In other words, Strega doesn't have a clue. But I bet the Colonel knows. And hopefully a few others.
Thanks
slips and skids
-
mcrit
[quote author=Colonel Sanders link=topic=5561.msg14545#msg14545 date=1486184969]
I frequently use a 90 degree banked side-slip on short final.
In that condition:
a) what is the AOA?
b) what is my stall speed?
Ask any TC Inspector for the answers. They know everything.
[/quote]
Depends, how much did you unload the stick?
I frequently use a 90 degree banked side-slip on short final.
In that condition:
a) what is the AOA?
b) what is my stall speed?
Ask any TC Inspector for the answers. They know everything.
[/quote]
Depends, how much did you unload the stick?
-
Colonel
- Posts: 3450
- Joined: Wed Apr 29, 2015 10:31 am
[quote]Is the indicated stall speed less in a slip and higher in a skid?[/quote]
Another trick question. A cheaper aircraft like a 172
will have a single static port (eg on left side) but a
more expensive aircraft (like a Mooney) will have 2,
but [i]in a different location[/i] - on [u]both sides[/u] at the
back of the fuselage instead of at the front like at 172.
Indicated airspeed is merely the pressure differential
between the pitot pressure and the static port, or if
there are two static ports, of the [b]sums [/b]of the two different
pressures at the static port, which makes us think about
the topology and diameter of the static tubing (how much air
can flow, between the static ports at different pressures, and
how fast? See fluid dynamics for that answer)
More detail is required to answer your question. Remember
that airspeed is merely a proxy for AOA. In your question,
the airflow is not symmetrical hence the two wings will be
at different AOA, so an AOA on each wing would be nice.
That single airspeed reading on your dashboard starts to
look like a pretty lousy proxy for the two different AOA's -
we're going to map a lot of different pairs to one scalar
value.
Oh god, I'm starting to sound like photofly. Must stop.
We are pilots, and pilots are a simple people.
[size=18pt][b]Skids are bad, slips are good[/b][/size].
The inside wing can stall in a skid, and the lift from the
outside wing can quickly roll you upside down. Most
pilots don't like being upside down at low altitude,
which I understand is an acquired taste.
Theoretically you can stall a wing in a slip, but you
really really really have to work at it, and if you do,
you roll wings level, which is probably easier to deal
with.
In a slip, lower the nose to keep the speed up and
piss away energy. Drag is a function of velocity
squared, remember.
I haven't even mentioned a really fundamental
consideration ... stall speed is also a function of G.
If you aren't pulling 1 G (eg in a slip, you're letting
the aircraft fall) your stall speed goes down.
Vs(G) = Vs(1G) x sqrt(G)
Remember at zero G, you cannot stall, because the
wings are not being asked to produce any lift.
So when you ask about a skid or a slip, you need to
know [i]how much[/i] of a skid or slip that you are performing,
and how much lift you are trying to produce at the time.
In my extreme example of a 90 degree banked slip,
you can see the rules start to change. Wings aren't
producing any lift - their AOA is zero - and the aircraft
is merely falling.
Or is it? In the case of the Pitts S-2B with it's large
canopy, rotund belly and channeling effect of the biplane
wings, level sustained knife-edge flight is possible with
enough airspeed. The fuselage produces that much lift -
the vectored thrust from the prop is second order at best.
The fuselage produces so much lift in knife-edge flight
that you can even do it in formation. It's that controllable -
Eric and I do it all the time.
I hope the above helps, and I apologize for being
mean to photofly. He's actually a great guy. Who
do you think did his instructor rating? ;D And fixed
his VOR antenna, after the paint shop fucked it up?
Digression: in 40+ years in aviation, I have yet to
meet one AME that comprehends what a balun is.
[img]http://avstop.com/maint/alterations/f3-10.jpg[/img]
You don't have to connect the end of the coax to anything, ok?
Another trick question. A cheaper aircraft like a 172
will have a single static port (eg on left side) but a
more expensive aircraft (like a Mooney) will have 2,
but [i]in a different location[/i] - on [u]both sides[/u] at the
back of the fuselage instead of at the front like at 172.
Indicated airspeed is merely the pressure differential
between the pitot pressure and the static port, or if
there are two static ports, of the [b]sums [/b]of the two different
pressures at the static port, which makes us think about
the topology and diameter of the static tubing (how much air
can flow, between the static ports at different pressures, and
how fast? See fluid dynamics for that answer)
More detail is required to answer your question. Remember
that airspeed is merely a proxy for AOA. In your question,
the airflow is not symmetrical hence the two wings will be
at different AOA, so an AOA on each wing would be nice.
That single airspeed reading on your dashboard starts to
look like a pretty lousy proxy for the two different AOA's -
we're going to map a lot of different pairs to one scalar
value.
Oh god, I'm starting to sound like photofly. Must stop.
We are pilots, and pilots are a simple people.
[size=18pt][b]Skids are bad, slips are good[/b][/size].
The inside wing can stall in a skid, and the lift from the
outside wing can quickly roll you upside down. Most
pilots don't like being upside down at low altitude,
which I understand is an acquired taste.
