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rickofudall
Joined: 19 Sep 2009
Posts: 1392
Location: Udall, KS, USA
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 Posted: Sat Jun 11, 2011 11:10 am Post subject: Four wingtips are NOT better than two |
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Yesterday morning I finished lowering the front of the engine to change the thrust line on the Mk IIIX. By reversing the forward Lord mount I was able to change the thrust angle by 5.25 degrees without having to make any new parts. Of course this meant I had to lower the radiator, too, but I was able to modify parts to do that, rather than make new. I started just after dawn on the radiator parts and by 9:00 am everything was reassembled and ready to go. The wind had stayed light so I taxied out, let the engine warm up and took off. Much less back pressure was required than on the previous flight on Tuesday, but the airplane was still pitch divergent even with full trim. I was comfortable enough with it, though, that I thought I'd try slowing down to see how optimistic the airspeed indicator is as the aircraft approached a stall.
At 50 something mph the aircraft broke to the right. I knew the ASI was reading on the high side, but I hadn't expected quite that high, so I didn't catch the exact reading. The aircraft's stall characteristics were so unlike my Mk IIIC that I thought I had done something wrong, so I tried it again. This time, at 53 mph, the aircraft broke to the left. The recovery was not as simple as my Mk IIIC where all you have to do is relax the back pressure to break the stall. I made the mistake of not holding the stick forward long enough and it broke a second time. I got the message and held the stick forward until the ASI was above 60 and then advanced the throttle enough to hold a nice descent back to pattern altitude. The landing was much more Kolb like and the roll out was half or so of those previous. I emailed Ken and told him I was grounding the airplane until a gap seal was installed, with the possible exception of one more flight to see if adding a gap seal to the horizontal stabilizers increased elevator authority.
Late in the afternoon I decided to call one of the members of my EAA chapter who had been an aerodynamicist at Beechcraft for many years before he retired. I gave him the short version of the story of this airplane. He was surprised at the amount of angular difference between the wing and tail. He said Beech engineers generally shoot for around 5 degrees, 3 degrees AOI for the wing and -2 degrees for the horizontal stabilizer. He made a few suggestions and the conversation turned to the morning's flight. I told him I felt the lack of a gap seal between the wings was causing the poor stall characteristics.
"Oh, I didn't realize you didn't have a gap seal for the wing. That's most likely responsible for the poor pitch characteristics, too. The vortex off the root of the wings is reducing the effectiveness of the elevator. I'll bet when you get a gap seal installed, that will solve your problem."
Enough said, I started the templates for the hot wire cutter last night.
Rick Girard
--
Zulu Delta
Mk IIIC
Thanks, Homer GBYM
It isn't necessary to have relatives in Kansas City in order to be unhappy.
- Groucho Marx
[quote][b]
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Dana
Joined: 13 Dec 2007
Posts: 1047
Location: Connecticut, USA
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| Posted: Sat Jun 11, 2011 6:41 pm Post subject: Four wingtips are NOT better than two |
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> I flew my Ultrastar without the center gap seal... once. Never again! Poor pitch control, poor climb, not fun. I didn't try any stalls, just once around the pattern, kept the speed up on final, just get out down.
-Dana
Richard Girard <aslsa.rng(at)gmail.com> wrote:[quote] Yesterday morning I finished lowering the front of the engine to change the thrust line on the Mk IIIX. By reversing the forward Lord mount I was able to change the thrust angle by 5.25 degrees without having to make any new parts. Of course this meant I had to lower the radiator, too, but I was able to modify parts to do that, rather than make new. I started just after dawn on the radiator parts and by 9:00 am everything was reassembled and ready to go. The wind had stayed light so I taxied out, let the engine warm up and took off. Much less back pressure was required than on the previous flight on Tuesday, but the airplane was still pitch divergent even with full trim. I was comfortable enough with it, though, that I thought I'd try slowing down to see how optimistic the airspeed indicator is as the aircraft approached a stall.Â
At 50 something mph the aircraft broke to the right. I knew the ASI was reading on the high side, but I hadn't expected quite that high, so I didn't catch the exact reading. The aircraft's stall characteristics were so unlike my Mk IIIC that I thought I had done something wrong, so I tried it again. This time, at 53 mph, the aircraft broke to the left. The recovery was not as simple as my Mk IIIC where all you have to do is relax the back pressure to break the stall. I made the mistake of not holding the stick forward long enough and it broke a second time. I got the message and held the stick forward until the ASI was above 60 and then advanced the throttle enough to hold a nice descent back to pattern altitude. The landing was much more Kolb like and the roll out was half or so of those previous. I emailed Ken and told him I was grounding the airplane until a gap seal was installed, with the possible exception of one more flight to see if adding a gap seal to the horizontal stabilizers increased elevator authority.
Late in the afternoon I decided to call one of the members of my EAA chapter who had been an aerodynamicist at Beechcraft for many years before he retired. I gave him the short version of the story of this airplane. He was surprised at the amount of angular difference between the wing and tail. He said Beech engineers generally shoot for around 5 degrees, 3 degrees AOI for the wing and -2 degrees for the horizontal stabilizer. He made a few suggestions and the conversation turned to the morning's flight. I told him I felt the lack of a gap seal between the wings was causing the poor stall characteristics.Â
"Oh, I didn't realize you didn't have a gap seal for the wing. That's most likely responsible for the poor pitch characteristics, too. The vortex off the root of the wings is reducing the effectiveness of the elevator. I'll bet when you get a gap seal installed, that will solve your problem."
Enough said, I started the templates for the hot wire cutter last night.
Rick Girard
--
Zulu Delta
Mk IIIC
Thanks, Homer GBYM
It isn't necessary to have relatives in Kansas City in order to be unhappy.
 - Groucho Marx
[b]
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John Hauck
Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)
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| Posted: Sun Jun 12, 2011 5:37 am Post subject: Four wingtips are NOT better than two |
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| Quote: | I flew my Ultrastar without the center gap seal... once. Never again! Poor pitch control, poor climb, not fun. I didn't try any stalls, just once around the pattern, kept the speed up on final, just get out down.
-Dana
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Ditto!
Experienced same thing with my US.
john h
mkIII
Burns Junction, Oregon
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John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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