If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#11
|
|||
|
|||
Constant speed prop question
John Smith wrote in
: In article , Thomas Borchert wrote: originated out of military teachings that applied to very different pilots doing very different things while flying very different aircraft. Actually, it couldn't have been all of the military. Many major cities in my home country of Germany would contain many more historic buildings today, if those B-17s hadn't run oversquare and lean of peak. The B-17s would never have reached them. We can all say thank you Charles Lindberg for teaching us this technique. Well, the 38 pilots in the pacific could, but leaning techniques as well as a lot of other things about how engines work, were well known to both manufactuers and pilots in the 30s. Some, strangely, have been lost in the mists of time only to be "rediscovered" when things go wrong. Remember the Lycoming crank problem? Moisture in the hollow portion of the shaft just behind the prop? i have several manuals, one form the 1920's , that address this problem and guess what? The same cure recommended in the SB for the lycomings was in those manuals. Bertie |
#12
|
|||
|
|||
Constant speed prop question
Terence Wilson wrote in
: In the course of trying to understand how a constant speed prop works I came across the following passage in one of the Jeppesen books: "If the throttle is advanced without decreasing the pitch of the prop blades to increase ___ rpm, the manifold pressure increases as the prop mechanism attempts to keep ___ rpm constant by increasing the blade angle. The combination of high manifold pressure and low ___ rpm can cause damage due to high internal manifold pressures." I found this paragraph to be confusing I'm not surprised. It's a **** poor explanation and actually misleading, not to say wildly inaccurate in some places. "High internal manifold pressures" WTF is that? The author has no understanding whatsoever ofwhat he's talking about. Bertie |
#13
|
|||
|
|||
Constant speed prop question
"Bertie the Bunyip" wrote in message
... "Mike" wrote in news:WPHgk.144$DS3.119@trnddc01: "Terence Wilson" wrote in message ... In the course of trying to understand how a constant speed prop works I came across the following passage in one of the Jeppesen books: "If the throttle is advanced without decreasing the pitch of the prop blades to increase ___ rpm, the manifold pressure increases as the prop mechanism attempts to keep ___ rpm constant by increasing the blade angle. The combination of high manifold pressure and low ___ rpm can cause damage due to high internal manifold pressures." I found this paragraph to be confusing because it makes several references to rpm but doesn't clarify whether it is engine or prop rpm. The blanks were inserted by me. Can someone help me out? Thanks in advance. As others have said, unless you have a gearbox (not many planes do), they are one and the same. You may also want to ditch your Jepp book as the "theory" they are describing really doesn't apply to most small piston aircraft. The old "don't run oversquare" mentality which has been taught for years originated out of military teachings that applied to very different pilots doing very different things while flying very different aircraft. Actually, they dont, since most military aircraft,even smaller ones, were supercharged and they ran well oversquare.. A 985, for instance, is around 37 inches max and a typical cruise MP might be in the order of 25 inches with a cruise rpm of something like 1850, depending on how fast you want to go and how much you want to burn. The geared engines were even less relevant to this argument, since almost everything larger than about 1500 c.i.d. was geared. The indicated RPM was usually engine rpm and max for somthing like an 1830 was around 2400 and max MP for takeoff was about 43 IIRC and cruise was around 30/2,000. The practice originates from a perceived need to simplify for light aircraft pilots new to variable pitch props. And that need is even more of a necessity in military trainers which have considerably more power and are much more easily red lined. That's why I always assumed the mentality came primarily from military instructors giving instruction in training aircraft. At any rate the myth still persists to this day even with instructors who should know better. |
#14
|
|||
|
|||
Constant speed prop question
Terence Wilson wrote:
