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Just out of curiosity - Airplane Guys

Discussion in 'The Lounge' started by Downeaster, Jan 25, 2019.

  1. Machine

    Machine Race the wind Top Contributor

    If #4 didn’t feather and became a wind drag, wouldn’t #2 & #3 require immediate power to compensate ?
    And I’m told here by someone airplane knowledgable that our modern fuel is not near as high octane as the fuel we “won the war” with back then.
    Do either of you know how truthful this is ?
     
  2. Jim

    Jim Beyond the edge is the unknown. Here be Dragons XS650.com Supporter Top Contributor

    If I remember... avgas back in the day was 130/145. 100LL (low lead) is all that's available nowadays. But them ole Wrights run just fine on 100LL. Just can't pull as much boost as they used to...
     
  3. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    Yeah, 145 purple.
    I recall reading thru dad's P-51 pilot's training book, where you would hit the 2nd stage supercharger on takeoff, and read 30" of boost!

    I don't think you can do that on 100LL...
     
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  4. Team Junk

    Team Junk XS650 Guru XS650.com Supporter Top Contributor

    I asked the pilot of Fifi back in the 70's why the slow climb outs even outside of airsho. He replied that airflow over the cylinders was much more important to life of the jugs.

    Engines designed for 130 fuel tend to lose exhaust valves because the lead in the purple gas would coat the valve seats. When it was introduced, 100ll caused problems even with engines designed for 100 octane. On the other hand 80 octane engines had problems when the red gas disappeared with lead deposits.
     
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  5. azman857

    azman857 '80 XS 650SG Rider XS650.com Supporter Top Contributor

    Some yrs back, the CAF brought Fifi and lots of other planes from the collection. It was Open house weekend here at Davis-Monthan AFB. Sunday afternoon, when the aircraft departed, Fifi came right over the house flanked by P-51s, C-47 or 2, and other great escorts of the winged kind. It was SO COOL! The sight of The CAF collection and the melody of those recip engines of the round and V inlines.
     
  6. Wordman

    Wordman XS650 Enthusiast

    Can you elaborate on "the impossible turn" for us non-aviation guys?
     
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  7. Team Junk

    Team Junk XS650 Guru XS650.com Supporter Top Contributor

    trying to turn around to fly back to the runway instead of looking for a place to set down straight ahead . The turn increases drag which causes you to lose airspeed and altitude.making it impossible to reach the runway.
     
  8. Team Junk

    Team Junk XS650 Guru XS650.com Supporter Top Contributor

    Oddly enough, for years the fatality rate after engine failure was much higher in multi engine planes than singles. The ugly truth is a twin engine plane becomes a very under powered single after an engine fails.
     
  9. Jim

    Jim Beyond the edge is the unknown. Here be Dragons XS650.com Supporter Top Contributor

    Yeah... old joke was that all a twin was good for was getting you to the site of the crash faster.
     
  10. Team Junk

    Team Junk XS650 Guru XS650.com Supporter Top Contributor

    Yep.
    Back when I was getting my instrument rating my instructor and I were having dinner one night and I mentioned that I was wondering what the difference was between a simulated engine out and a real engine failure.


    Several months later I was flying with him in a Cessna 150 under the hood and following simulated ATC clearances I was just beginning to wonder why we are up at 9000 feet in a 150 I don't think I've ever been that high in 150 before and about that time I felt a weird vibration and cheated and looked up just in time to watch the prop come to a stop vertically. He had pulled the mixture on me and was laughing cuz I was like oh crap but we were at 9000 feet and I looked around and saw Galveston Bay to my right and directly below me Spaceland airport. So we circle around on down and was really surprised at how different it was with the engine not actually turning I already had a few hours in gliders at that point but a 150 is a crap glider. it was a good lesson learned after I bought an AA1 which has a glide ratio of a brick.
     
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  11. Jim

    Jim Beyond the edge is the unknown. Here be Dragons XS650.com Supporter Top Contributor

    First instructor I had was constantly pulling power on me. In a 1hr flt, he'd pull it 2-3 times. Nailing Vbg (best glide) became a subconscious reaction... which of course, was the whole point of the exercise.
    One day he had me climb to about 6-8 thousand ft. He pulled power, I set up glide... recover.. back to altitude and repeat. On the last one he pulled the mixture. Prop never stopped, just windmilled. Established at Vbg, the picture out the windshield was very different.... a whole lot more green there and vsi showed a lot more down than it did with the engine idling. It was a lesson I never forgot.
     
    Last edited: Oct 11, 2019
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  12. Team Junk

    Team Junk XS650 Guru XS650.com Supporter Top Contributor

    The prop stopped because he had pulling up the nose for power off stall. Just wasn't expecting the power to be that off. And your right. The world became a lot greener instead of blue.
     
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  13. gggGary

    gggGary I'm listening, change my mind XS650.com Supporter Top Contributor

  14. MaxPete

    MaxPete Lucille, Betty, Demi & Gretel: I ask, THEY decide. XS650.com Supporter Top Contributor

    Indeed - and you do see a little US<->UK jingoism pushing some of the facts out of the way in that discussion.

    The truth is that all reciprocating aero-engines need supercharging to perform at high altitudes. The only open question is: shall it be a mechanically driven supercharger or an exhaust driven turbosupercharger (in those days, electrically driven "e-chargers" were not an option).

