Approach speeds
John Bartels
I've got a new question / topic.
Approach speed is predicated on lots of things. As cowboy will tell us,
there are certain legal requirements, but if we can forget them for a minute
(and they aren't always the deciding factor), the question is this:
" What is a good approach speed?".
Got that one worked out...ok. Now for the next part.
"Having found our ideal approach IAS, would it be changed if we had
speedbrakes in or out?"
The only type of speedbrakes I'm talking about here are the type that DON'T
affect the airflow over the wing. 767 type spoilers are out...but, what
about the split type on the tail of the 146 or the F28.
Oh, and if there is a change to the ideal approach speed, then why?
JB
Graeme Hogan
Bear in mind the approach speed has a bit to do with if you need to do a
go-around.
The beauty of speed brakes, is you can approach at your ideal speed, but
have your engines better spooled up, in other words, instead of you having
1/3 throttle, you have 2/3.
John Bartels wrote in message
<7c5a2v$diu$1...@reader1.reader.news.ozemail.net>...
Chris Furse
a great deal of additional power (it is usually pretty high any way). But they
will tend to shift the total drag curve towards lower speeds, this may mean the
difference between the approach speed being on the "front side" rather than the
"back side" of the drag curve. Speed control is somewhat easier when flying in
an envelope of speed stability (ie if speed increases, total drag increases
rather than if speed increases total drag decreases). So, from a handling
qualities view, one may be able to use a lower approach speed with speed brakes
extended (provided this is still above regulatory minimum speeds).
For JB, why don't you start a thread on why some jets have 1.3 Vs approach
speeds and others a lesser factor, ie the difference between traditional stall
speeds and 1G stall speeds.
regards,
cjf
ps out of circulation for some months from tomorrow, so can't observe the
thread.
mee...@hotmail.com
"John Bartels" <john_b...@NOSPAM.hotmail.com> wrote:
> Ok guys, we've had plenty of fun with stalling over the past week, but now
> I've got a new question / topic.
>
> Approach speed is predicated on lots of things. As cowboy will tell us,
> there are certain legal requirements, but if we can forget them for a minute
> (and they aren't always the deciding factor), the question is this:
> " What is a good approach speed?".
>
> Got that one worked out...ok. Now for the next part.
>
> "Having found our ideal approach IAS, would it be changed if we had
> speedbrakes in or out?"
>
> The only type of speedbrakes I'm talking about here are the type that DON'T
> affect the airflow over the wing. 767 type spoilers are out...but, what
> about the split type on the tail of the 146 or the F28.
>
> Oh, and if there is a change to the ideal approach speed, then why?
>
> JB
Awww JB, I'd rather talk about stalls!!!
Anyway, can't comment on the 146, but the F28 with speed-brake extended
had no requirement for a change in approach speed.
TTS (Vref) was calculated for the selected flap setting and weight, plus
there were specified additives for any wind gusts.
For one particular company I am aware of, speed brake extension was
mandatory for a wet runway landing, and retraction was automatic in the
event of a go-around. Obviously, increased thrust was required on the
approach due to the increased drag.
Regards,
Meeka69.
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James Gray
> " What is a good approach speed?".
If none is published - 1.3Vs
> "Having found our ideal approach IAS, would it be changed if we had
> speedbrakes in or out?"
Nope, you'd just come down faster (ie, RoD) and steeper (and make a
bigger hole in the ground).
> Oh, and if there is a change to the ideal approach speed, then why?
Not sure if you are referring to the "speedbrake" thing or other
operational requirements. Personally, I try and use less flap and about
an extra 7kts in a C210 for any crosswind over about 7-10kts. Provided
I've got enough runway that is.
From my gliding days, we didn't alter the approach speed with brakes out
but to maintain an optimum approach speed you had to adopt a much lower
nose attitude - speed stayed the same but we could descend awfully steep
and the RoD was up around 1000-1500fpm! Put the brakes away, raise the
nose and all was back to it's normal docile self.
John Bartels
>>I've got a new question / topic.
>>
>>Approach speed is predicated on lots of things. As cowboy will tell us,
>>there are certain legal requirements, but if we can forget them for a
>minute
>>(and they aren't always the deciding factor), the question is this:
>>
>>
>>speedbrakes in or out?"
