Blade stall at cruise speed?

[TurboHog]

Hey,

 

After the introduction of version 1.2.6 it is no longer possible to reach cruise speed (109kts) without the first symptons of retreating blade stall. In other words: there is a lot of shaking when you fly 109kts. From what I remember shaking always started more towards 120kts, which is closer to Vne for the Huey.

 

I don't think this behaviour is correct unless someone can prove otherwise.

[xxJohnxx]

Nah, shaking always stared at about 105 kts, but it is depending on your weight.

As far as I heard from a real pilot, cruise speed is more arround 90 knots.

Especially with the last update, crusing at those high speeds you mentioned you will drive the EGT into the red area.

[TurboHog]

Nah, shaking always stared at about 105 kts, but it is depending on your weight.

As far as I heard from a real pilot, cruise speed is more arround 90 knots.

Especially with the last update, crusing at those high speeds you mentioned you will drive the EGT into the red area.

 

Mhhm so maybe this is just more realistic, which is always a good thing :thumbup:

 

I can't remember shaking <110kts on previous versions though...

[TurboHog]

Yet something feels not quite right after some research.

 

FAT +15C, Sea level pressure altitude, 7500lbs (slick, 45% fuel), engine RPM 6400.

 

From the cruise chart:

V = 110 kts IAS roof indicated @ calibrated torque required = 32 PSI.

 

Correction factor is +1.1 so my indicated torque should be about 31 PSI.

 

Let's how accurate the BST Huey really is:

 

V = 95 kts IAS @ indicated torque 31PSI

V = 110 kts IAS @ indicated torque 40PSI, EGT above 30 min maximum, heavy shaking while symptons of retreating blade stall are supposed to kick in around Vne, which is 125 kts IAS roof indicated under these conditions.

 

I can safely say that the cruise characteristics are way off under these conditions and most likely under other conditions as well. The current flight model should not be allowed to make it to the final product. Off course this could be part of the beta WIP status.

 

I hope my efforts to improve this product are appreciated...

 

edit:

 

In the cruise chart, the fifth line from the right is for 7500lbs.

Edited September 14, 2013 by TurboHog

[xxJohnxx]

You are sure that this is for the UH-1H? Because the current cruise speeds and power settings fit that what I have been told by real UH-1H pilots.

[TurboHog]

You are sure that this is for the UH-1H? Because the current cruise speeds and power settings fit that what I have been told by real UH-1H pilots.

 

Info is based on the official UH-1H Huey manual from 15th of february 1988. Are you sure these pilots are talking about version 1.2.6?

 

Clearly cruise speeds and power settings do not match the cruise charts now (Not even within 20% as for torque settings).

Edited September 14, 2013 by TurboHog

[TimeKilla]

Nah, shaking always stared at about 105 kts, but it is depending on your weight.

As far as I heard from a real pilot, cruise speed is more arround 90 knots.

Especially with the last update, crusing at those high speeds you mentioned you will drive the EGT into the red area.

 

Yup i remember shaking around 110 knots and above would love for them to model engine overheating but thats another issue.

[TurboHog]

Yup i remember shaking around 110 knots and above would love for them to model engine overheating but thats another issue.

 

That may be, but Indicated torque/calibrated torque vs speed is still far from accurate.

[26-J39]

Info is based on the official UH-1H Huey manual from 15th of february 1988. Are you sure these pilots are talking about version 1.2.6?

 

Clearly cruise speeds and power settings do not match the cruise charts now (Not even within 20% as for torque settings).

 

The UH-1H in the manual you refer to is using the metal blades.

 

"2-43 Main Rotor

 

... The two all metal blades"

[TurboHog]

The UH-1H in the manual you refer to is using the metal blades.

 

"2-43 Main Rotor

 

... The two all metal blades"

 

And composite blades are responsible for this significant increase in torque requirements? I can imagine the opposite is true.

[26-J39]

And composite blades are responsible for this significant increase in torque requirements? I can imagine the opposite is true.

