Finless rocket

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Chicagonative17

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Is there a way to launch a finless rocket? I am not talking about launching a finless rocket the normal way you launch a finned rocket because it simply wouldn't work.

I guess my question is, are there any innovations and ideas out there about how to do this?

Some of the ideas I have thought about probobly won't work...

- spin launch a rocket out of a tube using air pressure and then fire the motor almost imediately after the pressure tank is fired. The gyration will help create stability.
- somehow mount the motor towards the front of the rocket

Basically I want to know if there is a way to have ZERO fin drag and achieve much better performance than a rocket with fins.
 
- spin launch a rocket out of a tube using air pressure and then fire the motor almost imediately after the pressure tank is fired. The gyration will help create stability.

That's possible. Inducing a spin might make the rocket stable.

- somehow mount the motor towards the front of the rocket

Having the motor in front won't make any difference unless you're doing it just to move the Center of Gravity forward.

Basically I want to know if there is a way to have ZERO fin drag and achieve much better performance than a rocket with fins.

Spin stabilization or active-guidance (through thrust vectoring) are the only two ways I can think of to meet that goal. Neither would be very easy to accomplish in a hobby rocket, but I think some have tried.

-- Roger
 
I too have thought about the bottle rocket, but I was leaning more towards a rocket with such great efficiency that with some design improvements, will rank up there with some of the highest high altitude birds with fins.
 
Depending on the size of the rocket, you could launch the rocket normally (no spinning) and then fire 4 smaller-than-the-main-motor rocket motors (mounted on the side of the rocket, pointing horizontally) to introduce spin.
 
Nice idea, but thats a little too complex. What I think would be the most efficient way is to do it with one motor.

I have a question to all the scientists out there, if you have fins underneith the rocket canted, could it induce spin from the exhaust coming out?
 
I think you can have fins under the rocket and the airflow will spin the rocket. Remember's Jamie's rocket from Mythbusters?
 
I have a question to all the scientists out there, if you have fins underneith the rocket canted, could it induce spin from the exhaust coming out?

This is called thrust vectoring. It was/is used all the time to control a rocket. The most obvious display would be the German V2.

What about a tube launched rocket that has guides along the inside of the tube that accept rail buttons. Think rifle barrel.

-Aaron
 
So a rifled tube, that catches rail buttons along the rocket, its worth a try. That kind of thing is pretty complex to get since it would need to be custom made for each diameter rocket.

If a tube (non-rifled) was long enough, would it still be stable with the vector fins under the rocket after it leaves the tube?
 
Maybe it would be, but from the friction that the rocket encounters from sliding up the long tube would probably decrease it's altitude by alot. I remember seeing someone's rocket on NARAMlive.com from NARAM 48 (or 49?). It was red (looked to be BT80 based, but could've been a 3") and had a 24mm motor mount at the very top. Basically the motor's thrust was dragging the rocket (or tube, as it didn't even have a nose cone) upwards, instead of pushing.
 
If the tube was very clean and polished and about 1/16th of an inch of room inbetween the rocket and tube on both sides, then I am almost possitive it would have less drag than a rocket with a launch lug/buttons and at least 3 fins.
 
Is there a way to launch a finless rocket? I am not talking about launching a finless rocket the normal way you launch a finned rocket because it simply wouldn't work.

I guess my question is, are there any innovations and ideas out there about how to do this?

Some of the ideas I have thought about probobly won't work...

- spin launch a rocket out of a tube using air pressure and then fire the motor almost imediately after the pressure tank is fired. The gyration will help create stability.
- somehow mount the motor towards the front of the rocket

Basically I want to know if there is a way to have ZERO fin drag and achieve much better performance than a rocket with fins.

Finless Model rockets have been done quite a few times over the past 40+ years.
Many novel methods, some have been semi successful, other not so. but your premise looking to match "fined model" altitudes isn't in the cards.
Spin stabiliztion has been used for years by nasa on most "unguided" sounding rockets. and spinning does give same a much more predictable flight path.. the down side is it also Lower attained altitude through friction and drag due to the spinning body thur the air.

Spin up of a model before launch as been done in a number of way, all having some trade offs in performance.
Many a comptition modeler as attempted to use a finless upper stage in altitude compeititons with very little success.
good thought tho;)
as for fins under the vehicle..look as the early bombardment rockets after Congreve which placed vanes in the exhaust path to spin the projectile.
 
