Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Staga on September 03, 2004, 01:44:37 AM
-
Was the change in propeller rotation in left and right engine made by reduction gears or by modifying the whole engine running "backwards" like some websites suggests ?
Gotta admit latter sounds a bit strange...
-
It runs backwards. Yes it sounds strange but that's how it was done. That of course creates a little bit of problems in the spare parts department.
-
Are you sure about that?
When installed in a twin-engine P-38, it was paired with a left-hand drive V-1710-55 engine to counteract the effect of torque. The only difference between the two engines was the direction of propeller-shaft rotation.
Taken from USAF museum:
http://www.wpafb.af.mil/museum/engines/eng1.htm
-
I seem to remember there was some constant annoying engine problems with the #1 or left hand engine on some of the p38s.
This is a good question for Slack, I remember him posting something on it some years ago.
-
I though for sure it was just a reduction gear change. I can check Vees for Victory tonight on this.
-
You'd need another crankshaft, but what else? Pistons just go up and down, so do valves, the Crankshaft is the boss of which direction.
Opps Camshaft.....
Whaddever, need to know better what the english terms are for these parts. Hope you know what I mean though :o
-
Another feature of the V-1710 design was the ability to turn the propeller either clockwise, or counter-clockwise, by simply assembling the engine with the crankshaft turned end-for-end, installing an idler gear in the drive train to the supercharger and accessories, and having a starter turning the proper direction. The ignition wiring and firing order were also arranged to accommodate the direction of rotation.
Thats from an article written by Daniel D. Whitney - Author, Vees For Victory! The Story of the Allison V-1710
-
Originally posted by Angus
You'd need another crankshaft, but what else? Pistons just go up and down, so do valves, the Crankshaft is the boss of which direction.
Opps Camshaft.....
Whaddever, need to know better what the english terms are for these parts. Hope you know what I mean though :o
Most any reciprocating engine will run is either direction. You would need a different cam, firing order and starter. Possibly a different crankshaft.
-
I forget which engine it is on the market today, for civilian use atleast - but I believe it was accomplished by some clever use of the magneto. As for the 38 - lord knows.
-
Has not been a problem for us to change any of our Allisons around.
-
Remember, Allison got into the business of liquid cooled aircarft engines by making them for airships...
-blogs
Originally posted by Staga
Was the change in propeller rotation in left and right engine made by reduction gears or by modifying the whole engine running "backwards" like some websites suggests ?
Gotta admit latter sounds a bit strange...
-
Well, some engines are designed to operate in only one direction. The DB's for instance had slightly different stroke and compression ratios on the two cylinder banks to help counteract torque, i.e. the pistons were pushing more on the crank from one direction of the inverted-V than the other, thereby creating a counter force to the torque generated at the crank.
-
Some engines have also a crankshaft moved a bitt offset from the centerline of the cylinder block; the angle between piston and connection rod stays smaller at the firing stroke = there's smaller forces affecting the piston sideways = less friction = less wear.
-
The Allison V1710 uses a crankshaft that may be installed in the block either way. To reverse rotation, you swap the crankshaft end for end, rewire the magnetos for a different firing order, and add an idler gear to the accessory drive. It was not necessary to change the camshafts. This is good since the Allison is a double overhead cam engine with four valves per cylinder operated by roller rocker arms. Changing cams is a nightmare unless you are highly skilled or intimately familiar with the system. The Allison V1710 was extremely advanced for its time, because Allison started out as a company that was focused on racing and custom engineeering.
It was desireable for the engine to turn backwards in order to create completely opposite torque from the other engine. Remember that the engine is mounted solid to the airframe, so if it ran in the same direction and simply reversed prop rotation, zero net torque would not be possible. Both engines would be exerting the same force on the airframe.
The problems were a result of problems in the early gearboxes which did not operate properly when rotation was reversed.
-
Originally posted by GScholz
Well, some engines are designed to operate in only one direction. The DB's for instance had slightly different stroke and compression ratios on the two cylinder banks to help counteract torque, i.e. the pistons were pushing more on the crank from one direction of the inverted-V than the other, thereby creating a counter force to the torque generated at the crank.
Never seen a different stroke stated, though the cr left/right had ~0.2 difference.
Do you have a source for different strokes?
-
You're right that the documents only list a 0.2 difference in compression ratio, but that difference is just an effect of either a difference in stroke or volume. I'm guessing stroke.
-
Originally posted by Staga
Are you sure about that?
Taken from USAF museum:
http://www.wpafb.af.mil/museum/engines/eng1.htm
Oops, my bad.
-
Originally posted by GScholz
You're right that the documents only list a 0.2 difference in compression ratio, but that difference is just an effect of either a difference in stroke or volume. I'm guessing stroke.
How would have this been done, eccentrically located crankshaft?
-
You don't see how what is possible?
