Vref & The CPL flight test guide.

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TopGun1234
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Vref & The CPL flight test guide.

#1 Post by TopGun1234 » Wed Feb 21, 2018 11:27 pm

According to the TC flight test guide (https://www.tc.gc.ca/eng/civilaviation/ ... 72.htm#ex2) we have to calculate Vref as per the following formula:

1.3 VSO KCAS (max. gross wt.) x square root (landing weight/gross weight).


My question, is that last (gross weight) in the square root the permissible Max T/O weight of the aircraft or is it the T/O weight of the flight?

I can't seem to find any literature that goes into detail about this. Its not in FTGU.

Thanks,
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Re: Vref & The CPL flight test guide.

#2 Post by trey kule » Wed Feb 21, 2018 11:41 pm

I actually read the link as I could not believe it said Vref for a small plane.
Anyway, I really think you should reread the applicable section...

“the final approach speed corrected for the predicted landing weight using available charts or tables for weights that are less than maximum take-off weight or, in their absence 1.3 VSO KIAS using the following formula:”

See that little word “or” in there.

Get a POH...Unless the aircraft if about 50 years old, the POH will have an “approach speed”

......kind of the same words in the TC guide.

Are there really examiners out there with so little common sense?
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Re: Vref & The CPL flight test guide.

#3 Post by trey kule » Wed Feb 21, 2018 11:41 pm

I actually read the link as I could not believe it said Vref for a small plane.
Anyway, I really think you should reread the applicable section...

“the final approach speed corrected for the predicted landing weight using available charts or tables for weights that are less than maximum take-off weight or, in their absence 1.3 VSO KIAS using the following formula:”

See that little word “or” in there.

Get a POH...Unless the aircraft if about 50 years old, the POH will have an “approach speed”

......kind of the same words in the TC guide.

Are there really examiners out there with so little common sense?
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Re: Vref & The CPL flight test guide.

#4 Post by TopGun1234 » Thu Feb 22, 2018 12:46 am

I am aware of the "Or". However, my question still stands. Also you're expected to do the calculation for the flight test. Or so I'm told.

is that last (gross weight) in the square root the permissible Max T/O weight of the aircraft or is it the T/O weight of the flight?
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Re: Vref & The CPL flight test guide.

#5 Post by jg24 » Thu Feb 22, 2018 2:17 am

MTOW of the aircraft as per POH
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Re: Vref & The CPL flight test guide.

#6 Post by photofly » Thu Feb 22, 2018 4:59 am

trey kule wrote:
Wed Feb 21, 2018 11:41 pm
I actually read the link as I could not believe it said Vref for a small plane.
Anyway, I really think you should reread the applicable section...

“the final approach speed corrected for the predicted landing weight using available charts or tables for weights that are less than maximum take-off weight or, in their absence 1.3 VSO KIAS using the following formula:”

See that little word “or” in there.

Get a POH...Unless the aircraft if about 50 years old, the POH will have an “approach speed”
I’ve never seen a little plane POH that references a final approach speed adjusted for and indexed by landing weight. The cessna ones just say “50-60 KIAS”, for example. There is no “available chart or table” that meets the requirement.

Therefore simply using the POH speed as written won’t do.

The candidate is required to estimate the weight at landing, calculate his or her own target airspeed, not make the error of performing the calculation using KIAS (i.e. he or she should correct to/from KCAS using POH airspeed correction data) and then fly that airspeed.

You might have an opinion about whether that’s sensible or necessary, but TC in its wisdom has decided it’s a skill to be demonstrated by a candidate for a Commercial Pilot Licence. Don’t get snippy at someone who wants to pass a flight test!

And why shouldn’t one refer to Vref? What would you prefer to call it? It is a term defined in the aircraft certification standards, just like V_a and V_ne, and we use those happily....
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Re: Vref & The CPL flight test guide.

#7 Post by trey kule » Thu Feb 22, 2018 7:47 am

I suppose you are right photo. I was being snippy. Though not towards the poster, but towards an examiner when it comes to calculation.
55-60 works for me for a 172. I really think there are more important practical things for a CPL testee to know. This is another one of those drifts that come from examiners who lack practical experience in the world outside an FTU.


As to Vref. Do you see it in the TC guide?
There is a reason they do not use the term.
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Re: Vref & The CPL flight test guide.

#8 Post by youhavecontrol » Thu Feb 22, 2018 7:54 am

It's is a perfectly reasonable calculation to do, even in a small aircraft. For example, if you are flying a Diamond Eclipse, the recommended landing speed is 55kts, regardless of your weight... because the POH is quite simplified (or dumbed-down), but if you do the Vref calculation, it can go down to 50kts, or sometimes a bit less, giving yourself about 100'-200' less on your landing distance. It's pretty handy.

The calculation uses 1.3Vso(cas) multiplied by the square root of your Landing Weight, divided by your max take-off weight (or Gross Weight). Once you finish crunching the numbers, remember to convert the Calibrated airspeed back to Indicated.

Vref seems like a very low approach speed at times, but remember that most recommended approach speeds are calculated at max gross weight, with max forward C of G, with the power at idle, while still giving wiggle room to land at the max demonstrated crosswind.
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Re: Vref & The CPL flight test guide.