>>
DON'T
>>affect the airflow over the wing. 767 type spoilers are out...but, what
>>about the split type on the tail of the 146 or the F28.
>>
>>
>>
>
>
Graeme Hogan wrote in message <7c5adr$r6g$1...@otis.netspace.net.au>...
>The approach speed should still be the same.
>Bear in mind the approach speed has a bit to do with if you need to do a
>go-around.
>The beauty of speed brakes, is you can approach at your ideal speed, but
>have your engines better spooled up, in other words, instead of you having
>1/3 throttle, you have 2/3.
>
James Gray wrote in message <36E71605...@ozemail.com.au>...
Ah, now gliding doesn't really count here James. I should have stated that
we want to maintain the normal approach path (let's just assume 3 degrees
across the board), and the standard flap settings.
All that is different is the speedbrakes being open or closed.
Yes, the extra drag will allow the engines to be spooled up, so that is a
potential plus, but not pertinent to the question (although some older a/c
could even fly approaches with drag chutes deployed to get the engines into
a reasonable range).
As for 1.3 Vstall. Nice number but somewhat arbitrary...
Apart from coverage of the rules, what should an 'ideal' approach IAS
provide?
Have a think about the drag curve. Where do we fly approaches, and why?
which position on the curve? And would the speed brakes change this....
JB
Charles Hellawell
It is used to calculate your approach speed and also identify your approach
category for instrument approaches. I do know that in the US, it is a
regulator speed (recommended for calculating your approach speed). Hence, if
they know that you are flying a single engine aircraft, you will always fall
into the same category, as all single engine aircraft are required to have a
stall speed below (I believe it is 69knots to meet FAA certification).
Apart from coverage of the rules, what should an 'ideal' approach IAS
provide?
***To me, I believe an ideal appraoch airpseed should give me "positive"
control of the aircraft in high wind situations, especially when low level
wind shear is present, and allow me to transition from an instrument
approach to visual when at minimums in a fairly relaxed pace, not "too"
rushed. So my approach speed does vary depending on the conditions of
flight, and the length of the runway. Who is going to fly a 3degree approach
when you have a short runway, heavy plane and want to clear an obstacle? Not
me, I prefer to come in with everything out, same speed, steeper angle and
stop short!!!
Have a think about the drag curve. Where do we fly approaches, and why?
which position on the curve? And would the speed brakes change this....
***As far as what I can read into your questions here, you are digging at
where about on a L/D curve the aircraft is flying when it is flying at an
approach speed (again calculated about 1.3 Vs). That puts you in the L/D Max
position, or best glide position (in most general aviation aircraft, as far
as big ones, I couldn't speak for those) where your drag is the least.
Putting out your speed brakes, creates excess parasite drag, so to maintain
your approach speed, would require more thrust (power), and move you back
towards L/D max.
My thoughts at 4am with 4 hours of sleep and no coffee yet, so if it makes
no sense, let me reread what I wrote when I get home tonight...
Cheers,
Charles.
Cameron Hines
> Have a think about the drag curve. Where do we fly approaches, and why?
> which position on the curve? And would the speed brakes change this....
>
Drag only speedbrakes would reduce the min drag speed and therefore
allow a slower approach speed.
Regards
Cameron
Wayne Rohde
On Wed, 10 Mar 1999 19:26:06 +1100, "John Bartels"
<john_b...@NOSPAM.hotmail.com> wrote:
-->Approach speed is predicated on lots of things. As cowboy will tell us,
-->there are certain legal requirements, but if we can forget them for a minute
-->(and they aren't always the deciding factor), the question is this:
--> " What is a good approach speed?".
1.3Vs is a good, safe number. We use 1.2Vs for short field
landings but you have to be right on the numbers or you are set up for
a heavy landing.
--> "Having found our ideal approach IAS, would it be changed if we had
-->speedbrakes in or out?"
-->
-->The only type of speedbrakes I'm talking about here are the type that DON'T
-->affect the airflow over the wing. 767 type spoilers are out...but, what
-->about the split type on the tail of the 146 or the F28.
I would suggest that an increase in approach speed would be
desirable, not for the approach itself but for the flare. F28s use
this technique in PNG as is allows them to get higher RoD to get into
some of the less accessible airfields. However if you don't raise the
approach speed, when you flare, the increase in drag will cause a
large deceleration prior to touchdown. If you get it wrong (by even
the slightest margin) then you would end up slamming it in.