-
Originally posted by GScholz
You're right that the documents only list a 0.2 difference in compression ratio, but that difference is just an effect of either a difference in stroke or volume. I'm guessing stroke.
You add more to the piston crown, which is not desirerable(weight), or shave some off the heads to increase the cr.
This pdf on the DB605 has the same bore and stroke, 154mmx 160mm for all models.
http://mitglied.lycos.de/luftwaffe1/aircraft/lw/DB605_varianten.pdf
To increase the stroke, the throw of the crankshaft has to increased, on one side for what you suggest. These long crankshafts were bad enough to balance without upsetting the balance by 2 throw lengths.
-
Originally posted by MiloMorai
You add more to the piston crown, which is not desirerable(weight), or shave some off the heads to increase the cr.
Then volume would be different. You can't have different compression ratios without having different volume, stroke or both.
-
Originally posted by GScholz
You don't see how what is possible?
How one cylinderbank has different stroke than other.
-
Originally posted by mora
How one cylinderbank has different stroke than other.
Why is that impossible?
-
:rolleyes:
The compression ratio is defined as (Swept Volume + Clearance Volume) / Clearance Volume
Shave some off the heads and you change the clearance volume. Very simple to do.
Until you show up with the DB,s throw dimensions(stroke),........
Mora, one has to have different crankshaft throw dimensions.
(http://www.pumaracing.co.uk/cylinder.jpg)
here is a web site to help explain, how shaving(milling) the heads changes cr, http://www.nightrider.com/biketech/hdhead_compression.htm
Notice that shaving the heads increases the cr by ~0.3 with a 0.020" cut. Yet Scholz would have us believe that the Germans would go to the hassle of making a crankshaft with different throws and all the hassles that involves.
-
Originally posted by MiloMorai
:rolleyes:
The compression ratio is defined as (Swept Volume + Clearance Volume) / Clearance Volume
Shave some off the heads and you change the clearance volume. Very simple to do.
Until you show up with the DB,s throw dimensions(stroke),........
Mora, one has to have different crankshaft throw dimensions.
(http://www.pumaracing.co.uk/cylinder.jpg)
here is a web site to help explain, how shaving(milling) the heads changes cr, http://www.nightrider.com/biketech/hdhead_compression.htm
If you shave some off the heads you change both clearance volume and total volume. The top of the head would travel farther down the cylinder since it is shorter.
... And what's with the ghey rolleyes emoticon?
Edit: fixed swept to total.
-
Originally posted by GScholz
Why is that impossible?
If you change the diameter of the crankshaft it will affect the stroke on both cylinder banks. In a V-engine there are 2 connecting rods attached to each crankshaft lobe, one from each side.
-
Originally posted by mora
If you change the diameter of the crankshaft it will affect the stroke on both cylinder banks. In a V-engine there are 2 connecting rods attached to each crankshaft lobe, one from each side.
True if the connecting rods aren't independent. V engines are designed with both paired and staggered cylinder banks, but I don't know about the DB.
-
Forgot about the forked and blade con rods, Mora.:)
-------------------------
Explain this then Scholz
Mill Heads - Compression Ratio
.000" 8.50
.020" 8.77
.040" 9.07
.060" 9.39
.080" 9.73
.100" 10.01
----------------
DB601 with fork and blade con rods.
(http://www.aviation-history.com/engines/db601na.jpg)
-
Explain what? If you file down the crown of the piston you decrease compression ratio, but increase volume. What is difficult to understand?
-
Originally posted by GScholz
Explain what? If you file down the crown of the piston you decrease compression ratio, but increase volume. What is difficult to understand?
File??:rofl :rofl :rofl How long will that take? And, can you guarantee that it will be the same depth of material removed in the x and y axis?:rolleyes: No waves allowed. The heads are over 1m long.
You remove metal from the head (you know, the part that has the valves, camshaft, valve springs, etc, etc) that is contact with the block. Is that so hard to understand?
-
This is a milling machine
(http://www.knuth.de/prod_img/fraesen_bohren/cnc_fraesen/werkzeug_universal/wf5cnc.jpg)
-
You still increase volume whatever you alter. Having two cylinders with the same bore, stroke and volume, yet different compression ratios is physically impossible. Something must be different.
And what's with the attitude? Are you incapable of having a discussion without being abusive?
-
Difference in DB's compression ratio between left and right bank is so small that easiest way to change it would be using cyl-head gaskets with different thickness.
-
It gets tiresome when some are talking nonsense. :)
They mill some off the head as in the example given in a previous post, which you fail to comprehend Scholz.
read carefully(numbers are for example only)
piston swept volume = 1000cc
clearance volume = 100cc
So (Swept Volume + Clearance Volume) / Clearance Volume
(1000+100)/100 = 11:1
remove 10cc from the clearance volume > 90cc
(1000+90)/90 = 12:1
You have 2 heads, so one head has its volume decreased by 10cc, the other has nothing removed. Guess what? You then have 2 compression ratios on a single engine.
