I posted this on the engineering forums and svt forums with little response, so I'll try you guys, I know there are some technical guys here, so here's what I have access to
Stuska Dynamometers - XS-111 Water Brake - up to 800HP
I know this is an engine water brake but we will gear it up to run off the wheels, what I'm attempting to build a hub style dyno w/ the XS-111 for sweep up tests only so I need help with the load calculations which closely simulate road conditions, so basically a constant braking force dyno, although it will change due to rolling and air drag, which is why I'm here.
The basic setup:
The dyno shares a common axle infront/rear of the car, and then dual #50 chains connected to the hub's, and of a strong steel framework, from the center of the common axle is another gear connected to a jack-shaft which couples to the water brake,
Remember this is a hub dyno, tire diameter, tie down load, tire pressure and correction issues are not included, the one reason I want this style dyno), let's go over a few variables:
Gear Ratio: 1:1 (4th)
Wheel Start RPM: 500 (2000 engine rpm, 40mph)
Wheel End RPM: 2000 (6500 engine rpm, 130mph)
(this isn't totally right, its more like 400-2100 but I want to the numbers to sync with the brake for this discussion)
Let's use these numbers for the XS-111:
Let's assume I'm driving the brake 4:1 (this may not be correct but its just for starters), so i'll throwout some numbers for a typical engine. Let's assume I have the brake load valve about 1/2 open, the brake torque is about 325 ft-lb constant and I'm getting the following data from the torque meter.
Sample: Car hp = (hp from LEFT column and brake rpm)*RPM / 5252
47 = 124 * 2000 /5252
Net hp = (Water Brake hp half open) + (car hp)
47 + 75 = 122
Question1) Is this the correct approach?
Question2) If correct, why am I getting the different hp from the transducer reading versus theoretical reading? (I'm assuming because the water brake hp is not correct).
So the next step is simulating the vehicle weight and find the correct load for the water brake.
I'm taking a look at this thread,
CR4 - Thread: Torque Required to Move a Hybrid Car
forget drag losses, I want to know the brake torque needed,
starting with reply #24 and #26
60 mph = 88 fps
over 10 seconds = 8.8fps^2
g's = 8.8fps^2 / 32.15 fps^2 = .274g
Looking again at your calculation, look at your following line:
" torque = 4000lb * .274g = 1094.9 lbs - ft "
This should read: Force = 4000 lb * 8.8 ft/s^2 / 32 ft/s^2 = 1100 lbf. (not ft-lbs, it is a force not torque.) F (in lbs) = m * a.
Now calculate the distance traveled: Dist = .5 * a* t^2 = .5*8.8*10s^2 = 440 ft.
From this you calculate the work or energy: E = F * D = 1100 lb * 440 ft = 484,000 ft-lbs.
The power is energy or work / time: 484,000 ft lbs /10 s = 48400 ft-lb/s,
divide that by the constant "550" for HP = 48400 / 550 = 88 hp. Same result as per my first answer.
Torque T = 88 * 5252 / 840 = 550 ft lbs. (coincidentally the same number as the conversion constant)
For my situation I'll go from 37.5mph(55fps) to 135mph(198fps), I'll use 10 seconds as well
so,
198-55/10 = 14.3 ft/s^2
14.3/32.2 = .444g
4000 lb * .444g = 1776 lbf
dist = .5*a*t^2 = .5*(14.3ft/s^2)*(10s)^2
= 715 ft
Work = 1776 lbf * 715 ft = 1,269,840 ft-lbs
power = 1269840/10seconds/550 = 232 hp
torque = 232 * 5252 / 1890rpm = 644 ft-lb
let's graph it
Question 3) Should I be getting a 1776 lbf @ half the speed or is it just a coincidence the other post did? So I conclude I need 644 ft-lb of braking torque from the water brake to simulate the vehicles weight, seems high to me.
Question 4)about the water control, obviously the load valve is the regulator, the question is why not just use a pressure regulator? we know that I will drain out to a small 1/2" orfice (just a number I threw out), there has to be pressure within the system, or is just atmosphere?
I welcome responses on the setup but I'm sure I have that part covered. OVERALL the question is can a water brake be used to do a sweep up test, I think yes but the load valve has to be controlled.
I talked to the designer and even after a few emails he was confused on what I was trying to do since he's only ever done WOT tests. I was taught to tune in vacuum gauge load increments, for example 10" 5" 0 5psi 10psi 15psi 20psi from 2000 to 6500 rpm, this is a sweep up test in my opinion, but instead of modulating the pedal we'll modulate the load valve, you all following me?
