TK hop twist barrels, are they worth it?

[Glenn]

Delfi, they don't understand how it works with any BB mass, so I'm not sure what kind of answer yo expect to get.

 

Sale, I still can't figure out why he linked us to two items that counter his argument, either.

[Delfi]

Delfi, they don't understand how it works with any BB mass, so I'm not sure what kind of answer yo expect to get.

 

Sale, I still can't figure out why he linked us to two items that counter his argument, either.

 

I'm thinking along the lines of angular momentum and MoI ... I'm sure you see where this is going :-)

 

D

[RSP1]

RSP1: The lift created by the hop-up relies not only on the spin, but also the forward movement. Off the top of my head, I would imagine that with a high velocity Airsoft gun you have to apply less spin to the BB, because otherwise it would curve up rapidly. A lower powered setup allows you to set the hop-up to give a faster spin to the BB, which means that the BB will have more spin downrange as well. This could explain why lower powered models would seem to achieve a longer range than we would imagine.

 

-Sale

 

I had the same explanation - but decided against including it for two reasons. First, that I hadn't verified it, and second that I did not feel it would be necessary to bring explanations into it, since I only needed the point that the effect is perceived to discuss other perceived-effect based arguments. If that makes any sense.

 

Still talking with the warning that I have not personally scientifically tested the advantage, it has appeared useful for me since starting skirmishing. In comparison to most others at the local site, who need to use stronger springs, larger batteries, tougher bushings, replacement pistons, etc. to fuel their high FPS setups I usually just throw in some decent hop-up bits, fix any compression issues that might exist, and sometimes toss in a good barrel as well and I'm happy.

[Glenn]

Actually, velocity and hop are more independent than not, I think. The backspin produces a relative velocity difference.

 

In very round, arbitrary numbers, the BB is traveling at 100 m/s, and rotating at 100 rad/s. The top of the BB is now moving away from the wind at .6 m/s, while the bottom rotates into the wind at .6 m/s. Thus, the relative velocity of the top of the BB is 100.6 m/s, 99.4 at the bottom. To conserve energy, low pressure occurs at the top, higher at the bottom. Lift.

 

Changing the initial BB velocity doesn't change the relative speed difference, or the lift.

 

 

 

What I've always speculated might matter is if we don't assume a no slip condition at the BB. At greater velocities, boundary layer flow will peel off later, thus giving BBs more air to grab onto to make lift. Thus, less hop needed.

 

 

At the same time, spin mucks this up. I think that at higher velocities, you may need more hop. An slightly over hopped BB will tend to rise later in flight, after a period of flat trajectory - this could only be the result of increased lift at lower velocity. I'm not sure what is actually happening, its an interesting question.

 

 

It is also important to remember that the spin a BB takes is loosely proportional to its velocity as it passes the hop up nub, and proportional to the friction/stiffness of the hop rubber itself. An interesting question indeed.

[Delfi]

Actually, velocity and hop are independent. The backspin produces a relative velocity difference.

 

But mass and hop aren't. So given the same pre-hop energy, more hop is taken by a heavier BB to spin it efficiently (the 'sweet spot' we all know) as you've said.

 

The upside is that the heavier the BB is the greater the longevity of the spin and the more resistance there is to deflection ... the downside is that muzzle velocity (and non hop range) takes a double hit.

 

D

[Glenn]

Mass and hop are independent. A more massive BB requires more hop to support it, but spin two BBs at the same rate, and they generate the same amount of lift, regardless of mass.

 

So for a heaver BB, you would need to crank down the hop a bit harder, losing a bit more muzzle energy in the process.

 

Its also easy to see the lift and mass are independent - BB mass doesn't show up anywhere in the lift calculation. But life you said, to get the the sweet spot (when lift equals gravity), you need more hop. We're on the same wavelength, just a clarification.

 

 

But, as had been proved time and time again, a heavier BB has more range. Search, read the Variable thread.

[Delfi]

Mass and hop are independent. A more massive BB requires more hop to support it, but spin two BBs at the same rate, and they generate the same amount of lift, regardless of mass.

 

So for a heaver BB, you would need to crank down the hop a bit harder, losing a bit more muzzle energy in the process.

