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Post by Tom/CalClassic on Feb 22, 2009 20:05:15 GMT -5
The standard procedure when shifting from low to high blower was to reduce MAP first, which lowered the stress on the engine. Therefore, I don't think the change was *that* much stress. The stress was the higher boost produced by the high blower at those higher altitudes. There was little or no stress going from high to low blower.
Why stay in high blower at lower altitudes when not needed?
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Post by sunny9850 on Feb 22, 2009 22:13:41 GMT -5
The Ref_Notes compiled by Howard for the Starliner give nicely detailed instructions on the proper procedure to be used when shifting "gears" so to speak. Just like when driving a manual transmission with a slightly worn clutch or synchronizer the FE reduced MP and RPM to a setting that was the least stressful for the mechanical drive of the blower.
And just like that manual transmission you don't start from a dead start in high gear either. One you don't need to pump that volume down low so you would have to "waste" it somehow and compressing denser air probably requires a different amount of torque in the air-pump drive.
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Post by ashaman on Feb 23, 2009 6:43:17 GMT -5
The Ref_Notes compiled by Howard for the Starliner give nicely detailed instructions on the proper procedure to be used when shifting "gears" so to speak. Just like when driving a manual transmission with a slightly worn clutch or synchronizer the FE reduced MP and RPM to a setting that was the least stressful for the mechanical drive of the blower. And just like that manual transmission you don't start from a dead start in high gear either. One you don't need to pump that volume down low so you would have to "waste" it somehow and compressing denser air probably requires a different amount of torque in the air-pump drive. I am aware that a higher "gear" blower would have been somewhat less efficient at lower flight levels and denser air. I live in a land where the almost totality of cars has a manual clutch to change gear, after all ( here in Italy automatic transmission is in the VERY rare side of extremely sparse, even with the latest technologies allowing for better efficiency of the hydraulic systems these need), and to learn to drive you MUST learn how to use " the stick" ( no sexual innuendo implied). ;D My question about a system with a constant high blower compressor with inbuilt wastegate, or other pressure cap control system, stemmed only from the problem ( that before it was raised in the previous posts was unknown to me) of the seemingly high rate of engines failures while in blower gear shift, in some cases with catastrophic fires that, always from what I read, at times even conditioned some flights to remain below 15.000 feet, so to not have to shift blower gear to minimize failure possibility. Be it ever clear that I know not, and only ask out of curiosity and willingness to learn. As for the excess air cut by the hypothetical pressure control system, it could have been used for added cooling of some system or whatnot. I simply went on a flight of fancy about a possible solution to an old problem that nowadays, with turbines-powered planes only in use, no one considers such anymore. Nothing wrong with idle speculation, right?
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Post by sunny9850 on Feb 23, 2009 12:04:56 GMT -5
Hi Ashaman, nothing wrong with a "flight of fancy" and I certainly did not mean to put it down. I simply stated my understanding of the system and it's application on those big engines. I have never flown a radial bigger than 9 cylinders and none with these charging systems. So I am going by what I know from the much less complex automotive side. As for bella Italia...I am very familiar with your country and have spent a lot orf time there. Mostly around Milano. And I still have a Alfa Romeo GTV6 2.5 parked in a garage back in Germany
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Post by ashaman on Feb 23, 2009 13:01:22 GMT -5
And I still have a Alfa Romeo GTV6 2.5 parked in a garage back in Germany Ack!!! That was the car I so wanted to buy for myself soon after I took my driving license, some 22 years ago, but was unable to because could not find one in passable shape ( the kind of car was already out of the assembly lines by then). Was unable to find even the one powered by the classic 4 cylinders in line 2.0 liters... not to say the very rare and most powerful of the kind with the V6 3.0 liters. I had to content myself with a BMW 318i instead ( rear traction drive lover here).
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Post by sunny9850 on Feb 23, 2009 21:32:06 GMT -5
I distinctly remember the first time I saw a 1750 GTV still with the small tail lights and the chrome bumpers...1974 model and I was 6. ;D Right then and there I knew I would own one at some stage...no matter what. My 6 2.5 is actually now a 6 3.5 24V with a single VW style G-Lader supercharger and a 6 speed ZF gear box almost identical to the 82/83 World Touring Car championship winning cars.
