Is high RPM normal when pulling collective?

[FalcoGer]

When I pull more collective, especially on takeoff, I get rotor RPM high if I pull too much, too fast. I find that curious as I'd have guessed that pulling collective increases torque requirement and thus slowing the blades down initially before the engines respond.

Is that right or is the PID just over-responding to the demand that it thinks the engines will need to provide?

It just seems strange to me. It also feels like I pull collective gently enough, so to avoid the warning i have to be really slow on takeoff with the collective. it feels off.

[sirrah]

12 hours ago, FalcoGer said:

When I pull more collective, especially on takeoff, I get rotor RPM high if I pull too much, too fast. I find that curious as I'd have guessed that pulling collective increases torque requirement and thus slowing the blades down initially before the engines respond.

Is that right or is the PID just over-responding to the demand that it thinks the engines will need to provide?

It just seems strange to me. It also feels like I pull collective gently enough, so to avoid the warning i have to be really slow on takeoff with the collective. it feels off.

It's not you.

Indeed you very quickly get a rotor RPM high warning when taking off now. Only when do take off really really gently, you won't get it. Also, as you said, high RPM warning at this point doesn't make sense at all. Low I understand, but high? (or please anyone, explain it to me )

 

Definitely something changed in this regard, in either the last OB update or its hotfix, because this didn't ever happen to me before (and fwiw, I have about 80 hours in the Apache at the moment )

Maybe one of the CM's or @Raptor9 can chime in on this matter? Was this changed on purpose?

 

(sorry for no track file, GF called me downstairs before I had the chance to make one . Maye I'll manage to upload one tomorrow)

 

Edited January 28, 2023 by sirrah
typo

[Floyd1212]

It seems to happen when quickly pulling pitch from 0 to just to the point where you go light on wheels, and then stop. 

[Amarok_73]

On 1/28/2023 at 4:52 PM, sirrah said:

Definitely something changed in this regard, in either the last OB update or its hotfix,

Actually, I observe this behavior since very beginning.

[sirrah]

1 hour ago, Amarok_73 said:

Actually, I observe this behavior since very beginning.

Really? Getting a RPM high warning when pulling collective quickly?

I can't recall I've ever had that before. RPM low, yes, but not RPM high.

 

Edit:

I just recorded a track, showing the potential issue ("potential", as I'm not sure if this is intended and correct, or if it's a bug)

Note that when I do a sudden collective increase, just to the point where she gets light on the wheels, I get a "rotor rpm high" warning.

The last time, I increase collective gently, and the warning stays out.

 

So, the question remains; when "quickly/violently" increasing collective with weight still on wheels, is it correct that you'd get a "rotor rpm high" warning?

Rotor rpm high.trk

Edited January 30, 2023 by sirrah

[sirrah]

@BIGNEWY, could you please take a look at my track file in the previous post and either move this thread to the bugs section, or verify/confirm that this is intended and correct behavior.

[Mad_Shell]

On 1/28/2023 at 3:57 AM, FalcoGer said:

When I pull more collective, especially on takeoff, I get rotor RPM high if I pull too much, too fast. I find that curious as I'd have guessed that pulling collective increases torque requirement and thus slowing the blades down initially before the engines respond.

Is that right or is the PID just over-responding to the demand that it thinks the engines will need to provide?

It just seems strange to me. It also feels like I pull collective gently enough, so to avoid the warning i have to be really slow on takeoff with the collective. it feels off.

I believe it's normal behaviour, if you pull fast on the collective, it'll increase the G-load on the rotor system, inducing a stronger cone effect (blades angling up) and creating a transient high rpm effect for a few seconds because of conservation of momentum. After a few seconds, the increased G-load, demanding more power from the engines to keep the rotor spinning, takes over and the rotor rpm will deacrease again (to the initial 101% value, or lower if you're asking too much from your engines because you carry a heavy payload)

 

[sirrah]

8 minutes ago, Mad_Shell said:

I believe it's normal behaviour, if you pull fast on the collective, it'll increase the G-load on the rotor system, inducing a stronger cone effect (blades angling up) and creating a transient high rpm effect for a few seconds because of conservation of momentum. After a few seconds, the increased G-load, demanding more power from the engines to keep the rotor spinning, takes over and the rotor rpm will deacrease again (to the initial 101% value, or lower if you're asking too much from your engines because you carry a heavy payload)

 

That makes sense!

Excellent explanation video 

 

Assuming that this is indeed what's happening for our Apache in DCS, I'm very impressed ED included this (rather small/occasional) detail  

[Floyd1212]

I just hopped in to check it out in external view, and there is a slight coning effect of the rotor system when pulling pitch while still on the ground, but I'm still skeptical that the Coriolis effect on the rotor system exceeds the drag on the blades and causes them to over-speed. 

Maybe I am underestimating the Coriolis effect in my mental analysis of these forces in my head, but we aren't talking about a figure skater tucking their arms and legs in tight to their body, we are talking bout raising the tips of their outstretched arms by 2 inches.

How much over-speed is necessary to induce the warning?

 

[bradmick]

This is normal. On the collective is the collective droop potentiometer. This is tied into the Transient Droop Improvement (TDI) part of the engine control system. If you rapidly increase the collective, the speed of light signal to the DECU leads the power demand by dumping more fuel into the engine to prevent a droop from occurring. This was added specifically to prevent a droop from occurring during recoveries from practice autorotations. Anytime you’re below something like 15% torque, this is automatically there. It doesn’t have anything to do with coning or other aerodynamic phenomenon, well, except for maybe drag. 