-
Originally posted by Staga
Difference in DB's compression ratio between left and right bank is so small that easiest way to change it would be using cyl-head gaskets with different thickness.
Yes Staga that is another way, but would suggest using 2 gaskets on one side and one gasket on the other. Saves on the parts count, though it does give another gap for blow-by.
-
If you remove 10cc from the clearance volume YOU REDUCE THE TOTAL VOLUME OF THE CYLINDER! That's what I have been saying all along!
-
Originally posted by GScholz
If you remove 10cc from the clearance volume YOU REDUCE THE TOTAL VOLUME OF THE CYLINDER! That's what I have been saying all along!
Is that why you kept on mentioning different stroke?
But glad you finally saw the light in your EDITED post. To bad you did not make a seperate post for your correction.
Now to put a wringle in, I believe the head of the DB engine was part of the cylinder block.
-
This is beyond moronic Milo. I edited that post only minutes after posting it when I noticed the error, 4 1/2 hours ago. Before you responded to it.
Originally posted by GScholz
You're right that the documents only list a 0.2 difference in compression ratio, but that difference is just an effect of either a difference in stroke or volume. I'm guessing stroke.
What is wrong with my initial post to your question? If there is a difference in compression there MUST be a difference in either volume or stroke if the bore is equal. The PDF does not state any difference in bore, stroke or volume, probably because the difference is minor, but the must be a difference. I guessed in stroke. You guessed in volume.
-
Bringing this back to topic, both Daimler-Benz and Allison bolted two V-12 engines together to make monster double-vee 24 cylinder engines! The V-3420 and DB-610 mounted two V-1710/DB 605 V-12s side by side in a double-vee configuration and geared the crankshafts together to make one engine.
V-3420 as used in P-75 (http://www.enginehistory.org/Gallery/JimBuckel/Allison%20V-3420%20for%20Fisher%20P-75A%20Eagle%201-17.JPG)
DB 610 as used in He 177 (http://www.preservedaxisaircraft.com/Luftwaffe/Engines/DB%20610%20Sinsheim.jpg)
-
Originally posted by GScholz
The PDF does not state any difference in bore, stroke or volume, probably because the difference is minor, but the must be a difference. I guessed in stroke. You guessed in volume.
Are you sure the total volume is even stated in that document? Usually it's the stroke volume which is stated, like in automobiles for example.
-
I don't know.
-
Originally posted by GScholz
This is beyond moronic Milo. I edited that post only minutes after posting it when I noticed the error, 4 1/2 hours ago. Before you responded to it.
Now the insults start, but what else to expect from him since he did not have a clue what he was talking about and still dosn't.
Actually it was 8 minutes. :)
Yah and I had my reply sitting there for 4:35 will I did some other things.:) Did some text changes in that 4:35 as well.
You were floundering around like a fish out of water.
-
This is pointless. You're back on ignore for good. Goodbye.
-
Typical MiloMoron thread. :aok
-
Originally posted by Delirium
I seem to remember there was some constant annoying engine problems with the #1 or left hand engine on some of the p38s.
This is a good question for Slack, I remember him posting something on it some years ago.
LOL that was my fictitious P38F that always leaked oil from the left engine I think :)
There were two different engines for the 38. With the P38F for example it was a -49 Allison or a -53. One swinging the prop left and one right.
It couldn't have been too tough to build the engines to swing the prop one way or another.
Kinda like the Griffon Spits turning the prop the opposite of the Merlins.
It gave the guys transitioning to Griffon Spits fits, if they weren't warned ahead of time as they cranked in rudder trim in the wrong direction based on their Merlin engined Spit experience. Lots of sideways take offs that way :)
Dan/Slack
-
Thing is that Griffons were built that way and not modified afterwards.
For example DeHavilland Hornet did had counter rotating propellers but its engines were ordinary RR Merlins and the change in rotation was done in reduction gears.
-
I have never heard of anyone putting two head gaskets on another to decrease compression. Not to mention in supercharged engines.
In automobile conversion kits from normally aspirated to supercharged there is just a thicker head gasket, not two of them. (Maybe in very low compressions but not on those close or over to 1.0 pressures.)
To decrease compression it is also adequate to use different pistons (the case in DB?). Or maybe the DB too had asymmetrically placed crankshaft and with connecting rods of equal length this naturally produces a slightly lower compression to other cylinder bank. Was this CR mod made to counter torsional vibrations in crankshaft?
BTW It is not advisable to machine the whole top lower as the piston rings may get stuck eventually but to machine a lower area to 4/5 part on the piston top provided that the top thickness remains thick enough.
-C+