Does Driver Weight Effect Dyno Output?
08-07-2009, 07:54 PM
#46
Rennlist Member
The reason the plane took off was due to lift and thrust, as is the reason any plane flies. I dont quite follow your question regarding the jet being suspended and being let go under full power. that doest represent what is happening here. the ONLY thing that is really happening, is that there is some wheel drag that the plane has to overcome to move forward to accelerate to take off speed. if its a Cessna, it might be near 55mph or so. the conveyor could be running 200mph backwards. It would only lengthen the time it would normally take to lift off the ground. (based on drag of wheels spinning at 200mph +55mph).
Think about this. what would it take for the plane to sit on the conveyor and be standing still even though the treadmill was going backward 200mph? Right! the drag of the wheels. say that force was 200lbs If the engine can make 600lbs of thrust (30% thrust to weight of a 2000lb plane), then it still has 400lbs of thrust to take off. Just tossing out numbers , but you get the idea. I think the experiement was actually using the same speed in reverse on the conveyor, to the plane. if so, it would be no different than the plane taking off in a 50mph tailwind, which is possible with enough runway .
Think about this. what would it take for the plane to sit on the conveyor and be standing still even though the treadmill was going backward 200mph? Right! the drag of the wheels. say that force was 200lbs If the engine can make 600lbs of thrust (30% thrust to weight of a 2000lb plane), then it still has 400lbs of thrust to take off. Just tossing out numbers , but you get the idea. I think the experiement was actually using the same speed in reverse on the conveyor, to the plane. if so, it would be no different than the plane taking off in a 50mph tailwind, which is possible with enough runway .
Mark, so what your saying is the main reason the experiment worked was due to engine speed and not lift?
So this theory could have been proven by suspending a jet plane motionless while letting it come to full power and letting go?
This could also be called a missile.
I understand you if you if this is correct
So this theory could have been proven by suspending a jet plane motionless while letting it come to full power and letting go?
This could also be called a missile.
I understand you if you if this is correct
08-07-2009, 07:59 PM
#47
Rennlist Member
I see your problem here!
you would be absolutely right if we were talking a car that generates forward thrust via its drive wheels. the faster the car went, the fastert the conveyor in the opposite direction and the car stays in one place not moving. OK?
BUT, for a plane, the thrust is from the propeller, independent of the rolling wheels. Thats why it would take off.
you would be absolutely right if we were talking a car that generates forward thrust via its drive wheels. the faster the car went, the fastert the conveyor in the opposite direction and the car stays in one place not moving. OK?
BUT, for a plane, the thrust is from the propeller, independent of the rolling wheels. Thats why it would take off.
08-07-2009, 08:22 PM
#48
Three Wheelin'
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I love this forum, I think I will test out of some engineering classes in a few more pages of this!
Mike, funny should ask about it being a measure of HP or Torque. There was another forum where similar discussions was going on about how torque is a better functional number. His 'argument' to things like this is that there is no HP without torque and HP is a by product of Torque or something along those lines, so I would normally say (as I beleive the consensus is) that it is a HP figure, but may be able to be argued that it is a torque number?
These discussions are awesome!
Mike, funny should ask about it being a measure of HP or Torque. There was another forum where similar discussions was going on about how torque is a better functional number. His 'argument' to things like this is that there is no HP without torque and HP is a by product of Torque or something along those lines
, so I would normally say (as I beleive the consensus is) that it is a HP figure, but may be able to be argued that it is a torque number? These discussions are awesome!
08-07-2009, 08:42 PM
#49
Rennlist Member
Trap speed is an indication of hp-seconds, a unit measure of work. (or ft-lb seconds at the rear wheels)
if you are talking engine torque, no. if you are talking rear wheel torque, after the gear ratios, I would say, "yes" as would be HP, as found at the rear wheels too.
Torque (engine torque I imagine you are talking about) isnt a better functional number unless you are talking torque AT the rear wheels, through the gear ratios. Or Force. Power incorporates torque, force, and speed, so if you know power at any speed, you can figure out force. If you know the force, you can calcuate power. if you know the rate of change of kinetic energy, that by definition is power.
