Lakeroadster's "T-Square" Rocket

Here's a canted cluster tractor motor design. It's a scale model of my ole trusty high school T-Square I used in the mid 1970's.

So is it a scratch build... or a scale build?

It's pretty simple. Just some laminated plywood for the blade and a head designed as a hollow box structure so (3) 12" chutes can ride on board to apogee.

Powered by (2) D-12-3 BP engines it sim's to nearly 1000 feet.

Should be an unusual build too.

I'm voting for you to make and post videos of your launches.

Also, how do you choose the canting angle?

I don't know but I've been told, two fin rockets are mighty bold...and inherently unstable. I have also been told forward mounted canard style fins are a bad idea and that motors plus at least three fins at the BACK of the rocket are required. I can sometimes have hearing issues from Excessive wax build up. At least you are doing some fine computer work and not using some silly mindsim!

Looking forward to the recovery system design. Flying compasses, desk lamps, stools and slide rules will pay tribute to the lost art of early and mid 20th century draftsmanship.

Funkworks said:

I'm voting for you to make and post videos of your launches.

Also, how do you choose the canting angle?

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The angle... I wish I had some hi-tech formula to tell you about... but I don't. So I make a CAD Model and let the function / geometry choose the form that works best.

If only one motor lights this may demonstrate a relatively axe-like like trajectory

It might look odd, but you could consider canting the motors the other direction (inward). If only 1 motor lights, it'll have a somewhat straighter trajectory if the thrust line is half way between the CP and CG.

I made a CAD model and some drawings.

The T-Square consists of 2 parts: The head and the blade.

The blade is just 2 pieces of 1/8" balsa glued together.

The head has 3 compartments: (2) are for the parachutes (recovery bays) and the center compartment is the motor mounts and the blade. It's made from balsa, various pieces glued together. The sides are 1/8" thick. The leading edge is 1/4" and radiused on the sides.

The motor mount will be a solid piece of 1-1/4" square balsa with a 24 mm hole bored through it. Then I'll use my radial arm saw to cut some grooves on the outside to act as ducts to vent the motor ejection charge over into the recovery bays.

Hinged recovery doors are used on the bottom, using a fabric hinge like are used on model airplanes. It will be taped shut... not much tape. Good candidate for a bench test.

What do ya think?

lakeroadster said:

What do ya think?

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Worth a shot! I'm certainly curious to see what happens.

If it ends up unstable and hits you, you are gonna be really Thor.

BABAR said:

If it ends up unstable and hits you, you are gonna be really Thor.

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I really don't mind.. I've been "hammered" a time or two.

Definite bench test. The winding gas channel and small port area is unorthodox

Nytrunner said:

The winding gas channel and small port area is unorthodox

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Oh yeah, other than those two things, it's a pretty typical rocket...….

Let's see, we have

3FNC (3 fins and a nose cone)
4FNC (4 fins and a nose cone)

I've also seen
2FNC (2 fins and a nose cone, the flying guitar rocket and the Lucky 7)
1FNC (1 fin and a nose cone, although the fin is a ring, the Odd'l Rockets CorkScrew)
1F3NC (1 Fin and 3 Nose Cones, Spirit of America)

This looks like 1FNNC (1 Fin No Nose Cone)

Interestingly though, wondering if you can get this to MonoCopter or Dicopter. Not exactly what you currently have on your board, but it might be flyable, entertaining, AND SAFE!
Turn the puppy 90 degrees, put it on a short thick and strongly fixed to the ground rod, take out one motor, direct the other one laterally, may not even need a chute.

https://archive.rocketreviews.com/reviews/all/aaw_hornet.shtml

BABAR said:

Oh yeah, other than those two things, it's a pretty typical rocket...….

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Despite D'isa's normal blather against traditional rockets, tractor motors are sound. CG forward, drag features or pendulum aft, it all checks out.

The only uncertain part is the ejection method which Lake already came up with the solution for: ground test

Nytrunner said:

Despite D'isa's normal blather against traditional rockets, tractor motors are sound. CG forward, drag features or pendulum aft, it all checks out.

The only uncertain part is the ejection method which Lake already came up with the solution for: ground test

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I'm not knocking tractor motors,

I was just thinking that the single blade fin/stick/board part only gives you stability in one dimension. Aside from Monocopters and CorkScrew designs (and you can argue that a ring fin is cheating), I am not aware of any successful stable SINGLE fin rockets.