 

Its also easy to see the lift and mass are independent - BB mass doesn't show up anywhere in the lift calculation. But life you said, to get the the sweet spot (when lift equals gravity), you need more hop. We're on the same wavelength, just a clarification.

 

That's exactly what I thought I said I totally agree.

 

What I meant by 'double hit' was from both the decreased initial linear energy and the necessary angular energy too.

 

D

[Delfi]

I now see the confusion here I think..... 'independent of oneanother' rather than 'independent of the overall outcpme'.

 

The former is correct :-)

 

D

[Sale]

Actually, velocity and hop are more independent than not, I think. The backspin produces a relative velocity difference.

 

In very round, arbitrary numbers, the BB is traveling at 100 m/s, and rotating at 100 rad/s. The top of the BB is now moving away from the wind at .6 m/s, while the bottom rotates into the wind at .6 m/s. Thus, the relative velocity of the top of the BB is 100.6 m/s, 99.4 at the bottom. To conserve energy, low pressure occurs at the top, higher at the bottom. Lift.

 

Changing the initial BB velocity doesn't change the relative speed difference, or the lift.

I have to say I'm a bit confused now. In my mind I've compared the BB to the wing of an aeroplane, which also creates a lift by allowing air to pass the top more easily than the bottom. A plane that flies too slow should lose altitude, but the wing angle can be increased to counter that. I would compare the larger angle to an increased spin of the hop-up. When flying faster, less angle/spin would be necessary to create the same amount of lift.

 

I have no deeper understanding of the theories involved, but this is how I've reasoned it.

 

-Sale

[Glenn]

Well Sale, to be perfectly honest with you, I've done some research. I've found three unique derivations and formulations for Magnus lift,

 

One says lift varies with velocity squared.

 

One says lift varies linearly with velocity.

 

The third says lift occurs independent of velocity.

 

Go figure. I'm still reading.

 

 

[Pablo]

I have absolutely no interest in the subject but if anyone tells anyone else to shut up again, they'll take a few days off. I don't care how exasperated you may feel about someone's opinion, there's no need to be rude about it. That goes for both sides btw.

 

On with the science then, I guess.

 

 

[Delfi]

The third says lift occurs independent of velocity.

 

Interesting stuff Glenn.

 

The above can't be right ... empirical evidence shows that you need less hop for more powerful guns.

 

D

[Glenn]

I did the reading

 

It didn't help.

 

Each equation turns out to be loosely proportional to velcoity...the others had their extra/missing V terms buried in different derived coefficients.

 

I plotted two of the equations for a .25g BB, optimally hopped, at .75-2J.

 

NASA says:

 

Fundementals of Fluid Dynamics, 5th ed says:

 

 

Clearly, there are some assumptions being made in the forumulation of both equations that they aren't being explicit about. I don't agree with either, but I think I trust the second plot a little more.

[Stealthbomber]

Without the aid of textbooks, I would have thought it's kinda obvious that lift and speed of a BB aren't entirely related.

 

Wind your hop-up pretty-much fully on.

Shoot a BB.

Watch as it goes straight for about 20m and then zooms up into the air.

 

My own perception of what's happening is that the backspin (and thus the lift) isn't decaying as quickly as the linear force driving the BB out the muzzle.

 

At first the linear force is the dominant one and then, as the linear force decays, the lift is proportionally greater thus allowing the BB to zing skyward.

 

I think that, as Delfi or Glenn (I forgot) says, the point is that lift is proportionally the same regardless of speed cos you always have the same proportion of air going over the top and bottom of the BB.

[Delfi]

At first the linear force is the dominant one and then, as the linear force decays, the lift is proportionally greater thus allowing the BB to zing skyward.

 

Brings us back to mass again :-)

 

Is it fair to say that the effect described happens closer and closer to the gun as the mass of the BB increases?

 

D

[Sale]

Interesting stuff Glenn.

 

The above can't be right ... empirical evidence shows that you need less hop for more powerful guns.

A more powerful gun will give the BB more spin with the same hop-up setting.

 

So yes, it does prove that the hop-up can be set lower for a more powerful gun. But we can't measure exactly how fast the BB is spinning in a 300 fps and 400 fps gun for example.

 

Without the aid of textbooks, I would have thought it's kinda obvious that lift and speed of a BB aren't entirely related.

