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Messages - Marc Zeitlin

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31
Hangar Flying / Re: Flying in SoCal
« on: December 16, 2012, 09:47:00 PM »
Can anyone regularly flying in southern California tell me whether or not there have been any large airspace revisions in the past couple of years?... Again, I just want to avoid the San Diego class C and LAX class B airspaces.
Well, Joe, if you think that SD is a Class C, then I'd say yes, there have been some pretty large revisions, because SD is a Class B, not a C.

Joe, you're a friend (and obviously as cheap as I am if not more so), but I will have to admonish you here and say either update the GPS or get a set of LA sectional and TAC charts ($11.85 for both from iPilot), or stay out of the LA airspace.  You cannot (however legal it may or may not be, and even if between the Class B airspaces or over the Class C's) safely and rationally fly around the incredibly complex airspace south of the San Gabriel Mountains without current charting information.

Bite the bullet - spend the $11.85 - I know that paper charts are a PITA in a LE - they're enough of a PITA in the COZY.  But you really don't have a choice - it's either that, or the GPS update.  You've got to know the Class B boundaries, on top, bottom and sides.  As well as the VFR corridors over LAX and the "tunnel" in the SD Class B.  Plus, the Class C's over Ontario and Burbank, and the innumerable Class D's.  I've flown in or around most of the Class B's in the US - the LA/SD combination is easily the most complex one there is, even including the BOS/NY/DC corridor.

32
Hangar Flying / Re: The Voyager Constant
« on: July 13, 2012, 11:07:58 AM »
Those speeds gave them that AOA but I donít know how they knew what speed to hold or if they were using an AOA indicator.
There was no AOA indicator.  In fact, there was a "deck angle" indicator (which is not an AOA gauge, but serves as something similar in 1G flight), but it broke during the flight.  See:

   http://www.oshkosh365.org/saarchive/eaa_articles/1987_02_01.pdf

for a description of the flight.

The object, in Voyager's case (or any distance goal) was to fly at the max L/D AOA, which is constant, or the max L/D speed, which changes with weight.  If you know how much you weigh, then you know what speed to fly (since L = W). Since Voyager knew how much fuel they were burning, they could estimate their weight at any given time, and thereby know what speed to fly to maximize range.  More work, but just as effective, IF you know your weight.

I know thereís a real name for it. There are several distinct AOAs like best L/D etc...
For Voyager (or Global Flyer, or any commercial airliner attempting to maximize range), it's Max. L/D AOA or speed.

With respect to your previous posting's questions, there are really three meaningful AOA's/speeds (and all this is for prop planes, NOT jets - they're slightly different, since their thrust different):

1) Max Endurance speed.  This occurs when the power required to stay in the air is a minimum (and so the fuel burn is lowest, so the fuel lasts the longest)

2) Max L/D speed.  This occurs at 1.32 * Max Endurance Speed, and is the speed to fly for maximum range. This occurs at the speed at which drag is the lowest.  You need more power than the Max. Endurance speed (obviously, since you're going faster), but you pick up a more range by going faster than you lose by burning fuel faster.

3) Carson speed. This occurs at 1.32 * Max L/D speed. This is the "Optimum" cruising speed to fly which optimizes the fuel flow/kt of speed.

For a COZY MKIV (which I fly), the Max Endurance speed is about 75 - 80 kts.  The Max L/D (range) speed is about 100 kts.  The Carson speed is about 132 kts.  Now, these speeds do change with weight, but since I always fly between 1700 - 2100 lb, they don't change much (not like Voyager or Global Flyer, which burned 80-90% of their weights during their flights, or a commercial airliner that might burn 1/2 it's MGW on a flight).  It might be a few kts slower at lower speeds to keep the same AOA.  Remember that lift is proportional to velocity squared, so a 25% decrease in weight will lead to an 11% decrease in speed for the same AOA.

So my max endurance speed might drop to 70 kts at light weight, etc.

Interestingly enough, since I almost always fly above 7500 ft, my IAS is generally in the 145 kts - 125 kt. range (between 7500 - 13.5K ft).  This puts me squarely in the Carson speed area.  I'd have to fly a lot higher (with lower IAS's) to get near the Max L/D speed.

If you fly low, you have to slow down a lot to get to the Carson speed, and a LOT to get anywhere near the Max L/D speed.

Here are three articles that explain what's going on in a lot more detail, and with some math if you want it.

http://www.eaa1000.av.org/technicl/perfspds/perfspds.htm

http://cafefoundation.org/v2/pdf_tech/MPG.engines/AIAA.1980.1847.B.H.Carson.pdf

http://www.flyingmag.com/very-best-speed-fly


PS - still waiting to hear how all of this applies to the Kennedy crash...

33
Hangar Flying / Re: The Voyager Constant
« on: July 10, 2012, 09:45:11 AM »
Bingo! And it also keeps you alive, IE the Kennedy crash a while back at night.
Please elaborate.  How would maintaining a constant AOA (any particular AOA - whether the max L/D AOA or not) have affected Kennedy flying in marginal VFR conditions at night with no horizon and not using the autopilot or staying near shore so as not to become disoriented and enter a spiral dive?

34
Hangar Flying / Re: The Voyager Constant
« on: July 10, 2012, 09:39:54 AM »
Max Endurance AOA = minimum thrust required...
Tsk, Tsk, Tsk.  I'm embarrassed for you, Joe :-).  Max _ENDURANCE_ AOA?  Max. Endurance AOA <> Max. Range AOA (i.e., best L/D) for propeller driven aircraft, which Voyager was.  You're stuck in Boeing's jet world :-).  You got the "min thrust required" right, but that's not "max endurance".

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