 

Just pointing out the differences, although I would think the same due to lower weight. There is blade profile and overall design differneces to think about but I'm not sure at all there.

[VanjaB]

I have to say that the Huey behaves a whole lot differently in 1.2.6, I cant put my finger on it but something feels off.

[TurboHog]

I have to say that the Huey behaves a whole lot differently in 1.2.6, I cant put my finger on it but something feels off.

 

See my little experiment from post # 4

 

The relation between speed, torque and EGT does not seem to be correct.

 

The fact that our Huey has composite blades (citation needed) does not explain the significant difference. In fact it should perform even better with 'lighter' blades.

[iFoxRomeo]

And composite blades are responsible for this significant increase in torque requirements? I can imagine the opposite is true.

 

You´re right. The opposite is true.

Griffin has a newer version of the flight manual with charts for composite blades. Chapter 7.1.

 

A quote from another discussion:

That's older version of what's available. We have a documentation thread here but the link to the original seems dead again. I uploaded the 1988 manual to my drive though.

Here's the link:

 

TM 55-1520-210-10

 

 

The Vcruise is 90Kts. This is because of the 5° forward tilt of the MGB/Main Rotor Mast. At 90 Kts strait and level flight the fuselage is nearly in level attitude, thus producing lesser drag compared to other attitudes.

As far as i remember vibrations are low at 75-80Kts and increasing to 90Kts. From 90Kts the vibrations increase in a more exponential than linear function up to Vne.

 

 

Fox

[iFoxRomeo]

...

The fact that our Huey has composite blades (citation needed) does not explain the significant difference. In fact it should perform even better with 'lighter' blades.

 

Lighter blades:

 

The Main Rotor Head with composite blades has 99,36% of the mass of the Main Rotor Head with metal blades.

 

 

 

For CB in the DCS Huey check DCS UH-1H Flight Manual Chapter 2.2 at the bottom of page 11.

Quote:

"Note. The composite rotor blades provide a 6% improvement in the UH-1H's hovering capability and a 5 to 8 percent reduction in fuel flow in forward flight."

 

 

 

Fox

[TurboHog]

Lighter blades:

 

The Main Rotor Head with composite blades has 99,36% of the mass of the Main Rotor Head with metal blades.

 

 

 

For CB in the DCS Huey check DCS UH-1H Flight Manual Chapter 2.2 at the bottom of page 11.

Quote:

"Note. The composite rotor blades provide a 6% improvement in the UH-1H's hovering capability and a 5 to 8 percent reduction in fuel flow in forward flight."

 

 

 

Fox

 

So the cruise chart from post 4 should be more or less accurate... In that case the relation between torque and speed is not. (almost 25% off in some cases considering torque setting.)

 

Oh actually, the cruise and torque calibration charts that I've used come from the 15th feb 1988 manual so they should provide correct info.

Edited September 17, 2013 by TurboHog

[iFoxRomeo]

So the cruise chart from post 4 should be more or less accurate... In that case the relation between torque and speed is not. (almost 25% off in some cases considering torque setting.)

 

Oh actually, the cruise and torque calibration charts that I've used come from the 15th feb 1988 manual so they should provide correct info.

 

Your flight manual is from feb 1988 with changes 1 to 3. And the charts are from flight tests done in november 1970. But the flight manual provided by Griffin has changes 1 to 19 incorporated with the latest change from 31.December 2002. And there is an additional Chapter 7.1 "Performance" explicitly for the composite blades. Flight test of the composite blades was done in june 1988.

 

Comparing metal blade and composite blade:

At +15°C and sea level: Max. t/o weight and 30PSI torque -> 94 KTAS with metal blades and 104KTAS with composite blades.

 

 

The engine of the DCS Huey needs finetuning.

 

 

Fox

[VanjaB]

Lighter blades:

 

The Main Rotor Head with composite blades has 99,36% of the mass of the Main Rotor Head with metal blades.