And I thought it's obvious that it is. An F1 wing produces more downforce (the opposite of lift) at higher speeds, no?

 

Wind your hop-up pretty-much fully on.

Shoot a BB.

Watch as it goes straight for about 20m and then zooms up into the air.

Just quoted to make sure we are on the same page here. Yes, this is what happens.

 

My own perception of what's happening is that the backspin (and thus the lift) isn't decaying as quickly as the linear force driving the BB out the muzzle.

 

At first the linear force is the dominant one and then, as the linear force decays, the lift is proportionally greater thus allowing the BB to zing skyward.

The linear force doesn't force the BB anywhere but forwards. The lift and gravity fight over the up-down axis of the BB regardless of how fast it's going forward.

 

As soon as the BB exits the barrel it starts to accelerate upwards, if the weapon is over-hopped. You only see this effect clearly later in the trajectory, because the lift can't make the BB move up suddenly. If you shoot at targets at a closer range with various hop-up settings, you'll notice a shift in the point of impact even from 5 meters.

 

I think that, as Delfi or Glenn (I forgot) says, the point is that lift is proportionally the same regardless of speed cos you always have the same proportion of air going over the top and bottom of the BB.

I have to think about this a bit to explain better how I see it. Right now I don't have an explanation that I'd be satisfied to post, but only analogies like the wing of an aeroplane or F1 car.

 

Ever shot a BB into water and noticed how it curved rapidly into the direction of hop-up? I'm thinking that the air or fluid resistance ("friction" on the surface of the BB) isn't linear, so at a greater speed the effect would be amplified. In the same way as the BB gets a more wild spin from the hop-up with a more powerful gun, it would be a similar thing in reverse with air.

 

EDIT: I suspect the lift is amplified because the faster moving BB will face more air molecules in the same time. IE. the air for the faster BB is "denser". The density does effect the lift, right? In water I can see it working very strongly, while in a vacuum the spin would not generate lift.

 

-Sale

[tome]

Just had a quick scan through the thread and I think i see what delfi is saying. .....The mass of the bb is proportional to the "rotational" momentum of bb in flight for a given rate of rotation.

 

So for a given rate of rotation a heavier bb will have a larger angular momentum (ie more energy will have gone in to spin it). If we assume that the surface of all bb are the same (they're not) then at a the same bb velocity, the forces acting to slow the rotation would be the same. Thus meaning that it will take longer to stop the rotation of the heavier bb.

 

I find what delfi is suggesting quite interesting So firing a relatively heavier bb from the same AEG, the bb will experience the "double hit" in muzzle velocity due to the greater energy required to do both given increased mass. However the effect of hop will be present for longer, so if the balance is right between the amount of time the hop is effective and the muzzle velocity, you could maybe get a greater range than a lighter bb. No matter how fast a bb flies, as soon as the hop effect is finished it will drop "like a stone" (albeit moving forwards at the same time)

 

TBH i'm not sure what this has to do with TK barrels anymore sorry hehe, but i'm enjoying reading the discussion here.

 

Another thing we have to consider is the human perception of what the bb is doing once it has left the barrel. I would say that it's very hard to spot "large" changes in trajectory, and we can only spot "very large" changes such as when the hop runs out and bb "nosedives". I say this because when i see the bb shot from my TM HiCapa with its V-hop, the trajectory appears to be very flat compared with other guns i have and it has surprising range. But logically this makes no sense to me, since as Sale said the bb has spin rate and velocity only as it's properties of motion so how can the v-hop produce a "different" effect from a normal hop. I would imagine that the trajectory with my hop setting on the hicapa is a very slow upward arc, slight enough that i still perceive it as flat. My personal theory is that guns capable of long range have hop units capable of more discrete settings so you can get more settings between "drop to the ground" and "reach for the sky" giving a more adjustable trajectory.

 

Sorry again for the early morning rant

[Delfi]

TBH i'm not sure what this has to do with TK barrels anymore sorry hehe, but i'm enjoying reading the discussion here.

 

Well, I figure that if we can explain how a conventional hop works then we can see how that could possibly apply to a TK barrel.

 

I have to admit that the more that we discuss this the more skeptical I'm becoming about the TK unit.

 

D

[Sale]

It will take longer to stop the rotation of the heavier bb.