#9 Post by photofly » Thu Feb 22, 2018 8:04 am

trey kule wrote:
Thu Feb 22, 2018 7:47 am
I suppose you are right photo. I was being snippy. Though not towards the poster, but towards an examiner when it comes to calculation.
55-60 works for me for a 172. I really think there are more important practical things for a CPL testee to know. This is another one of those drifts that come from examiners who lack practical experience in the world outside an FTU.


As to Vref. Do you see it in the TC guide?
There is a reason they do not use the term.
The examiner is bound to follow the flight test guide. If you think the flight test standards are wrong, that’s a different matter.

Personally I think it’s worth noting the difference in sensible landing speeds between a lightly loaded 172 and a heavy one.

Why don’t you like the term Vref, and can you give us an acceptable alternative for “target airspeed on short final”? I don’t want to get snagged on terminology, so if you have something you prefer to call it...
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Re: Vref & The CPL flight test guide.

#10 Post by trey kule » Thu Feb 22, 2018 8:31 am

Ok...in your words..”The examiner...follow the flight test guide..”

Where in the guide for the CPL does it use the term Vref? I am not familiar with the CPL FTG, so I will stand corrected if the term is in there. If not, why is it being used? From having to almost literally teach CPL licensed pilots to think and fly from the failure of the FTUs ( not universal..some do a great job), to teach them the basics while focussing on the rather silly things, I have found that the best pilots are those that are able to differentiate between the common sense and the silly things.
Calculating Vref on a 172 or most every other basic trainer is a exercise in futility. And, as I suppose the justification for it will be that it demonstrates an understanding of the relationship between weight and approach speed, so it is a good thing to include in a flight test..

You mentioned something like 55-60:from a POH. I would rather a candidate explain to me when they would use 55 and when they would use 60, and then demonstrate in the air that they can actually fly that speed accurately on approach without treating the throttle like it was a pump on meth.

I dont see an issue with the FTG. I think the issue is examiners’ interpretation of it, and unfortunately, that has, and, I expect will always be a problem.
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Re: Vref & The CPL flight test guide.

#11 Post by trey kule » Thu Feb 22, 2018 8:57 am

You have control....

Did it occur to you that if you go below the recommended speeds to save a 100 or 200 feet on landing, that you may be bumping into other issues. For example, once you slip onto the backside of the power curve on an approach, you are putting yourself in a place you might not want to be if you need to extend the glide..

Not sure where you are flying that a 100 feet is going to make a difference, and so require a calculation.. IMO better to find a runway that does not require your super pilot skills...one hotter than average day, you may find that 100 feet was not enough. Or getting to the runway was a bit difficult using your calculated slower approach speed.

Just the words of a jaded old guy who has seen to many overly smart kids think their way into a problem
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Re: Vref & The CPL flight test guide.

#12 Post by rob-air » Thu Feb 22, 2018 9:44 am

1.3 VSO KCAS (max. gross wt.) x square root (landing weight/max. gross wt.)

there fixed it for you

as in if you are landing max. gross wt. no change in vref....

1.3 VSO KCAS (@2300lbs) x square root (2300lbs/2300lbs)

1.3 VSO KCAS (max. gross wt.) x square root (1)

1.3 VSO KCAS (max. gross wt.) x 1
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Re: Vref & The CPL flight test guide.

#13 Post by ahramin » Thu Feb 22, 2018 10:44 am

TopGun1234 wrote:
Wed Feb 21, 2018 11:27 pm
According to the TC flight test guide (https://www.tc.gc.ca/eng/civilaviation/ ... 72.htm#ex2) we have to calculate Vref as per the following formula:

1.3 VSO KCAS (max. gross wt.) x square root (landing weight/gross weight).


My question, is that last (gross weight) in the square root the permissible Max T/O weight of the aircraft or is it the T/O weight of the flight?

I can't seem to find any literature that goes into detail about this. Its not in FTGU.

Thanks,
I find this a bit of a strange question and the answers here so far just say max T/O weight without explaining why. It seems to me that it should be obvious from the question that the answer is Max T/O weight and not T/O weight of the flight. After all, what are we doing here? Adjusting the approach speed based on a lower stall speed. Lower than what? 1.3 VSO KCAS (max gross weight)). If the stall speed is based on max gross weight, then the reduction factor must also be based on max gross weight.
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Re: Vref & The CPL flight test guide.

#14 Post by youhavecontrol » Thu Feb 22, 2018 11:49 am

trey kule wrote:
Thu Feb 22, 2018 8:57 am
Did it occur to you that if you go below the recommended speeds to save a 100 or 200 feet on landing, that you may be bumping into other issues. For example, once you slip onto the backside of the power curve on an approach, you are putting yourself in a place you might not want to be if you need to extend the glide..

Not sure where you are flying that a 100 feet is going to make a difference, and so require a calculation.. IMO better to find a runway that does not require your super pilot skills...one hotter than average day, you may find that 100 feet was not enough. Or getting to the runway was a bit difficult using your calculated slower approach speed.

