acknowledged The huey's performance profile is unacceptably inaccurate (documentation provided)

[Tim_Fragmagnet]

To put the TLDR first, our huey is underperforming by 3400lbs while being provided a lower available power than the real thing, and made slower than it's actually supposed to be at low altitude (which is where it normally operates)

So what are my sources?

Before that, lets start with a very simple summary of HOW WRONG the module's performance actually is.

null

Now, I won't act like that's the whole story with all the context, because it's definitely not. There are things like the transmission limit to take into account.

But those sources, lets see them.

Here are the 3 main sources, there are several other minor sources as well, however the majority of the data comes from these 3 documents.

null

So allow me to clarify something, our huey is one with a 1990s refit, it is the one with composite blades. You may have noticed, one of those sources explicitly mentions the composite blades in the title. 
That source is a performance profiling of our exact model of huey. Refits and all.

Now, there's something else to talk about, the huey's operations manual. You might be familiar with this chart.

This chart is useless. This chart doesn't tell us where the transmission limit is, it doesn't tell us how much engine power is being used to generate those speeds, it doesn't tell us ANYTHING.
That chart is a significant misrepresentation of the huey's performance capabilities, because all that chart shows is a paper limit on the huey's speed.

Vne, Velocity, never exceed. A scary term, used to define a speed you are to not exceed for assorted reasons. For the huey, the Vne is in place to keep the pilots from accelerating into retreating blade stall, nothing more.
It's a paper limit to keep the pilots safe, it tells us NOTHING about how the aircraft performs.

However, if you look at the bottom of that chart, "Data basis AEFA Project No. 84-33"
Go back and look at top of the source that mentions the composite blades, that is AEFA Project No. 84-33. The data from that document was used to generate that chart in the manual.

So before we go farther, how do we corroborate all our sources to make sure they're on the same page and providing us valid information.

Cross checking.
Take one set of data, and see if the patterns within it match the patterns in another set of data.

We can do that.

Here is the overall performance of a huey with the standard blades at 7,500lbs, derived from the data within the UH-1H flight profile performance handbook.
Pay attention to the density altitude of 7500ft, you see where the yellow and red (transmission limit and power limit) lines intersect, that is where the engine can no longer provide enough power to max out the transmission.

Now here is the hover performance chart from the composite blade document.
Look at the rightmost line. "2ft IGE, standard day".

You might have already noticed it.
Incase you didn't.

So our documents are in agreement, what do we do with this information?
We start comparing it to the performance of our huey in DCS.

Lets start with a more complete performance profiling of the real huey with the standard blades, once again, this data is derived from the UH-1H flight profile performance handbook. This data is for a huey with non composite blades.

So there are multiple plots here, let me walk you through them.
The first one that likely sticks out is the blue line since it's away from all the others, that is the Vne. The fact that it is placed lower than all the other data reminds us of the chart in the manual. I said that chart was useless, because as you can see by this graph, every single other plot of data performs significantly over what the Vne would have you believe.

The next two that likely stick out are the red and teal lines. These are the performance of the DCS huey plotted onto the same graph, the red line abides by the incorrect EGT limit placed upon the module, the teal line ignores said limit and properly maxes out the transmission where it can.

Next would be the green and yellow lines, the green line shows the maximum power the engine can normally push, regardless of any other factor, at sea level that would be 1340shp.
The yellow line shows the maximum CONTINUOUS power the engine can push. This means the engine can run at this power setting indefinitely without much issue.

And finally, the orange line, this line shows the safe limit of the transmission, specifically, 1158shp, or 50psi on the torque indicator. This is the huey's military thrust it can use this power for 30 minutes.
This is not the LIMIT of the aircraft's performance, the transmission CAN PUSH HARDER, it just does so at the risk of being damaged. Yes, this means that, per this data, the huey should be able to reach 141knots in level flight.

Something you'll notice, the teal line, our huey's performance, can't even reach the transmission limit at sea level. While, conversely, our huey's performance actually PASSES the real huey's maximum possible performance at higher altitudes.

So, from this alone, you can see that the module's performance accuracy is not great.
But that's not the whole story, that's just for the standard huey, and we haven't even gotten into engine performance per speed yet.

We'll do that now.
Here is a chart from the composite blade document, it shows the level flight performance in speed compared to the shaft horsepower generated by the engine to achieve said speed at a gross weight of 9500lbs at sea level in 15C temperature air, ISA conditions.
On it, you will see a pink data plot.
That is our huey measured by the same metric. 9500lbs, Sea level, 15C air temperature, ISA conditions.

You'll notice that our huey isn't even performing as well as the huey with the standard blades, let alone the one with the composite blades.