Correctomundo.

 

Firing a relatively heavier bb from the same AEG, the bb will experience the "double hit" in muzzle velocity due to the greater energy required to do both given increased mass. However the effect of hop will be present for longer, so if the balance is right between the amount of time the hop is effective and the muzzle velocity, you could maybe get a greater range than a lighter bb. No matter how fast a bb flies, as soon as the hop effect is finished it will drop "like a stone" (albeit moving forwards at the same time)

In practice, adjusting the hop-up doesn't directly decrease or increase the muzzle energy. At zero hop-up, some guns tend to have a lower muzzle energy, because a bit of resistance holding the BB in place allows the pressure to build up. The BB is accelerated in the barrel after passing the hop-up, so it only makes sense that the effect is small.

 

When you chrono various guns with different weight BBs, the heavy BBs almost always show a higher muzzle energy. This is a combination of various factors. The two most solid ones are: 1) A heavy BB travels slower, so it faces less resistance. 2) A heavy BB spends more time in the barrel, under the effect of the air pressure.

 

Even with a fixed muzzle energy, a heavier BB will travel longer. We don't even need to take hop-up into account, because it's simply a matter of conservation of momentum. As the lighter BB is faster, it faces more air resistance. As it's lighter, it is more subjectible to said resistance. As a result, a 0.25g BB reaches 30 meters in the same time as a 0.2g BB, when both are fired with the same energy. From there the heavier BB will only increase its "lead" on the light BB, and in the end it drops to the ground further away than the light BB.

 

TBH i'm not sure what this has to do with TK barrels anymore sorry hehe, but i'm enjoying reading the discussion here.

Now that we have a discussion, I'm enjoying it. I'd like to see this as a separate thread maybe, but going through the physics of Hop-Up can also help us understand why the Tanio Koba Hop-Twist barrel - a good precision barrel - does not make the BB fly longer.

 

Another thing we have to consider is the human perception of what the bb is doing once it has left the barrel.

 

My personal theory is that guns capable of long range have hop units capable of more discrete settings so you can get more settings between "drop to the ground" and "reach for the sky" giving a more adjustable trajectory.

The ability to make adjustments in small increments, as well as dual pressure points to center the BB for a consistent spin, are characteristics of a good hop-up. A good hop-up can do wonders to the accuracy of the gun, which does improve effective range. The ability to tune the amount of spin accurately is important to achieve the best trajectory.

[Delfi]

Here's one 'from left field' that I haven't seen mentioned yet.

 

Does terminal velocity play a part here? Again mass related. the lighter BB being more likely to be affected.

 

D

 

[tome]

Here's one 'from left field' that I haven't seen mentioned yet.

 

Does terminal velocity play a part here? Again mass related. the lighter BB being more likely to be affected.

 

D

 

I don't think terminal velocity is applicable here. Terminal velocity is when the accelerating force and retarding force are equal, resulting in a constant velocity of an object. This occurs when the retarding force if positively proportional to the velocity of the object. Since the bb stops accelerating "forwards" horizontally once it's left the barrel, the idea of terminal velocity doesn't apply (you can see this as the bb is slowing down from the moment it leaves the muzzle rather than maintaining a constant velocity)

 

Of course the bb is still being accelerated by gravity, (only in the vertical direction) but i'm assuming you're interested in terminal velocity in the horizontal direction

[Delfi]

Of course the bb is still being accelerated by gravity, (only in the vertical direction) but i'm assuming you're interested in terminal velocity in the horizontal direction

 

Yep and your point about the acceleration of the BB is noted (& correct!).

 

But, given an impulse energy (again complicated because this is not instantaneous) is there a terminal velocity in the barrel and what does that depend on? What are the consequences of it? This all sounds very very complicated to me.

 

Still, it's a fun thing to discuss

 

D

[Stealthbomber]

The linear force doesn't force the BB anywhere but forwards. The lift and gravity fight over the up-down axis of the BB regardless of how fast it's going forward.

Yep, you're right.

What I mean is that the lift remains constant (if we ignore that the rate of spin is slowing down).

It's just that the BB flies forwards with relatively no lift because the forward velocity is so great, at first.

When the forward velocity reduces the amount of lift (proportional to forward speed) is greater and the BB zooms upwards.

