Short-Field Ops: Publications?

[Capt. Chaos]

I realize this is the CFI forum but holy crap guys, minutae much?

That better?

Short Field skill sharpeners.
Slow flight with slow descents and go around recovery.. then do it again with the airspeed covered.. KNOW what the airplane feels like, then do it again at gross weight.
Practice spot landings.. need to be able to put the airplane on the mark on demand.
Now start work on short field landings and takeoffs, start figuring out the actual distances required. Do it at gross weight too. And make a note of the difference.
Then throw in some steep arrivals behind the power curve.. some 180 turns with forward slips.. etc.

 

[Roger Roger]

That better?

Short Field skill sharpeners.
Slow flight with slow descents and go around recovery.. then do it again with the airspeed covered.. KNOW what the airplane feels like, then do it again at gross weight.
Practice spot landings.. need to be able to put the airplane on the mark on demand.
Now start work on short field landings and takeoffs, start figuring out the actual distances required. Do it at gross weight too. And make a note of the difference.
Then throw in some steep arrivals behind the power curve.. some 180 turns with forward slips.. etc.

Das' mo' betta.
I don't even know if we've had a single charter out there this summer. Sad.

 

[nosehair]

All the POH stall numbers in all the single-engine pistons I ever flew are always published at full "gross weight".
Most short field training in most 172s occur at a couple hundred pounds less.
We all know that indicated stall speeds are less at less weights, and short field approach speeds should be appropriately slower. It should be 1.3 x the indicated stall speed.
IAS is effected by temperature, altitude, probably humidity, age and accuracy of that particular instrument in that flight condition.
Calculations from a POH are to get you in the ball park, but the only real world way of establishing the real short field approach speed is to stall the airplane in the expected landing config in it's current weight on that day in that flight condition.
See what the ASI indicates as the stall occurs, and 1.3 x that ias.
Try it. It really works.

 

[Hammertime]

Approach speeds in the 172R are 60-70 knots with the short field approach procedure calling for 62. Best glide is 65, a higher, not lower margin. Again though, it really doesn't matter. Flying at 62 (1.34 Vso) only matters for achieving the book values for landing distance. You could fly it slower if you're comfortable with a smaller safety margin, or faster if you're comfortable with a longer than book value landing distance.

I'm having trouble seeing why you think L/D max is relavent though. Perhaps your next reply will clear this up for me.

I'm working, so I don't have access to my arsenal, but read my paragraph on best glide speed from my earlier post carefully. Best glide should to be compared to Vs1 Flaps UP stall speed. Also, if you get a chance, read through the Airplane Flying Handbook on Short Field Approach and Landing. It refers to flying at minimum controllable airspeed and operating on the backside of the power curve several times. The idea being that to clear the obstacle you need to make as steep an approach as is possible (without making a smoking hole at your aiming point), and flying at or near best glide speed is the exact opposite of that...

P.S. Say a prayer to all that is good and holy in aviation that the evil deity EWR doesn't ruin my last day tomorrow (they've got one runway shut down all week)!

 

[shdw]

We all know that indicated stall speeds are less at less weights, and short field approach speeds should be appropriately slower. It should be 1.3 x the indicated stall speed.

So because you may not be at gross weight it's ok to use the wrong numbers because your error won't be as bad an error as would be the case at gross weight? Is this some kind of joke?

In case it's not, let's run them still using the 172R:

Refresher: 1.3 Vso of IAS gives 43 knots IAS or 50 knot CAS speed, or 1.06 Vso.

Actual 1.3 Vso is 60 IAS (61 CAS). Let's say we are at 2000, which is about the lightest you'll ever be single pilot with 1/4-1/2 tanks. 61 * sqrt (2000/2450) = 55 CAS or 54 IAS.

So unless you take your wings, landing gear, and engine off to save weight, you still should be faster than 43.


Error is error, period. And the case of calculations from stall speed it's down right dangerous. No student/private pilot should be doing approaches at 6 percent above stall speed. No pilot should be doing that without at least knowing the situation they are in. Clearly neither of you would have a clue.