But first, how did I get the horsepwer data from the DCS huey, we don't have access to that data.
Except we do. We are given the torquemeter, which when combined with the rotor RPM, we can derive the current SHP put out by the engine.
As per our previously unreferenced source "Helicopter drive system load analysis".

Pages 43-44 detail a formula to do exactly that, derive shaft horsepower from our torquemeter reading, and rotor RPM.
Here is that formula. SHP=3.88*((10^-3*Rotor RPM)*((17.76*Torquemeter Torque)+33.33))

Now, you'll notice that graph shows the composite blades as being measured with the rotor at 314rpm, that's ok the difference in the result isn't exceptional, however here is a table showing the same data and including 324rpm on the composite blades.

So, 639shp to push the helicopter to 100knots at sea level at 15C at a gross weight of 9500lbs.
That would be 26.745psi on the torque indicator in the cockpit.
As you can see by the pink line on the graph, however, we didn't even get close.
We hit 36, possibly 37psi on the torque indicator at those parameters. Level flight, 9500lbs, sea level, 15C, 100knots.

36psi at 324rotor rpm, as per the formula, is about 845shp, over 200shp too high.

Now, we can use this formula to find something dire.

Lets make the huey as light as we can and see how it performs.
6100lbs, all it has is about 9 minutes of fuel
Sea level
15C
100knots level flight

about 30.5psi in those parameters.
722.8shp at 100knots.

The real huey pulls 639shp in those parameters at 9500lbs.

Our huey, at 6100lbs, is performing WORSE than the real huey at 9500lbs.

Our huey is underperforming by over 3400lbs at low altitude.

That is unacceptable.

Interestingly, these high torque values also explain why we need an unrealistic amount of left pedal, which when combined with the incorrectly modeled tail rotor, brings about some interesting comparisons.

So, now that we have the well documented performance profile from the standard blade huey, honestly, we could just use that one for our huey and it would be fine, the overall speed differences shouldn't be drastic, it'd be far more accurate than what we have now.

As for why our huey overperforms so much at high altitude, I don't know. All my efforts were aimed at understanding its performance at low altitude as that's generally where players utilize the aircraft. I suspect it may be a combination of the engine not losing enough power at altitude and rotor mach drag not being modeled.

However, for now, I believe this should be sufficient to warrant the developers looking at it. Please.

Properly implemented, our torque indicator should actually max out at around 58.15psi while the N1% (gas producer) gauge reads 100%
As it stands, we are using too much power, to generate too little speed, at too high of an EGT, causing us to have even less power.
We are underperforming by over 3400lbs at sea level, it needs to change.

Edited February 27, 2023 by Tim_Fragmagnet

[Rudel_chw]

So, we have been flying the DCS Uh-1 for 7 years now, and yet no one had noticed such great performance difference before?

I have not flown a real-life uh-1h, so I have no idea if it is performing as it should or not, but on this forum there have been real life uh pilots and yet this is the first time that I see such a huge difference in performance being pointed out. Seems odd to me.

[snocc_]

wow someone at ED should really do something about this

[Schmidtfire]

5 minutes ago, Rudel_chw said:

So, we have been flying the DCS Uh-1 for 7 years now, and yet no one had noticed such great performance difference before?

I have not flown a real-life uh-1h, so I have no idea if it is performing as it should or not, but on this forum there have been real life uh pilots and yet this is the first time that I see such a huge difference in performance being pointed out. Seems odd to me.

Credit where credit's due, a lot of effort went into this report.

Even after 7 years, It is important to challenge the developers work and not to take everything we see at face value. In the end it makes for better products and benefit us and ED. So Im intrigued about this report, but let the helicopter experts discuss. Hopefully someone from former BST can chime in.

[bradmick]

I would like to respectfully rebut the above. For reference, exhibit A, it is dated 1988, but is distrobution A. The below screen grab is from page 37 of this PDF: https://www.uh1ops.com/_files/ugd/9f78cd_60998a9ed26b4cbe8a65351e9cc076e9.pdf

Using the correct Chapter 7 for CB (as was referenced in the original posters post) I took the charts and based on 7500lbs, "slick" (i.e. no hardpoints):

15 degrees celsiuus, Sea Level

5 foot hover torque of 25.5 psi

100KTAS (96kts IAS) torque of 25psi

 

I then set this same configuration up in DCS and flew it. At 5 foot in DCS I found the helicopter to hover at appx 25.5 PSI, which is pretty dead accurate with what I calculated. I then accelerated until to 100kts, and noted i was pulling about 30 psi of torque. I reduced torque until I got to around 25.5 psi and found I was at about 94 knots. I'm pretty sure the airspeed guage is indicated airspeed, so that puts me within 0.5 psi of torque and 2 knots of airspeed from the reference. This would also be really, really close to reality as well, enough so that I could safely say your assertion is way, way off. 
 

