I was just under the impression that EMRR hadn't had a chance to get it formatted and posted yet.


Hmmmm. No record of it, but there was a time that the reviews were not coming through. I have fixed the issue completely.

Can you resubmit?

(Jim, thanks for taking this up - I wasn't sure where to post it either.)

it isn't roll (the rocket tube spinning nicely around), it's more of a corkscrewing motion - but it isn't a regular motion. more of a woo woo WOO woo WOO woooo.

the first time it happened to me I thought maybe the motors didn't all light at the same time. second time it happened to me I thought ah, maybe I didn't do the motor mount correctly.

I measured the motor mount angles and it's within a few degrees ... anyways the model stands up straight, resting on all 3.

the last clue is that it only seems to happen near burn-out, which means the rocket is going about as fast as it is going to go - which implicates aerodynamics - fins. one of my fins has a chip so maybe I should fix it or trim the others to match. otherwise, the fins are all on straight and symmetrical.

what the heck, I should put a little more work in to it, the Tres demands a better paint job than "all-white-with-chips".

I will try to get some video and post it.
Thanx, any and all information is helpful.

I noticed a slight spin about the axis of mine at NSL also, but attributed it to fin damage and high winds. Previous flights, even in wind, were arrow straight (Jason, Eugenio, remember Florida??)

As for a cork-screw, man that sounds like something was *way* off. A large rocket like that is not prone to such motion and I would begin to suspect wind or nozzle problems.

weird... :)
Originally posted by jflis
(Jason, Eugenio, remember Florida??)

Yup! That thing was QUICK! Straight up too. I don't remember seeing any corkscrewing at all, but then again...it was almost 8 months ago...

Well, I just finished mine and I will also be flying it on three C6-5's.

I'm curious if I will have any stability issues with mine but I'll find out this weekend. I think it should be fine as I took my time with the build and followed the instructions exactly. The only change I made was that I added some kevlar to supplement the elastic.
Well, I flew my Tres today on three C6-5's as intended and it flew great. No corkscrewing, twirling, spinning at maxq, etc. Using a Thrustline 3 motor clip whip made life so much easier too.

Straight as an arrow up to about 800-1,000 feet and a successful recovery.:D :D :D
very cool :) I just got back from a CMASS launch where 2 different Tres flew and one of them flew on A's, B's and C's. All 4 flights were rock steady, arrow straight with chute at apogee.
I just flew mine this afternoon on three B6-4s. It flew nice and straight.
My daughter took the picture, and almost missed it. All three motors are burning you just can't see one very well.
The standoff must have hooked somewhere because you can see it in the air:confused:
Anyway, perfect flight. I can't wait to try it on C6-5s:)
Floating safely back to earth, under a Thrustaero neon yellow chute.
It's even cooler on the C6-5's! You'll like it, but your daughter will have to be REALLY quick on the shutter release for it!