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'