The primary error that led to the entirety of the discussion being invalid is that the primary refrence was the  airspeed operating limits chart out of chapter 5, which is the Vne chart for the helicopter. It tells you the fastest you're allowed to go for the input conditions. This is why there isn't a torque associated with it. The shaft horespower equation, which good for approximating things, doesn't take into account all the various other factors that effect performance of the aircraft, so i'd be careful in it's use. It can definitely get you in the ballpark, but it's typically off by a fair amount. Attached are the various supporting screen shots and chart references to support my statements above.

 

My first image is the Distrobution Statement from the reference doc. The next is the hover chart for a composite blade helicopter. Next is the torque value from DCS at 5-foot. Next is the cruise chart for SL and 15 degrees C followed by the cruise torque and airspeed in level flight. Finally I provided a picture of my configuration.

[Rudel_chw]

1 hour ago, Schmidtfire said:

So Im intrigued about this report, but let the helicopter experts discuss.

 

I was just expressing a reasonable doubt that the huey's performance is unacceptably inaccurate, as it would have been detected long ago. But yes, the technical aspects of helicopter flight are way above my head, so I will too wait for the opinion of SME, hopefully there is one still on the forum.

[Tim_Fragmagnet]

1 hour ago, bradmick said:

I would like to respectfully rebut the above. For reference, exhibit A, it is dated 1988, but is distrobution A. The below screen grab is from page 37 of this PDF: https://www.uh1ops.com/_files/ugd/9f78cd_60998a9ed26b4cbe8a65351e9cc076e9.pdf

Using the correct Chapter 7 for CB (as was referenced in the original posters post) I took the charts and based on 7500lbs, "slick" (i.e. no hardpoints):

15 degrees celsiuus, Sea Level

5 foot hover torque of 25.5 psi

100KTAS (96kts IAS) torque of 25psi

 

I then set this same configuration up in DCS and flew it. At 5 foot in DCS I found the helicopter to hover at appx 25.5 PSI, which is pretty dead accurate with what I calculated. I then accelerated until to 100kts, and noted i was pulling about 30 psi of torque. I reduced torque until I got to around 25.5 psi and found I was at about 94 knots. I'm pretty sure the airspeed guage is indicated airspeed, so that puts me within 0.5 psi of torque and 2 knots of airspeed from the reference. This would also be really, really close to reality as well, enough so that I could safely say your assertion is way, way off. 
 

The primary error that led to the entirety of the discussion being invalid is that the primary refrence was the  airspeed operating limits chart out of chapter 5, which is the Vne chart for the helicopter. It tells you the fastest you're allowed to go for the input conditions. This is why there isn't a torque associated with it. The shaft horespower equation, which good for approximating things, doesn't take into account all the various other factors that effect performance of the aircraft, so i'd be careful in it's use. It can definitely get you in the ballpark, but it's typically off by a fair amount. Attached are the various supporting screen shots and chart references to support my statements above.

 

My first image is the Distrobution Statement from the reference doc. The next is the hover chart for a composite blade helicopter. Next is the torque value from DCS at 5-foot. Next is the cruise chart for SL and 15 degrees C followed by the cruise torque and airspeed in level flight. Finally I provided a picture of my configuration.

First, you're referencing an outdated version of the huey's manual, yours only has changes 1-18, afaik 1-20 is the most recent, granted I've only found one with 1-19. 

Second, I didn't use the operating speeds chart as a reference, I refuted it as a viable reference for the reasons you stated.
It tells you the fastest you're ALLOWED to go, but not the fastest the machine can physically push itself. It cannot be used as a reference for the actual performance of the machine.

Third, you're measuring against the nose pitot IAS, our huey has the pitot on the roof, so the inner scale is the correct one, not the outer one. So it should actually read 100knots at sea level, if not 101.

Fourth, add more weight, at 9500lbs in a 100knot sea level 15C cruise,
as per YOUR chart, you should be at about 29psi

You won't be

 

 

Fifth, "The shaft horespower equation, which good for approximating things, doesn't take into account all the various other factors that effect performance of the aircraft, so i'd be careful in it's use. It can definitely get you in the ballpark, but it's typically off by a fair amount."

 

If the aviation engineers figuring this out by hand so that they can properly profile the load placed on the drive system say it's good enough.

It's good enough.