Acceleration = power/(mass x velocity)
Accelertion = Force/mass
if you are talking engine torque, no. if you are talking rear wheel torque, after the gear ratios, I would say, "yes" as would be HP, as found at the rear wheels too.
I love this forum, I think I will test out of some engineering classes in a few more pages of this!
Mike, funny should ask about it being a measure of HP or Torque. There was another forum where similar discussions was going on about how torque is a better functional number. His 'argument' to things like this is that there is no HP without torque and HP is a by product of Torque or something along those lines, so I would normally say (as I beleive the consensus is) that it is a HP figure, but may be able to be argued that it is a torque number?
These discussions are awesome!
Mike, funny should ask about it being a measure of HP or Torque. There was another forum where similar discussions was going on about how torque is a better functional number. His 'argument' to things like this is that there is no HP without torque and HP is a by product of Torque or something along those lines
, so I would normally say (as I beleive the consensus is) that it is a HP figure, but may be able to be argued that it is a torque number? These discussions are awesome!
Acceleration = power/(mass x velocity)
Accelertion = Force/mass
08-07-2009, 08:50 PM
#50
Nordschleife Master
I love this forum, I think I will test out of some engineering classes in a few more pages of this!
Mike, funny should ask about it being a measure of HP or Torque. There was another forum where similar discussions was going on about how torque is a better functional number. His 'argument' to things like this is that there is no HP without torque and HP is a by product of Torque or something along those lines, so I would normally say (as I beleive the consensus is) that it is a HP figure, but may be able to be argued that it is a torque number?
These discussions are awesome!
Mike, funny should ask about it being a measure of HP or Torque. There was another forum where similar discussions was going on about how torque is a better functional number. His 'argument' to things like this is that there is no HP without torque and HP is a by product of Torque or something along those lines
, so I would normally say (as I beleive the consensus is) that it is a HP figure, but may be able to be argued that it is a torque number? These discussions are awesome!
Still an interesting question, does trap speed more accurately describe torque or HP? ***
This is a FUN place, but asking technical questions is like trying to get medical advice in a biker bar.
*** Not that I "know" the answer, but my suspicion is that trap speed reflects the relation between torque curve and gear ratio's, and the estimate of HP is only valid in as much as the HP curve fits some standard normal curve.
08-07-2009, 09:24 PM
#51
Nordschleife Master
Tell me you cant be serious!
number 1 rule of aviation. airplanes need lift and forward momentum to fly if they dont have a 1:1 thrust ratio.
But, for a plane to fly, you need air moving over the wings to the requirements of just above full power, full flaps stall speed.
DynoJets. There is no "calibration" nesessary. If we take the actual output,
As you know there are too many factors to list for drag racing results. If there wasnt, you would just turn in your dyno sheets for a trophey.
mk
number 1 rule of aviation. airplanes need lift and forward momentum to fly if they dont have a 1:1 thrust ratio.
But, for a plane to fly, you need air moving over the wings to the requirements of just above full power, full flaps stall speed.
DynoJets. There is no "calibration" nesessary. If we take the actual output,
As you know there are too many factors to list for drag racing results. If there wasnt, you would just turn in your dyno sheets for a trophey.
mk
Is there some functional difference between a serious argument and a amusing argument?
Momentum gives you stability, lift alone is adequate to keep from falling out of the sky. At full power and full flaps the prop is sending a fair amount of air over the wings, and the air speed pitot is sensibly located away from this flow. I have a REAL good memory of the event, zero happened, didn't last a long time, but forward movement ceased, and I happily traded some altitude to get it back.
"There is no "calibration" nesessary." Of course there isn't, dyno's are a tuning tool never intended to measure real HP, just show the effects of tuning changes from run to run. What would be the point of making them accurate, and how would anybody sell hot rod parts?
ET in drag racing is very complicated and heavily related to driver actions, trap speed is not. This is why ET is the basis of the contest, driver vs driver. Trap speed MPH is the reality check, and remarkably consistent.
