Vanes ?

A thread here on TRF, that turned ugly , got me thinking/brainstorming/daydreaming of a rocket that I started dreaming about back during the Gemini Missions . I never liked the plastic fins on the Titan-Gemini Vehicles model rockets. As myself & my knowledge grew, I realized that a finless rocket was just about impossible. However, when I became a BAR 3 years ago I started to think about more realistic slow take off. Well that thread started me thinking again! :jaw: (I hate when that happens).
I thought why not a V-2 with vanes at the exhaust? Just like the real one. Now I am NOT wanting a guidance system, NO targeting/landing guidance. Just a way to keep the nose of the rocket pointed UP, during a slow initial boost.
Now I know the hobby does not need this, & I am perfectly happy to launch my low to mid power and watch high power (planning on L1 Cert. within a year [heads up DARS guys]) as is. But why not try something new (I am sure others have thought about this, but I don't know if anyone has tried this). Why climb a mountain, because it's there.:blush:
I know if this is tried it will not be cheap (which rules me out) & it will take someone from our community with experience & great skills (also rules me out).
So here it goes, basically a V-2 with the vanes, controlled by a gyro via push rods like RC aircraft control surfaces. I know the devil is in the details. Weight of the components, placement of components (ease of access & CG), reliability, power to overcome the force of the exhaust to redirect it, not to mention $$$$$$. And the vanes would have to be replaced regularly.
Well that's my brain F^£T, go ahead and say I am crazy & beat me up. You can't insult me, I already know I am crazy.:wink:

Unless you're building a big bird with a 6-7+ second burn time, I don't think the exhaust will be there long enough to do anything. For LPR/MPR the burn is over before the vanes can react.

mikemech said:

Unless you're building a big bird with a 6-7+ second burn time, I don't think the exhaust will be there long enough to do anything. For LPR/MPR the burn is over before the vanes can react.

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Oh yeh, defiantly an HP Bird, most likely a L3. But this is just an exercise in bouncing the idea around.

TALON said:

Oh yeh, defiantly an HP Bird, most likely a L3. But this is just an exercise in bouncing the idea around.

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Vanes won't live long, as you guessed. But some other people have done experiments with swivelling the motor mount on gimbals. This, presumably, was not an option for the rather larger motor employed by Wernher von Braun. See if you can find any threads on the forum about gimballed motor mounts.

Yeah, the thread I referred to in my first post was talking about gimbals. I will research threads on that. But I still think it would be cool to put vanes on a V-2, to make it more to scale. Anyhow, I was just thinking about it and see what others think. Thanks for the reply.

Use what the Germans' used for vanes and we use for nozzles, graphite. A nice long burn (I65, J90) in the main mount with fast-burn outboards to get it going. Would be an interesting project.

The graphite vanes used by the V-2, Redstone, and a few other rockets reduced the thrust due to the "drag" in the exhaust plume. That is one reason why gimbaled engines are better.

For a model/HPR sized rocket, the exhaust plume is not very wide, so the vanes would need to stick into the exhaust a lot, maybe nearly all the way into the center, almost touching each other (yet designed/shaped to not collide with each other, think of a sideways baseball "home plate" where the points nearly touch each other). Or possibly mechanically simpler….. one big vane fully across the exhaust plume for pitch and another vane (underneath) fully across at 90 degrees for yaw….. but even more of a performance hit on the effective thrust.

This is one of those things that if you did it, it would be a neat achievement, but not very practical. A gimbaled engine is more practical to do, although gimbaled models are not too practical overall because the faster they fly, the more the aerodynamic stability fights against the gimbal steering (and aerodynamic forces go up with the square of the velocity, a rocket flying at 100 mph has 4 times the aerodynamic forces on it as when it is flying at 50 mph).

The best engine to fly a "thrust vector" rocket with is a G12 reload. Burns for 8 seconds, has a thrust spike for liftoff then a near-constant sustainer thrust level of about 30 ounces IIRC. And also for other guidance models that use aerodynamic controls, the G12 is nice. I never flew my sunguidance model on a G12, since it is a BT-60 rocket that does not need that much thrust. But I did fly it a few times on an E6, also 8 second burn, and those were great flights.

For HPR, the I49, I59, and I65 would be good for Guidance models. I like the look of the I59 thrust curve going to a near-constant sustainer from 2 seconds to 7 seconds, burning out at 8 seconds. The thrust spike for the first 2 seconds is a bit high, which might be a problem for thrust-vectored rockets but not much of a problem for aerodynamic control.

BTW - The V-2 and Redstone (Which was sort of a V-2 2.0, redesigned and built bigger) used air rudders in addition to graphite vanes. The vanes in the exhaust helped to steer it at lower velocity, then as it got faster the air rudders had more force. So, ideally, a model/HPR rocket using thrust vectoring should also have aerodynamic control. At the US Space & Rocket Center in Huntsville, I saw inside the tail section of a Redstone type (might have been a Jupiter-C, the tail sections were all the same). There was quite literally, a chain and sprocket assembly connecting a vane and an air rudder to the same common "actuator" that rotated a sprocket to move the chain, which steered the vane and air rudder at the same time. I wish I had taken a photo to show that.

As the air got thinner as it flew higher, the vane steering then could become more effective than the air rudders, depending on how high it was (how thin the air), how fast, and whether it still had the fuel to keep thrusting before burnout. Once it burned out….. the air rudders could still have some effect as long as there was some atmosphere. In the case of the Redstone, it's warhead section separated and had a set of steering fins to help to steer it to the target during re-entry, though accuracy was poor (really poor with conventional warhead, nuclear warhead helped make up for accuracy error to an extent).

In the case of the V-2, I do not think the V-2 even tried to steer itself after the engine burned out, certainly not likely for as long as re-entry. And the V-2 was very inaccurate, as far as trying to hit a specific target. But was "good enough" to simply be aimed towards London and other cities, where by sheer numbers enough would hit to have the desired "Vengeance Weapon" effect.

UPDATE: I forgot to mention that when I did a gimbaled engine project in 1989, in mid-project I addressed that problem by having four small fins attached to the gimbaled engine mount, as well as four fixed fins of the same size attached to the rocket tail section. So, half of the aerodynamic fin surface area in the tail were used for steering control. Effectively like the V-2 and Redstone combined use of thrust vectoring (vanes) an air rudders, without chains and sprockets or additional pushrods.

- George Gassaway

Well put George. I don't think there is anyone here on this forum that knows more about rocket than you.
All of your post brings inlightment to many things.
Nothing that I will ever use or could afford, but just the same...
Your knowledge is a bank vault full of Gold Bullion to me.
God Bless

Wow, thanks George, never thought about the drag the vanes would produce, nor the small size of the exhaust plume with respect to the vanes. I guess this weekend I will buy a bottle of Tanqueray Gin and find a solution:wink:
Thanks to all that replied, nothing better than posting an idea and gaining more knowledge.