reported Cannot feather prop after damage; no damage works fine

[Nealius]

On a good airplane that has taken no damage, I can feather the props just fine. Throttle off, let RPM sink until it's 2500 or so, press the feather button in, prop feathers, stops, and the button pops back out.

 

When my engine has taken hits, this does not work. The prop windmills at ~1500rpm and the feather button remains depressed for the duration of the flight. Upon landing, the prop is still not feathered, and the feather button remains depressed. Even after shutting off fuel and mags. 

 

I can reproduce this every time when flying ONLINE, but these are 60-minute tracks. This doesn't seem reproducible offline, so it looks like it may be an ONLINE only issue.

[Nealius]

Track attached. FFW to around 24 minutes. Track file

 

Right engine damaged. Throttle idle. RPM would not fall sufficiently. Cut RPM. Cut fuel. Clicked and held feather button for 10 seconds. Prop refused to feather.

Left engine not damaged. Throttle idle. Cut RPM. Cut fuel. Clicked and held feather button for 10 seconds. Prop feathered as normal. 

[ViFF]

It's very likely the damage is also to the feathering mechanism. You need electricity to drive the oil pump that pushes oil into the constant speed governor mechanism that actually turns the blades into the oblique angle. That's 3 vital components that need to remain undamaged in order for the feathering to properly work. In the vast majority of cases damage in the engine area will kill your ability to feather the prop. Also notice the shaking. You definitely have damage to the prop. I wouldn't expect the feathering to work. The natural force of the blades is to go to fine pitch (max rpm). You can test if you go full throttle and max RPM if it will go over 3,000 RPM you have no more control of the prop's blades pitch - forget about feathering...

Cheers!

 

[Robi-wan]

So I had this issue today as well. And I understand about needing oil to feather the prop, I've feathered a prop or two IRL. These are the steps and the order I took within seconds of sensing engine/airframe vibration.

Left throttle -- Closed/Idle

Left prop control -- Aft/Coarse

Left feather button -- Push (it stayed in)

Now I'm in DCS test pilot mode...asking myself, "Self do you think the engine will stop if you turn off the fuel cock and turn off both Left mags?" I tell myself, "Sure, no fuel, no spark engine's gonna quit."

Left fuel cock -- Off

Left Magnetos both -- Off

And for another 15 minutes (until I quit the mission) the fan kept turning.

[grafspee]

So your prop wasn't feathered, if you got combat damage feathering mechanism could be damaged or prop it self could be damage and pitch mechanism could be jammed.

[Robi-wan]

8 hours ago, grafspee said:

So your prop wasn't feathered, if you got combat damage feathering mechanism could be damaged or prop it self could be damage and pitch mechanism could be jammed.

Aye laddie, I genuinely understand that. [edit] In my case the rpm did vary with moving the prop levers, down to ~1800 if you zoom in on the screen above.[/edit]The point I was trying to make but apparently failed to communicate, was this. After realizing the prop would not feather I tried UNSUCCESSFULLY to shut the engine down by removing the fuel source and turning the mags off. Damage to the prop governor would not affect them.

Currently with a small sample size of this thread, it appears that ANY engine battle damage renders the prop governor u/s 100% of the time. That IMHO makes modeling prop feathering a questionable effort or a bug.

I'll report back if I take engine damage and successfully feather the prop.

Edited March 21, 2022 by Robi-wan

[Bozon]

I had my starboard engine destroyed by ground fire in MP yesterday. The engine died immediately and the prop was stopped. I hit the feather button without doing anything else and to my surprise it feathered just fine.

So I guess your bug happens only on some specific conditions.

[Robi-wan]

1 hour ago, Bozon said:

I had my starboard engine destroyed by ground fire in MP yesterday. The engine died immediately and the prop was stopped. I hit the feather button without doing anything else and to my surprise it feathered just fine.

So I guess your bug happens only on some specific conditions.

Cool, so at least with a reported sample of one, a seized/destroyed engine's prop will feather. That's something to work with.  Have you successfully feathered the prop to a damaged/smoking engine with the prop still turning? How about shutting down a damaged engine with turning the fuel cock to off or the mags off? You probably have over a hundred hours "flying" this, I'm just getting started.

And to be clear, I have zero knowledge of the Dev's damage criteria that renders feathering u/s.

[Reflected]

It seems that as soon as the engine gets a few hits, the feathering doesn't work - which defeats its purpose, who would want to feather a working engine?

I've seen exceptions, but 49 times out of 50, the props wouldn't feather. (despite still having oil pressure)

I really hope this will be ironed out for when the Mossie comes out of early access.

[NineLine]

I am going to do some tests and check and see if the feathering unit has its own damage cell, etc. I will report back.

[Reflected]

Thanks NL! AFAIK, and please @Robi-wan correct me if I'm wrong, but the feathering should only break if a) there is no oil pressure, or b) the propeller hub receives hits. And with b), not even 100% of the cases.

[Robi-wan]

I confess I cannot post with certainty about a) no oil pressure because I don't have the reference document (AP 1538D, Vol I) for the de Havilland hydromatic propeller. On modern twin engine airplanes the loss of engine oil would allow the oil to drain from the constant speed unit with the piston in the hub driving the prop toward the feathered position. It's a bit more complicated than that, but that's the idea. I don't know if the de Havilland prop worked like that. 

A fine unit history of the 345th BG, Warpath Across the Pacific Vol I frequently mentions losses where the pilots were unable to feather a (Hamilton Standard) prop and they abandoned the aircraft.