Hey, I've never posted here before but i think i have an idea for this one. I got my idea when i was thinking about a cruise ship which attains its stability in water not only by its massive size but also by the gyroscope revolving inside the ship itself.

What if you put at gyroscope inside the rocket? All you need is a small motor which revolves two small weights aligned vertically inside the rocket.


Although the weight of the gyroscope might cancel out the advantage of not having fin drag.


just an idea...
 
Would that actually work? Would you place it in the NC?

If so, that would be SOOOOOOOOOO cool!
 
You would want to place it at the CG most likely. Gyros help A LOT, but for a rocket, I am not sure. They are used on RC helis, planes, and other odds and ends like high speed RC cars.
 
What about clustering? Like the Delta 2, have one motor in the middle then have like four other motors around it slanted a bit toward the middle.:cool::D
 
It might work, but you need to know the minimum angle of the motors for stability without fins. If the angle is large than the body diameter might be large as well.
 
What about clustering? Like the Delta 2, have one motor in the middle then have like four other motors around it slanted a bit toward the middle.:cool::D

That would not make it any more stable.

Despite what you might think, angling the motors inwards would not help stability at all - the total force vector is really all that matters.
 
Back in the early 1980s, Korey Kline (K2) tested many reduced fin and no-fin rockets at the Lucerne, CA, launch site.

Many of these were documented in California Rocketry magazine.

Korey built a no-fin rocket which used two canted D12s and had the launch rod go up through the center of the rocket. It worked!
 
- spin launch a rocket out of a tube using air pressure and then fire the motor almost imediately after the pressure tank is fired. The gyration will help create stability.

The density of the typical model rocket is not high enough to produce a sufficient moment of inertia with a reasonable roll rate. Even a min diameter rocket would have to be large in diameter and spinning at a significant rate.

Basically I want to know if there is a way to have ZERO fin drag and achieve much better performance than a rocket with fins.

The percentage of total drag due to the fin drag is typically very small. Removing the launch lug will reduce the drag more than removing the fins.

Several people have made elementary active stability demonstrator with model rockets, gyros, and various pitch actuators.

Keep in mind that dynamic stability problems can result in more drag than what is predicted for a statically stable rocket at zero angle-of-attack. The time spend correcting, overshooting, coning, etc., will produce more drag.

Several people have built 'finless' rockets, such as a Delta II, that have flown stable trajectories. Cone-shaped rocket, such as a "DC-X" can also be made to fly stable.
 
The density of the typical model rocket is not high enough to produce a sufficient moment of inertia with a reasonable roll rate. Even a min diameter rocket would have to be large in diameter and spinning at a significant rate.



The percentage of total drag due to the fin drag is typically very small. Removing the launch lug will reduce the drag more than removing the fins.
....

Disagree on the last point. Fins usually acct for 20 percent or much more of total drag, lugs, buttons and the like should be well under 10 percent. This has come up numerous times on TRF--what we need is a collapsing fin that decreses in size with velocity...
 
Disagree on the last point. Fins usually acct for 20 percent or much more of total drag, lugs, buttons and the like should be well under 10 percent. This has come up numerous times on TRF--what we need is a collapsing fin that decreses in size with velocity...
Nope. Go do some googling of NASA (or older NACA) docs. And look for a NAR R&D report on the subject (wind tunnel tests).

An aerodynamic fin at a small angle of attack is almost zero drag. Essentially only skin drag. A poorly shaped find also has shape drag, base drag, and vortex energy loss.

Lugs and buttons are irregular protrusions. They break the laminar flow. They also increase the cross-sectional area but are typically not included in the frontal area (just the BT is used usually). Depending on the relative size of the rocket diameter compare to the lug/button, and depending on the Reynolds number (length and speed of the rocket) the lug/button could be 5% to 30% of the drag. The other effect is the side torque of the lug that will make the rocket fly at a slightly greater angle of attack, which increases frontal area and Cd for the whole rocket.
 
Lugs and buttons are irregular protrusions. They break the laminar flow. They also increase the cross-sectional area but are typically not included in the frontal area (just the BT is used usually). Depending on the relative size of the rocket diameter compare to the lug/button, and depending on the Reynolds number (length and speed of the rocket) the lug/button could be 5% to 30% of the drag. The other effect is the side torque of the lug that will make the rocket fly at a slightly greater angle of attack, which increases frontal area and Cd for the whole rocket.