(PM me your email, I'll send the operation manual for the XS111-211.
Stuska Dynamometers - XS-111 Water Brake - up to 800HP
I know this is an engine water brake but we will gear it up to run off the wheels, what I'm attempting to build a hub style dyno w/ the XS-111 for sweep up tests only so I need help with the load calculations which closely simulate road conditions, so basically a constant braking force dyno, although it will change due to rolling and air drag, which is why I'm here.
The basic setup:
The dyno shares a common axle infront/rear of the car, and then dual #50 chains connected to the hub's, and of a strong steel framework, from the center of the common axle is another gear connected to a jack-shaft which couples to the water brake,
Remember this is a hub dyno, tire diameter, tie down load, tire pressure and correction issues are not included, the one reason I want this style dyno), let's go over a few variables:
Gear Ratio: 1:1 (4th)
Wheel Start RPM: 500 (2000 engine rpm, 40mph)
Wheel End RPM: 2000 (6500 engine rpm, 130mph)
(this isn't totally right, its more like 400-2100 but I want to the numbers to sync with the brake for this discussion)
Let's use these numbers for the XS-111:
Let's assume I'm driving the brake 4:1 (this may not be correct but its just for starters), so i'll throwout some numbers for a typical engine. Let's assume I have the brake load valve about 1/2 open, the brake torque is about 325 ft-lb constant and I'm getting the following data from the torque meter.
Sample: Car hp = (hp from LEFT column and brake rpm)*RPM / 5252
47 = 124 * 2000 /5252
Net hp = (Water Brake hp half open) + (car hp)
47 + 75 = 122
Question1) Is this the correct approach?
Question2) If correct, why am I getting the different hp from the transducer reading versus theoretical reading? (I'm assuming because the water brake hp is not correct).
So the next step is simulating the vehicle weight and find the correct load for the water brake.
I'm taking a look at this thread,
CR4 - Thread: Torque Required to Move a Hybrid Car
forget drag losses, I want to know the brake torque needed,
starting with reply #24 and #26
60 mph = 88 fps
over 10 seconds = 8.8fps^2
g's = 8.8fps^2 / 32.15 fps^2 = .274g
Looking again at your calculation, look at your following line:
" torque = 4000lb * .274g = 1094.9 lbs - ft "
This should read: Force = 4000 lb * 8.8 ft/s^2 / 32 ft/s^2 = 1100 lbf. (not ft-lbs, it is a force not torque.) F (in lbs) = m * a.
Now calculate the distance traveled: Dist = .5 * a* t^2 = .5*8.8*10s^2 = 440 ft.
From this you calculate the work or energy: E = F * D = 1100 lb * 440 ft = 484,000 ft-lbs.
The power is energy or work / time: 484,000 ft lbs /10 s = 48400 ft-lb/s,
divide that by the constant "550" for HP = 48400 / 550 = 88 hp. Same result as per my first answer.
Torque T = 88 * 5252 / 840 = 550 ft lbs. (coincidentally the same number as the conversion constant)
For my situation I'll go from 37.5mph(55fps) to 135mph(198fps), I'll use 10 seconds as well
so,
198-55/10 = 14.3 ft/s^2
14.3/32.2 = .444g
4000 lb * .444g = 1776 lbf
dist = .5*a*t^2 = .5*(14.3ft/s^2)*(10s)^2
= 715 ft
Work = 1776 lbf * 715 ft = 1,269,840 ft-lbs
power = 1269840/10seconds/550 = 232 hp
torque = 232 * 5252 / 1890rpm = 644 ft-lb
let's graph it
Question 3) Should I be getting a 1776 lbf @ half the speed or is it just a coincidence the other post did? So I conclude I need 644 ft-lb of braking torque from the water brake to simulate the vehicles weight, seems high to me.
Question 4)about the water control, obviously the load valve is the regulator, the question is why not just use a pressure regulator? we know that I will drain out to a small 1/2" orfice (just a number I threw out), there has to be pressure within the system, or is just atmosphere?
I welcome responses on the setup but I'm sure I have that part covered. OVERALL the question is can a water brake be used to do a sweep up test, I think yes but the load valve has to be controlled.
I talked to the designer and even after a few emails he was confused on what I was trying to do since he's only ever done WOT tests. I was taught to tune in vacuum gauge load increments, for example 10" 5" 0 5psi 10psi 15psi 20psi from 2000 to 6500 rpm, this is a sweep up test in my opinion, but instead of modulating the pedal we'll modulate the load valve, you all following me?
(PM me your email, I'll send the operation manual for the XS111-211.