There is always a first time. People said you can only Black Powder gap stage to 11". I've seen 53".

Nytrunner said:

Despite D'isa's normal blather against traditional rockets, tractor motors are sound. CG forward, drag features or pendulum aft, it all checks out.

The only uncertain part is the ejection method which Lake already came up with the solution for: ground test[/QUOTE

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I love all your blather too!

BABAR said:

I was just thinking that the single blade fin/stick/board part only gives you stability in one dimension.

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That was my concern. The canted motors are both in a single plane, so helping give stability around only one axis. And the destabilizing effect of the canards is perpendicular to that axis. To me, this looks not just like a heads-up launch but like heads-up, shoes-on, starter-crouch.

Also:

lakeroadster said:

So is it a scratch build... or a scale build?

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Lots of scale models are scratch built. The question would be is a scale build or an odd roc?

jqavins said:

That was my concern. The canted motors are both in a single plane, so helping give stability around only one axis. And the destabilizing effect of the canards is perpendicular to that axis. To me, this looks not just like a heads-up launch but like heads-up, shoes-on, starter-crouch.

Also:Lots of scale models are scratch built. The question would be is a scale build or an odd roc?

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A scale build of a non aerodynamic structure ( not a missile or rocket or any sort of aircraft) would be both a scale build AND an OddRoc

I also thought about the forward ends of the straight edge as canards, but I think the are (barely) aft of the CG, so they may act as fins, although with a VERY short Moment.

Two fins... that will never work..

Question for the OR gurus: If this configuration is unstable, why would OR show a good flight and an apogee of 1333 ft?
(In post #1).
Is there some kind of limitation where OR would show a deficient design as stable?

Why cant the motors? Unless you're doing so to point them at the CG (which isn't the case here), I don't see the point.
Two fins can work, if they're not in the same plane. But yours are in the same plane.
The problem with having two motors, canted, in the same plane as the fin, is that unless you get exactly the same thrust from each motor at exactly the same point in time, the thing is guaranteed to cartwheel off the pad. If one motor ignites a fraction of a second before the other, or the thrust curves do not match exactly, it's a lost cause.

Kelly said:

Why cant the motors? Unless you're doing so to point them at the CG (which isn't the case here), I don't see the point.
Two fins can work, if they're not in the same plane. But yours are in the same plane.
The problem with having two motors, canted, in the same plane as the fin, is that unless you get exactly the same thrust from each motor at exactly the same point in time, the thing is guaranteed to cartwheel off the pad. If one motor ignites a fraction of a second before the other, or the thrust curves do not match exactly, it's a lost cause.

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Canting helps to direct the exhaust away from the blade, thus helps minimize burning the blade.

In regard to your points about "cartwheeling" that is true for any cluster motors, canted or not. But in a tractor motor configuration, where the cg is below the motors, where the motors are pulling the rocket up, verses pushing the rocket up, the cartwheeling is dramatically reduced.

It's the pendulum effect.

Take a yardstick and balance it on your finger with the 3 ft yard stick pointed to the sky.. not very stable is it. Take that same yard stick and hold it at the top.. pretty stable isn't it.

I may very well be full of guano.... but it makes sense to me.

It's basically a "stick rocket", ought to work fine if you get both motors lit. Personally I would want to move the CG further back though to help make up for the canard fin area. Post launch video!

Kelly said:

Two fins can work, if they're not in the same plane. But yours are in the same plane.

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John posted the Guitar video that proved that two co-planar fins CAN work (although they were really THICK fins, not sure how that helped but I think it did.). In this case I see only one fin, the stick piece. The forward side pieces I don’t think are going to HELP provide any stability, although jury is out as to whether they will function as Canards as @jqavins suggested and make it actively UNSTABLE.

I think John has said he has a private property field to fly his creations, so I am thinking that as long as he stays below the high power threshold he can try anything he wants.

Interesting thought about UNSTABLE rockets. Aside from the fire danger from a rocket coming to earth while under thrust or delay charge (a smoking gun, so to speak), from a physical impact standpoint a severely unstable rocket seems LESSS dangerous than a borderline stable rocket, at least shy of high power. The severely unstable rocket just does cartwheels and hits the ground, it can’t get up enough velocity to impact anything very hard. So mainly a fire hazard. A borderline stable rocket may eventually BECOME stable after it acquires a lethal trajectory, meaning it acquires enough velocity to fly straight, but it ain’t aimed upward. I think this is one of the big fears with multistage rockets, either they go unstable before the upper stage lights and are not aimed skyward, or there is a delay in ignition of the upper stage and the stack arcs over before the sustainer lights.

