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I got an airspeed indicator off ebay and plan on sending it off to be overhauled. Part of the overhaul will include putting custom markings on the face to reflect the Bearhawk speeds. I was looking through old emails and what Russ Erb had put on his airspeed indicator. The full-flap stall speed (bottom of the white arc) is 45MPH/39KTS. The clean, no flap stall speed (bottom of the green arc) is also 45MPH/39KTS. Is this true? It seems the full flap stall speed should be less than the clean stall speed. Any insights?
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Of course each airplane will vary according to weight, rigging, etc. but my O-360 equipped Bearhawk, weighing 1300 lbs stalled as follows: Clean = 50 MPH IAS 15 degrees flaps = 50 MPH IAS 25 degrees flaps = 48 MPH IAS 40 degrees flaps = 45 MPH IAS-
In flight testing my Patrol I had similar results. I did a series of stalls and found it indicated 50mph clean, and around 48mph with any amount of flaps. I was quite surprised at the little difference when extending flaps. So I had another very experienced pilot do the full series of stalls and he found exactly the same thing. The system is a Dynon HDX with the fancy pitot tube with the second hole for AOA. My Patrol is 1200lbs empty and has the O-360.
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I think this may be one of those "measure with a micrometer, cut with an ax" situations. At such low speeds, the ASI is not going to be very accurate, and if things are going right, you aren't going to be looking at it anyway!Comment
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We have confirmed with GPS and we see anywhere from 33* kts to 42 kts depending on the weight. *we have vortex generators installed
Our usual final speed is 40KIAS with 2 pax and 50% fuel, touchdown about 35-ish I guess, but I am never looking.Comment
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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. -
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. -
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, 04:48 PM.
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Thanks guys! This gives me what I need to go forward.Comment
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Originally posted by Battson View Post
How do you ensure totally calm winds when you do this? That seems like a huge error/unknown when making airspeed measurements with a ground speed tool. Do you do it in multiple directions and average?Comment
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When the GPS says 50kts GS and the ASI says 50 KTAS coincidentially, same again at 45kts etc, as you approach the stall, you can reasonably assume the GS is giving you a consistent reading with the ASI. Good enough for my purposes anyway. In my machine, they start to diverge below 45kts as the AoA gets larger.
My avionics are constantly monitoring the wind in the same way, which it displays on screen.
PS. For me, the last ~5 kts between the stall buzzer kicking in and the actual onset of the stall is the "expert zone" for approach speeds. I rarely venture into that region, unless I am really forced into pushing the limits for some reason - which only happens on a perfect weather day when I am very, very current.Last edited by Battson; 09-24-2014, 05:42 PM.Comment
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If you fly three courses 90 degrees apart and record gps groundspeeds for each, it is a matter of math to determine the error.Comment
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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:
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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.Comment
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So you have VGs installed right? I would love to see your cockpit video proof too!
Sent from my XT1031 using Tapatalk
Mark
Scratch building Patrol #275
Hood River, ORComment
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Scratch building Patrol #254Comment
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Haha - I know you believe me, but here's the evidence:Originally posted by Chewie View Post
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.Comment
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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.Comment
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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.Originally posted by jaredyates View Post
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.
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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
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