General Forums => Aircraft and Vehicles => Topic started by: 38ruk on September 29, 2016, 03:08:07 PM
Title: P-38 Rpm
Post by: 38ruk on September 29, 2016, 03:08:07 PM
I've noticed as much as a 400 rpm drop when doing hard vertical maneuvers with a P-38. Is this normal behavior for constant speed props ? I haven't notice as big of a drop with other planes . thanks
Title: Re: P-38 Rpm
Post by: oboe on September 29, 2016, 03:11:40 PM
Very interested in this answer as well. Seems to be the worst in P-38G to me.
Title: Re: P-38 Rpm
Post by: Golfer on September 29, 2016, 04:01:16 PM
Might have to do with the propellers being electrically actuated rather than hydraulic.
No idea how it works, it's all black magic and wizardy but that's my first guess.
Title: Re: P-38 Rpm
Post by: Chalenge on September 29, 2016, 04:06:12 PM
More than you ever wanted to know about constant speed propellers:
Title: Re: P-38 Rpm
Post by: Golfer on September 29, 2016, 04:10:01 PM
Does it address electrically actuated propellers or just standard hydraulic propellers?
Title: Re: P-38 Rpm
Post by: GScholz on September 29, 2016, 04:27:35 PM
In AH3 there is a lag modeled in the prop governor. Quick changes in speed (typically during vertical maneuvering) will now result in RPM changes until the governor can catch up.
Title: Re: P-38 Rpm
Post by: Golfer on September 29, 2016, 04:42:37 PM
I love the feature. The first time I heard it during a short beta stint I was surprised and impressed because it sounded and behaved authentically. I had a geeky smile.
I'm just wondering if the voodoo of the electric props explains the difference between the 38 and other airplanes.
Title: Re: P-38 Rpm
Post by: oboe on September 29, 2016, 11:42:03 PM
If I recall correctly, the P-39 had an electric prop as well.
Title: Re: P-38 Rpm
Post by: Randy1 on September 30, 2016, 06:19:42 AM
This just another neat feature of AH3. There are many. Note too, there are times when the rpm exceeds 3000 rpm.
Title: Re: P-38 Rpm
Post by: hitech on September 30, 2016, 08:32:39 AM
I love the feature. The first time I heard it during a short beta stint I was surprised and impressed because it sounded and behaved authentically. I had a geeky smile.
I'm just wondering if the voodoo of the electric props explains the difference between the 38 and other airplanes.
I had the same thing when I took the sim RV out for some areo. Suddenly it was wow that really changes the feel of how it actually sounds and the ques you do not realize you are using in real flight.
HiTech
Title: Re: P-38 Rpm
Post by: Mongoose on September 30, 2016, 02:38:31 PM
So what exactly was the change that was made? Somewhere along the line I missed that announcement.
Title: Re: P-38 Rpm
Post by: colmbo on September 30, 2016, 03:17:46 PM
I don't understand why you would lose RPM even if working the airplane hard. The engine is capable of turning the prop at 3000RPM at low airspeed....it does every takeoff. The change in speed isn't going to be so abrupt that even a slow electric prop can't keep up with the change.
Was the prop pitch set by an electric motor? Or was it just an electric governor controlling the prop which still uses engine oil pressure/spring pressure to set pitch? The B-24 used the latter setup. The prop controller was prone to failure, usually required an engine shut down and a whack with a rubber mallet (more easily accomplished on the ground).
Title: Re: P-38 Rpm
Post by: Golfer on September 30, 2016, 03:56:42 PM
I'm not sure. Whenever I've read about them they are distinguished as electrically actuated propellers.
I'm curious and was sure someone would know.
Title: Re: P-38 Rpm
Post by: Golfer on September 30, 2016, 04:45:18 PM
I've been googling. Seems they use an electric motor.
I don't understand why you would lose RPM even if working the airplane hard. The engine is capable of turning the prop at 3000RPM at low airspeed....it does every takeoff. The change in speed isn't going to be so abrupt that even a slow electric prop can't keep up with the change.