Im completely baffled that this thread has gone on beyond what I showed in my very first reply to hammer regarding this discussion:

VS0—the calibrated power-off stalling speed or the minimum steady flight speed at which the aircraft is controllable in the landing configuration. (Emphasis added)

Even the damn FAA has the technical side behind this right this time around, despite their history of completely f'ing it up. The same book makes a point to mention using 1.3 Vso when no approach speed is published and their definition of Vso tells you to use calculated. What's left to discuss is beyond me.

 

[shdw]

Best glide should to be compared to Vs1 Flaps UP stall speed.

Oops, you do have me here. I forgot to take into account flaps reducing Vg. Vg still has no place in this discussion, but at least I see your mental block anyhow. So thank you.

Now it's your turn to admit you are wrong about 1.3 Vso being of IAS. If you'd like another source visit page 35 of aerodynamics for naval aviators. If you'd like more sources let me know, I've got plenty if the PHAK quote and this are insufficient. Here's what this one says:

The stall speed of the aircraft in level flight is related by the equation: (lift equation rewritten) where: Vs - stall speed, knots TAS.

Recall that the calculation of TAS begins with CAS, not IAS. Really we should do 1.3 Vso of that speed to be entirely accurate. But if we did Roger would be right, errors would be minutiae(<5% in all but extreme conditions). Where as IAS vs CAS is not a small error in my book, or 80 percent error in your margin from stall (6 vs 30 percent) in the 172R.

 

[nosehair]

So because you may not be at gross weight it's ok to use the wrong numbers because your error won't be as bad an error as would be the case at gross weight? Is this some kind of joke?

.

You may have misunderstood my suggestion.
I didn't mean to use the IAS numbers in the POH. I agree to use CAS, then convert to IAS for the calculated value, but then the actual ias at stall might be less due to less weight, hi temp, instrument error, etc. so if you stall the airplane in that day's flight condition, and use 1.3 x that ias on that flight, you will have the correct ias for that approach.

 

[shdw]

You may have misunderstood my suggestion.
I didn't mean to use the IAS numbers in the POH. I agree to use CAS, then convert to IAS for the calculated value, but then the actual ias at stall might be less due to less weight, hi temp, instrument error, etc. so if you stall the airplane in that day's flight condition, and use 1.3 x that ias on that flight, you will have the correct ias for that approach.

Oh thank god! I certainly did misunderstood you! I did not think you would be a guy here to disagree with me from our earlier interactions years ago on this forum, which I must admit had me thoroughly confused when I read your reply. Thank you for clearing that up. You had me so damn mad I wanted to go skin the neighbors pet -_-

Haha. Yes, there are far more corrections to be made beyond this, I agree. I'm glad, however, that you agree that it all starts with using the real flight speed. The calibrated flight speed. Thank you again and my apologies sir.

 

[shdw]

so if you stall the airplane in that day's flight condition, and use 1.3 x that ias on that flight, you will have the correct ias for that approach.

This is what happens when I gloss over your reply and read, "I agree use CAS." I blame the booz.

Anyways, this is what the entire discussion's been about. You will not be at the correct approach speed in the quoted example. Since the indicated speed will be slower than the actual speed your approach speed will be less than 30 percent above actual stall speed. The indicated speed is an erroneous speed, you cannot use it and end up with accurate answers.

 

[nosehair]

You will not be at the correct approach speed in the quoted example. Since the indicated speed will be slower than the actual speed your approach speed will be less than 30 percent above actual stall speed. The indicated speed is an erroneous speed, you cannot use it and end up with accurate answers.

I think I see your point here. Let's see.
If the POH CAS stall speed is 50, and 1.3x = 65, and POH says 65cas 63 IAS, so we stall the airplane and see the actual indicated stall speed is 40, so I 1.3x 40 = 52. Yeah, the error is using 40ias in my example. The 40ias should be corrected to a CAS, but that won't be 50.
A final at 52 is too slow, but a final at 63 is too fast. I would split it in the middle and use 57.