08-07-2009, 09:46 PM
#52
Rennlist Member
I guess your right. I can toss a ball in the air and it will float too.
(albeit for a very short time. ) in otherwords, if you were at "0" air speed, you were not flying, you were falling or beginning to fall. you would certainly need to be pointed straight up to have that happen as well. (force vector)
How do you logically explain how you could be pointed straight ahead or with a high angle of attack, that your air speed could ever get to "0"? I told you what you probably saw, a high angle of attack and an ironious air speed reading of "0".
If you are not hanging on the prop, you are moving forward, regardless of the air flow acting on the control surfaces via the air flow from the prop.
im not talkingabout the pitot tube being out of the air flow of the prop, im talking about its directional position. near stall, it sees the air flow, that the wing will see. It can see 0 , even though there is air moving over the wing because of a high angle of attack.
If what you are saying is that you saw it for a brief instant, Ill buy that. you cant keep the plane in the air at 0 airspeed, regardless of your power and flap setting. Right?
a rolling dyno measures,very accurately, a rate of change of kinetic energy, or HP. It is not as good as a brake dyno for precise RPM point tunining. you either move the drums fast or you dont. how fast is your HP. (or rear wheel torque through the gears at any registered speed)
Im with you on the Drag comments.
Mk
(albeit for a very short time.
) in otherwords, if you were at "0" air speed, you were not flying, you were falling or beginning to fall. you would certainly need to be pointed straight up to have that happen as well. (force vector)How do you logically explain how you could be pointed straight ahead or with a high angle of attack, that your air speed could ever get to "0"? I told you what you probably saw, a high angle of attack and an ironious air speed reading of "0".
If you are not hanging on the prop, you are moving forward, regardless of the air flow acting on the control surfaces via the air flow from the prop.
im not talkingabout the pitot tube being out of the air flow of the prop, im talking about its directional position. near stall, it sees the air flow, that the wing will see. It can see 0 , even though there is air moving over the wing because of a high angle of attack.
If what you are saying is that you saw it for a brief instant, Ill buy that. you cant keep the plane in the air at 0 airspeed, regardless of your power and flap setting. Right?
a rolling dyno measures,very accurately, a rate of change of kinetic energy, or HP. It is not as good as a brake dyno for precise RPM point tunining. you either move the drums fast or you dont. how fast is your HP. (or rear wheel torque through the gears at any registered speed)
Im with you on the Drag comments.
Mk
Pretty sure I can be serious, but its kind of like holding my breath, so I don't do it anymore than I have to.
Is there some functional difference between a serious argument and a amusing argument?
Momentum gives you stability, lift alone is adequate to keep from falling out of the sky. At full power and full flaps the prop is sending a fair amount of air over the wings, and the air speed pitot is sensibly located away from this flow. I have a REAL good memory of the event, zero happened, didn't last a long time, but forward movement ceased, and I happily traded some altitude to get it back.
"There is no "calibration" nesessary." Of course there isn't, dyno's are a tuning tool never intended to measure real HP, just show the effects of tuning changes from run to run. What would be the point of making them accurate, and how would anybody sell hot rod parts?
ET in drag racing is very complicated and heavily related to driver actions, trap speed is not. This is why ET is the basis of the contest, driver vs driver. Trap speed MPH is the reality check, and remarkably consistent.
Is there some functional difference between a serious argument and a amusing argument?
Momentum gives you stability, lift alone is adequate to keep from falling out of the sky. At full power and full flaps the prop is sending a fair amount of air over the wings, and the air speed pitot is sensibly located away from this flow. I have a REAL good memory of the event, zero happened, didn't last a long time, but forward movement ceased, and I happily traded some altitude to get it back.
"There is no "calibration" nesessary." Of course there isn't, dyno's are a tuning tool never intended to measure real HP, just show the effects of tuning changes from run to run. What would be the point of making them accurate, and how would anybody sell hot rod parts?
ET in drag racing is very complicated and heavily related to driver actions, trap speed is not. This is why ET is the basis of the contest, driver vs driver. Trap speed MPH is the reality check, and remarkably consistent.