Was the prop pitch set by an electric motor? Or was it just an electric governor controlling the prop which still uses engine oil pressure/spring pressure to set pitch? The B-24 used the latter setup. The prop controller was prone to failure, usually required an engine shut down and a whack with a rubber mallet (more easily accomplished on the ground).
Is do to the deacceleration. Rpm has to decrease before it can take less bite and increase. How much and how quickly I have no info on. Just went by feel of how RV sounds in loops.
HiTech
Title: Re: P-38 Rpm
Post by: FLS on September 30, 2016, 05:53:09 PM
The big RPM drop in game happens when there is a load perpendicular to the thrust.
Title: Re: P-38 Rpm
Post by: hitech on September 30, 2016, 05:56:37 PM
The big RPM drop in game happens when there is a load perpendicular to the thrust.
Can you explain? I am not sure what you mean.
Title: Re: P-38 Rpm
Post by: FLS on September 30, 2016, 06:49:47 PM
Pulling up or pushing down quickly will drop the RPM. Snap rolling a P-38 will drop the RPM as the engines describe a circle. The reason I thought it was affecting the vertical snap roll departures is because that's when I noticed the quick drop in RPM. I'm guess a side load on the prop but I don't know how it's modeled.
Title: Re: P-38 Rpm
Post by: colmbo on September 30, 2016, 07:27:56 PM
I was playing around with it...pull hard into buffet and the RPM drops 4-500 RPM with some fluctuation. That is a huge RPM drop. Now if I could get my hands on a P-38 to go out and test this.....
Title: Re: P-38 Rpm
Post by: 38ruk on September 30, 2016, 08:34:19 PM
I was wondering if the RPM drop of 4-500 rpm during hard maneuvers is why i am see a difference in performance between AH2 and 3. The plane seems more unstable ( easier to stall and harder to pull threw maneuvers like in AH2) .... I'm guessing the 4-500 rpm drop causes a lack of power compared to the steady 3000 rpm that Ah2 had modeled ? I could be totally off base so that why this should be looked at as a question and not a statement .
Also .... from the deck to 5k or so the 38 will run at a full 3000 rpm , up higher it stays at 2900rpm unless you dive , in a dive ive seen 3100 max. Thanks for the info.
Title: Re: P-38 Rpm
Post by: hitech on September 30, 2016, 10:40:49 PM
It's so to speed change not the load
Title: Re: P-38 Rpm
Post by: FLS on September 30, 2016, 11:27:54 PM
... The plane seems more unstable ( easier to stall and harder to pull through maneuvers like in AH2) ....
38ruk a few people have posted about stalling more and I suspect the new stall buffet sound is a factor. If you are listening for the old sound you will stall before you hear it. You can still see the cockpit shake but you may be looking elsewhere in a fight. Pull to the buffet and get acquainted with the new sound if you haven't already.
Title: Re: P-38 Rpm
Post by: hitech on October 01, 2016, 09:57:30 AM
Btw after thinking about this last night I will be making a change. Right now the RPM change is linear with speed change (I.E. Acceleration Deceleration). After giving it some thought the system would be acting faster the further you are from set point. I.E. Valve open more as distance from set point is increased.
This has the effect of making the change exponential instead of linear. Net result will be the small changes you hear will be the about the same, but it will not continue to increase so drastically as you increase to hard maneuvering.
HiTech
Title: Re: P-38 Rpm
Post by: colmbo on October 01, 2016, 12:15:18 PM
Thank you
Title: Re: P-38 Rpm
Post by: GScholz on October 01, 2016, 01:06:35 PM
Sounds good. The electrically actuated props like on the P-38 and 109 were on/off deals, no gradual movement, but there would still be a slight lag as the system must detect an rpm change then activate the electric motor.
Title: Re: P-38 Rpm
Post by: GScholz on October 01, 2016, 02:19:54 PM
Title: Re: P-38 Rpm
Post by: GScholz on October 01, 2016, 02:28:53 PM
Also in the 109 (F series onward) the throttle and RPM were linked to one control. I.e. the throttle lever would adjust both throttle and RPM. So moving the throttle back to cruise setting would also lower the RPM to cruise, full throttle would set the RPM to max etc.
