Wheel brake effectiveness standards

Does anyone have any data, preferably quantitative, about what sort of braking performance is required? On the one hand, it would seem that effective braking is primordial for safe landing in the event of an outlanding, but on the other hand many gliders seem to have inadequate brakes, to put it charitably. And these brakes oftentimes are not easily actuated, for instance in a B-4 or L-23 where squeezing the wheel brake handle requires releasing the air brake. So it's fair to conclude that brake performance is (or was) a very distant thought.

I've looked through CS-22, but there are no given standards for wheel brakes, only a loose admonition that "If the main landing gear consists only of one or more wheels, the sailplane must be equipped with mechanical braking devices, such as wheel brakes."

In particular, I'm trying to calculate how much energy the brakes need to absorb. An easy analysis is simply calculating the kinetic energy of the plane when landing 5kts faster than stall (since it's hard to glue the plane to the ground when going much faster). However, this grossly underestimates the amount of energy dissipated through rolling and air resistance. It also doesn't account for what might occur if brake forces were so high that the plane tips forward and skids on its nose.

Still, since the consequence of underspeccing the brakes is brake fade and glazing, and the consequence of overspeccing is additional weight and cost, it's worth trying to right-size the system.

Does anyone have any domain specific experience they could share?

On Friday, October 16, 2020 at 10:55:16 PM UTC-4, Kenn Sebesta wrote:

Does anyone have any domain specific experience they could share?


Any properly adjusted brake will work well enough to stop your glider.

I fly an LS 1-f with the brakes and spoilers on the same control. The spoilers will open fully and a little more pull on the spoiler control will actuate the brakes. I have the standard drum brakes and I can brake hard enough to cause the nose of my glider to pitch forward and rub on the ground. I do not do this very often.

My point is, there is enough brake power to stop your glider without over thinking this. Proper maintenance is the most important. You need to adjust the brakes to work as intended.

I'm pretty sure that in some cerfification standard there is this specification: "pilot should be able to move some lever is the cockpit marked as wheel brake, and preferably hear scratching sound while pulling it, so that he feels like he is applying wheel brake. No decelaration is needed, however."

At least this is how they were made for decades, before someone invented hydraulic disc brakes.

krasw wrote on 10/17/2020 6:50 AM:
I'm pretty sure that in some cerfification standard there is this specification: "pilot should be able to move some lever is the cockpit marked as wheel brake, and preferably hear scratching sound while pulling it, so that he feels like he is applying wheel brake. No decelaration is needed, however."

At least this is how they were made for decades, before someone invented hydraulic disc brakes.

You describe my experience with my Std Cirrus in the early '80s :^)

I am told owners now know much more about improving the braking ability and maintaining it. If
the OP opts for a Std Cirrus, he should contact other owners, and take their brake advice.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

The Tost drum brake on my PIK20D, if you turned the drum, relined the shoes and had them arced perfectly to the drum, and carefully assembled everything clean and neat, would stop the glider (or put it on its nose). For the first flight. By the fourth or fifth flight, just adequate. By the tenth flight, you'd be better off opening the canopy and dragging your foot. In contrast, on my ASH26, the Cleveland disk brake will skid the wheel flight after flight, year after year. If I have the choice of a couple of extra pounds to overkill the brake, or dragging my foot to stop, give me the former.

On Saturday, October 17, 2020 at 6:50:35 AM UTC-7, krasw wrote:
I'm pretty sure that in some cerfification standard there is this specification: "pilot should be able to move some lever is the cockpit marked as wheel brake, and preferably hear scratching sound while pulling it, so that he feels like he is applying wheel brake. No decelaration is needed, however."

At least this is how they were made for decades, before someone invented hydraulic disc brakes.

On Friday, October 16, 2020 at 10:55:16 PM UTC-4, Kenn Sebesta wrote:
Does anyone have any data, preferably quantitative, about what sort of braking performance is required? On the one hand, it would seem that effective braking is primordial for safe landing in the event of an outlanding, but on the other hand many gliders seem to have inadequate brakes, to put it charitably. And these brakes oftentimes are not easily actuated, for instance in a B-4 or L-23 where squeezing the wheel brake handle requires releasing the air brake. So it's fair to conclude that brake performance is (or was) a very distant thought.

I've looked through CS-22, but there are no given standards for wheel brakes, only a loose admonition that "If the main landing gear consists only of one or more wheels, the sailplane must be equipped with mechanical braking devices, such as wheel brakes."

In particular, I'm trying to calculate how much energy the brakes need to absorb. An easy analysis is simply calculating the kinetic energy of the plane when landing 5kts faster than stall (since it's hard to glue the plane to the ground when going much faster). However, this grossly underestimates the amount of energy dissipated through rolling and air resistance. It also doesn't account for what might occur if brake forces were so high that the plane tips forward and skids on its nose.