I agree with you that b) the propeller hub receives hits makes more sense. In my reading of Mosquito squadron ORBs, I can't think of a single mention of the inability to feather a prop. Obviously those samples are limited to guys that survived. At the same time coming home on one engine with battle damage was a frequent occurrence. It's pretty eye opening the number of single engine accidents in the OTUs and Operational squadrons resulting in aircraft damaged beyond repair.

 

[NineLine]

SO I have been testing, and continue to. But I do see times when I can feather just fine, and others when I cannot. I have yet to fine the correlation between when I can and can't except that when I am a little more quick to feather it seems to work. I will keep looking into it though, some aspects of engine damage are not in/correct yet, such as oil leak with oil pump failure, not noticeable in any meaningful way currently.

[grafspee]

Looks like feathering has it's own oil pump so it should be possible to do if engine seized, but single damage to prop governor oil lines will make it impossible or damage to governor cylinder will make it unable to feather too, too many fragile things which are necessary to feather. 

https://www.enginehistory.org/Propellers/HamStd/hsf.shtml

Edited March 23, 2022 by grafspee

[Bozon]

1 hour ago, grafspee said:

Looks like feathering has it's own oil pump so it should be possible to do if engine seized, but single damage to prop governor oil lines will make it impossible or damage to governor cylinder will make it unable to feather too, too many fragile things which are necessary to feather. 

https://www.enginehistory.org/Propellers/HamStd/hsf.shtml

 

Thanks, the system is illustrated very nicely. So, it seems that if the main oil pressure (the yellow) is lost, the remaining feathering oil pressure (the green) will tend to push the piston towards the feathering position. However, I can’t see what supplies the pressure to the feathering oil line, so in case of damage the feathering pressure may drop quickly as well.

If oil is drained from both sides of the piston will it leave the blades to pitch freely? If so, then in a stopped engine the blades will tend to feather themselves or just about as this is the position of least pitch torque on the blades from the air flow.

[grafspee]

@Bozon this is whole page https://enginehistory.org/Propellers/HamStd/hamstd.shtml

What i showed is only when feather button is pushed, from description, it seems that feathering circuit is cut out when governor is working and vice versa.

Oil for feathering pump is supplied form main engine oil reservoir so if this one get empty no feathering will be possible, but engine seizure will not prevent prop from feathering, only direct damage to prop governing or feathering system.

 

Edited March 23, 2022 by grafspee

[Art-J]

12 hours ago, Robi-wan said:

I confess I cannot post with certainty about a) no oil pressure because I don't have the reference document (AP 1538D, Vol I) for the de Havilland hydromatic propeller. On modern twin engine airplanes the loss of engine oil would allow the oil to drain from the constant speed unit with the piston in the hub driving the prop toward the feathered position. It's a bit more complicated than that, but that's the idea. I don't know if the de Havilland prop worked like that. 

A fine unit history of the 345th BG, Warpath Across the Pacific Vol I frequently mentions losses where the pilots were unable to feather a (Hamilton Standard) prop and they abandoned the aircraft.

I agree with you that b) the propeller hub receives hits makes more sense. In my reading of Mosquito squadron ORBs, I can't think of a single mention of the inability to feather a prop. Obviously those samples are limited to guys that survived. At the same time coming home on one engine with battle damage was a frequent occurrence. It's pretty eye opening the number of single engine accidents in the OTUs and Operational squadrons resulting in aircraft damaged beyond repair.

 

I agree modern feathering Hartzells and McCauleys use springs and flyweights to naturally stay in feathered position until oil pressure builds up (as seen on many planes powered by turboprops). 

DeHavillands were actually license-built Hamilton Standard Hydromatics, however, so the opposite rule applies - when there's no oil pressure on either side of the dome piston, natural twisting moments will alwas want to rotate blades towards lowest pitch (highest RPM) state. Only sufficient oil pressure provided by feathering pump can make the prop feather.

We know the system uses main engine oil supply, but I wonder if that pump is strong enough in itself to do the job if the main engine oil pressure drops for whatever combat reason. i've read that it "boosts up" the existing pressure when everything works OK, but what if there's nothing left to boost?

I seem to recall that was advertized as one of advantages of Curtiss Electrics - one could alwasy feather them if there was some electrical power in batteries left, while Hamiltons without oil meant serious trouble.

On the other hand, we can see YT videos with stationary Hamilton feathering tests being done on museum restored planes on the ground, so guys obviously do it somehow even when engine's not running.

Edited March 23, 2022 by Art-J

[grafspee]

@Art-J if you can look at page which i linked, there is a table with operating pressure levels and pressures for feathering and unfeathering are 5 times higher then normal gavernor pressure, it is obvious that prop can be feathered w/o engine oil pump. Oil pressure provided by engine is not enough for gavernor to work so governor as well uses additional oil pressure booster.

Edited March 23, 2022 by grafspee

[Bozon]

25 minutes ago, Art-J said:

…

DeHavillands were actually license-built Hamilton Standard Hydromatics, however, so the opposite rule applies - when there's no oil pressure on either side of the dome piston, natural twisting moments will alwas want to rotate blades towards lowest pitch (highest RPM) state. Only sufficient oil pressure provided by feathering pump can make the prop feather.

…

Highest RPM would be when the engine is running, and the greatest component of airflow on the blades is due to the rotation. When the engine is dead the airflow is all in the direction of motion, so if you let the blades rotate freely, they should tend to align with that. Not so?

[NineLine]

Ok guys I think I have ID'd an issue with it, I will report this. Thanks all!