Glide ratio with full brakes and side slip

On Wednesday, May 4, 2016 at 11:39:52 AM UTC-4, son_of_flubber wrote:
On Tuesday, May 3, 2016 at 12:30:09 AM UTC-4, George Haeh wrote:

With full brakes you can point reasonably
modern gliders at the threshold and come
down at a constant airspeed. Once you
level off the airspeed comes off rapidly
with full brake.

I've a friend who does this in a PW-6 from 1000 AGL on short final and have been in the back seat several times. I've done many steep finals at 70-80 knots due to turbulence, so I've given it some thought.

My understanding is that the flare expends the energy used to generate the lift that arrests the vertical speed, and that expenditure of energy reduces the horizontal speed in the flare. Do I have that right?

I teach that dive brakes/spoilers control the rate of descent(at constant air speed) and control rate of deceleration in and after the round out. The change in drag resulting from the lift to arrest the rate of descent is pretty much meaningless compared to the power of the air brakes.
UH

On Wednesday, May 4, 2016 at 12:58:11 PM UTC-4, wrote:

I teach that dive brakes/spoilers control the rate of descent(at constant air speed) and control rate of deceleration in and after the round out. The change in drag resulting from the lift to arrest the rate of descent is pretty much meaningless compared to the power of the air brakes.
UH

Let's say the glide ratio of a steep descent is 1:7 and IAS is 70 knots when entering the flare. So the vertical component of the airspeed before flare is 10 knots. The horizontal component of the airspeed before the flare is 60 knots. (Are these assumptions correct?) After the flare the vertical component of the airspeed goes to +/- zero. What is the horizontal airspeed at the end of the flare? 60 knots?

On Wednesday, May 4, 2016 at 1:01:08 PM UTC-5, son_of_flubber wrote:
On Wednesday, May 4, 2016 at 12:58:11 PM UTC-4, wrote:

I teach that dive brakes/spoilers control the rate of descent(at constant air speed) and control rate of deceleration in and after the round out. The change in drag resulting from the lift to arrest the rate of descent is pretty much meaningless compared to the power of the air brakes.
UH

Let's say the glide ratio of a steep descent is 1:7 and IAS is 70 knots when entering the flare. So the vertical component of the airspeed before flare is 10 knots. The horizontal component of the airspeed before the flare is 60 knots. (Are these assumptions correct?) After the flare the vertical component of the airspeed goes to +/- zero. What is the horizontal airspeed at the end of the flare? 60 knots?

Your airspeed vector during descent is the hypotenuse of an upside down right triangle. The long axis is the 7 horizontal component and the short axis is the 1 vertical component. The square of the hypotenuse is equal to the sum of the squares of the other two sides of that triangle.

My algebra tells me that at IAS 70 knots at the beginning of the flare, for a 7:1 descent rate, your vertical descent rate is around 9.9899 knots and your horizontal speed is around 69.2965 knots, not 60 knots.

If you are targeting 60 knots at the end of the flare, you need to burn off about 9 knots of excess horizontal velocity.

There are three states to consider
assuming constant wind:

Approach - Steady State if airspeed
constant and gravity vector at acute angle
to longitudinal axis and drag vector,

Round Out - my calculus is too many
decades stale, but note gravity vector
rotating to close to 90°.

Note the equations for transformation of
PE to KE do not take drag and lift into
account. Work is produced when force is
exerted over distance. Some of the papers
discussing windshear resort to differential
equations which would be needed to
analyze the round out.

Hold Off - Drag reducing airspeed, gravity
vector close to 90°.


At 15:39 04 May 2016, son_of_flubber
wrote:
On Tuesday, May 3, 2016 at 12:30:09 AM
UTC-4, George Haeh wrote:

With full brakes you can point
reasonably
modern gliders at the threshold and
come
down at a constant airspeed. Once you
level off the airspeed comes off rapidly
with full brake.

I've a friend who does this in a PW-6
from 1000 AGL on short final and have
been in the back seat several times. I've
done many steep finals at 70-80
knots due to turbulence, so I've given it
some thought.

My understanding is that the flare
expends the energy used to generate the
lift that arrests the vertical speed, and
that expenditure of energy
reduces the horizontal speed in the flare.
Do I have that right?

Too much math for me, but after 6000 hours of glider and taildragger ive learned land with as low energy as is safe given the wind/gust factor. Do whatever it takes to get down with a non-flat or non-super steep approach angle. That may take 1/2 spoilers, full spoilers or full spoilers and slip, doesnt really matter as long as the energy is kept low.
Dan

This I will agree with.

I consider needing, "full dive brakes and a full slip" to get down means:
- I waited too long to pick a good field
- I did NOT manage energy correctly during the pattern (regardless of pattern length).

Sorta edit, in the past, I was requested by CFIG's that were better than I to demonstrate a "max, hang it all out" decent.
Yes, we should ALL push the envelope at the home field now and then to prepare for when when poor judgement/planning requires superior skills in the real world.
What's easy for me may be beyond what you can do..............

On Friday, April 29, 2016 at 4:40:57 AM UTC-4, wrote:
I was wondering if anyone had an idea of what sort of glide ratio you get with full brakes and slide slip? An instructor used this to correct a very high approach but I was curious what the side slip adds to the descent rate.

Its a Forward Slip...Not a side slip...

Reminds me of a radio broadcast overheard, Pilot: "Tower Cessna November 123 with information alpha, inbound for landing" Tower: Cessna November 123 would that be a Cessna 150 or a Cessna Citation.


On Wednesday, June 8, 2016 at 11:06:06 AM UTC-7, 4881828 wrote:
On Friday, April 29, 2016 at 4:40:57 AM UTC-4, wrote:
I was wondering if anyone had an idea of what sort of glide ratio you get with full brakes and slide slip? An instructor used this to correct a very high approach but I was curious what the side slip adds to the descent rate.

Its a Forward Slip...Not a side slip...

Related, but sorta off topic.

I was flying a C-150 at a sorta busy regional airport with my CFI, I was number 7 in the pattern. Tower called me and asked if I could speed up because of a twin behind me, I answered, "cannot comply, full throttle as it is........ Permission to do a 360 to let the twin pass?" , reply was, "permission granted to do 360".

My instructor thought it was a good response by me to an odd situation.......

Originally Posted by 4881828

On Friday, April 29, 2016 at 4:40:57 AM UTC-4, wrote:
I was wondering if anyone had an idea of what sort of glide ratio you get with full brakes and slide slip? An instructor used this to correct a very high approach but I was curious what the side slip adds to the descent rate.

Its a Forward Slip...Not a side slip...

I've only ever done side slips. Maybe if I lived somewhere else in the world I may have been doing forward slips instead lol