Title: Re: P-38 Rpm
Post by: 38ruk on October 01, 2016, 02:49:36 PM
38ruk a few people have posted about stalling more and I suspect the new stall buffet sound is a factor. If you are listening for the old sound you will stall before you hear it. You can still see the cockpit shake but you may be looking elsewhere in a fight. Pull to the buffet and get acquainted with the new sound if you haven't already.
FLS , I was an alpha and beta tester so the sound isn't really new to me . That said , It was hard to find fights in the alpha /and early beta so i didn't really see the effects of hard maneuvers compared to and E/A pulling the same moves to counter mine .
My biggest complaint is I've been flying a 38 since 01 and knowing to a decent degree what i used to be able to do at certain air speeds all of the sudden change when the FM hasn't changed. I do appreciate your help and suggestions. I really do , but after all the years of flying it , it's hard to believe that im fluttering out of the sky and basically a sitting duck at speeds that used to able to bring the nose through. I'm not saying your wrong .....and i'm not saying I'm right . Just trying to figure out why i cant do things that are like second nature to me in the new version . <S> and thanks for the constructive conversation .
Believe me ..... I'm not one to think Im always right , just looking for something i might be doing wrong or possibly there something has changed minutely that is throwing me off. I'd like to think i know the bird pretty well , but there is always more to learn. Thx again and <S> 38
Title: Re: P-38 Rpm
Post by: FLS on October 01, 2016, 03:03:04 PM
I understand your point. I had a similar experience with stall departures. :D
You can compare the stall by matching speed and g load on the accelerometer between AH2 and AH3. Pulling past the stall to departure will let you compare recovery.
I assume you have the same advanced stick settings and calibration.
Title: Re: P-38 Rpm
Post by: 38ruk on October 01, 2016, 03:10:49 PM
Yes on the advantaged stick scaling , dead band and damping. Calibration was done in AH and Win7 as usual. Thanks for the reply sir !
Title: Re: P-38 Rpm
Post by: Randy1 on October 02, 2016, 08:02:29 AM
I fly the P-38 a lot. The AH3 version SEEMS to fly heavier than the AH2. Note I said SEEMS. I am not sure if it is just the way the graphics are displayed that gives us a different perception of speed.
Title: Re: P-38 Rpm
Post by: Ack-Ack on October 02, 2016, 02:51:12 PM
P-38 flies no different than it did in AH2.
Title: Re: P-38 Rpm
Post by: FLS on October 02, 2016, 03:11:01 PM
I fly the P-38 a lot. The AH3 version SEEMS to fly heavier than the AH2. Note I said SEEMS. I am not sure if it is just the way the graphics are displayed that gives us a different perception of speed.
Does it seem to have a slower climb rate on the gauges?
Title: Re: P-38 Rpm
Post by: GScholz on October 02, 2016, 06:28:17 PM
I can attest that Ack-Ack flies the P-38 with the same deadly intent that he used to in both AH and AH2... :old:
Title: Re: P-38 Rpm
Post by: 38ruk on October 02, 2016, 06:59:36 PM
Hard to argue with you about the 38 , but in AH2 i didnt see a 4-500 rpm drop when maneuvering the plane hard.
Am I wrong to assume that when the plane drops down to 2600 rpm @ 60'' of manifold pressure that it doesn't produce the same power as it would at 3000 rpm 60''?
Title: Re: P-38 Rpm
Post by: FLS on October 02, 2016, 07:03:01 PM
Hard to argue with you about the 38 , but in AH2 i didnt see a 4-500 rpm drop when maneuvering the plane hard.
Am I wrong to assume that when the plane drops down to 2600 rpm @ 60'' of manifold pressure that it doesn't produce the same power as it would at 3000 rpm 60''?
The prop pitch governor lag is a new feature in AH3.
Title: Re: P-38 Rpm
Post by: ACE on October 25, 2016, 09:40:33 AM
I understand your point. I had a similar experience with stall departures. :D
You can compare the stall by matching speed and g load on the accelerometer between AH2 and AH3. Pulling past the stall to departure will let you compare recovery.