Still, since the consequence of underspeccing the brakes is brake fade and glazing, and the consequence of overspeccing is additional weight and cost, it's worth trying to right-size the system.

Does anyone have any domain specific experience they could share?

... for instance in a B-4 or L-23 where squeezing the wheel brake handle requires releasing the air brake.
I flew my club's B4 a bit and as far as I remember, the wheel brake was actuated by a bike-brake type handle on the stick, so one didn't have to release the spoiler handle.
Anyhow, I owned a H301 with a low serial number. It had the hub of a German post-WW-II Zündapp moped wheel, which was somewhat borderline for stopping a mass of 300kg from 80km/h. However, if properly cared for and adjusted, I could lock up the wheel on grass or make the glider lift the tail on hard surfaces.
The old Schleicher gliders Ka6, Ka8, etc. had a 'steel band over the tire' brake, which worked ok in dry conditions but were useless on wet grass, yet they were certified gliders. IIRC, the POH called it an 'emergency' brake, i.e. only use them if you are about to go through a fence.
I would call 'locking up the wheel at touchdown-speed and MTOW' the upper spec limits of any requirement.
Unless your glider is equipped with an ABS system, locking up the wheel (or wheels in my case) doesn't make you stop any faster but only produces flat-spots on the tread.
The old drum brakes are still adequate as built but require some more attention than the modern hydraulic disc brakes and that may be the core of their bad reputation.

Uli
'AS'

On Saturday, October 17, 2020 at 10:29:03 AM UTC-4, AS wrote:
I flew my club's B4 a bit and as far as I remember, the wheel brake was actuated by a bike-brake type handle on the stick, so one didn't have to release the spoiler handle.

If you think about the ergonomics of that handle, you need to release pressure on the airbrake handle in order to open your hand and warp your fingers around the wheel brake lever. It's extremely unergonomic to actuate the two at the same time with any degree of precision, which is what leads me to believe that they didn't really design the system to have great braking performance. It strikes me more like an afterthought, something they threw in so that we could control how far we roll once we're below 10km/h.

The old Schleicher gliders Ka6, Ka8, etc. had a 'steel band over the tire' brake, which worked ok in dry conditions but were useless on wet grass, yet they were certified gliders. IIRC, the POH called it an 'emergency' brake, i.e. only use them if you are about to go through a fence.

This is a great data point!

I would call 'locking up the wheel at touchdown-speed and MTOW' the upper spec limits of any requirement.

Immediately on touchdown there's very little force on the wheel because most of the plane's weight is still carried by lift. Do you mean that you should be able to lock it up at any point during touchdown?

On Saturday, October 17, 2020 at 12:01:39 PM UTC-4, Kenn Sebesta wrote:
On Saturday, October 17, 2020 at 10:29:03 AM UTC-4, AS wrote:
I flew my club's B4 a bit and as far as I remember, the wheel brake was actuated by a bike-brake type handle on the stick, so one didn't have to release the spoiler handle.

If you think about the ergonomics of that handle, you need to release pressure on the airbrake handle in order to open your hand and warp your fingers around the wheel brake lever. It's extremely unergonomic to actuate the two at the same time with any degree of precision, which is what leads me to believe that they didn't really design the system to have great braking performance. It strikes me more like an afterthought, something they threw in so that we could control how far we roll once we're below 10km/h.

The old Schleicher gliders Ka6, Ka8, etc. had a 'steel band over the tire' brake, which worked ok in dry conditions but were useless on wet grass, yet they were certified gliders. IIRC, the POH called it an 'emergency' brake, i.e. only use them if you are about to go through a fence.

This is a great data point!

I would call 'locking up the wheel at touchdown-speed and MTOW' the upper spec limits of any requirement.

Immediately on touchdown there's very little force on the wheel because most of the plane's weight is still carried by lift. Do you mean that you should be able to lock it up at any point during touchdown?

... you need to release pressure on the airbrake handle in order to open your hand and warp your fingers around the wheel brake lever. It's extremely unergonomic to actuate the two at the same time with any degree of precision, which is what leads me to believe that they didn't really design the system to have great braking performance.

Hi Kenn - not sure I understand! In the B4 and any other glider I am familiar with, the spoiler handle is on the left side and there is no brake actuation via the spoiler handle - not by pulling it back fully or by a brake lever on that handle. The right hand is on the stick and the brake handle is mounted on it to the front of it. It does not take a lot of dexterity of the hand to wrap two or three fingers around the brake handle and squeeze it while continuing to hold the stick back.