08-07-2009, 09:53 PM
#53
Rennlist Member
yes, you almost got it below. the answer is all the torque curves that are being used together through the run, x the gear ratio, x the time spent in those gears for a total amount of energy used. Thats why I like HP-seconds, or ft-lb seconds , if we are talking about rear wheel torque. I dont understand the last sentence of your commnet though. 
In drag racing, he who puts down (applies to the ground) the most amount of ft-lb-seconds , Force-seconds, will win. (or hp-seconds, same thing)
mk
In drag racing, he who puts down (applies to the ground) the most amount of ft-lb-seconds , Force-seconds, will win. (or hp-seconds, same thing)
mk
The logic is twisted in those torque vs HP threads, and the comment purely for Marks amusement.
Still an interesting question, does trap speed more accurately describe torque or HP? ***
This is a FUN place, but asking technical questions is like trying to get medical advice in a biker bar.
*** Not that I "know" the answer, but my suspicion is that trap speed reflects the relation between torque curve and gear ratio's, and the estimate of HP is only valid in as much as the HP curve fits some standard normal curve.
Still an interesting question, does trap speed more accurately describe torque or HP? ***
This is a FUN place, but asking technical questions is like trying to get medical advice in a biker bar.
*** Not that I "know" the answer, but my suspicion is that trap speed reflects the relation between torque curve and gear ratio's, and the estimate of HP is only valid in as much as the HP curve fits some standard normal curve.
08-07-2009, 09:58 PM
#54
In Your Face, Ace
Rennlist Member
Rennlist Member
08-07-2009, 10:35 PM
#55
Nordschleife Master
Mark, I'll just have to take you up and show you, much easier than explaining details. Pretty sure I could do the first part again.
Regarding dyno's, too much empirical evidence of error to trust them. OTOH a timeslip ...
Regarding dyno's, too much empirical evidence of error to trust them. OTOH a timeslip ...
08-08-2009, 01:57 AM
#56
Rennlist Member
Tell me what you are going to show me? full power, flaps down, and you will show me indicated 0 air speed? Like I said, impossible. air flow from the prop over the wings cant generate lift. thats like putting a fan a sail boat and pointing it to the sail hoping you will move. . It does help tremendously with conrol though. So, you did this at an altitude where you could see the ground wasnt moving? I dont know, I dont want to be more than 2 mistakes high with any pilot, and do any stalls.
Indulge me. How can a plane stay in the air, with 0 indicated airspeed, even with full power and flaps? (unless it is a jump jet,with 1:1 thrust to weight, or thrust vectoring?)
You can trust the dynos just too many external factors at the track as you say, to do any coorelation. ram air, drag, alignment, inertia, grip slip, driver, shift, etc etc.
. It does help tremendously with conrol though. So, you did this at an altitude where you could see the ground wasnt moving? I dont know, I dont want to be more than 2 mistakes high with any pilot, and do any stalls. Indulge me. How can a plane stay in the air, with 0 indicated airspeed, even with full power and flaps? (unless it is a jump jet,with 1:1 thrust to weight, or thrust vectoring?)
You can trust the dynos just too many external factors at the track as you say, to do any coorelation. ram air, drag, alignment, inertia, grip slip, driver, shift, etc etc.
08-08-2009, 02:10 AM
#57
Administrator - "Tyson"
Lifetime Rennlist
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Lifetime Rennlist
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Even if you spin the conveyor belt four times faster than the takeoff speed of the plane it's still going to takeoff.
It's a simple test, fire up a treadmill and put a toy car on it. No matter how fast your spin the belt, it takes almost zero effort to push the toy forward.
Same principle applies to the thrust produced by the planes engines.
08-08-2009, 03:09 AM
#58
Nordschleife Master
Maybe 40 feet in the air after a hard bounce during a flubbed landing.
Joking on showing you, not on my list of things to repeat.
BTW you get some kind of ground effect up to about two and half times the wingspan.
Joking on showing you, not on my list of things to repeat.
