dyno question

[mk e]

I thought load on the engine doesn't change?

The total load doesn't change unless you close the throttle.

Total load = brake load + inertial load.

Reducing the brake or measured load allows the engine to accelerate, but the acceleration creates an inertial load because acceleration is no longer 0. The engine makes the power it makes and the forces always have to balance, there's just no way around it.

[Warp Speed]

I thought load on the engine doesn't change?

The total load doesn't change unless you close the throttle.

Total load = brake load + inertial load.

Reducing the brake or measured load allows the engine to accelerate, but the acceleration creates an inertial load because acceleration is no longer 0. The engine makes the power it makes and the forces always have to balance, there's just no way around it.

K

[Stan Weiss]

If the engine always sees the same total load. Wouldn't you see a variable acceleration rate during the test?

Stan

[turbobaldur]

Land & Sea water brakes servo control water flow into the brake, versus a superflow that controls water flow out... so yes you can control on the inlet. Flow through the pump is the physical means of control for a water break, but as far as control scheme with decent software you can control off any combination of RPM, Load, & throttle position - might have to tune a PID loop if your chosen method isn't provided by the manufacturer. Gdlk!

Yeah and both methods have their merits.
The downside of the L&S method is that to reduce fill and thus allow the engine to reach higher RPM where it produces more power, you are reducing water flow and thus reducing the brake cooling.
The Superflow method of controlling the outlet makes more sense in that aspect, at minimum fill (load valve fully open) you've got maximum water flow and thus maximum cooling. The downside is the reduced range of control, hence the need to adjust the inlet valve for the RPMs you're testing at.
DTS did this the best, using servos for both inlet and outlet.

[mk e]

If the engine always sees the same total load. Wouldn't you see a variable acceleration rate during the test?

Stan

Yes.

This is left over from a different thread so it's incomplete here. The original point was the total load is always equal and opposite to the power the engine produces. If the throttle is open then the cylinders are filling , fuel is burning, and the engine is making the HP it makes (at whatever RPM it's at) and that is true whether an external load is applied to hold it to a constant RPM or there is no external load and it is accelerating as fast as it can against inertia and at every point in between.

[Zmechanic]

Another "both are correct" moment

RPM is the input to the controler, servo position the output. Servo position changed the load, the load changes the RPM, the controller sees the RPM change and moves the servo.....and around and around we go

In systems speak we are controlling RPM because that is what the control system is monitoring and reacting too, but in reality its the servo being "controlled" so you're both right IMO.

This is how I was demonstrating it originally, but I'm perfectly willing to agree (because it's the truth) that the dyno's final output to the motor is torque. Yes of course it could be less torque or more torque than the engine could put out, otherwise it would actually have NO control at all. That's control theory 101. However I feel the discussion is starting to turn towards arguing for the sake of arguing.

[DaveMcLain]

Land & Sea water brakes servo control water flow into the brake, versus a superflow that controls water flow out... so yes you can control on the inlet. Flow through the pump is the physical means of control for a water break, but as far as control scheme with decent software you can control off any combination of RPM, Load, & throttle position - might have to tune a PID loop if your chosen method isn't provided by the manufacturer. Gdlk!

Yeah and both methods have their merits.
The downside of the L&S method is that to reduce fill and thus allow the engine to reach higher RPM where it produces more power, you are reducing water flow and thus reducing the brake cooling.
The Superflow method of controlling the outlet makes more sense in that aspect, at minimum fill (load valve fully open) you've got maximum water flow and thus maximum cooling. The downside is the reduced range of control, hence the need to adjust the inlet valve for the RPMs you're testing at.
DTS did this the best, using servos for both inlet and outlet.

That is sort of true but the brake's water flow rate also increases with RPM so on an engine that has the brake filled to a certain amount around peak torque and filled to a lesser amount at higher RPM around peak HP the amount of water that actually is flowing through the system can be about the same overall. The real trick is getting the outlet restrictor sized correctly for the water supply so that the brake can respond about the same to either increasing the load or decreasing it and so that the outlet water temperature stays below the boiling point.

Land and Sea has dramatically improved their stuff over the years. The newer style toroidal brakes have less internal volume (respond to the control more rapidly) and they can hold more torque with a given water supply.

[cpmotors]

Land & Sea water brakes servo control water flow into the brake, versus a superflow that controls water flow out... so yes you can control on the inlet. Flow through the pump is the physical means of control for a water break, but as far as control scheme with decent software you can control off any combination of RPM, Load, & throttle position - might have to tune a PID loop if your chosen method isn't provided by the manufacturer. Gdlk!

