Effective NA Power Mods

[Ultramaroon]

Originally Posted by CSG Mike

I'm gonna let you think about that one

There may be a constant RPM, but it doesn't mean there are no forces involved

Forces at equilibrium. Sheesh!

[Spartarus]

Originally Posted by CSG Mike

I'm gonna let you think about that one

There may be a constant RPM, but it doesn't mean there are no forces involved

Originally Posted by justatroll

So someone please tell me how rotational inertia can affect to torque produced at constant RPM?
(hint I already told you above)
If it is such simple physics, it should be a simple answer right? [/SIZE]

I'm going to take the controversial view that reducing rotating mass on a 4 banger will decrease constant-RPM torque at low RPMs, but increase constant-RPM torque if measured at higher RPM's, and I have experience and a tested theory to back that claim.

It involves 3RZ's.

[justatroll]

Originally Posted by CSG Mike

I'm gonna let you think about that one

There may be a constant RPM, but it doesn't mean there are no forces involved

Certainly there is a force, in this case a torque.
However when measuring the torque there is no acceleration.
Therefore the mass does not matter, the force will be the same regardless of the mass.

When performing the test, there is not supposed to be any acceleration while measuring the torque (force).
Again - a dyno test is not a race from one RPM to another.
It is supposed to be a series of discrete measurements at constant RPM (and constant Torque).

[justatroll]

Originally Posted by DSLeach

If you are able to reduce the rotational mass of the engine and drive train, you will get a higher HP reading on the chassis dyno. Less power used to accelerate rotating mass means more is available to spin the dyno drum.

One more comment on this one: On the chassis dyno, the car is not accelerating, and when performing the wheel torque measurements, the system is supposed to be at steady state.
So again NOTHING is accelerating, not the car, not the rotating assembly of the engine, not the drivetrain.
No acceleration - then the mass does not matter - it is a STATICS problem.

NOW - IF you take a stock car and perform a 1/4 mi run, then using the time it took and the mass of the car, you can calculate the HP.
Next - reduce the rotational mass of the rotating assembly and perform the same test again - WOW faster!
If you do NOT account for the reduced mass of the vehicle as a whole, and do you calculations again, the result will be - MORE HP.

BUT - if you recalculate using the new mass of the car (disregarding the change in rotational inertia of the rotating assembly) your answer will show the same HP to within about 1%.
This is because you can reduce the rotational mass of the flywheel and the pulley, and the driveshaft, and the wheels.

But when compared to the mass of the ENTIRE rotating mass: Pulley(s), belt, alternator, water pump, AC pump, timing chain, cams, crankshaft, pistons, wrist pins, rings, rods, flywheel, pressure plate, clutch disk, transmission input shaft, lay-shaft, gears, driveshaft, DS-bearings, differential, CV joints, axles, wheel bearings, disk brake rotors, wheels, lugs nuts, tires - You cannot reduce the MOI of that entire mass by more than about 1%.

[MuseChaser]

Originally Posted by Cole

Yes, but we're talking entirely theoretical here. If there's no air moving over and under the wings, no lift can be generated. Like if you're on a treadmill that's matching your speed exactly and you're wearing a parachute. Is that parachute going to fill up with air?

Your statement, "If there's no air moving over and under the wings, no lift can be generated" is of course true, but the treadmill would not cause that condition to exist. On the ground and in level or climbing flight (and to a certain degree descending flight under power), airplanes move forward due to air being forced rearward. Once they reach a certain speed, the wing starts to develop lift because of the difference in airflow speeds above and below the wing. Air travels faster over the top of the wing, developing an area of lower pressure than below the wing... this is "lift." Groundspeed (and airspeed to varying degrees) is determined by the air being forced backwards, and increases as the airplane overcomes inertia and gains momentum. As the speed increases and lift develops, the airplane gets lighter so there's less drag at the wheels/ground, speed continues to increase, and the airplane lifts off once it generates more lift than it weighs. Again, there's more to it than that, but that's a pretty good basic way to look at it.

Back to the treadmill and your human-w/-a-parachute scenario. If the human was walking or running on the treadmill and was not going forward in real space, then of course his parachute would not inflate; it would be stationary. BUT... if the person on the treadmill had on roller skates or was on a skateboard and had a big ol' powerful fan strapped on in such a way that airflow was unimpeded (and the treadmill was very very long, like one of those moving walkways in an airport), they'd develop forward motion no matter what. If the treadmill was going so fast that the friction in the wheel bearings of the skateboard heated up and seized, preventing the wheels from turning faster than the treadmill, then you'd be correct. As long as the skateboard's wheels spin freely, the treadmill is immaterial... our hero will move forward just as he would on non-moving surfaces due to the air being forced behind him.