    The turbosupercharger worked fine - when it worked - but the design of the necessary ducting and the exhaust turbines and of the intake boost impellors is really complex and the metallurgy of making something like a turbine stay together at those high temperatures was also non-trivial. Also, all of this additional hardware was bulky (P-47) and heavier than a well-designed mechanical supercharger like was available on the Merlin and the German DB601 inverted V12 plus several other German Vee and radial engines made by Jumo and BMW.

    The US did eventually work it all out very well - juuuuusssttt in time for gas turbine engines (aka turbojets) to take over and eliminate the market for large capacity piston aero-engines. That was why one saw the golden age of piston engines like the Wright R3350 TurboCompound and big Pratt & Whitney R4360 Wasp Major really come-on strong in the mid-late 1940s-1950's - and then largely disappear by the early 1960s.

    The other thing that gave turbosuperchargers a bad reputation during WW-2 was that while the US did have workable technology, due to security concerns in 1939-40 it would not usually allow even trusted Allies like the British to buy it. So, when the UK evaluated the Curtis P-40, Lockheed P-38 and the Bell P-39, they were stuck with un-turbosupercharged versions which were complete dogs above about 10,000 feet. The Allison engines were fine and the airplanes were good - but without turbosuperchargers, they simply could not compete in the European theatre.

    EDIT: As for the North American P-51 Mustang, it was originally designed for the British (not the US) and so as an export product, it was not eligible to have a turbosupercharger installed - and so after a few Allison-engined versions were built, they installed a Merlin with a mechanically-driven supercharger and WAH-LA.

    Anyhow, thank goodness for the R-R Merlin and Sir Stanley Hooker....
     
    Last edited: Oct 16, 2019
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  15. Jim

    Jim Beyond the edge is the unknown. Here be Dragons XS650.com Supporter Top Contributor

    Just to clarify for you non-airplane folks.... as it relates to aircraft turbochargers, there's 2 kinds. One engine is said to be "turbocharged" and the other "turbo-supercharged."

    Turbocharged, or more correctly... turbo-normalized works by boosting only to maintain sea level pressure to it's critical altitude. In other words, at sea level where where the pressure is about 30"hg, the waste gate is fully open and the turbo is not boosting pressure at all. As the aircraft climbs, atmospheric pressure drops... the waste gate will gradually close, allowing the turbo to boost the engine only to sea level pressure. Eventually the aircraft will reach an altitude where it can no longer maintain that 30"hg sea level pressure. This is called the "critical altitude".... usually about 25,000ft. What this means in practical terms is than an engine rated for 1000 hp can produce that 1000 hp all the way to it's critical altitude.

    The turbo-supercharger on the other hand, is used to make more power. We take the same 1000 hp engine at sea level pressure and boost it. Let's say for example we boost the intake manifold to 40"hg. Now the same engine produces 1300 hp. A relatively easy and inexpensive way to make a lot more power. The down side to this is that power will gradually fall off as the aircraft climbs... Everything else being equal, both engines will produce the same 1000 hp when critical alt. is reached... and power drop off will be the same for any alt. above that. The turbo-supercharged engine has the advantage in that it will reach that altitude much quicker than the other. The turbo-normalized engine has the advantage in that it's hp is not boosted, so it's service life will be longer than the other.
     
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  16. MaxPete

    MaxPete Lucille, Betty, Demi & Gretel: I ask, THEY decide. XS650.com Supporter Top Contributor

    ...yeah - like he said!

    I just didn't want to get all nerdy on ya'all. :rolleyes:
     
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  17. Hunter Shelby

    Hunter Shelby XS650 Member XS650.com Supporter

    An alternative view:

    1 Concorde awesome
    2 SR71 even more awesome but not British
    3 Hurricane workhorse
    4 Spitfire glamorous thoroughbred
    5 B747 shrunk the world
    6 Any Cessna..taught thousands of pilots; me included
    7 P-51 average until they put a Merlin in it
    Joint 8 Lancaster & B17 the bravery it took to fly those to Germany and back
    9 Any airframe that helped to make flying accessible to the masses.
    10 Any Homebuilt that’s dedication and bravery, to fly something you’ve built yourself
     
  18. halfmile

    halfmile XS Builder XS650.com Supporter Top Contributor

    1,319
    4,512
    263
    kansas
    This is one of the many thousands of topics our table of knowledge covered at the coffee shop this morning.
     
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  19. azman857

    azman857 '80 XS 650SG Rider XS650.com Supporter Top Contributor

    Hunter, I agree with you except on #5. Boeing 707 shrunk the word. 747 did it too, but on a bigger scale. On #8, add the B-24.
     
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  20. Hunter Shelby

    Hunter Shelby XS650 Member XS650.com Supporter

    Azman, fair point. The Comet would have done it if it hadn’t developed a habit of falling out of the sky.
    707 was the original world shrinker but the 747 crammed them in and still flies today; a testament to brilliant design.
    Liberator certainly belongs up there; another metal coffin crewed by those whose sense of duty outweighed the sheer terror. Even the Wellington and Mosquito, wood and fabric and so small and vulnerable compared to today’s multi million dollar stand off war machines. How far we’ve come in such a short space of time
     

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