 

 

 

For CB in the DCS Huey check DCS UH-1H Flight Manual Chapter 2.2 at the bottom of page 11.

Quote:

"Note. The composite rotor blades provide a 6% improvement in the UH-1H's hovering capability and a 5 to 8 percent reduction in fuel flow in forward flight."

 

 

 

Fox

 

This is very strange indeed, from memory alone the difference in power requirements to simply lift the heli off the ground is huge. At least 30-40% more power is needed in 1.2.6. Either 1.2.5 had it very wrong or this new patch is if FUBAREd.

 

Try flying the MEDIVAC mission near the start of the campaign, I think its the third of foruth mission.

 

A lot more power is required to reach those unstable flying speeds of 140 knots, what is even stranger is that for some reason Im not using as much left rudder as I used to, something is very wrong here...

Edited September 18, 2013 by VanjaB

[TurboHog]

1. Engine power has not been reduced. However collective control handle “rigging” is altered to better match real collective handle settings required throughout the engine power demand envelope. This is why you are seeing higher collective requirements during takeoff, for example. The engine torque and actual rotor blade collective angles are the same (possibly slightly different as there was some tuning of dynamics as well), but the cockpit handle positioning is what is updated.

 

Nothing wrong with engine power.

 

The problem could be simplified to a drag problem. Less drag will increase speed at the given calibrated torque. But I can imagine the AFM works much more complex than that.

[TurboHog]

This is still an issue.

 

Dear BST, see post #4 and the discussion that followed.

 

The relation between EGT, Torque and true airspeed is still way off. In post #4 I mentioned that this shouldn't make it to the final version, but it did. That is no problem but please consider this for future patches.

 

Indicated torque at a given airspeed is up to 50% off. (too high)

 

Airspeed at given torque is up to 20% off. (too low)

 

information based on UH-1H manual with changes 1 - 19. Charts for UH-1H with composite blades.

 

I've taken into account things such as OAT, correction factor for indicated to calibrated torque, weight, configuration, altitude and engine/rotor RPM.

[outlawal2]

Also remember that the phenomena is related to the speed of the BLADE, not just the helicopter... So if you are flying INTO the wind, you can actually fly a bit faster as the retreating blade is moving WITH the wind.. And if you are flying WITH the wind, you will get into retreating blade stall earlier than if the day was perfectly calm...

 

Windspeed and direction have a noticable effect on retreating blade stall...

[TurboHog]

Also remember that the phenomena is related to the speed of the BLADE, not just the helicopter... So if you are flying INTO the wind, you can actually fly a bit faster as the retreating blade is moving WITH the wind.. And if you are flying WITH the wind, you will get into retreating blade stall earlier than if the day was perfectly calm...

 

Windspeed and direction have a noticable effect on retreating blade stall...

 

This is no longer about blade stall, it's about cruise performance and the wrong torque/speed relation. Of course I tested in no wind conditions. Please read post #4 and onwards more carefull.

[outlawal2]

This is no longer about blade stall, it's about cruise performance and the wrong torque/speed relation. Of course I tested in no wind conditions. Please read post #4 and onwards more carefull.

 

My apologies.. That is what happens when you skim these topics while working...

 

:doh:

[P3CFE]

Also remember that the phenomena is related to the speed of the BLADE, not just the helicopter... So if you are flying INTO the wind, you can actually fly a bit faster as the retreating blade is moving WITH the wind.. And if you are flying WITH the wind, you will get into retreating blade stall earlier than if the day was perfectly calm...

 

Windspeed and direction have a noticable effect on retreating blade stall...

 

Sorry, while i know this reply was off topic, i'd like to react on this.

Wind speed has nothing to do with the airspeed of the Blade during flight.

The airspeed, indicated on the Airspeed Indicator (when flying fwd. with no sideslip) is the only Airflow-factor that effects the Rotorblades and anything else on the chopper.

The movement of the column of Air, where you are flying in, over the ground (wind), is only affecting groundspeed and track.

 

Just to get it straight.

 

Greetz.