 

If lift was proportional (I shouldn't have used the word "related" before. Obviously they're "related" in some way. ) to speed then surely, in our over-hopped gun, you'd see the opposite?

The BB would whizz upward out of the barrel and then flatten out as the velocity reduced?

 

And I thought it's obvious that it is. An F1 wing produces more downforce (the opposite of lift) at higher speeds, no?

See, this is one of those things where I KNOW there's a difference but I'm having trouble defining it.

 

When a wing is stationary it's generating no lift at all. The wing needs to be moving to generate lift.

A BB doesn't need to move to generate lift. It needs to spin. As long as it's spinning correctly, the velocity doesn't matter.

 

If we shoot a BB at 100m/sec, the air above the BB is traveling at (say) 105m/sec and the air below it is traveling at 95m/sec. This 10m/sec differential generates a specific amount of lift in a 6mm, 0.2g BB.

If we shoot the same BB at 200m/sec, the air above the bb will (if we assume the backspin is the same) be traveling at 205m/sec and the air below it is traveling at 195m/sec. In theory, the same lift will be generated due to the 10m/sec differential, regardless of the increase in speed.

 

I admit that, in practical terms, it wouldn't work quite like this since firing a gun at 100m/sec would generate backspin of (say) 500rpm whereas firing the gun with the same amount of hop a t 200m/sec would probably generate a greater amount of backspin.

Thing is, though, that generates more spin (and thus more lift). For the purposes of this discussion we're talking about the same amount of spin at different speeds, right?

 

Basically, it seems, to me, it'd be better to compare a BB to a helicopter rather than an aeroplane. In a helo' the lift is controlled independently of speed.

 

I'm sure there's a term for this. Something like passive lift vs active lift or static lift vs dynamic lift.

[Glenn]

Because I didn't actually see anyone answer Sale's question, yes lift depends directly on fluid density. My intuition and every equation I've dug up agree.

 

The difference in lift isn't as differnt as you'd think. It's just delta P across a body, and in each case it is generated by a change in stream velocity across different surfaces of a body.

 

A wing does this with a specific form factor, and is dependant on speed becuase it needs to develop voritcity to actually build sufficient lift.

 

A helicopter blade is the exact same thing, except it's rotating around a point rather than moving linearly. The lift is the same, except it varies with the tangential velocity of the blade as you move along its length.

 

A BB is different only in that it a symetrical object, it still generates lift through a velocity differential.

 

 

But, remember, a BB DOES need to move to generate lift. If the BB is spinning, free in space, the air above it moves at some velocity, and the air below it moves at the same velocity in the opposite direction...no velocity differential, no pressure gradient. Same pressure all around the BB.

 

You already know this, though. Ever hear of the right hand rule? Point your right index finger along the flight path of the bb (forward). Point your middle finger along the BBs rotating axis (90 degrees from your index finger) Now point your thumb so its perpendicular to both index and middle fingers. You're pointing up, and this is the direction the lift force acts.

 

If you point your index finger in some other direction, you can see that your thumb, and lift, are now pointing else where, too. To have lift, you need to have a velocity gradient, which comes from airflow perpendicular to the BB's axis of rotation. Without airflow, you can't point your thumb, don't get lift.

 

But like I said, you know this. If the BB made lift without airflow, why would it point up? Would it not just point in all directions equally? It'd be fine to think about it as equal lift pointing radially around the BB. The BB, and the airflow around it, would be symmetrical when viewed on the plan perpendicular to the rotating axis. No net force, no lift. Becuase the BB flies forward, you get lift, in vectors that match the right hand rule. Think of turning your AEG to the side...the vectors still mactch the right hand rule...just tilt your hand.

[Stealthbomber]

A helicopter blade is the exact same thing, except it's rotating around a point rather than moving linearly. The lift is the same, except it varies with the tangential velocity of the blade as you move along its length.

I meant the way a helicopter, as a whole, works, rather than just the wing.

 

Point being that a helicopter generates a given amount of lift regardless of speed. A helicopter can generate 1500kg of lift while doing 0mph or doing 150mph.

 

If you could get a BB to backspin while standing still it'd be the same.

It'd generate the same (ignoring that lost to friction, I assume) lift at rest as it would at speed... IF you could control the velocity while still keeping it spinning.