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Bearhawk Stall Speeds

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  • Battson
    replied
    Since we installed the longer wingtips (per Bob's specification) we have been consistently seeing stalls at 28 KIAS for light to moderate loads. At heavier loads stalls are around 31 to 33 KIAS.
    This represents a few knots improvement over the stock wingtips.
    Wind has been a problem lately so I can't confirm ground speeds, but I am expecting to see a few knots improvement there too.

    Leave a comment:


  • Battson
    commented on 's reply
    Some subsequent testing suggests there is at least a few knots of error at very high AoA (16 degrees plus).
    The error seems to vary depending on the day...

    So for clarity's sake, all the numbers discussed above should be considered as what they are - IAS.

  • Battson
    commented on 's reply
    I checked with Dynon about their Pitot design. Their short answer is yes - it's less susceptible to those errors than garden-variety pitot tubes.

  • Battson
    commented on 's reply
    For safety's sake - I wanted to clarify that I didn't go out and try this cold-turkey on Saturday.

    I've been working up to this kind of slow approach and landing, with practice at a safe altitude over the last 18 months. I've been doing far more extreme manoeuvres to find the limits of the wing at various weights - manoeuvres like medium turns, abrupt elevator movements, and unbalanced flight near or at the critical angle of attack. I have also been experimenting in light to moderate turbulence.

    If you want to see how slow you can fly, I strongly suggest doing a lot of practice above 3000ft AGL first

  • Battson
    replied
    Originally posted by jaredyates View Post
    Does the video show ground speed? I'd be curious to see how much error your ASI has at those speeds. Most planes start to get pretty inaccurate at such high AOAs.
    The Dynon AoA Pilot has another dynamic pressure port angled 45 degrees downward on the pitot mast, which uses to measure differential pressure and determine AoA. So that may help their system avoid that angle problem? You can see in the video that the AoA is about 16-17 degrees.

    In that flight regime I wasn't able to focus on each instrument and compare them carefully, as well as holding the camera and the plane steady. I did look for error briefly and didn't notice any significant difference. It was certainly one of those rare perfect days when you can truly say there was nil wind near the ground.

    Upon one landing I did have a one-wing stall as I pulled the stick hard back, just as the tailwheel touched down (first), which led to a wing dropping. The left wheel fell about 6" to 12" onto the grass. The suspension and big tires soaked it up no problem in this case, but it certainly kept me focussed outside the cockpit.

    Leave a comment:


  • jaredyates
    replied
    Does the video show ground speed? I'd be curious to see how much error your ASI has at those speeds. Most planes start to get pretty inaccurate at such high AOAs.

    Leave a comment:


  • Battson
    replied
    Originally posted by Chewie View Post
    So you have VGs installed right? I would love to see your cockpit video proof too!

    Sent from my XT1031 using Tapatalk
    Haha - I know you believe me, but here's the evidence:

    It was possible to hold her there steady, for longer than I do in the video, but I didn't like distracting myself with the video on approach to land.

    Yes we have the VGs installed. I detailed my install location and results in the VGs thread if you are interested.

    Leave a comment:


  • DRLPatrol
    replied
    Originally posted by Chewie View Post
    ....I would love to see your cockpit video proof too!
    Mark,are you saying that you don't believe him

    Doug

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  • Chewie
    replied
    So you have VGs installed right? I would love to see your cockpit video proof too!

    Sent from my XT1031 using Tapatalk

    Leave a comment:


  • LukeS
    replied
    Wow! I would say unbelievable, but I just watched the video. That's some serious "pucker factor" STOL performance. I would never have thought the four-place could fly so slow. Thanks for the video.

    Leave a comment:


  • Battson
    replied
    Flying very lightly loaded yesterday, although not extraordinarily light, I was able to keep flying with full control at down to 29-30 KIAS. I was very surprised as I was sure 33kts was the limit. I have cockpit video proof too

    I practiced a number of approaches and touchdowns at this speed, the weather was perfectly still making such speeds possible near the ground. It certainly makes a difference compared to carrying a my usual safety margin. It would be possible to land a much smaller spot at that speed, but of course there is no room for error and weather needs to be dead calm.

    Unbeknownst to me, I was being filmed from the ground and I happened upon the video by chance:
    Last edited by Battson; 07-26-2015, 04:31 PM. Reason: Change URL to video link

    Leave a comment:


  • Battson
    commented on 's reply
    Thanks for the kind words. I am using the STOLspeed VGs, which just adhere with a simple 3M sticker. You install over the paint, this is more than strong enough even with my crumby paint.
    The VGs are also kinda flexible and have rounded edges, which helps if you ever had to refuel without a step ladder.
    The important part is the distance from the LE, to ensure they are fully exposed to the airflow when the wing is at the stall AoA. There is a thread on here which discusses this location, a Google search including "site:bearhawkforums.com" will find it.
    Last edited by Battson; 11-09-2014, 03:48 PM.

  • LukeS
    commented on 's reply
    So, sorry for the Spanish inquisition here, but do you remember which VGs you went with? Also is it preferred to install them before painting so they're stuck to the metal instead of just held on by whatever bond strength the paint has? I think I've been watching your youtube (whosaidyoucandance?) videos, and the performance is pretty impressive. If these are yours, thanks for posting them. They're great motivation.

  • Battson
    commented on 's reply
    Our stall speed reduced about 3 kts, but the approach speed came down a lot more. Probably 5-8 kts while maintaining the same AoA margin above the stall.
    They were definitely worthwhile for the kind of flying I do.

    The benefits are heavily dependent on getting the placement right. Some BH pilots have installed VGs and seen no measurable improvement.

  • LukeS
    commented on 's reply
    Do you know what your stall speeds were before adding the VGs? Were they worthwhile in your opinion?
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