I am not advocating anyone should ever launch a rocket that they think probably WILL be unstable. Only that on private land (or with full RSO approval and supervision) with non-High Power Rockets it is reasonable to try rockets that are “probably stable.”

definitely should be a Heads Up launch!

I still think this would make a great MonoCopter design, just air foil the stick.

BABAR said:

John posted the Guitar video that proved that two co-planar fins CAN work (although they were really THICK fins, not sure how that helped but I think it did.).

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The theory on the guitar is that the "fins" were *so* thick that it was largely stabilized by base drag. I don't see what else could explain it's going straight.

lakeroadster said:

Canting helps to direct the exhaust away from the blade, thus helps minimize burning the blade.

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Ah, I see.

lakeroadster said:

In regard to your points about "cartwheeling" that is true for any cluster motors, canted or not.

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No, because in a 'traditional' rocket, one or more fins oppose the tendency of the rocket to tilt. It will tilt a bit, until the lift from the fin cancels out the torque from the uneven cluster, at which point it will stop cartwheeling and fly in a skewed attitude. With this rocket, there is no fin surface area to cancel out the torque. If the motors were in the plane perpendicular to the plane of the blade, you would be ok (in this regard).

lakeroadster said:

But in a tractor motor configuration, where the cg is below the motors, where the motors are pulling the rocket up, verses pushing the rocket up, the cartwheeling is dramatically reduced.

It's the pendulum effect.

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No, it doesn't work that way. The pendulum effect is a fallacy. Other people have explained it better than I will here, so you should definitely google that.

neil_w said:

The theory on the guitar is that the "fins" were *so* thick that it was largely stabilized by base drag. I don't see what else could explain it's going straight.

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Yeah, that's what I was thinking. In the "T-square" rocket, you might get a little bit of base drag from the head, but that's exactly where you don't want it: ahead of the CG.

BABAR said:

I think John has said he has a private property field to fly his creations, so I am thinking that as long as he stays below the high power threshold he can try anything he wants.

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Yeah, I'm not telling him he can't do this, just applying 'rocket science' to point out the the likely issues from doing it.

BABAR said:

I still think this would make a great MonoCopter design, just air foil the stick.

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That's a great idea; definitely a better way to get a flying T-square.

neil_w said:

The theory on the guitar is that the "fins" were *so* thick that it was largely stabilized by base drag. I don't see what else could explain it's going straight.

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Thanks, I have been wondering about that for years now!

Thanks for all the comments guys. I'm going to build it... but it may be a while before it gets onto the workbench though.

I'll tell ya what.... I'll attach a 8 ounce weight at the bottom for the first launch to move the cg down a bunch.

What do ya think.. sound like a plan?

Top men in the ways of science have told me the pendulum theory is bunk. An ancient theory that went the way of that comforting Earth centered universe we held for so long. Proven wrong by 20th Century aerodynamics the age of the tractors was over, only useful for LES applications and silly oddrocs.

The Apogee tech paper on 2 fined rockets with the fins and motors in back (Where they should be! I sure do love my traditional 34FNC rockets!) Says that sort of design won't work.

As for canted motors you can get by with a little sin, just needing them to light roughly at the same time. Lord willing they will burn roughly the same amount of time with roughly the same amount of thrust on each side. Pop-pop on the ejection timng is roughly the norm as is the more than adequate power of the ejection charge.

Now you add sin with less than ideal launch conditions. You add sin by not having a nice thick and long rod or rail or any fault in launch system or igniters. You add a little sin going all two dimensional. Keeping away from too much sin is hard to do.

Do not underestimate the power of the D motors ejection charge. In such a small area and venting sideways you need super strength for an instant, which may mean stamped steel construction like a cheap, late model Chicom AK. Lord willing you will not get a motor (s) with a shotgun ejection charge.

Would plugged motors with electronic ejection, maybe even CO2, be less sinful than a potential bomb of 2 side vented D12's?

Well enough blather already, don't want to upset the real rocket scientists.