[sirrah]

30 minutes ago, bradmick said:

This is normal. On the collective is the collective droop potentiometer. This is tied into the Transient Droop Improvement (TDI) part of the engine control system. If you rapidly increase the collective, the speed of light signal to the DECU leads the power demand by dumping more fuel into the engine to prevent a droop from occurring. This was added specifically to prevent a droop from occurring during recoveries from practice autorotations. Anytime you’re below something like 15% torque, this is automatically there. It doesn’t have anything to do with coning or other aerodynamic phenomenon, well, except for maybe drag. 

Forgive my ignorance, but I'm not sure if I understood that completely 

Did I understand correctly; that a sudden increase in collective, initiates a (short) "fuel boost" to the engine to compensate for the expected higher rotor drag? 

And when there is no rotor drag increase (weight on wheels), that extra fuel to the engine results in a temporary high rpm. 

Did I get that right?

 

[admiki]

3 hours ago, sirrah said:

Forgive my ignorance, but I'm not sure if I understood that completely 

Did I understand correctly; that a sudden increase in collective, initiates a (short) "fuel boost" to the engine to compensate for the expected higher rotor drag? 

And when there is no rotor drag increase (weight on wheels), that extra fuel to the engine results in a temporary high rpm. 

Did I get that right?

 

Yes

[Moxica]

On 1/28/2023 at 4:52 PM, sirrah said:

It's not you.

Indeed you very quickly get a rotor RPM high warning when taking off now. Only when do take off really really gently, you won't get it. Also, as you said, high RPM warning at this point doesn't make sense at all. Low I understand, but high? (or please anyone, explain it to me )

 

Definitely something changed in this regard, in either the last OB update or its hotfix, because this didn't ever happen to me before (and fwiw, I have about 80 hours in the Apache at the moment )

Maybe one of the CM's or @Raptor9 can chime in on this matter? Was this changed on purpose?

 

(sorry for no track file, GF called me downstairs before I had the chance to make one . Maye I'll manage to upload one tomorrow)

 

 

Can confirm, I get that to.

[sirrah]

2 hours ago, Moxica said:

Can confirm, I get that to.

Of course you do, we all do 

It's correct/intended behavior, as can be read a few posts up, by @bradmick

[Caldera]

Hey all,

Just about every time I lift off I get this warning?  Is this something that I am doing wrong, real to life or a glitch?

I also notice that if I set the throttles to 100%, vice all the way forward, the dang will not lift off (ex: 50% fuel and 16 Hellfires).  But if I shove the throttles all the way forward to 103% it has no issues.  Normal?

Thanks in advance,

Caldera

[MAXsenna]

What are your settings under "special". If I use my Warthog for the levers and use "jump over" I get some weird results around the fly position. It's almost like it changes between the two settings.

Sent from my MAR-LX1A using Tapatalk

[Floyd1212]

Throttle levers should be set to FLY and left there.  Verify in the cockpit with your mouse if they are all the way to 100% when your HOTAS is pushed all the way to your FLY setting.

I couldn't find the exact thread where this was discussed, but if memory serves, there is some anticipation logic in the onboard computers that bumps the RPM when it expects a lot of drag on the rotor system.  Bring the collective up more slowly and smoothly to avoid this when lifting off.

[MAXsenna]

23 minutes ago, Floyd1212 said:

Throttle levers should be set to FLY and left there.  Verify in the cockpit with your mouse if they are all the way to 100% when your HOTAS is pushed all the way to your FLY setting.

Sure, but how can you verify that they are exactly at the fly position? With the mouse you say? How?

I try to watch the controls indicator, but I'm not sure if you're supposed to be right before or on the bar/stop. Looking at the label on the cockpit doesn't really help.  

I really wish ED would implement custom detent settings for relevant modules like Razbam and Aerges. 

Cheers! 

[Floyd1212]

You put your mouse over them and click and drag up. If they move at all, they weren’t all the way up. 

[MAXsenna]

You put your mouse over them and click and drag up. If they move at all, they weren’t all the way up. 

Even if you select "jump over" in the special settings? My problem is more or less the opposite, that I get over torque.

Sent from my MAR-LX1A using Tapatalk

[Floyd1212]

4 hours ago, MAXsenna said:

Even if you select "jump over" in the special settings?

Ah, sorry, my suggestion was directed at the OP, and assumed they did not have Jump Over" enabled.

Not sure how to solve your issue, but this is what the CI looks like with the throttles set to FLY.

[Archer.xd]

You should set the throttles to fly and leave them like that. You are getting the RPM high warning likely because you are rapidly increasing the collective. When you do it, engine will run at higher RPM to compensate the higher drag coming from rotor. So you basically get a temporary high RPM. 

[Caldera]

Thanks All,

I don't really pull the collective all that fast, but I will try slower. 

To me it still makes no sense that the "High RPM" warning should sound at all.  If any, it would seem more logical that the "Low RPM" should sound if I raise the collective to fast.

I get this warning just once as I lift off.  I am assuming that no else gets this warning on lift off?

The only other time the "High RPM" warning comes in as I have lost parts of the rotor blades (oops!).

Caldera

[pii]

51 minutes ago, Caldera said:

I get this warning just once as I lift off.  I am assuming that no else gets this warning on lift off?

I get it all the time I just ignore it unless it continues

[Floyd1212]

Found the original thread I was remembering, and Bradmick's response...

o