On Sun, 20 Jul 2008 08:31:45 -0500, "Steven P. McNicoll" wrote: Terence Wilson wrote: In the course of trying to understand how a constant speed prop works I came across the following passage in one of the Jeppesen books: "If the throttle is advanced without decreasing the pitch of the prop blades to increase ___ rpm, the manifold pressure increases as the prop mechanism attempts to keep ___ rpm constant by increasing the blade angle. The combination of high manifold pressure and low ___ rpm can cause damage due to high internal manifold pressures." I found this paragraph to be confusing because it makes several references to rpm but doesn't clarify whether it is engine or prop rpm. The blanks were inserted by me. Can someone help me out? Thanks in advance. It's engine rpm Just to clarify, it's engine rpm for all the blanks? Yes. Or propeller. Either would be correct as there is a fixed ratio between engine rpm and prop rpm. In a direct drive engine that ratio is 1. |
#15
|
|||
|
|||
Constant speed prop question
"Mike" wrote in news:qNIgk.158$oU.42@trnddc07:
"Bertie the Bunyip" wrote in message ... "Mike" wrote in news:WPHgk.144$DS3.119@trnddc01: "Terence Wilson" wrote in message ... In the course of trying to understand how a constant speed prop works I came across the following passage in one of the Jeppesen books: "If the throttle is advanced without decreasing the pitch of the prop blades to increase ___ rpm, the manifold pressure increases as the prop mechanism attempts to keep ___ rpm constant by increasing the blade angle. The combination of high manifold pressure and low ___ rpm can cause damage due to high internal manifold pressures." I found this paragraph to be confusing because it makes several references to rpm but doesn't clarify whether it is engine or prop rpm. The blanks were inserted by me. Can someone help me out? Thanks in advance. As others have said, unless you have a gearbox (not many planes do), they are one and the same. You may also want to ditch your Jepp book as the "theory" they are describing really doesn't apply to most small piston aircraft. The old "don't run oversquare" mentality which has been taught for years originated out of military teachings that applied to very different pilots doing very different things while flying very different aircraft. Actually, they dont, since most military aircraft,even smaller ones, were supercharged and they ran well oversquare.. A 985, for instance, is around 37 inches max and a typical cruise MP might be in the order of 25 inches with a cruise rpm of something like 1850, depending on how fast you want to go and how much you want to burn. The geared engines were even less relevant to this argument, since almost everything larger than about 1500 c.i.d. was geared. The indicated RPM was usually engine rpm and max for somthing like an 1830 was around 2400 and max MP for takeoff was about 43 IIRC and cruise was around 30/2,000. The practice originates from a perceived need to simplify for light aircraft pilots new to variable pitch props. And that need is even more of a necessity in military trainers which have considerably more power and are much more easily red lined. That's why I always assumed the mentality came primarily from military instructors giving instruction in training aircraft. At any rate the myth still persists to this day even with instructors who should know better. Well, outside of the T-34 I can't think of anything that would fit the "square" scenario, and military instructors would not have taken any sort of soft route with the students in any case. For instance, I happen to know any Navy student would have to have memorised a very lengthy series of checklists at the primary student stage for a T-28, for instance. That's ALL of the checklists. Ever single one, emergencies and all. And having seen them I know they were very, very complicated indeed. They also had to be able to touch every single switch, dial, and lever in the airplane blindfolded. I can't see them going soft on a little thing like not having to memorise a given MP RPM combo. Now, during aerobatics, it would make sense to have a nominal max MP a bit shy of normal max, as you say, but for operations outside of that, they certainly would not have done that. No, the only place I've ever seen he practice touted s by FBOs renting airplanes or using them for comercial instruction. Bertie , |
#16
|
|||
|
|||
Constant speed prop question
Those cities would also have contained many more historic buildings if your
elected leaders hadn't invaded Poland, France, Czechoslovakia, and a few other minor countries. Jim -- "It is the mark of an educated mind to be able to entertain a thought without accepting it." --Aristotle "Thomas Borchert" wrote in message ... Many major cities in my home country of Germany would contain many more historic buildings today, if those B-17s hadn't run oversquare and lean of peak. |
#17
|
|||
|
|||
Constant speed prop question
Terence,
Just to clarify, it's engine rpm for all the blanks? There is no difference between the two. Change one, and the other changes in the same way. -- Thomas Borchert (EDDH) |
#18
|
|||
|
|||
Constant speed prop question
RST,
Those cities would also have contained many more historic buildings if your elected leaders hadn't invaded Poland, France, Czechoslovakia, and a few other minor countries. No doubt about it. It seems your wink-o-meter might need adjustment. -- Thomas Borchert (EDDH) |
