1600 rpm is not settable in DCS.

[-0303-]

Used to think 1600 was an extremely low. No, it was a used setting. DCS manual states:

 

Quote

 

When the trial was complete however, and he throttled back to 1 .600 rpm to return to Martlesham

 

and also from a book, a homecoming panicky Spitfire over London "I got 7 gallon!". Flight leader: "You can break formation, set 1700 rpm Boost 4 and go home". Also discussed, 1 lb 2650 rpm gives the same speed as 4 lb and 1700 rpm (but the latter will save 7 gallons an hour *1).

~

 

I find I can set 1800 rpm and I can set 1200 rpm but nothing in between. Thought at first RPM-lever problem but running Thrustmaster "Target Script Editor" -> "Device Analyzer" (scale of 0-I6384) I can see that RPM-lever setting:

 

15974 -> 1200 rpm

and

15972 -> 1800 rpm

at both 0 boost or 4+ boost.

 

Made a chart. RPM-lever is readout Thrustmaster "Target Script Editor" -> "Device Analyzer".

Never mind the dropping line, the interesting part is the linearity (lack thereof after ~15970).

 

By "throttle" I actually mean RPM lever (chart below).

 

 

Anyone run Release version? A simple test might be interesting. Can 1600 be set with pre 2.7 version?

~

 

*1) Not a typo, flying slow as you can is NOT the most fuel or range efficient, this war time memo emphasizes, because of dynamics of slow speed drag.

 

Edited May 15, 2021 by -0303-

[grafspee]

I just made quick look through spitfire pilots notes, looks like 1800 is minimum rpm which you can set by rpm lever.

Why game allow to set rpm lower then that i dont know.

 

 

 

Edited May 11, 2021 by grafspee

[Art-J]

RPM range attainable depends first and foremost on propeller type fitted, engine type second. The quote from DCS manual is irrelevant here, as it describes Spit prototype when it was fitted with fixed pitch prop. Quotes from the book - I don't know, I'm not familiar with it - do they refer to Spits with de Havilland or Rotol props? Which versions of the Spits?

 

The in-game 1200 RPM sounds very sketchy in itself (especially in the light of what Graf found in Pilot's Notes), but I checked and it's indeed selectable straight down from 1800. 

 

I also don't know if it's one of the new bugs 2.7 brought, or it was already there in previous version.

[-0303-]

Indeed "PILOT*S NOTE'S for SPITFIRE IX, XI, XVI" says (pdf):

 

Quote

...governed r.p.m. from 3,000 down to 1,800

 

but a "Pilot's Manual for SUPERMARINE SPITFIRE IIA and IIB" says: (this is provided by Zeno's Warbirds, it's a little produced in that it's converted to searchable text).

 

Quote

(iv) Maximum range is obtained with WEAK mixture, 1,700 R.P.M and at the lowest speed at which the machine can be comfortable flown.

Couldn't easily find it in my photocopied slightly different "original" IIA and IIB pilots manual pdf.

 

A Griffon manual "Seafire 45 & 46" says "2,750 down to below 1,800".

Edited May 12, 2021 by -0303-

[grafspee]

It's spit MK IIA/B different engine, different prop, same with griffon engine.

I also checked Merlin engine manual, it seems that 1800rpm is minimum engine rpm for Merlin 66,67,70,71,76,77 & 85.

Pilot's notes for Griffon 65 also mention ability to reduce rpm below 1800rpm but its says only to expend glide range in case of engine lose.

Looks like DCS spit has this feature, this would explain non linearity behavior, something similar to prop feathering. 

Edited May 12, 2021 by grafspee

[-0303-]

Quote

Looks like DCS spit has this feature, this would explain non linearity behavior, something similar to prop feathering.

Neat if true but is it more than your speculation? Also, why would the Griffin mechanism be non - linear? Non - linearity would require some extra mechanism. I could imagine some simple "brake wire" thing to prevent <1800 ever set accidentally. Seems something the halfwits-up-front would need.

 

Interestingly later version Spitfire IX had same/similar feature (throttle - rpm interconnection ie). Seems ours is "early" (Pilot's notes Spitfire IX, XI, XIV.pdf). I'm curious, I've never seen the "override lever", doesn't seem to be pictured in this source.

 

 

 

Edited May 12, 2021 by -0303-

[grafspee]

Interconnection similar to system available in Bf-109.

It is explained that, override lever looks like rpm lever on early versions, so no visual differences, only changed, way it works.

If pulled all way back it engages interconnection,

If move forward pilot can control rpm.

Yes this sudden drop from 1800 to 1200 rpm is only my speculation, why i think it should drop that sudden, because below 1800 is not useful range , so no need for precision rpm control.  

Edited May 12, 2021 by grafspee

[-0303-]

Looked up how rpm regulation works. Spring loaded flyweights. Two links: Hamilton , really simplified here.

 

Spring loaded flyweights are obviously linear. To make it non-linear one would need to add some extra mechanical bits. Maybe opening / closing an oil valve at levers lower end or something. So either dropping below 1800 is a part of the Spitfire prop design or it's a bug. As long it has enough throttle it should stick at 1800.

