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Author Topic: Modeling fuel consumption using Lockheed 487 Report.  (Read 27970 times)

JNev

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Re: Modeling fuel consumption using Lockheed 487 Report.
« Reply #30 on: April 23, 2012, 11:26:22 AM »

I've never heard anyone discuss AE's protocol for use of the superchargers.

It seems to me that she had an effective service ceiling of 10,000 feet--at least, if I remember correctly, that was as high as she intended to go in her flight planning.  No oxygen system on the aircraft.

If her superchargers were intended only for above 14,000 feet, then it seems that they were pretty much useless for her purposes.

AE's engines were boosted full-time.  The blower was driven off the crankshaft through the accessory drive at 10:1 with no means of disengagement.  Boost was a function of throttle position in that arrangement - therefore AE's protocol for supercharger use would necessarily be that of obtaining the desired boost settings via throttle position (and reading the manifold pressure gages).

Some later types had 'high' and 'low' blower available; I had not realized that the R-2800 had a blower that could be fully disengaged, as William Thaxton has described, and would have thought it might have had the two-stage (variable ratios) blower.  I'll trust William's recollection on that, of course.

And of course there are many variants of the R-2800, just as there are variants of the Wasp - those William flew on the Convair being one of the R-2800 variants.

LTM -
- Jeff Neville

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Gary LaPook

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Re: Modeling fuel consumption using Lockheed 487 Report.
« Reply #31 on: April 23, 2012, 04:22:40 PM »

Also, you are correct about the "supercharged" engines but the superchargers weren't normally used in the low altitude environment.  In fact, procedurally, we never engaged the blowers below 14,000'.  Again, it was that pesky engine life curve.  The superchargers helped "trick" the engine into thinking it was at a lower altitude by packing air into the carburetor.  When used at low altitude this could easily blow a cylinder.  While I suppose there could be an emergency situation where such use might be approporiate it certainly would not be a normal course of events.  This would indicate that, in normal flight at low altitude, AE would have been flying a normally aspirated aircraft and the supercharger would not have been engaged.

William
Now I'm confused. How did you get the takeoff manifold pressure of a minimum of 44.0 inches and all the way up to 58.0 inches without using the supercharger as specified in the attached TCDS?

gl
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William Thaxton

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Re: Modeling fuel consumption using Lockheed 487 Report.
« Reply #32 on: April 23, 2012, 09:42:51 PM »

OK, before this gets out of hand....

I'll admit that I am working strictly from memory and that memory set is about 40 years old.  I may be remembering a shift from "low blower" to "high blower" instead of a completely disengaged supercharger.  Even in that case, temperature remains a significant variable in power output  of the engines.  If "low blow" is the norm and is required to achieve normal power output then power output will be reduced at high ambient temps.  I could probably have avoided this misunderstanding by saying "carburated" instead of "normally aspirated".  In any case, increased temperature equates to increased density altitude which equates to decreased power output.  While this applies to any "air breathing" engine, it is more critical in recips than in turbines.  As to the usefulness of superchargers used only above 10,000', the Electra 10-E had a service ceiling of 19,400'.  The 10,000' limitation was self-imposed based on AE's decision not to carry oxygen.  For comparison, the T-29 had a service ceiling of a bit under 24,000' (the Convair 440 lists 24,900' but we were a good bit heavier due to installed military equipment).

Sorry for the "low blow"/"no blow" confusion (which is totally the fault of my memory) but the basic consideration still stands.  I don't honestly think temperature had much (if any) effect on the final outcome.  I've seen nothing which indicated AE and FN ran out of gas early.  At the same time I believe in examining every realistic possibility and temperature is certainly a contributing factor in recip engine performance.

Thanks for keeping me honest!

William
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William Thaxton

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Re: Modeling fuel consumption using Lockheed 487 Report.
« Reply #33 on: April 24, 2012, 09:03:53 PM »

"Beast" is an appropriate description, J. C.!  There was something utterly visceral about cranking those big radials and thundering down the runway.  Jets were the king even during my tenure in recips (early to mid 1970's) but that caused some really interesting interactions when we flew into bases which werent used to recip traffic.  But that is a subject for a different forum since it really sheds no light on the AE/FN question.

Overall, I've been impressed with the level of discussion in this forum.  Questions are asked, discussed and tested for whatever light they might shed on this 75 year old mystery.  In fact, I only became involved in this thread as something of an academic exercise.  As I stated earlier, I've never seen anything that indicated AE ran out of gas short of Howland Island... only that she might have missed Howland and found Gardner instead.  Considering the accuracy and limitations of over water navigation in those days such a scenario is quite believable.  Things hadn't changed all that much since Magellan! 

By the way, J. C., were you around for the "gold plug" fiasco?

William
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