Stand outside in a strong wind and face the wind. You'll find yourself leaning forward, like you would if you were standing on a very steep hill, even though you're on level ground. Turn so the wind is at your back, but stand in the same place. Now you have to lean backwards so you don't get blown forward or fall over. The ground hasn't changed, yet your "attitude" is different. The wind doesn't care about the ground (again, vast oversimplification... ground effect, airflow over obstacles, blah blah blah.. but for our purposes, we can ignore that stuff for now). Nor will the airflow over the airplane be influenced by the treadmill. The ONLY way for a treadmill to have any influence on an airplane's speed is if the airplane's WHEELS are prevented from spinning completely freely.

Let me try one more.. even simpler. Stand outside on the road (watch out for cars) on a very windy day. You won't go anywhere. Now, stand on a skateboard in the same place. The wind will blow you down the road. The speed of the road surface hasn't changed; you've just lowered the friction component between you and the road (your feet on the road vs. the skateboard's wheels on the road) so you move down the road under the force of the wind.

You are right about the airflow over the wings being necessary to produce lift. It doesn't matter how that airflow is produced. If the airplane was completely stationary but a fan was generating airflow over the wings at a high enough velocity, the airplane would still lift off. There's a REASON we "tie down" airplanes when parked outside hangars; airplanes can be and ARE knocked over and even spontaneously relocated by very strong winds.

In real world physics, there's probably a limit as to just how fast the wheels on a given plane COULD turn before creating enough heat to burn out the bearings and seize up. If you could somehow create an airplane-sized treadmill capable of whatever that speed is (so already we're leaving the real world again) and you could cause that condition before the airplane took off, then I guess you could win the argument. It would have to happen very quickly, because no matter how fast the treadmill was moving, the airplane WOULD start to move forward the instant the prop starting pushing air rearwards.

One more point - airspeed and groundspeed are two very different things. Airplanes can hover over a point on the ground. W/ full flaps down, my plane can fly as slow as 40mph. If I fly directly into a 40mph headwind, my net forward progress is 0mph, yet there's enough airflow caused by my prop and the headwind to generate enough lift to hold altitude.

Somebody nudge @Ultramaroon ... I think he nodded off after the first sentence...

Barry

[go_a_way1]

Originally Posted by MuseChaser

Your statement, "If there's no air moving over and under the wings, no lift can be generated" is of course true, but the treadmill would not cause that condition to exist. On the ground and in level or climbing flight (and to a certain degree descending flight under power), airplanes move forward due to air being forced rearward. Once they reach a certain speed, the wing starts to develop lift because of the difference in airflow speeds above and below the wing. Air travels faster over the top of the wing, developing an area of lower pressure than below the wing... this is "lift." Groundspeed (and airspeed to varying degrees) is determined by the air being forced backwards, and increased as the airplane overcomes inertia and gains momentum. As the speed increased and lift develops, the airplane gets lighter so there's less drag at the wheels/ground, speed continues to increase, and the airplane lifts off once it generates more lift than it weighs. Again, there's more to it than that, but that's a pretty good basic way to look at it.

Back to the treadmill and your human-w/-a-parachute scenario. If the human was walking or running on the treadmill and was not going forward in real space, then of course his parachute would not inflate; it would be stationary. BUT... if the person on the treadmill had on roller skates or was on a skateboard and had a big ol' powerful fan strapped on in such a way that airflow was unimpeded (and the treadmill was very very long, like one of those moving walkways in an airport), they'd develop forward motion no matter what. If the treadmill was going so fast that the friction in the wheel bearings of the skateboard heated up and seized, preventing the wheels from turning faster than the treadmill, then you'd be correct. As long as the skateboard's wheels spin freely, the treadmill is immaterial... our hero will move forward just as he would on non-moving surfaces due to the air being forced behind him.

Stand outside in a strong wind and face the wind. You'll find yourself leaning forward, like you would if you were standing on a very steep hill, even though you're on level ground. Turn so the wind is at your back, but stand in the same place. Now you have to lean backwards so you don't get blown forward or fall over. The ground hasn't changed, yet your "attitude" is different. The wind doesn't care about the ground (again, vast oversimplification... ground effect, airflow over obstacles, blah blah blah.. but for our purposes, we can ignore that stuff for now). Nor will the airflow over the airplane be influenced by the treadmill. The ONLY way for a treadmill to have any influence on an airplane's speed is if the airplane's WHEELS are prevented from spinning completely freely.

Let me try one more.. even simpler. Stand outside on the road (watch out for cars) on a very windy day. You won't go anywhere. Now, stand on a skateboard in the same place. The wind will blow you down the road. The speed of the road surface hasn't changed; you've just lowered the friction component between you and the road (your feet on the road vs. the skateboard's wheels on the road) so you move down the road under the force of the wind.

You are right about the airflow over the wings being necessary to produce lift. It doesn't matter how that airflow is produced. If the airplane was completely stationary but a fan was generating airflow over the wings at a high enough velocity, the airplane would still lift off. There's a REASON we "tie down" airplanes when parked outside hangars; airplanes can be and ARE knocked over and even spontaneously relocated by very strong winds.