Just the words of a jaded old guy who has seen to many overly smart kids think their way into a problem
Vso is the stall speed at landing configuration, at max gross weight, with max forward C of G, with the power at idle.
Considering most landings are power-assisted, done without max forward C of G, and are almost always NOT at Max Gross weight... add to that the safety buffer that 1.3Vso gives, it's well within reason to expect a safe approach for short-field. (which is why it's a recommended method on the TC flight test guide) Of course, wind conditions can change the number, there's no arguing there.

The recommended approach speed published, as the POH says, is calculated at Max Gross, Max forward C of G, and allows for a max demonstrated crosswind of 20kts. That's at 55, which is only 5kts faster than the lowest Vref speed I've flown at... which I would never fly at in 20kts crosswind anyways.

About the 100' thing... On a hot day in a Diamond +5kts of airspeed translates to about 200' longer on the flare. The aspect ratio is very high and those things just float forever.
Yes, it has occurred to me that precision on landing is important, regardless of the fact I usually land on a 6000+ foot runway.

I'm not overly smart, but I'm not a kid either. I don't need to be schooled for defending the approach speed calculation on the TC exam.
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Re: Vref & The CPL flight test guide.

#15 Post by trey kule » Thu Feb 22, 2018 1:16 pm

Well then, I shall defer to your extensive aviation experience .

“About the 100' thing... On a hot day in a Diamond +5kts of airspeed translates to about 200' longer on the flare. The aspect ratio is very high and those things just float forever. “

Just to be clear..5kts represents about 10% of a Diamond’s approach speed. And, because of a pilot’s calculations, it is ok to deviate from the POH numbers, because, you know, those pesky manufacters really know nothing. So it is ok to drag it on the approach. If speed in the flare is an issue no sense in slowing it down just before crossing the fence.

Btw..wasnt schooling you. Just giving my opinion. Experience will eventually give you the wisdom.
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Re: Vref & The CPL flight test guide.

#16 Post by lhalliday » Thu Feb 22, 2018 2:28 pm

I learned to fly in Cherokees where final approach speed was 70 MPH IAS with full flaps, regardless of weight. You greased them in or smacked them on the numbers and they landed.

On the other hand, my Musketeer's POH says 79 MPH IAS. This is 1.3 Vso at maximum gross. If I land that fast when I'm light (as I usually am) I'm guaranteed a long, floaty, bouncy landing. If I correct Vref for weight I get a squeak of the stall warning right when the tires chirp. Perfect. I'm planning to update the checklist this spring and will include a Vref vs landing weight table.

The flight test guide also includes a note that you must be able to explain your actions if you deviate from SOPs. Somebody who is contemplating a CPL fight test should know what they need to do and when.

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Re: Vref & The CPL flight test guide.

#17 Post by youhavecontrol » Thu Feb 22, 2018 6:07 pm

trey kule wrote:
Thu Feb 22, 2018 1:16 pm
Well then, I shall defer to your extensive aviation experience .

“About the 100' thing... On a hot day in a Diamond +5kts of airspeed translates to about 200' longer on the flare. The aspect ratio is very high and those things just float forever. “

Just to be clear..5kts represents about 10% of a Diamond’s approach speed. And, because of a pilot’s calculations, it is ok to deviate from the POH numbers, because, you know, those pesky manufacters really know nothing. So it is ok to drag it on the approach. If speed in the flare is an issue no sense in slowing it down just before crossing the fence.

Btw..wasnt schooling you. Just giving my opinion. Experience will eventually give you the wisdom.
Opening with a line like, "Did it occur to you..." sounds like an attempt at schooling. ..but anyways, EVERYTHING I just mentioned in my previous posts comes from the recommended procedure in the CPL flight test guide. NOTHING I said before is outside of the recommended procedure from TC. Diamond gives one blanket approach speed for everything and it's not corrected for weight and they have no charts to calculate anything outside of max Gross Weight. Like I laid out before, 55kts is calculated for the most adverse flying condition within it's envelope.

"the recommended final approach speed, corrected for the actual landing weight in accordance with POH charts or tables (+10/–5 knots); or in the absence of charts or tables... 1.3 VSO corrected for the landing weight as determined in Ex.2B (+10/–5 knots)"

That's a quote right from the Flight Test guide.

You're reading way too much into what I've been writing and thinking I'm some sort of stupid cowboy or something. It's not like I said to fly the approach like that for a 5 mile final.
"Experience will eventually give you the wisdom." ...thanks, I'll log that away.
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Re: Vref & The CPL flight test guide.

#18 Post by AuxBatOn » Thu Feb 22, 2018 6:24 pm

jg24 wrote:
Thu Feb 22, 2018 2:17 am
MTOW of the aircraft as per POH
I would argue it is the Gross Weight for which Vso is valid. Generally speaking, but not always, it is published for MTOW, which is a worst case number.
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Re: Vref & The CPL flight test guide.

#19 Post by TopGun1234 » Thu Feb 22, 2018 7:57 pm

jg24 wrote:
Thu Feb 22, 2018 2:17 am
MTOW of the aircraft as per POH
Thanks for all the answers guys!
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