60-130 in Cooler weather

[Autopart101]

Best 60-130 and pass to date. 4200lbs, 15psi Whipple, 2200ft and 3600DA. Running the Gen 6 blower this year and going to 18psi.

That's moving out with just 15psi and high DA.

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[Autopart101]

After some research I believe the Dragy DA calculation is flawed. I think its not taking gains of water/humidity in the air in their model. I live 10 miles away and almost the same Alt as Florence Speed way. They have a live weather station reporting 24/7. Dragy reported DA2500ft DA. Florence Speedway DA 3100ft. I think this is why I see some wildly different 60-130s with the same combo. That might be why in the fall/spring months with similar DA as the summer. I see over .5 difference in 60-130.

 

[cbrtrx]

After some research I believe the Dragy DA calculation is flawed. I think its not taking gains of water/humidity in the air in their model. I live 10 miles away and almost the same Alt as Florence Speed way. They have a live weather station reporting 24/7. Dragy reported DA2500ft DA. Florence Speedway DA 3100ft. I think this is why I see some wildly different 60-130s with the same combo. That might be why in the fall/spring months with similar DA as the summer. I see over .5 difference in 60-130.

The Dragy DA is not always the most accurate however in some situations 10 miles away can have a noticeable impact on DA. Regardless of what the DA is showing on the Dragy the time is not corrected for DA so it is still the time you ran at that time. On a boosted car it's not uncommon for it to pick up .5 second in cooler air, some cars pick up even more.

 

[Autopart101]

The Dragy DA is not always the most accurate however in some situations 10 miles away can have a noticeable impact on DA. Regardless of what the DA is showing on the Dragy the time is not corrected for DA so it is still the time you ran at that time. On a boosted car it's not uncommon for it to pick up .5 second in cooler air, some cars pick up even more.

I understand the dragy is not correcting for DA. I have pulls same location same set up. Dragy DA within 1-300 ft. .5 difference in 60-130. I just have a hunch Dragys model doesn't include gains of water in the air. I think it's just going by Alt and Temp. Still a great tool to use.

 

[Angrey]

DA is an imperfect estimation of oxygen content. Would be a curious history research project as to why it's not more commonly computed as O2 density. I'm guessing that while O2 content is useful to aircraft engine and power output, DA is also as useful for lift and takeoff/landing distance calcs, max load, etc.

It's similar to why aerospace measures fuel in weight/mass instead of volume.

 

[Autopart101]

DA is an imperfect estimation of oxygen content. Would be a curious history research project as to why it's not more commonly computed as O2 density. I'm guessing that while O2 content is useful to aircraft engine and power output, DA is also as useful for lift and takeoff/landing distance calcs, max load, etc.

It's similar to why aerospace measures fuel in weight/mass instead of volume.

I have an Aircraft Dispatch certificate. I haven't practiced but do work for a large Airline. This clip is right from the FAA on DA and humidity. Humidity effects the Enigne power not the Aero preformance of the AC. This is why even with similar DA. Two runs can be widely different.

Humidity is not generally considered a major factor in density altitude computations because the
effect of humidity is related to engine power rather than aerodynamic efficiency. At high ambient tempera￾tures, the atmosphere can retain a high water vapor content. For example, at 96 o
F, the water vapor content of
the air can be eight (8) times as great as it is at 42 o
F. High density altitude and high humidity do not always
go hand in hand. If high humidity does exist, however, it is wise to add 10 percent to your computed takeoff
distance and anticipate a reduced climb rate.
Check the Charts Carefully

 

[Pistol_91]

Heres some of my runs with ET street R's. After you spin them a few times they get bad on the street and dont work well. Was hazing to like 120 mph on some of these runs



My best runs were actually on all season continental dws 06+ (end part of this video)

Gandy?

 

[Angrey]

I have an Aircraft Dispatch certificate. I haven't practiced but do work for a large Airline. This clip is right from the FAA on DA and humidity. Humidity effects the Enigne power not the Aero preformance of the AC. This is why even with similar DA. Two runs can be widely different.

Humidity is not generally considered a major factor in density altitude computations because the
effect of humidity is related to engine power rather than aerodynamic efficiency. At high ambient tempera￾tures, the atmosphere can retain a high water vapor content. For example, at 96 o
F, the water vapor content of
the air can be eight (8) times as great as it is at 42 o
F. High density altitude and high humidity do not always
go hand in hand. If high humidity does exist, however, it is wise to add 10 percent to your computed takeoff
distance and anticipate a reduced climb rate.
Check the Charts Carefully

Yes, that's essentially what I indicated in my post. DA is useful for lift. What's useful for engine output is oxygen density (rather than using DA with some sorta humidity modifier). Simply calculate or measure the O2/cubic meter and be done with it. Then it really doesn't matter if it's Nitrogen or Water Vapor or trace gases, each cube of air coming in has x amount of 02 available for combustion. In situations where the water grains are low, the 02 content will be higher for a given DA, in situations where the water grains are high, the 02 content will be slightly less for a given DA.

Must have something to do with instrumentation over the years. Most weather station type instruments can measure moisture content so they can do a back handed calculation to arrive at the 02 (if you assume some small fixed contributions from trace gases) which could yield 02 content (by inference) or they could just have an 02 sensor measure it directly.

At any rate, we all agree that DA is an imperfect metric to estimate engine output if there's meaningful changes given the humidity in the air (which there is). Or rather, DA + the second step to account for hygrometer measurements............which was kinda the point of my post. Why don't they just skip the calcs and measure the O2 content which is the metric we're ultimately trying to arrive at to predict combustion engine output.

 

[SolarFlare]

I went to the track often during a 5-6 year period in south Florida and you can see similar DA days in the “winter” but the low water grains really get the car moving on those dry days. Which is why I don’t really compare the times down here with some of the times the more fortunate guys up north run.

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