I assume you have the same advanced stick settings and calibration.
What do you mean advanced stick scailing? I used to tweak my sliders in the advanced tab long ago but I have forgotten my settings. Can you elaborate.
Title: Re: P-38 Rpm
Post by: FLS on October 25, 2016, 10:56:24 AM
Title: Re: P-38 Rpm
Post by: Hajo on October 25, 2016, 09:38:00 PM
I do know that todays prop pitch on a C130 is set to engine torque. In other words set the torque setting in which you wish to fly and the prop pitch automatically changes accordingly.
I am wondering if any WWII aircraft had that ability?
Title: Re: P-38 Rpm
Post by: hitech on October 28, 2016, 09:51:53 AM
I do know that todays prop pitch on a C130 is set to engine torque. In other words set the torque setting in which you wish to fly and the prop pitch automatically changes accordingly.
You sure about this? This would mean the prop is not constant speed.
HiTech
Title: Re: P-38 Rpm
Post by: Hajo on October 28, 2016, 10:31:58 AM
You sure about this? This would mean the prop is not constant speed.
HiTech
Yes I am. I have two friends in the 910th tactical C-130 squadron based at Youngstown Air Base. While sitting in the cabin with the Pilot, (wife) and flight engineer (husband) I asked about prop pitch.
They both told me pitch was determined by torque. They set the torque and the 130s prop pitch adjusts accordingly. They showed me the torque setting on the instrument panel for each engine (separate gauges)
Made sense to me.
Title: Re: P-38 Rpm
Post by: Golfer on October 28, 2016, 10:53:22 AM
I snapped a screenshot and sent off to a C130 aircraft commander who has been in Hercs for a good while for a more thorough explanation and confirm that what's been understood here is or isn't what actually happens. Not sure what part of the world he's in at the moment.
Title: Re: P-38 Rpm
Post by: Hajo on October 28, 2016, 12:11:45 PM
I snapped a screenshot and sent off to a C130 aircraft commander who has been in Hercs for a good while for a more thorough explanation and confirm that what's been understood here is or isn't what actually happens. Not sure what part of the world he's in at the moment.
What you don't believe what I was told by Air Force C-130 crew? Kathy and Paul are good friends of mine. Unusual that the wife is a Pilot and Paul flight engineer.
Btw Paul brought me back an American flag flown over their base in Iraq. I've yet to pick it up........I'm lazy. I am trying to get in touch with them through operations
at the 910th at Youngstown Air Base. Been so long I talked with Maintenance at the 910th and Paul is no longer there. They may have retired, good for them.
Their Air Base: http://www.youngstown.afrc.af.mil/Home.aspx
Title: Re: P-38 Rpm
Post by: Golfer on October 28, 2016, 04:44:46 PM
Didn't say I didn't believe you or your friends weren't anything other than wonderful.
I don't know em so I can't ask em.
Title: Re: P-38 Rpm
Post by: Golfer on October 28, 2016, 04:54:25 PM
FWIW I believe you. I'm asking someone to learn how it works. I haven't any first hand experience with a Herc.
Title: Re: P-38 Rpm
Post by: Hajo on October 28, 2016, 06:22:06 PM
FWIW I believe you. I'm asking someone to learn how it works. I haven't any first hand experience with a Herc.
It's marvelous aircraft. I was interested in the hydraulics chiefly. So Paul took me through the aircraft. He said "this is the reservoir". I couldn't believe it. It was the size of a coffee can.
Sitting in the Pilots seat looking down to my left floor level, covering the window was a square piece of plywood with what appeared to be fuses and fusible links. I told Paul hey!
You guys fix things like we do at the plant. We both had a good laugh at that. Multimillion dollar aircraft and the Govt. patches it with good old American know how. Whatever works!
Title: Re: P-38 Rpm
Post by: DaveBB on October 28, 2016, 10:11:56 PM
I worked with a former C-130 crew chief. It is actually possible to overstress the aircraft just from giving it full power. For some reason a C-130 had to go to full power from a very low power setting, and it required a major inspection. Found a crack in one of the engine mounts after that. If I remember correctly, the engines want to twist the wings upward, almost like they are on a swing.