Theoretically you can stall a wing in a slip, but you
really really really have to work at it, and if you do,
you roll wings level, which is probably easier to deal
with.
In a slip, lower the nose to keep the speed up and
piss away energy. Drag is a function of velocity
squared, remember.
I haven't even mentioned a really fundamental
consideration ... stall speed is also a function of G.
If you aren't pulling 1 G (eg in a slip, you're letting
the aircraft fall) your stall speed goes down.
Vs(G) = Vs(1G) x sqrt(G)
Remember at zero G, you cannot stall, because the
wings are not being asked to produce any lift.
So when you ask about a skid or a slip, you need to
know [i]how much[/i] of a skid or slip that you are performing,
and how much lift you are trying to produce at the time.
In my extreme example of a 90 degree banked slip,
you can see the rules start to change. Wings aren't
producing any lift - their AOA is zero - and the aircraft
is merely falling.
Or is it? In the case of the Pitts S-2B with it's large
canopy, rotund belly and channeling effect of the biplane
wings, level sustained knife-edge flight is possible with
enough airspeed. The fuselage produces that much lift -
the vectored thrust from the prop is second order at best.
The fuselage produces so much lift in knife-edge flight
that you can even do it in formation. It's that controllable -
Eric and I do it all the time.
I hope the above helps, and I apologize for being
mean to photofly. He's actually a great guy. Who
do you think did his instructor rating? ;D And fixed
his VOR antenna, after the paint shop fucked it up?
Digression: in 40+ years in aviation, I have yet to
meet one AME that comprehends what a balun is.
[img]http://avstop.com/maint/alterations/f3-10.jpg[/img]
You don't have to connect the end of the coax to anything, ok?
-
cgzro
indicated stall speed in a slip/skid
All indicated airspeeds will be off by some amount (positive or negative) depending on the pressure change in the area where the static port is located. There are three cases:
1- If the static port is in an area of low pressure then the difference between the pitot pressure and static will be larger and therefore the ASI will read higher than your actual airspeed.
2- If the static port is in an area of high pressure then the difference between the pitot pressure and static will be smaller and therefore the ASI will read lower than your actual airspeed.
3- if there are multiple static ports connected together then its likely they won't both be in high or low pressure at the same time and tend to balance each other (CS's Moonie case). In which case the ASI will read more or less your actual airspeed.
So the answer to the question is quite difficult and depends on the static port (s) design.
Since a slip and a skid can both produce areas of low or high pressure over the static ports both slips and skids can cause under reading or over reading of the airspeed depending on the aircraft design and degree of slip/skid.
The important thing to remember however is that the plane will snap in the direction that the rudder is deflected. So if your wing is low and your are pressing rudder toward the low wing .. well watch out.. if your wing is high and you are pressing rudder toward your high wing well still watch out but at least you get an extra 1/2 second or so before you end upside down which is more than enough to stop pulling and prevent anything nasty from happening.
All indicated airspeeds will be off by some amount (positive or negative) depending on the pressure change in the area where the static port is located. There are three cases:
1- If the static port is in an area of low pressure then the difference between the pitot pressure and static will be larger and therefore the ASI will read higher than your actual airspeed.
2- If the static port is in an area of high pressure then the difference between the pitot pressure and static will be smaller and therefore the ASI will read lower than your actual airspeed.
3- if there are multiple static ports connected together then its likely they won't both be in high or low pressure at the same time and tend to balance each other (CS's Moonie case). In which case the ASI will read more or less your actual airspeed.
So the answer to the question is quite difficult and depends on the static port (s) design.
Since a slip and a skid can both produce areas of low or high pressure over the static ports both slips and skids can cause under reading or over reading of the airspeed depending on the aircraft design and degree of slip/skid.
The important thing to remember however is that the plane will snap in the direction that the rudder is deflected. So if your wing is low and your are pressing rudder toward the low wing .. well watch out.. if your wing is high and you are pressing rudder toward your high wing well still watch out but at least you get an extra 1/2 second or so before you end upside down which is more than enough to stop pulling and prevent anything nasty from happening.
-
John Swallow
- Posts: 319
- Joined: Fri Jun 03, 2016 1:58 pm
The picture of the "Typical VOR Antenna Balun" looks positively lewd!
Did I mention I had trouble with the Rorschach test also? (Well, I wasn't the one with the dirty pictures...)
Did I mention I had trouble with the Rorschach test also? (Well, I wasn't the one with the dirty pictures...)
-
Colonel
- Posts: 3450
- Joined: Wed Apr 29, 2015 10:31 am
-
vanNostrum
- Posts: 338
- Joined: Wed Nov 04, 2015 9:04 pm
Probably for the same reason RG 59 is 75 Ohms ;D
I'm not an ame
I'm not an ame
-
Liquid Charlie
- Posts: 524
- Joined: Sun Aug 23, 2015 1:34 pm
[quote]How many AMEs do you know that can explain why RG58 is 50 ohm cable ? Probably the same number that can understand what a balun is....[/quote]
Not sure about AME's but ask any good CB'er or Ham operator O0
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