In real world physics, there's probably a limit as to just how fast the wheels on a given plane COULD turn before creating enough heat to burn out the bearings and seize up. If you could somehow create an airplane-sized treadmill capable of whatever that speed is (so already we're leaving the real world again) and you could cause that condition before the airplane took off, then I guess you could win the argument. It would have to happen very quickly, because no matter how fast the treadmill was moving, the airplane WOULD start to move forward the instant the prop starting pushing air rearwards.

One more point - airspeed and groundspeed are two very different things. Airplanes can hover over a point on the ground. W/ full flaps down, my plane can fly as slow as 40mph. If I fly directly into a 40mph headwind, my net forward progress is 0mph, yet there's enough airflow caused by my prop and the headwind to generate enough lift to hold altitude.

Somebody nudge @Ultramaroon ... I think he nodded off after the first sentence...

Barry

TL;DR ??

[gramicci101]

Originally Posted by go_a_way1

TL;DR ??

Airplane go forward, treadmill go backward. You can't explain that.

[Tcoat]

Originally Posted by MuseChaser

In real world physics, there's probably a limit as to just how fast the wheels on a given plane COULD turn before creating enough heat to burn out the bearings and seize up. If you could somehow create an airplane-sized treadmill capable of whatever that speed is (so already we're leaving the real world again) and you could cause that condition before the airplane took off, then I guess you could win the argument. It would have to happen very quickly, because no matter how fast the treadmill was moving, the airplane WOULD start to move forward the instant the prop starting pushing air rearwards.

Barry

I did this experiment for a grade 9 Science Fair. Using an gas powered string controlled Spitfire (was a great excuse to buy a flying model) and a belt sander hooked up to a rheostat I set out to prove or disprove the old wives tale that it would just sit there.

Now, that was 40 years ago so I do not recall all the numbers but the basic results were:

Plane at take off power + Sander with smooth belt at low speed = Normal take off
Plane at take off power + Sander with smooth belt at medium speed = Plane struggled and lost a bit of ground on sander but still managed to take off
Plane at take off speed + Sander with smooth belt at high speed = Plane could not overcome the belt and slowly fell of the back of the sander (where it promptly smacked the prop on the table and smashed it to pieces)


Plane at take off speed + sander with course belt at slow speed = Plane could barely get enough speed to take off
Plane at take off speed + sander with course belt at medium speed = Plane could not take off and slid off back again (and another prop bit the dust)
Didn't even bother to try high speed.
Oh, and I went through 4 sets of wheels during the process.


What was readily observable was that the friction between the belt and the wheels would eventual start to turn them backwards. Low friction and high speed or high friction at low speed would turn the wheels backwards enough to overpower the thrust of the engine and the wheels would stop turning and game over.
This is where what you said above comes in though. I did the math based on the HP of the model and the RPM speed of the sander and then took it up to full scale. Like I said I do not recall the real numbers but in order for the same results to happen with a real Spitfire the belt would have had to be going someplace in the neighborhood of 850 MPH. To the best of my knowledge even now there are no treadmills capable of hitting 850 MPH and if there was (like you said) the tires would blow well before the plane sat still. So could a plane on a treadmill just sit there? Sure, but there is not a hope in hell of having it happen in reality. Myth was BUSTED.

[justatroll]

Oh and @DSLeach,regarding the MOI and rotational inertia thing?
I have a 'rough' idea what is going on.
In fact I began modeling the entire rotating assembly and drivetrain in solidworks, but could not obtain the weights of enough of the individual components so I gave up:





I model in Onshape when at home and can import the models into SW at work.

And since I guess I have to defend my credentials when challenged on it:
I am a Principle Test Engineer/Staff Consultant at one of the most advanced environmental test facilities in the country with over 20 years experience.
My office is in the dynamics lab.
The item I am currently in charge of testing costs more than a nuclear submarine.
But I have learned to not lead with that.

[Ultramaroon]

Originally Posted by justatroll

Oh and @DSLeach,regarding the MOI and rotational inertia thing?
I have a 'rough' idea what is going on.

Stu, you have way more than a rough idea. I'm sure you know the whole thing can be modeled pretty effectively using first principles in a closed form. I'm just extending my support for your argument.

[MuseChaser]

Originally Posted by go_a_way1

TL;DR ??

NLE;DU

[go_a_way1]

Originally Posted by MuseChaser

NLE;DU

"Never Learn English; Don't urinate" ????

[Captain Snooze]

Originally Posted by justatroll

When performing the test, there is not supposed to be any acceleration while measuring the torque (force).
Again - a dyno test is not a race from one RPM to another.

All the torque here sorry I mean talk here seems to be about brake dynos. I am suggesting an inertia dyno will show an increase in power if the rotating mass is reduced sufficiently.

Originally Posted by justatroll

Again, dynos do NOT measure how fast you can change RPM.

Sorry but inertia dynos DO work that way.

"accelerate that mass from a low rpm to a high rpm...."
[ame="https://www.youtube.com/watch?v=FF0JeV8EowU"]Inertia Dynamometer - YouTube[/ame]

[MuseChaser]

Originally Posted by go_a_way1

"Never Learn English; Don't urinate" ????

Not Long ENOUGH; Didn't Understand