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Thread: Differential Braking on Quad PPC

  1. #1

    Differential Braking on Quad PPC

    Hi folk - this is a repost from my thread for building a powered parachute:

    The uncontrolled airport nearest me is not level. In fact, it goes downhill for half the length and uphill for the rest. So, I think I'll need brakes to control my PPC during takeoff and landing.

    I'm thinking about using differential braking on my quad to steer the PPC on the ground. I'd put the discs on the rear wheels of the quad. I'm thinking I'd use Azusa 8 inch wheels:

    http://www.aircraftspruce.com/catalo...zusa8astro.php

    With Shimano hydralic disc brakes and 8 inch (or smaller) discs:

    https://www.bikenashbar.com/cycling/...set-sh-blm8000
    https://www.bikenashbar.com/cycling/...md-adbr03-base

    I would prefer not to caster the front wheels - do you folks think this setup would provide enough ground steering?

    Thanks, Michael

  2. #2

    Join Date
    Jan 2012
    Posts
    271
    The quick answer is yes but the question implies that your understanding of PPC operations is not adequate for the design of a successful unit.

    First, will you be on concrete or grass? I am not convinced you will need any wheel brakes. A steerable wheel would be much more useful and that may not be required.

    Landings and aborted takeoffs are made by killing the engine so the lines do not contact the spinning prop and the wing provides more than enough stopping power. I have difficulty envisioning a field with enough slope to require brakes.

    I can see you may want the brakes in a big heavy high power (rotax 912) two seater but I was under the impression your plans were for more of a powered paraglider.

  3. #3
    It's not a grass strip - it's a paved runway. It actually had a large grassy strip on each side that has been used for paramotor launch. It's pretty hard to find a public grass field here in this part of NC, and there are tons of trees, so the airport is one of the places that I could use. I'd really have to search to find others. The brakes wouldn't necessarily be needed to stop the PPC initially, but they would prevent it from rolling downhill on the pavement once stopped and could provide steering to turn the cart away from the collapsing chute lines (by turning slightly to the side of the collapse).

    Besides, I'm basing my aircraft on the greeneagle, and it has a PPC version and also has a brake option (though not differential that I know of). I'm trying to think of a way to deal with PPC foot parachute control, ground steering, and braking control. Obviously the parachute and ground steering aren't accomplished with the same foot bar and need to provide the option to be independent. I think differential braking would give less turning rate than the normal PPG quad foot steering, but might still be good enough. Also, not having a steerable front end might make a bad landing more controllable since the front end wouldn't swivel with uneven touchdown and would pivot the whole cart around the first wheel to impact both vertically and horizontally.

  4. #4
    In addition, there's ground and taxi testing, and the wheel brakes would help with that too.

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