Since the OP is not prepping for a checkride and is interested in real world techniques for short field ops, these are methods of arriving at real useful numbers in actual operations. I find actual stalling and using actual indicated speeds to be more useful, sometimes.
Another big changing factor id use of power. The stall speeds in most single pistons are power off. Using power during the approach lowers the stall speed and should be considered when stalling to establish a final approach speed. Stall it with what power you usually use, and with power off. Using a lower flatter approach angle with more power right up til touchdown will significantly lower the stall/approach speed.
Of course, now I'm talking basically slow flying it to the ground which could be at 5 or so kts ias above the actual ias of slow flying power stall.

That's how you put it on the dime.

 

[shdw]

Yeah, the error is using 40ias in my example. The 40ias should be corrected to a CAS, but that won't be 50.

Exactly, using IAS in your example you're actually flying 1.04 Vso (52/50). An error of 87 percent.

I find actual stalling and using actual indicated speeds to be more useful, sometimes.

In the particular airplane you fly, maybe. You're just using an erroneous speed though, that will vary from a/c to a/c, and flying under false pretense. That is, you think you're 1.3 Vso when you're 1.04 Vso, or some other lower than anticipated margin.

Alternatively to your method, have a glance at the calibrated speed chart during pre-flight. Take an average IAS-CAS difference at the low end, say 7 knots. When flying, grab the indicated value, add 7, and then do 1.3 of that. Or if you find that speed to be too fast, do 1.2. This will still have some error, but far less. Further, you are now flying at the margin you are comfortable with, instead of a margin you simply think is there.

My point is this, there are all kinds of reasons to fly slower for short field. As pilots, however, our goal should always be to balance utility and safety. To do this, in the case of short field ops, it is recommended to fly 30 percent greater than stall speed. You may wish to use less, and that's fine. Whatever margin you choose should be one you accurately calculate. The only way to do this is by use of actual flight speeds, not the ones falsely presented on your instrument.

 

[nosehair]

there are all kinds of reasons to fly slower for short field. As pilots, however, our goal should always be to balance utility and safety. To do this, in the case of short field ops, it is recommended to fly 30 percent greater than stall speed.

This balance of safety and utility varies greatly and is influenced by many constantly changing factors. Why use a constant like 30%?
30 percent above stall is the energy required to flare, or arrest, the descent moment from a power off glide. If you are making the final before flare at full weight and no power, you will need the 30% to flare it before stalling into a touchdown. It isn't really 30% above stall for safety alone.
Usually, short fields are approached with power right up til a few feet from the aiming spot, and really, 1.2xVso was the normal speed to use. We do practice slow flying at just above a stall, and 1.2 can become a very comfortable feel if you practice it.
In actual real short field, or emergency off-airport landings, excessive speed can be just as dangerous a insufficient speed.

 

[swisspilot]

T/o: Flaps 0deg on paved, full power while on the brakes, release, maintain positive backpressure but not too much, when the nose comes up put 20deg and rotate

Land: full flaps, trimp for 1.15 Vso and add power as needed so the plane doesn`t drop, this should be a lot more power then you are used to on final, take it like this all the way in ground effect short of your touch down point, when in ground effect raise the nose and apply more power, when you are over the touch down point remove the power and land, or keep some power and retract the flaps without lowering the nose, make sure you are not higher then 3 feet or you will hit pretty hard.

This is how I do it. But I have learned it with a proficient CFI don`t attempt it unless.

For those runway lenghts on paved surface you don`t really need a short field takeoff or landing...

 

[shdw]

This balance of safety and utility varies greatly and is influenced by many constantly changing factors. Why use a constant like 30%?

You may wish to use less, and that's fine. Whatever margin you choose should be one you accurately calculate.

This 30 percent is what FAA publications recommend as an approach speed when no speed is published, and I'd agree is what should be used in most (99%) circumstances.

Keep in mind, the limiting factor for most aircraft, with regard to runway use, is takeoff. Not landing. Run the published short field speeds for any aircraft you have a POH for and you'll find they are ~30 percent. The 172R chart we discussed in this thread is based on 34 percent.

As far as emergencies go, unless you routinely practice ops at low approach speeds this isn't a time to be trying it. Perhaps it is something you are comfortable with, I am not. I fly best glide to the ground in an emergency because that's what I practice routinely.

 

[African_Swallow]

Just thought I'd put this out there...iTunes-U has some maneuvers vids. Through iTunes University, go to UND's AeroCast vids.