#19
|
|||
|
|||
Constant speed prop question
Thomas Borchert writes:
It seems your wink-o-meter might need adjustment. The wink-o-meter tends to cloud up when it winks at 100 million dead. |
#20
|
|||
|
|||
Constant speed prop question
On Jul 20, 10:48 am, Bertie the Bunyip wrote:
"Mike" wrote innews:qNIgk.158$oU.42@trnddc07: "Bertie the Bunyip" wrote in message .. . "Mike" wrote in news:WPHgk.144$DS3.119@trnddc01: "Terence Wilson" wrote in message ... In the course of trying to understand how a constant speed prop works I came across the following passage in one of the Jeppesen books: "If the throttle is advanced without decreasing the pitch of the prop blades to increase ___ rpm, the manifold pressure increases as the prop mechanism attempts to keep ___ rpm constant by increasing the blade angle. The combination of high manifold pressure and low ___ rpm can cause damage due to high internal manifold pressures." I found this paragraph to be confusing because it makes several references to rpm but doesn't clarify whether it is engine or prop rpm. The blanks were inserted by me. Can someone help me out? Thanks in advance. As others have said, unless you have a gearbox (not many planes do), they are one and the same. You may also want to ditch your Jepp book as the "theory" they are describing really doesn't apply to most small piston aircraft. The old "don't run oversquare" mentality which has been taught for years originated out of military teachings that applied to very different pilots doing very different things while flying very different aircraft. Actually, they dont, since most military aircraft,even smaller ones, were supercharged and they ran well oversquare.. A 985, for instance, is around 37 inches max and a typical cruise MP might be in the order of 25 inches with a cruise rpm of something like 1850, depending on how fast you want to go and how much you want to burn. The geared engines were even less relevant to this argument, since almost everything larger than about 1500 c.i.d. was geared. The indicated RPM was usually engine rpm and max for somthing like an 1830 was around 2400 and max MP for takeoff was about 43 IIRC and cruise was around 30/2,000. The practice originates from a perceived need to simplify for light aircraft pilots new to variable pitch props. And that need is even more of a necessity in military trainers which have considerably more power and are much more easily red lined. That's why I always assumed the mentality came primarily from military instructors giving instruction in training aircraft. At any rate the myth still persists to this day even with instructors who should know better. Well, outside of the T-34 I can't think of anything that would fit the "square" scenario, and military instructors would not have taken any sort of soft route with the students in any case. For instance, I happen to know any Navy student would have to have memorised a very lengthy series of checklists at the primary student stage for a T-28, for instance. That's ALL of the checklists. Ever single one, emergencies and all. And having seen them I know they were very, very complicated indeed. They also had to be able to touch every single switch, dial, and lever in the airplane blindfolded. I can't see them going soft on a little thing like not having to memorise a given MP RPM combo. Now, during aerobatics, it would make sense to have a nominal max MP a bit shy of normal max, as you say, but for operations outside of that, they certainly would not have done that. No, the only place I've ever seen he practice touted s by FBOs renting airplanes or using them for comercial instruction. Bertie , The whole idea of don't run oversquare is not a military technique taught, but rather a technique taught to radial pilots back in the day. These pilots then moved over to our flat engines, and decided running oversquare would still be a bad idea. I agree with the other guys-and having been through an Advanced Pilot Seminar, I can certainly say-you will know much more about your engine after going through the seminar. There is another seminar coming up later this year, and I'm thinking of attending it again. Also those pelican perch articles are fantastic, and if Deakin ever shows up to a seminar, you get to meet the author. |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
PA28: Difference in constant speed prop vs fixed pitch | Nathan Young | Owning | 25 | October 10th 04 04:41 AM |
Constant speed prop oil leak | DP | Piloting | 23 | April 21st 04 10:15 PM |
Practicing SFLs with a constant speed prop - how? | Ed | Piloting | 22 | April 16th 04 02:42 AM |
Constant Speed Prop vs Variable Engine Timing | Jay | Home Built | 44 | March 3rd 04 10:08 PM |
Constant speed or constant attitude? | Jim | Soaring | 37 | September 3rd 03 12:41 PM |