Title: Re: P-38 Rpm
Post by: colmbo on October 29, 2016, 11:23:22 AM
Found this on the C-130 prop:
Quote
How the 54H60 Prop System Functions. The 54H60 propeller assembly is a constant speed, fully feathering, hydro-mechanical propeller. During aircraft operation, the 54H60 prop system has two distinct ranges, beta (ground) and alpha (flight) ranges. These ranges are differentiated by what component is controlling blade angle.
In the beta range, blade angle is controlled by the throttles from 0-34°, but in alpha range, the propeller governor is attempting to maintain a constant speed of 1020 RPM. Conversely, the alpha range is from 34-90°.
Title: Re: P-38 Rpm
Post by: flatiron1 on October 29, 2016, 03:20:11 PM
I have noticed that the throttle in b-17's does not control rpm like in ah2. I have to reduce rpm manually to be able to slow doen for landing. I compared it to ah2 and is definitely different.
Title: Re: P-38 Rpm
Post by: Golfer on October 29, 2016, 03:26:50 PM
How do you mean?
You'll have a harder time slowing down with the prop pulled back than with it in a fine pitch (full forward)
There is a definite mismatch in engine sound but I've not noticed any such change. The engine noise makes one think you're pulling more power than you really are IMO.
Title: Re: P-38 Rpm
Post by: mikeWe9a on November 06, 2016, 12:32:45 PM
What you don't believe what I was told by Air Force C-130 crew? Kathy and Paul are good friends of mine. Unusual that the wife is a Pilot and Paul flight engineer.
Btw Paul brought me back an American flag flown over their base in Iraq. I've yet to pick it up........I'm lazy. I am trying to get in touch with them through operations
at the 910th at Youngstown Air Base. Been so long I talked with Maintenance at the 910th and Paul is no longer there. They may have retired, good for them.
Their Air Base: http://www.youngstown.afrc.af.mil/Home.aspx
I believe that there was a slight misunderstanding in the discussion. C-130 crews use torque as their measurement when setting power, as that is the direct measurement of aircraft power. The propeller, however, does not act to maintain torque - it acts to maintain RPM. I have approximately 4,000 hours as a pilot in the EC-130H. The propeller works to maintain 100% RPM when in flight, unless the engine is shut down, in which case it feathers to reduce drag.
Mike
Title: Re: P-38 Rpm
Post by: FLS on November 06, 2016, 12:49:05 PM
I have noticed that the throttle in b-17's does not control rpm like in ah2. I have to reduce rpm manually to be able to slow doen for landing. I compared it to ah2 and is definitely different.
What's different is the sound. Reducing throttle works the same as it did in AH2 it just sounds different. Reducing RPM makes it sound like AH2 while performing differently.
Title: Re: P-38 Rpm
Post by: GScholz on November 06, 2016, 07:34:49 PM
People who don't understand how rpm and power change the sound of the engine have never driven a stick shift... ;)
Title: Re: P-38 Rpm
Post by: hitech on November 08, 2016, 03:53:42 PM
I believe that there was a slight misunderstanding in the discussion. C-130 crews use torque as their measurement when setting power, as that is the direct measurement of aircraft power. The propeller, however, does not act to maintain torque - it acts to maintain RPM. I have approximately 4,000 hours as a pilot in the EC-130H. The propeller works to maintain 100% RPM when in flight, unless the engine is shut down, in which case it feathers to reduce drag.
Mike
Ahhhhhhhh I feel much better now, physics make sense again.
HiTech
Title: Re: P-38 Rpm
Post by: Scca on December 08, 2016, 10:10:39 AM
I have noticed that the throttle in b-17's does not control rpm like in ah2. I have to reduce rpm manually to be able to slow doen for landing. I compared it to ah2 and is definitely different.
As far as I remember, the B-17 throttles never controlled RPM except after landing (just like they do now). What you're hearing now is different, but the action in the air is the same....