Yeah and both methods have their merits.
The downside of the L&S method is that to reduce fill and thus allow the engine to reach higher RPM where it produces more power, you are reducing water flow and thus reducing the brake cooling.
The Superflow method of controlling the outlet makes more sense in that aspect, at minimum fill (load valve fully open) you've got maximum water flow and thus maximum cooling. The downside is the reduced range of control, hence the need to adjust the inlet valve for the RPMs you're testing at.
DTS did this the best, using servos for both inlet and outlet.

That is sort of true but the brake's water flow rate also increases with RPM so on an engine that has the brake filled to a certain amount around peak torque and filled to a lesser amount at higher RPM around peak HP the amount of water that actually is flowing through the system can be about the same overall. The real trick is getting the outlet restrictor sized correctly for the water supply so that the brake can respond about the same to either increasing the load or decreasing it and so that the outlet water temperature stays below the boiling point.

Land and Sea has dramatically improved their stuff over the years. The newer style toroidal brakes have less internal volume (respond to the control more rapidly) and they can hold more torque with a given water supply.

So if an older L&S unit is leaking water out of the exhaust side of the brake, does that negatively affect its ability to hold as RPM increases?

[DaveMcLain]

Yeah and both methods have their merits.
The downside of the L&S method is that to reduce fill and thus allow the engine to reach higher RPM where it produces more power, you are reducing water flow and thus reducing the brake cooling.
The Superflow method of controlling the outlet makes more sense in that aspect, at minimum fill (load valve fully open) you've got maximum water flow and thus maximum cooling. The downside is the reduced range of control, hence the need to adjust the inlet valve for the RPMs you're testing at.
DTS did this the best, using servos for both inlet and outlet.

That is sort of true but the brake's water flow rate also increases with RPM so on an engine that has the brake filled to a certain amount around peak torque and filled to a lesser amount at higher RPM around peak HP the amount of water that actually is flowing through the system can be about the same overall. The real trick is getting the outlet restrictor sized correctly for the water supply so that the brake can respond about the same to either increasing the load or decreasing it and so that the outlet water temperature stays below the boiling point.

Land and Sea has dramatically improved their stuff over the years. The newer style toroidal brakes have less internal volume (respond to the control more rapidly) and they can hold more torque with a given water supply.

So if an older L&S unit is leaking water out of the exhaust side of the brake, does that negatively affect its ability to hold as RPM increases?

Not all that much from what I've seen because the way the water comes out of the brake at high speeds it would have to be a heck of a big leak to matter. With my older style brake I used it for years with no restrictor in the -10 outlet line at all.

[Circlotron]

Something to think about: If the engine is past its torque peak then reducing the torque load should allow the rpm to increase and vice versa. But if the engine is below its torque peak so torque is still rising with rpm then it would be impossible to control rpm with a simple friction brake if you had no rpm feedback. Does a water brake have a property something like a torque converter so that for a given control setting, if the rpms try to increase the brake digs in harder without any external influence?

[MadBill]

I'm sure there are numerous Speedtalkers with much more experience and who will weigh in, but here's my US c 1.62-worth:
I've operated a simple dyno with a lb./oz. scale for torque and a rope wrapped around a flat pulley as the literal 'brake'. As long as there is reasonable flywheel effect it's not that difficult to control below peak torque; you just back off the drag a touch, then quickly crank it back to a tad more than before to stabilize the RPM at the higher torque value.

I've also used a chainsaw dyno with an ounce scale and a hand operated water valve to supply the absorber. It was easier to control the load but more importantly could be run indefinitely without overheating.

Also, yes, as for a torque converter, a water brake's torque capacity increases rapidly with RPM (perhaps as the square of same?) so at a given water level in the absorber, it takes much more torque to spin it faster. At the other end of the scale, it quickly loses capacity as the revs drop, so lots of thousand plus HP water brake dynos can't drag a stout street Big Block down below perhaps 3,500 RPM.

[PRH]

I thought load on the engine doesn't change?

During typical engine dyno operation, where the throttle is brought to WOT prior to making a "pull", when the engine is running steady state...... The load equals the tq output.
If you wanted the rpm to change from that point, you either need to decrease the load(engine rpm goes up), or increase the load(engine rpm goes down).
If you leave the throttle wide open, and the load remains the same, the rpm won't change.