Lakeroadster's X-FLR6 Rocket Build (AKA the TINTIN Rocket)

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Do you think you can light all three simultaneously?
Close enough to get up to speed and off the launch rod, yes.
Do you think you can get fairly identical burn times? Do you think they even have the same starting mass?
One mix, poured or rammed with a scale, yes and yes.

Lots of leverage turns a small force into considerable torque for a low moment of inertia object.
Small --> considerable, yes.
Miniscule --> very small.
The very small off axis forces combined with a sizable engine thrust will give a center of thust that is a miniacule distance off axis.

But we're beating a dead horse. Only a few launches would give the definitive answer. And that's if anyone were about to launch this (or a similay rocket) in such a configuration.
 
Really fella's? It's LPR not HPR. Don't be such buzz kills.

I share my mistakes to keep others from having them. Promoting safety should never be referred to as “Buzz Kill.”

I had an 18mm engine rocket (don’t remember if A B or C) come off the rod, arc over and land in short mowed dry grass about 45 feet from pad under power. (Or at least will smoke delay was coming out.) I had flown it before and flight was stable, so I don’t know what went wrong. I was the only person in the field. Took me a minute before I could even see the grass was on fire. I was able to stomp out the fire (fortunately.) winds were about 10 mph, and at the edge of the field was a forest with nearby houses. Wind was definitely fanning flames in direction of the trees.

It could have been really bad.

I don’t know about your field, but unless it is just rock or desert, even low power rockets can do bad things, even with short mowed grass. Had it been dry brush or a wheat field or something........

I routinely do off axis clusters for my long gap staged rockets, but the off axis motor mount is minimally “off” (basically plaster against the main rocket body tube and certainly not at the lateral margin of a fin), as far as I can tell the asymmetry doesn’t affect the flight.

I have seen a post of a guy who did 6 outboard clusters which I think staged to sustainers, but pretty sure he had a really big main engine, so outboards we’re going to be overwhelmed by the main in any case.
 
Love TinTin's rocket and love the design you've come up with. I tried to replicate TinTin's rock with a modified V2.

Good luck with your rocket.

20190220_231424.jpg
 
Post irrelevant as I was too late to the conversation. ;-)
 
Last edited:
Twenty feet tall? No testing with smaller prototypes?
That was a joke. It's about 20 or 21 inches.
4 large engines 5 feet apart?
No one has suggested anything more than an E engine central and, maybe, A's or smaller in the pods, and even that is pretty much off the table. I've been talking about smoke generators that would best be characterized as -0-P motors (i.e. nil total impulse class, zero average thrust, and plugged). And only 5 inches or so apart. And I'm not the one building it.
 
No one has suggested anything more than an E engine central and, maybe, A's or smaller in the pods, and even that is pretty much off the table. I've been talking about smoke generators that would best be characterized as -0-P motors (i.e. nil total impulse class, zero average thrust, and plugged). And only 5 inches or so apart. And I'm not the one building it.

Like he said ^^^^^ Thanks Joseph

John "The Builder"
 
We're all agreed that fin tip motors are a bad idea. Unless - MAYBE unless - they are greatly outgunned by a central motor. In the failure of one motor to light properly is one of the reasons it's generally a bad idea. The breaking of one of the MMTs is more than the usual problems. A bad flight overall, probably due in part to a bad build, on top of a flawed design.
 
We're all agreed that fin tip motors are a bad idea. Unless - MAYBE unless - they are greatly outgunned by a central motor. In the failure of one motor to light properly is one of the reasons it's generally a bad idea. The breaking of one of the MMTs is more than the usual problems. A bad flight overall, probably due in part to a bad build, on top of a flawed design.

It's a challenge, that's what makes it so intriguing.

What is needed is a locking mechanism to prevent launch until all motors are verified to be lit. That's not impossible, it's SOP on most real rockets, it's just different for LPR / MPR.

Basically blast deflectors that sense thrust and thus complete a circuit to disengage a lock holding the rocket onto the pad.

Or it could be done visually, with a mechanical locking pin pulled by the operator.
 
The thing is, you'd be at different moments along the thrust curve, pretty much guaranteeing unbalanced thrust, which is bad enough just with manufacturing variances. The last motor to light is on the initial thrust spike while the others are coming off of it, and off you go sideways. That is, if the pod motors constitute a significant part of the total thrust.
 
By canting the outboard motors the thrust could be aligned with the rockets CG, thus helping to minimize the assymetric thrust in the event of thrust variations.
 
Indeed, that would help. I see two potential pitfalls still, but without trying it (or hearing from someone who has) I can't say how bad they are.

First, to angle the motors just right you have to know just where the CG is, so you're locked into one motor set. Changing the fin pod motors (or the central motor if there is one) moves the CG and then the pod motors are no longer aligned perfectly. If you stay within the same propellant and letter, maybe it's close enough. But going from, say, 3 A motors on the fins to three B motors, or three A's on the fins plus a C in the middle and changing the middle to a D would move the CG probably enough to be a problem. But, "probably" I say, not knowing.

