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Vx Vy Vmc V1 V2 Vne

pa19guy

Registered User
Anchorage, AK
Vx Vy Vmc V1 V2 Vne

Please help!

Getting some dual the other day and was grilled that I did not know the basic speeds of a cub. Sure thought I did. I had replied they were all the same in a Super cub 150 with tundra tires and an 8242.

70 mph is written down in my docs as a "good normal" climb out speed, and I use it. What do you use?

What speed do you all climb out at if you had to pop it up and climb like a home sick angel for a couple three or four hundred feet.

Chris
 
Chris,

The easiset thing to do is change instructors to someone who understands that the airspeed indicator in these plane is so innacurate that they speeds are moot anyway.

Fly the attitudes...

sj
 
V speeds

you must have a young instructor those speeds are good to know however they are not so important in a super cub. if your flying a twin or other type spam can they can be very important. and if you are going to take a ride with the feds it is required to know the v speeds. i agree with steve get rid of him
 
Vmc? In a cub? lol. I think you should put a blue line on your asi in your cub and ask him what that is for.


One point that you need to be aware of that as you get lighter (have less gross weight) Va (manuvering) speed goes xx down. duh.
 
Run far , run fast! That guy isn't a cub instructor. When you find the guy whose mission is to make you proficient in both wheel landings and 3-points, then you have a cub insrtuctor!
 
behindpropellers said:
One point that you need to be aware of that as you get lighter (have less gross weight) Va (manuvering) speed goes up.

tim

Va decreases as weight decreases.

Easiest way to remember.... a light boat bounces off the waves (turbulence) while the same boat loaded heavier plows through the waves.

It's the bounce that causes structural failure. Va is airspeed where the aircraft will stall before it breaks (exceeds structural limit)..... thus the slower Va for the lighter weight.
 
Chris,
I'll take a different tack on answering this question. Maybe you should find the correct answer.

The next time you're out on a relatively still day write down the temp/pressure and accurately load out the plane (so you can compare later at different weights). Take a clipboard and stopwatch.

Then go find a spot of clear airspace and climb at full power holding a constant indicated airspeed. Between two altitudes at least 500 ft apart measure the time interval. Return to the initial altitude and repeat timing the stabilized climb between the same two altitudes at 5 mph (or knots if you chose) increments from say 5 mph above stall until you are definitely not climbing as fast (75/80). If you have the time, search on the web for "bootstrap method john lowry" he has excel spreadsheets and a method for getting a bunch of data from climbs and glides.

When you get home, plot the times vs the airspeed. The bottom of the arc (in other words the fastest rate of climb between those two altitudes) is Vy at those conditions on YOUR airspeed indicator. Vx is always less except at absolute ceiling where they are both 0.

Officially, in the copy of a PA-18-150 book I have (not sure what year it's for I didn't scan all the pages), Vx is 45 and Vy is 75. Since you're required to have a POH, look in it for your airplane's official numbers (the FAA doesn't approve changes to POH's often, except for STC's which rarely address Vx or Vy). Vx and Vy go up with weight and Vy goes up with increasing drag.

I have not seen official numbers for V1, V2 or Vmc for a cub. Vmc is very close to stall in my plane. Vs1 and Vso go up with weight.

Vne is 153 from the type certificate for PA-18-150 landplane
Va is 96 mph at gross
Vfe is 85 mph
Vsc is 121 mph
Check your POH though.

It never hurts to have good information. Then you can answer the stupid *&^% question and get back to the flying.
 
Interesting I have always only thought of VMC in relation to multi-engine flying, but I suppose it is possible to have loss of directional control without stalling. Was this more true in early single designs?

sj
 
Chris

In a nutshell the three that you will be concerned with are Vx Vy and Vne. Vne is in the book and should be pretty self explanatory. Above this speed things may start to come apart, literally.
For Vx and Vy there are two types of aircraft, props and jets.(turbines fall in between the two and have there own weird characteristics).

For a recip prop aircraft Vx will always be somewhere near the stall speed. The oldtimers used the phrase " Hang it on the prop". This will give the best angle of climb.

Vy will be at the L/D max point, which in a Cub will be somewhere around 60 to 70 depending on weight and other factors. In a prop aircraft, best rate of climb(Vy) occurs at L/D max.

( in a jet Vx occurs at L/D max and Vy is much faster)

This subject can get pretty complicated but the above rules of thumb will help.

Bill
 
KLM has it right. if you dont know your speeds how are you going to know what speed to use to glide the farthest in an engine out. looking at the wing isnt going to cut in that spot.
or in very rough air you must know Va.
and what if you have to climb out over some trees close by. how can you be sure without knowing the speed your plane will stall at in its present configuration.
flying by attidtude is usually just fine. but in an emergency or tight situation it helps to have a number pegged.
 
klm_ak said:
I have not seen official numbers for V1, V2 or Vmc for a cub. Vmc is very close to stall in my plane. Vs1 and Vso go up with weight.

V1 (Also called "Decision Speed") is for multi engine aircraft. If you lose an engine below that speed, you can (Theoretically) abort the landing and get stopped before you run out of pavement. At or above that speed, you're better off to continue the takeoff.

Not something we need to worry about. If we lose an engine, we're just SOL. I suppose if one of you gents with an Experimental SC wanted to get really creative...

If I remember correctly, V2 is equal to or greater than Vmc x 1.1 (Or Vs x 1.2). Just the speed at which you have a safety margin above a stall.

Steve said:
...the airspeed indicator in these plane is so innacurate that the speeds are moot anyway.

Fly the attitudes...

Amen.
 
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