BTW you get some kind of ground effect up to about two and half times the wingspan.
08-08-2009, 03:34 AM
#59
Former Sponsor
Hmm....
The great "dyno" debate, again. I love this stuff! Hell, I'm old enough to have/remember V-8 engines from Detroit that barely made one horsepower per cubic inch that would snap your head off. Now, things have evolved to the point if you can't make 1.5 horsepower per cubic inch (to the rear tires, naturally aspirated) you shouldn't be allowed to own tools. However, these engines don't seem to be much faster than the "old school" engines. Something got inflated or deflated, over the years. I suspect that it is the "dyno".
I've had a real interesting dyno experiment, over the past couple of months. Not going to go into details...the information has been very time consuming/expensive to gather...but I've learned a whole bunch about dynos and automatic 928's in the past couple of months.
I'm going to go with Danglerb, here...dyno results are worthless, when compared to ET's. My dyno results are always very low...hell, there's people doing minor changes to stock engines that claim they make more horsepower than my strokers do. This confuses me. The supercharger guys all seem to make over 500hp...some 150 horspower than most of my strokers. Funny that these guys can never seem to cross the finish line before we do.....this confuses me, even more.
I'm even more confused by the really "big" horsepower 928 engines. It's always been my understanding that on naturally apsirated engines, the only way to increase horsepower was to either make the engine bigger, increase the volumetric efficiency, or move the power range up in the rpm range (assuming that combustion is close to optimium efficiency.) For a given rpm range and a given displacement, it is pretty easy to come up with how volumetric efficient an engine is, once you know the horsepower....this is not rocket science. So, if I'm working on engines that make "X" horsepower and are close to 90% volumetrically efficient, what's the volumetric efficiency of an engine that makes "1.5X" horsepower? And more importantly than that, how the hell do you make a naturally aspirated engine that is 135% volumetric efficient? There's a whole bunch of really smart automotive engineers that would love to know how to do this....and, of course, so would I.
Of course, I'm easy to confuse. It's the age thing.
The great "dyno" debate, again. I love this stuff! Hell, I'm old enough to have/remember V-8 engines from Detroit that barely made one horsepower per cubic inch that would snap your head off. Now, things have evolved to the point if you can't make 1.5 horsepower per cubic inch (to the rear tires, naturally aspirated) you shouldn't be allowed to own tools. However, these engines don't seem to be much faster than the "old school" engines. Something got inflated or deflated, over the years. I suspect that it is the "dyno".
I've had a real interesting dyno experiment, over the past couple of months. Not going to go into details...the information has been very time consuming/expensive to gather...but I've learned a whole bunch about dynos and automatic 928's in the past couple of months.
I'm going to go with Danglerb, here...dyno results are worthless, when compared to ET's. My dyno results are always very low...hell, there's people doing minor changes to stock engines that claim they make more horsepower than my strokers do. This confuses me. The supercharger guys all seem to make over 500hp...some 150 horspower than most of my strokers. Funny that these guys can never seem to cross the finish line before we do.....this confuses me, even more.
I'm even more confused by the really "big" horsepower 928 engines. It's always been my understanding that on naturally apsirated engines, the only way to increase horsepower was to either make the engine bigger, increase the volumetric efficiency, or move the power range up in the rpm range (assuming that combustion is close to optimium efficiency.) For a given rpm range and a given displacement, it is pretty easy to come up with how volumetric efficient an engine is, once you know the horsepower....this is not rocket science. So, if I'm working on engines that make "X" horsepower and are close to 90% volumetrically efficient, what's the volumetric efficiency of an engine that makes "1.5X" horsepower? And more importantly than that, how the hell do you make a naturally aspirated engine that is 135% volumetric efficient? There's a whole bunch of really smart automotive engineers that would love to know how to do this....and, of course, so would I.
Of course, I'm easy to confuse. It's the age thing.
08-08-2009, 06:55 AM
#60
Rennlist Member
Actually they just need lift. A head wind > than stall speed will allow a plane to fly for hour's without momentum.