Just my 2 cents worth.
Regards,
Wayne...
"I didn't spend 7 years in Evil Medical School to be
called Mr Evil!" - Dr Evil, Austin Powers...
John Bartels
Cameron Hines wrote in message <36E955...@ozemail.com.au>...
Correct.....
The initial question took away any legal requirements (the 1.3 stuff).
Most approach speeds are slightly faster than min drag. That way the a/c is
speed stable. Flying at min drag would mean that there would be a drag
increase for any speed variation - okay if slightly fast, but not too good
if you've slowed. And flying on the back side of the drag curve is hard
work, and something to leave to the delta drivers....
Drag only speed brakes increase the form drag, and have no effect on induced
drag. The overall drag curve will be greater (i.e. more drag everywhere),
but the min drag airspeed will be lower. So, if your target airspeed was
just slightly faster than min drag, and the min drag point is now at a lower
airspeed, you could reduce your approach airspeed....
JB
John Bartels
> 1.3Vs is a good, safe number. We use 1.2Vs for short field
>landings but you have to be right on the numbers or you are set up for
>a heavy landing.
Ah, but why is is a good safe number? Why not 1.1, or 1.5 Vstall. Why not
min drag, or min drag times 1.1?
>
> I would suggest that an increase in approach speed would be
>desirable, not for the approach itself but for the flare.
Not really answering the question Wayne. Bet your teachers loved you....
Anyway, this can be countered by simply leaving the power on until
touchdown.
>F28s use
>this technique in PNG as is allows them to get higher RoD to get into
>some of the less accessible airfields. However if you don't raise the
>approach speed, when you flare, the increase in drag will cause a
>large deceleration prior to touchdown. If you get it wrong (by even
>the slightest margin) then you would end up slamming it in.
Flying a steeper than normal path is a different problem entirely. The
question is about flying the normal approach path, but with speedbrakes
extended.
JB
mee...@hotmail.com
JB and Cameron,
I agree the minimum drag speed is reduced with speed brakes out.
Not sure though about the lower approach speed.
The approach speed with at least two F28 local operators is the same,
speed brakes in or out.
Speed brake use for landing is optional, though it is required for a
wet runway landing.
An F28 operation I am aware of in Europe uses the brake for ALL landings,
but if for some reason it is not used, the speed is then unchanged.
Perhaps the unchanged speed is simply to "keep it simple"; the last
thing you would need is a re-calculation of Vref after a late decision
to use the brake!
As you are aware, CAO 20.7.1B lists the landing requirements - Vref
is based on 1.3 Vs for the configuration and landing weight - speed
changes (if any) with speed-brake use are certainly not covered in that CAO.
With the F28 speed brake extended, stall speed would be the same, so
perhaps CASA also simply like to "keep it simple!!"
It all makes for an interesting discussion though!
John Bartels
>
>JB and Cameron,
>
>I agree the minimum drag speed is reduced with speed brakes out.
>Not sure though about the lower approach speed.
>
>The approach speed with at least two F28 local operators is the same,
>speed brakes in or out.
>Speed brake use for landing is optional, though it is required for a
>wet runway landing.
>An F28 operation I am aware of in Europe uses the brake for ALL landings,
>but if for some reason it is not used, the speed is then unchanged.
>
>Perhaps the unchanged speed is simply to "keep it simple"; the last
>thing you would need is a re-calculation of Vref after a late decision
>to use the brake!
>
>As you are aware, CAO 20.7.1B lists the landing requirements - Vref
>is based on 1.3 Vs for the configuration and landing weight - speed
>changes (if any) with speed-brake use are certainly not covered in that
CAO.
>With the F28 speed brake extended, stall speed would be the same, so
>perhaps CASA also simply like to "keep it simple!!"
>It all makes for an interesting discussion though!
>
>Regards,
>Meeka69.
The aim of this question was simply to come up with an unusual, but
solveable aerodynamic problem. The first thing that I did was to remove the
legal ramifications...but they kept on reappearing in the musings.
The a/c that I was using has an approach speed of roughly 115 knots, a stall
speed of 100 knots, and a min drag (in the landing configuration) of 225. An
F28 it isn't...
JB