Many years a friend of mine called me to say they got this "Alfa Coupe" in trade and the rest was as they say history. She was in terrible shape...engine blown by the idiot who owned her and ran her on the Autobahn with only half the required oil in the engine. 3 years and way more money than I ever thought possible later and she was finally on the road again. Along with a '67 Osso de Sepia Spyder and a Citroen CX Pallas and a DS to round out my personal little collection.
When I moved from Germany to California I sold the Citroens and the Spyder to a friend who keeps them with his many many other cars....and I can still drive them when visiting. But the GTV will never be for sale.
Stefan
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Post by ashaman on Feb 25, 2009 12:42:36 GMT -5
Returning to matters aviation related... It's all the day now that I've gone mentally over the facts of the R-3350 ( boredom can do that to you), and at one time a pair of questions popped up into the devastated labyrinth that is my brain. ;D All right, we can now say with no fear of mistaking that the R-3350 was supercharged only by mechanical means, that its mechanical blower had two " gears" to allow for high altitude operations ( gears shifting which at times generated problems), and the only exhaust turbines used ( at least on the civilian engines) were the PRT. Two question now surge like battling twin storms through the wastelands that are my mind. ;D 1) Was the R-2800 ( the main competitor of the R-3350) only mechanical supercharged with a two speed mechanical supercharger as well, or did it have a mixture mechanical/exhaust superchargers for operations low/high blowers? 2) Given that the DC7 and Constellations were bound to a maximum ceiling of approximately 25.000 feet, what kind of modifications went through the engines of the B29, plane capable of the declared service ceiling of over 33.000 feet? Or it was not strictly a matter of engines ( Pressurization? Aerodynamics? Other?)? Hope my question are not getting the thread out of its tracks.
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Post by Maarten on Feb 25, 2009 17:34:11 GMT -5
1) Was the R-2800 ( the main competitor of the R-3350) only mechanical supercharged with a two speed mechanical supercharger as well, or did it have a mixture mechanical/exhaust superchargers for operations low/high blowers? In the case of the postwar CA15, CA17, CA18, CB16 and CB17 (and their military counterparts) only mechanically supercharged with a two speed blower. In the case of the CA3, CB3 and CB4 the high speed blower was deleted as those engines were used for lower altitudes only. Some versions of the Martin 2-0-2 and Convair 240 that didn't need to fly at high altitudes had CA3 engines installed instead of the CA18, and the Canadair CL-215-1A10 amphibious waterbomber also had/have the CA3 and in some cases the virtually similar CB3 installed. Many Douglas DC-6A's and freighter-converted DC-6B's had their CB-16/17 engines converted to CB3's after their cabin pressurisation systems had been deleted. Cheers, Maarten
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Post by Tom/CalClassic on Feb 25, 2009 18:08:22 GMT -5
Hi,
The only common US airliner that had a turbocharger was the Boeing B377 Stratocruiser. All other US airliners (all powered by R-1820, R-1830, R-2000, R-2800 and R-3350 engines) used only a mechanical supercharger.
I believe the FL250 limit was imposed by the FAA during the certification process. I don't know why they limited them to that altitude.
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Post by sunny9850 on Feb 25, 2009 21:05:14 GMT -5
The altitude limitation is most likely due to the extremely short time available to get the airplane down in case of a pressurization failure above 25000ft.
One other reason that comes to mind is the separation problem. The CAA was just in the process of having the flight test teams at KEDW evaluate a possible reduction of the vertical separation requirements when a Connie and a Douglas DC-7 collided over the Grand Canyon. However that crash was not caused by Altimeter errors.
In the test the EDW used both civilian airliners and military aircraft, usually 3 or 4 per type and they found discrepancies of +/- 500 ft on a large number and up to +/-1000 on some.
With the discrepancies getting worse the higher the aircraft flew.