So has anybody recessed their launch lugs? You know, spring load them and build them into a recess so that they can be drawn out to join the launch rail but as soon as they reach the end of the rail, zip, they suck into the recess and under the area of skin effect.

This could theoretically work for launch lugs in LPR too but would be more difficult on small diameter rockets and the mechanism would add weight. I'm not sure it would be worth it, then again a 30% reduction in drag could easily compensate for some additional weight.

Just thinking out loud.
 
Hey, I've never posted here before but i think i have an idea for this one. I got my idea when i was thinking about a cruise ship which attains its stability in water not only by its massive size but also by the gyroscope revolving inside the ship itself.

What if you put at gyroscope inside the rocket? All you need is a small motor which revolves two small weights aligned vertically inside the rocket.


Although the weight of the gyroscope might cancel out the advantage of not having fin drag.


just an idea...
What!!!! You actually think the gyro stablizes a ship, ROFLMFAO!!!!

Back in the early 1980s, Korey Kline (K2) tested many reduced fin and no-fin rockets at the Lucerne, CA, launch site.

Many of these were documented in California Rocketry magazine.

Korey built a no-fin rocket which used two canted D12s and had the launch rod go up through the center of the rocket. It worked!
This is what I was thinking but with 3 motors on a slight cant.

So has anybody recessed their launch lugs? You know, spring load them and build them into a recess so that they can be drawn out to join the launch rail but as soon as they reach the end of the rail, zip, they suck into the recess and under the area of skin effect.

This could theoretically work for launch lugs in LPR too but would be more difficult on small diameter rockets and the mechanism would add weight. I'm not sure it would be worth it, then again a 30% reduction in drag could easily compensate for some additional weight.

Just thinking out loud.
I am working on a rail button design.
 
DH,
I looked but could find nothing to support the assertion that launch lugs create more drag than fins. I looked at Demars well done R&D project, and once again at numerous NACA reports I've reviewed in the past. Perhaps you can point me to a good paper or two which breaks down the relative contributions, based on windtunnel or flight measurements.

What I do know is that out of much of the work you appear to be citing arose the datcom methodology for providing a first order approximation to Cd computation. Doubtless this has been refined in the era of supercomputing with various competing methodologies to a much higher level of precisicion.

Rocksim uses the Datcom methodology. I believe Aerodrag uses Newtonian plate methodology. In my hands at least I get a high level of concordance between the two--and whats more generally predict within 5 to 10 percent accuracy most flights.

Both of these programs provide for a Cd breakdown. In neither case do they agree with your assertion. Instead, fins generally contribute 25 percent or so to the total drag of a typical model rocket, ie fineness ratio of 10 to 20, no aft boattail, a cone of L/D 3 to 5, etc.

Finally I have never noticed any tendency of a rocket to fly in the direction of the launch lug. First, almost all rockets s pin to some extent, and secondly for such a parasitic drag effect to be present, one would expect to observe this much more readily on various assymetric configurations including camera carrying vehicles.

I would very much like to be proven wrong here....
 
So has anybody recessed their launch lugs? You know, spring load them and build them into a recess so that they can be drawn out to join the launch rail but as soon as they reach the end of the rail, zip, they suck into the recess and under the area of skin effect.

This could theoretically work for launch lugs in LPR too but would be more difficult on small diameter rockets and the mechanism would add weight. I'm not sure it would be worth it, then again a 30% reduction in drag could easily compensate for some additional weight.

Just thinking out loud.

https://www.freepatentsonline.com/4170923.html

I haven't heard of that being used for hobby rockets. But launch lugs that fall away have been used. A more common approach is to eliminate the launch lug by using a tower.

-- Roger
 
I would very much like to be proven wrong here....

I think we're both correct, but are looking at different constraints on the problem.

Once I get caught up on a few things, I'll see if I can locate the old papers that discuss various drag components.

Here's something to ponder.... if a lug (or button) contributes to drag and it is an asymmetrical feature (one side of the rocket), then it provides a torque that pitches the rocket. There will be an angle of attack where the corrective force of the fins/body balances the side torque of the lug. Even a small angle of attack adds significant drag. Depending on the masses and moments, there may be a dynamic condition where the rocket oscillates and rolls because of the asymmetrical disturbance. This further adds to the drag that was computed under static assumptions.
 
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