 

 

 

 

[grafspee]

I know how it works in basic, but actual construction may be not simply. Like you said it could be additional valve activated, or non linear spring.

Any way manual for merlin 66 or for spit IX dost not mention, about any possibility of going below 1800rpm. 

So i would set it as bug then.

I look at Pilot's notes for spitfire MK V, looks like 1800rpm is lower limit for engine rpm as well.

Edited May 12, 2021 by grafspee

[Art-J]

2 hours ago, -0303- said:

Looked up how rpm regulation works. Spring loaded flyweights. Two links: Hamilton , really simplified here.

 

Spring loaded flyweights are obviously linear. To make it non-linear one would need to add some extra mechanical bits. Maybe opening / closing an oil valve at levers lower end or something. So either dropping below 1800 is a part of the Spitfire prop design or it's a bug. As long it has enough throttle it should stick at 1800.

 

In those Hamilton Standard prop versions that could feather, there was a separate, additional oil line and valves, which cut off standard governor operation and pushed the actuating piston to/from feather position when needed. Check the rest of the enginehistory.org site - you linked to its page with counterrotating HS SuperHydromatics, but there's also a page with classic Hydromatic (and more drawings) as well. There's also a page with neat cutaways of all Rotols, though without description...

 

... which is not an issue, because If someone's has really a lot, and I do mean a LOT of free time on his hands, guys at ww2aircraft posted a complete, almost 300-pages-long maintenance manual for the Rotol Prop used in "our" Spit - post # 14 here:
https://ww2aircraft.net/forum/threads/rotol-and-d-h-constant-speed-prop-operation.54714/post-1592963

 

You can try searching for the answer there, I'm not sure I will ;).

[-0303-]

Added to my collection. I will read ... a bit ... for fun. Almost posted a Bf109 constant speed link from that website but images were gone.

Tested, P-51 doesn't drop below 1600 (green arc).

 

I'll probably make a bug thread in a while.

Edited May 13, 2021 by -0303-

[-0303-]

Not a bug (I think). Looks DCS Spitfire IX has prop feathering. Note prop angle indication "57" lower right corner (that new?).

 

 

If I read  the 298 pages ROTOL docs right ... the angle arc is 35 degrees. Minimum indicated "angle" in DCS is "20", max angle is "57". 37 degrees, close enough?

 

(edited out stuff abt ROTOL docs that was wrong)

 

Simple ground feathering experiment: Spawn and idle, rpm lever max forward. Prop angle 20'. Pull RPM lever back a bit, nothing, keep pulling back ... at 97.5% pulled back (15974/16384 * 100), that's the feathering threshold. Now it climbs to 57 and returns to 20 when pushed forward over the threshold again.

 

ROTOL doc is a lot. It did talk about non-feathering props at one point so ... there's feathering props to.

 

Edited May 16, 2021 by -0303-

[grafspee]

So my speculations weren't farfetched after all

Thanks for your time, reading this book

[-0303-]

I edited out the ROTOL doc comment above out because it was wrong. I think I grasp it better now:

 

ROTOL doc

Updated at least to 1951. Seems to be only about propellers for Mk VII, VIII and IX. Pdf pages of interest:

 

-PDF 3 "NOTES TO READERS" - explains the document, kind of.

 

-PDF 4 "ROTOL EQUIPMENT FOR SPITFIRE Mk VII, VIII & IX AIRCRAFT" - List of contents,  6 "PART"'s. PART 1.xx seems to be non-feathering props. Part 2.x includes Spitfire IX ("non-feathering" subtitle stops occurring)

 

-PDF 5 "LIST OF EQUIPMENT" - names Spitfire IX, Merlin 66 propeller as "R.12/4F5/4", spinner as "4CM/4" & governor as "CGR/1A".

 

-PDF 35 "PART 2.02 PROPELLER -/4F5/-" - First page of PART 2.xx. All props in the 4F5 series?. Names ROTOL ref 7282 as detailing the "R.12/4F5/4" propeller.

Note the 4 digit ROTOL references (like 7284, 7001, 7124) does NOT reference specific pages, they're like document categories, they can and do appear on multiple pages. ROTOL states them "internal use only" but they were the only way I managed to navigate ...

 

-PDF 48 PROPELLER R.12/4F5/4 - 35 degree pitch range stated along with other specifics (weight, diameter ...)

 

The last document (PDF 48). decided to not inflict all of  them. The Spitfire IX, Merlin 66 propeller details.

 

Maybe if i scour the rest of the 298 pages for category 7282 I'll find something explicit about feathering, maybe in a governor section (or not, (Pdf 5) "For details of the CGR/1A Governor Unit apply to Rotol Limited").

 

 

 

Edited May 16, 2021 by -0303-

[Droning_On]

On 5/11/2021 at 3:18 PM, -0303- said:

"I got 7 gallon!". Flight leader: "You can break formation, set 1700 rpm Boost 4 and go home"

that was me the other night on multiplayer server lol. Ditched in the sea 2miles of the isle of white as a P-51 Buzzed me lol.     Bugger …
 

Dont think that worked for me, i couldnt keep altitude at 1800rpm and low boost….. need to try again….

[grafspee]

4lbs at 1800rpm is pretty high boost for that rpm.