Edited February 27, 2023 by Tim_Fragmagnet

[Harlikwin]

1 hour ago, Rudel_chw said:

So, we have been flying the DCS Uh-1 for 7 years now, and yet no one had noticed such great performance difference before?

I have not flown a real-life uh-1h, so I have no idea if it is performing as it should or not, but on this forum there have been real life uh pilots and yet this is the first time that I see such a huge difference in performance being pointed out. Seems odd to me.

You don't know what you don't know. Simple as. 

[bradmick]

The airspeed indicator is in indicated airspeed. The roof mounted pitot tube doesn’t matter. The true airspeed column is there for the e purposes of filing flight plans, but the aircraft flew indicated airspeed, this is why I used and referenced indicated airspeed.
 

I work off the references I can find and that meet the forum rules for posting. I did 7500lbs because to get to 9500lbs I needed to have the pylon mounts and weapons. To ensure the conditions matched the chart, I went to the closest GWT I could and met the cruise chart configuration assumptions. If you’re going to do an accurate test, you need similar conditions/configurations which is what I did because the baseline configuration is the slick configuration. 

Edited February 27, 2023 by bradmick

[Tim_Fragmagnet]

16 minutes ago, bradmick said:

The airspeed indicator is in indicated airspeed. The roof mounted pitot tube doesn’t matter. The true airspeed column is there for the e purposes of filing flight plans, but the aircraft flew indicated airspeed, this is why I used and referenced indicated airspeed.
 

I work off the references I can find and that meet the forum rules for posting. I did 7500lbs because to get to 9500lbs I needed to have the pylon mounts and weapons. To ensure the conditions matched the chart, I went to the closest GWT I could and met the cruise chart configuration assumptions. If you’re going to do an accurate test, you need similar conditions/configurations which is what I did. 

I'm not talking about true airspeed for the inner scale

I'm talking about the roof pitot scale

You're flying too slow in your tests.

your indicator should in fact actually read 100 if not 101 knots IAS at sea level for a TAS of 100knots.


The pitot was moved to the roof because it was more accurate than the nose pitot.

Our module has the roof pitot.

This thing 


Also if I do the 7500lbs cruise at sea level 15C at the correct IAS

0



We get 34psi

Edited February 27, 2023 by Tim_Fragmagnet

[SPAS79]

2 hours ago, Rudel_chw said:

So, we have been flying the DCS Uh-1 for 7 years now, and yet no one had noticed such great performance difference before?

I have not flown a real-life uh-1h, so I have no idea if it is performing as it should or not, but on this forum there have been real life uh pilots and yet this is the first time that I see such a huge difference in performance being pointed out. Seems odd to me.

Really, you need a real life engineer for this stuff, not a pilot. 

[bradmick]

Now I understand the confusion, my bad. Using the inner scale on the left side of the page, she's about 5 knots slow.

 

I also sat down and adjusted my base torque value taking into account the IR suppressor, which adds 2 square feet of drag. Per the manual, you use:

change in area / 10 * Delta PSI

this worked out to: 

2 sq ft for the suppressor / 10 * ~4.5 Delta PSI = 0.2 * 4.5 = 0.9

Base cruise torque was 25 psi, so this takes us up to 25.9 which is about 30 psi. At 30 psi, she's about 5 knots slow. That's not half bad. Again, this is for a slick configuration.nullnull

[EnvyC]

Ily tim

[=RS= Hart]

Tim's dedication to correcting the Huey is absolutely admirable 

[khajaja]

Tim once again proving he is simply built different

[Tim_Fragmagnet]

36 minutes ago, bradmick said:

Now I understand the confusion, my bad. Using the inner scale on the left side of the page, she's about 5 knots slow.

 

I also sat down and adjusted my base torque value taking into account the IR suppressor, which adds 2 square feet of drag. Per the manual, you use:

change in area / 10 * Delta PSI

this worked out to: 

2 sq ft for the suppressor / 10 * ~4.5 Delta PSI = 0.2 * 4.5 = 0.9

Base cruise torque was 25 psi, so this takes us up to 25.9 which is about 30 psi. At 30 psi, she's about 5 knots slow. That's not half bad. Again, this is for a slick configuration.nullnull

 

 

and I believe I have found the sticking point 

I'll ask you again, try it at 9500lbs.

While speed is part of the problem, the main problem is the total engine output. The problem is lift capacity.

As modeled, our engine pushes the torque to 50psi at 100% N1, meaning at max output, our engine is only putting out 1158shp.

That's the problem, because it's SUPPOSED to be able to push 1340shp, pushing the torque all the way up to 58psi.

 

As modeled, our huey is performing like it's 3400lbs heavier.