Second, thrust imbalance will push the rocket sideways and it will turn as if into a breeze. Or maybe into a strong wind? Just how strong is the sideways motion? Again, I don't really know. That, at least, can probably be overcome by a high thrust central motor, just as weather cocking is overcome by a high speed takeoff.
 
Just last week I was asked about putting smoke generators on rockets.

NFPA 1127:
4.11 Payloads.
4.11.1* A high power rocket shall not carry a flammable or
explosive payload.

NFPA 1122:
4.6 Model Rocket Payloads. A model rocket shall not carry a payload that is designed to be flammable, explosive, or harmful to persons or property.

It’s possible to interpret homemade smoke generators in the fin pods as either uncertified model rocket motors or flammable payloads.
Chemical smoke generators which produce little or no heat and could not start a fire would not be a concern.
Steve
 
First, to angle the motors just right you have to know just where the CG is, so you're locked into one motor set.

Only if the fin mounted motor's have fixed motor mounts. No reason the motor mounts couldn't be adjustable such that they can be aimed once the actual "as built" CG of the rocket is determined.

Envision a bore in the pods larger than the motor. Once the rocket is built, then the motor mount are made as sub-ass'y's that slide into the bore of the pods, secured via tape.

Sliding the centering rings for and aft changes the angle of the motor relative to vertical.
Adjustable motor mount.jpg
 
Last edited:
Thanks. That's the definitive answer to the question I asked all those posts ago. (But it's too bad, 'cause a triple smoke trail would be cool.)

If only one of the motor companies would certify a long burn A smoky motor (basically a delay grain).
Or fly it at a Research Launch with a central motor that has enough thrust to be mostly immune to the effects of the low thrust pod bay motors.
 
If only one of the motor companies would certify a long burn A smoky motor (basically a delay grain).
Or fly it at a Research Launch with a central motor that has enough thrust to be mostly immune to the effects of the low thrust pod bay motors.

Or fly it yourself on private property.
 
The fliskits Tres uses a canted cluster, these are in the main body tube, much closer to the rocket central axis than fin pods would be, but I wonder where exactly the cg of that rocket falls relative to the intersection point of the canted engines’ thrust axes. I would guess close to or maybe slightly aft of the cg, but not in front. No idea, but I would think it should be slightly aft.

Not advocating the fin pod engines, but trying to better understand the rationale of how a proven existing kit works using a similar principle to a less extreme degree.

I would think measuring the cg with new engines and spent engines may give an appropriate range for where you want to point a canted cluster common thrust point, maybe?
 
Last edited:
Thanks to Neil-W for his tutelage in creating a more accurate Open Rocket simulation of the X-FLR6.

Upgraded to a F44-4.

X-FLR6 Full.jpg

X-FLR6.jpg

And the controversial cluster, using a main F44-4 motor and (3) canted A10-P motors in the pods. As a fella once said "It'll either blow, or go, either way it'll be spectacular". ;)

Clustered.png
 
Last edited:
It is a pretty rocket! ... and so here's mine. It's about 62 inches tall w/o the antenna. It's a thin fiberglass shell over a 4" paper tube core. It has a single 54mm motor mount. It has not flown yet, hopefully I'll get to it this year.

IMAG0302.jpg

And since I made the molds ... I went ahead and made the parts for 3 more :)

IMAG0301.jpg
 
The fliskits Tres uses a canted cluster, these are in the main body tube, much closer to the rocket central axis than fin pods would be, but I wonder where exactly the cg of that rocket falls relative to the intersection point of the canted engines’ thrust axes. I would guess close to or maybe slightly aft of the cg, but not in front. No idea, but I would think it should be slightly aft.

Not advocating the fin pod engines, but trying to better understand the rationale of how a proven existing kit works using a similar principle to a less extreme degree.

I would think measuring the cg with new engines and spent engines may give an appropriate range for where you want to point a canted cluster common thrust point, maybe?
You can compute what one might call the center of thrust in much the same way as the center of mass for a set of point masses, but a bit more complicated because each thrust is a vector where masses are not. I don't have time to recreate and present the algebra now, but in the end you get both a net thrust vector (the easy part) and an effective point of origin for that thrust.

Now, if the engines are placed symmetrically around the centerline, and are all angled toward a common spot on the centerline, then the vector will be straight along the center line and therefore go through the CG, no matter whether said point is above it or below.

(In this context, the well worn problem of mismatched thrust manifests as the net thrust vector and origin point both deviating from their ideal values.)
 
And the controversial cluster, using a main F44-4 motor and (3) canted A10-P motors in the pods. As a fella once said "It'll either blow, or go, either way it'll be spectacular". ;)

View attachment 383606

I think your F motor will overwhelm any asymmetric thrust from your A10-Ps. So you are probably okay no matter what.

Does the A10-P have a smoke charge? If not, it’s gonna burn out quickly and won’t Have a prolonged effect.. I am wondering if you may be better off with aA3-4T longer burn and delay engines. This may give you what I think you want, prolonged 4 smoke trails. You can either have these engines eject (I know, some people don’t like this, but it is a routine thing at many launches.) Or you can put in a sort of vent to allow the ejection charges to discharge safely. One way of doing this is gaps in the centering rings so the charge goes forward and then back down out the bottom of the rocket between motor mount and outer tube.
 
Back
Top