Stefan
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Post by ashaman on Feb 25, 2009 22:46:46 GMT -5
Interesting. But... Forgive me, I am the one-thousand question man. ...this begs the question: if the R-2800 ( like the almost totality of contemporary engines, beside the R-4360) was mechanically supercharged exclusively, did it ( and the other two-speed supercharger engines as well) have the same problems with gear shifting from low to high ( and, I guess, the other way as well) the R-3350 seemed to have? About the mid-air collision on the Grand Canyon, wasn't it caused ( by what I read around) by accidentally poorly executed navigation, that allowed VFR to be liberally mixed in the melting pots that were the flight plans back then, and was the reason, from then on, for the rules to change ( at least in the USA) and make so a whatever liner HAD to fly IFR exclusively, with no VFR "escapades" allowed? Please note that what I wrote above about the Grand Canyon accident is what I found on the net by various sources. I wasn't there and cannot tell, nor I want to seem like I'm boasting knowledge I have not ( it may seem trivial written here, but I know for sure that I do not know).
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Post by herkpilot on Feb 26, 2009 0:52:10 GMT -5
I believe the FL250 limit is based on the FAA requirement that pressurized acft have a passenger oxygen system for flight above that level. The pilots of pressurized acft, however, must have supplemental oxygen "readily" available for flights above 10,000 ft (if I remember correctly).
Above FL250, the rules are more restrictive, requiring oxygen "immediately" available to flight-crew and pax. In the C130, with no pax on board we could climb above FL250, but since we did not generally have quick don masks, one of the pilots had to wear a mask, which no body really liked doing. The rules are somewhat different for unpressurized acft.
As an aside, during the early jet years in Hawaii, the inter-island flights never briefed the use of masks to pax since they never got above FL250. That changed, I think, following the Aloha "topless" 737 incident.
Hy
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Post by Maarten on Feb 26, 2009 6:18:48 GMT -5
...this begs the question: if the R-2800 ( like the almost totality of contemporary engines, beside the R-4360) was mechanically supercharged exclusively, did it ( and the other two-speed supercharger engines as well) have the same problems with gear shifting from low to high ( and, I guess, the other way as well) the R-3350 seemed to have? Not that I am aware of. I never read or heard about shifting problems with the R-2800's (still talking about the CA and CB series). As far as I know the regular R-3350 didn't have those problems too although they had their problems during the early years when used on the Boeing B-29 and Lockheed C-69. Most of those problems have been solved. (please anyone, correct me if I'm wrong here). Unless I'm getting confused I thought we were talking about the extremely troublesome (some call it sophisticated) Turbo-Compound R-3350. The R-2800 and regular R-3350 are much less complicated engines. Like mentioned in an earlier thread, the R-2800 was popular because of its reliability and economics. The R-3350 remained more sensisitive but still showed far less problems that the Turbo-Compound version. Cheers, Maarten
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Post by ashaman on Feb 26, 2009 7:22:16 GMT -5
Unless I'm getting confused I thought we were talking about the extremely troublesome (some call it sophisticated) Turbo-Compound R-3350. The R-2800 and regular R-3350 are much less complicated engines. In other words only the Turbo Compound had problems of supercharger gear shift? Were the superchargers used on the Turbo Compound then a different kind than the ones used on the regular, non-Turbo Compound, R-3350? Because if they weren't, and both kind of engines had the same kind of supercharger, how comes this mechanical piece only gave fits on the Turbo Compound?
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Post by Maarten on Feb 26, 2009 8:57:20 GMT -5
In other words only the Turbo Compound had problems of supercharger gear shift? Were the superchargers used on the Turbo Compound then a different kind than the ones used on the regular, non-Turbo Compound, R-3350? Because if they weren't, and both kind of engines had the same kind of supercharger, how comes this mechanical piece only gave fits on the Turbo Compound? I don't know if the superchargers of the regular R-3350 and the TC R-3350 were the same or not. I don't have those manuals, but it only seems logical that the TC-units were an advanced version since the TC-engine was a much more complicated unit, prone to cause more malfunctions than the 'orthodox' engines. And it hasn't been said that the supercharger only gave fits on the TC-version. It remains a fact however that the supercharger was a weak point in the TC-engine. Just to illustrate, I quote a few lines about maintenance of the R-3350-32WA Turbo-Compound engines that powered the Dutch Lockheed SP-2H Neptunes: "Breakdown of the impeller primary pinion carrier has always been one of the main causes that led to the numerous repairs that have been done on the Neptune-engines. In 90% of all cases this was the reason to repair the engine." (From: "Op de grens van zee en lucht - 30 years Neptune in service of the Royal Netherlands Navy" by F.C. van Oosten a.o., 1982) Cheers, Maarten
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