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Old 09-06-2007, 01:57 PM   #1  
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Default Multicom/Unicom?

If I understand this correctly, the AIM says Multicom includes "Activities of a temporary, seasonal, emergency nature, etc, and for airports with no tower, FSS, or UNICOM..."

A DPE around here likes to grill on this for whatever reason, and a specific question is how do you find it on a sectional?... I would assume any airport with 122.9 or 122.925(both MULTICOM frequencies) in the UNICOM slot... so then, what is the difference at the airport that lists a MULTICOM frequency in place of a UNICOM... and is there any actual difference in the type or way of communicating, or who you are communicating with?

This is very confusing after reading it, so sorry for not being clear, but I dont understand the difference, or why you would list a MULTICOM frequency instead of just a UNICOM for an airport...


Another puzzler, forward and side slips... the FAA - Airplane Flying Handbook has the "wing-low" method as being a sideslip... which I thought was the opposite and that a forward slip was the wing-low method used for landings... this is all very confusing, and even after reading the definitions in the book it still doesnt make any sense
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Old 09-06-2007, 04:33 PM   #2  
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Nevermind... when in doubt, google everything

If anyone was wondering the same thing... "

Multicom is different from Unicom. When Multicom is used around airports, that usually means the airport has no fixed base operator. Like Unicom, pilots broadcast their position and intentions out into the area on a Multicom frequency. However, responses from other airplanes may not always be expected, and no responses will return from the ground.
Multicom's main purpose is to alert other aircraft of the pilot's intentions. Usually small planes use Multicom. Large aircraft could use it, but it would be meaningless. If the airport is too small to have a base operator, then it probably does not have enough runway space for large aircraft. Its most common frequency is 122.900, but there are many others.
The problem about Multicom is if aircraft in the sky need to communicate to the ground, there is no base operator to respond. That is the primary reason most aircraft divert away from airports that use Multicom. "
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Old 09-07-2007, 01:47 AM   #3  
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Default slips vs. fwd slips

FAA Airplane Flying Handbook has a completely useless illustration in it for differentiating slips from forward slips. They are separate, different techniques with enough similarities to be confusing. One illustration is just the other illustration turned slightly sideways (check it out). I recommend asking local experts what the difference is between them, how they work, when and why to use them. You could also study the problem using a toy airplane and do them in a flight sim or in the air. A good flight sim can show you that certain aircraft must be landed using sideslips if there are crosswinds present (tailwheels). We also had a thread on this subject here earlier this year.
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Old 09-07-2007, 05:54 AM   #4  
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Ya I think I remember seeing that thread, better do a search... and yes those two figures in the Airplane Flying Handbook are the exact same figure only with one turned in a different direction.

From what I gathered reading every small detail and squeezing out everything the FAA is trying to make up about it is they are the same maneuver only one is done to keep the longitudinal axis parallel to the runway (sideslip/wing low method) in a landing situation. The Forward slip is used to create more drag and lose altitude at a greater rate than normal in the approach... thats my story and I'm stickin' to it

Thanks for the help though!
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Old 09-07-2007, 07:25 AM   #5  
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Sounds good to me. I have yet to take the CFI checkride because of working too much, but I am optimisitic that things are going to change when I go to another job location next month.

Don't tell the examiner this unless he asks... but for discussion, the principle that allows forward slips to quickly lose altitude can be found in the nature of the induced drag curve. Induced drag goes up exponentially as speed is reduced and angle of attack is increased. You can determine what speed this occurs at, by trying speeds at or below 70 kts in a typical trainer. A wing at high AOA has exponentially increasing drag and wants to trade altitude for airspeed. If you look at the drag curves for a given wing, parasite drag goes exponentially up with speed, but on the low end induced drag goes exponentially up with a drop in speed.

Last edited by Cubdriver; 09-07-2007 at 02:03 PM.
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Old 09-07-2007, 09:48 AM   #6  
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I know the induced drag will increase due to the decrease in airspeed, but I thought the initial loss of airspeed and thus altitude was due to the planes longitudinal axis being turned perpendicular to the relative wind, creating more surface area for a stronger form drag(parasite drag)... meaning the entire side of the plane is exposed to the relative wind due to direction of flight being away from where the nose is heading... compared to straight and level flight only exposing the nose and leading edges to form drag.

(And I keep saying form drag, but is it form or profile drag when you change the surface area being exposed to relative wind?)
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Old 09-07-2007, 12:45 PM   #7  
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Form drag. This is part of it, but if you doubt the fact of an exponential drag increase at lower speeds due to the byproduct of lift, do a forward slip at say 85-90 kts and you will see that the airplane hardly loses any more altitude than it would without the crossed control inputs. Once high AOA starts inducing a lot of drag, the crossed inputs places the side of the aircraft broadside to the wind, this is indeed form drag. However, form drag does not exponentially increase by slowing down, it exponentially increases by speeding up. This is why hi-speed aircraft are shaped to make their surfaces line up smoothly with the wind. If you know how induced drag acts with change of airspeed you can control it.

And with this I have hit my 500th useless post, which if you ask me deserves some celebrating.

Last edited by Cubdriver; 09-07-2007 at 12:56 PM.
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Old 09-07-2007, 01:33 PM   #8  
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Man, we're dorks, you think the examiner would mind if I printed this out and took it in for the one question he will now undoubtedly ask? haha


And, congrats on 500! Its the right night to celebrate such a thing; but, after you toast to it dont expect your friends to look at you like you have a brain in your head
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