Also

If I do the 9500lbs cruise test but instead normalize to the proper PSI for 100knots

Edited February 28, 2023 by Tim_Fragmagnet

[Harlikwin]

1 hour ago, SPAS79 said:

Really, you need a real life engineer for this stuff, not a pilot. 

Yup. 

[Tim_Fragmagnet]

Alright how about one more test
this time we'll cross reference 2 different datapoints


We'll run the huey at the same parameters as usual, at 9500lbs, and we will normalize to about 33psi, as per the chart, this should get us about 110knots





It doesn't.

 

 

 

 

 

OK
now lets cross reference something
Lets run the huey at 6100lbs, and normalize to about 33psi, this should blast past 110knots and should even pass the Vne

 

Except we don't.

 

 

Our huey, at 6100lbs, at 33psi, can't even reach the speed it should get at 9500lbs at 33psi


Do you see what's happening now?
Where is the power output? We are underperforming by over 3400lbs.

How does the our DCS huey at 6100lbs 33psi, perform how the real huey should at 9500lbs 30psi. A heavier weight, at a lower power output.

Edited February 28, 2023 by Tim_Fragmagnet

[bradmick]

What was your configuration for those different weights? What components were on the aircraft? All of your stuff is moot without that information. The baseline for the charts is a slick aircraft, and then you have to add the IR suppressor because that's installed by default in DCS. Without knowing what the external configruation of the aircraft is, the data you're presenting means nothing. The only way you can get to 9500lbs is by loading all the external stores on the bird, which will effect drag. However, how do i account for the rocket pods and mini guns plus the external hardpoints? That info isn't available. So until you tell me what your actual aircraft configruation is, and that it's standard across every test (which should be slick...and then because of DCS, add the 2 square feet for the IR suppressor) your data doesn't mean anything.

[Tim_Fragmagnet]

50 minutes ago, bradmick said:

What was your configuration for those different weights? What components were on the aircraft? All of your stuff is moot without that information. The baseline for the charts is a slick aircraft, and then you have to add the IR suppressor because that's installed by default in DCS. Without knowing what the external configruation of the aircraft is, the data you're presenting means nothing. The only way you can get to 9500lbs is by loading all the external stores on the bird, which will effect drag. However, how do i account for the rocket pods and mini guns plus the external hardpoints? That info isn't available. So until you tell me what your actual aircraft configruation is, and that it's standard across every test (which should be slick...and then because of DCS, add the 2 square feet for the IR suppressor) your data doesn't mean anything.

I'm running the slick huey with the IR suppressor and to get 9500lbs you can use an internal cargo trigger to add weight to the aircraft. At full fuel (7438lbs), 935kg should get you to around 9500lbs

That configuration at 6100lbs would be somewhere just under an extra 2psi, the drag curve doesn't extend that high up so you have to eyeball it.
at 9500 it would be +1.2psi

 

\

 

Even with the corrected torque value

our huey at 6100lbs is performing how it should be at 9500lbs.

We are underperforming by 3400lbs

Something is wrong, power we should be getting just isn't there.

Edited February 28, 2023 by Tim_Fragmagnet

[khajaja]

tim is of course highly trained in the field of aeronautical engineering

[Harlikwin]

5 hours ago, bradmick said:

 

Base cruise torque was 25 psi, so this takes us up to 25.9 which is about 30 psi. At 30 psi, she's about 5 knots slow. That's not half bad. Again, this is for a slick

I mean, 4.1 PSI doesn't sound like much to engineers, but like if you inserted 4.1 PSI into my lungs at an instant I'd die in rather horrible ways. Its not a trivial amount of pressure. 

[ustio]

8 hours ago, Rudel_chw said:

So, we have been flying the DCS Uh-1 for 7 years now, and yet no one had noticed such great performance difference before?

I have not flown a real-life uh-1h, so I have no idea if it is performing as it should or not, but on this forum there have been real life uh pilots and yet this is the first time that I see such a huge difference in performance being pointed out. Seems odd to me.

To be fair, the Viggen FM was recently updated and corrected after 6 years of release after they show up with documentation.

[=RS= Hart]

9 hours ago, Rudel_chw said:

So, we have been flying the DCS Uh-1 for 7 years now, and yet no one had noticed such great performance difference before?

I have not flown a real-life uh-1h, so I have no idea if it is performing as it should or not, but on this forum there have been real life uh pilots and yet this is the first time that I see such a huge difference in performance being pointed out. Seems odd to me.

A reminder that people also stated the Gazelle flight model was correct based on "feel", feel means nothing if the numbers don't match.

[HILOK]

@Tim_Fragmagnet thank you so much for all your dedication, patience and perseverance