Do you mean that you should be able to lock it up at any point during touchdown?
No - only after the wheel(s) are firmly planted on terra firma can any meaningful brake action begin. That's why the big planes have 'squat switches', which look at the condition of the landing gear struts/dampers and only allow braking to start in earnest when they are activated, i.e. after the landing gear is 'loaded'.

Uli
'AS'

On Sat, 17 Oct 2020 13:51:16 -0700, AS wrote:

Hi Kenn - not sure I understand! In the B4 and any other glider I am
familiar with, the spoiler handle is on the left side and there is no
brake actuation via the spoiler handle - not by pulling it back fully or
by a brake lever on that handle. The right hand is on the stick and the
brake handle is mounted on it to the front of it. It does not take a lot
of dexterity of the hand to wrap two or three fingers around the brake
handle and squeeze it while continuing to hold the stick back.

Most of the single seaters I've flown (Libelle, Discus 1, Pegase 90 use
that arrangement, but I flown a few fairly common types that don't:

- ASK-21: the wheel-brake is applied by pulling the air-brake handle back
past the (spring-loaded) fully air-brake stop. Both brakes work well.

- SZD Puchacz: the air-brake handle is too far back which makes it
awkward enough that some people can't get full air-brake, not that this
is a problem because the air-brakes and HUGE, fully speed-limiting and
tend to stay where you leave them. Just as well because the wheel brake
is a black knob on the left just in front of the air-brake handle's
forward position. Both brakes work well.

- the SZD Junior originally has a bicycle handbrake type wheel-brake but
it was on the air-brake handle rather than the stick, where its pivot
severely weakened the air-brake control assembly. There was an AD to fix
this by deleting the bicycle handbrake control and connecting the wheel
brake to the air-brake handle so that pulling against the stop with the
brakes fully out applies the wheel-brake.

- IIRC the Grop G.103 Acro also has the wheel-brake connected to the
air-brake lever but its been a long time since I flew a G.103 and our
club no longer has one so I can't check.

And lets not forget the much older gliders with nose skids (Slingsby
T.21, Schweitzer 2-33, unmodified ASK-13s*) which don't have a wheel-
brake: you just put the nose skid on the ground and maybe push on the
stick a bit to make them stop quicker.

* most of the K-13s I've flown were retro-fitted with a nose-wheel and
wheel-brake.


--
Martin | martin at
Gregorie | gregorie dot org

On Saturday, October 17, 2020 at 5:51:58 PM UTC-4, Martin Gregorie wrote:
On Sat, 17 Oct 2020 13:51:16 -0700, AS wrote:

Hi Kenn - not sure I understand! In the B4 and any other glider I am
familiar with, the spoiler handle is on the left side and there is no
brake actuation via the spoiler handle - not by pulling it back fully or
by a brake lever on that handle. The right hand is on the stick and the
brake handle is mounted on it to the front of it. It does not take a lot
of dexterity of the hand to wrap two or three fingers around the brake
handle and squeeze it while continuing to hold the stick back.

Most of the single seaters I've flown (Libelle, Discus 1, Pegase 90 use
that arrangement, but I flown a few fairly common types that don't:

- ASK-21: the wheel-brake is applied by pulling the air-brake handle back
past the (spring-loaded) fully air-brake stop. Both brakes work well.

- SZD Puchacz: the air-brake handle is too far back which makes it
awkward enough that some people can't get full air-brake, not that this
is a problem because the air-brakes and HUGE, fully speed-limiting and
tend to stay where you leave them. Just as well because the wheel brake
is a black knob on the left just in front of the air-brake handle's
forward position. Both brakes work well.

- the SZD Junior originally has a bicycle handbrake type wheel-brake but
it was on the air-brake handle rather than the stick, where its pivot
severely weakened the air-brake control assembly. There was an AD to fix
this by deleting the bicycle handbrake control and connecting the wheel
brake to the air-brake handle so that pulling against the stop with the
brakes fully out applies the wheel-brake.

- IIRC the Grop G.103 Acro also has the wheel-brake connected to the
air-brake lever but its been a long time since I flew a G.103 and our
club no longer has one so I can't check.

And lets not forget the much older gliders with nose skids (Slingsby
T.21, Schweitzer 2-33, unmodified ASK-13s*) which don't have a wheel-
brake: you just put the nose skid on the ground and maybe push on the
stick a bit to make them stop quicker.

* most of the K-13s I've flown were retro-fitted with a nose-wheel and
wheel-brake.


--
Martin | martin at
Gregorie | gregorie dot org

and SZD-55 wheel brake is at the rear of spoiler handle travel as well.