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HGRAFF(at)aol.com
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 Posted: Mon Aug 10, 2009 7:18 pm Post subject: Kolb Mark III first flight report |
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First flight is always interesting and I thought to share it with the gang.
A group of us built the standard Kolb Mark III, with a 65HP Hirth geared engine, I was selected as the test pilot for its first flight. Somebody else had already taxied it elaborately and almost wiped it out. It cost a taxi light. I am a comm/instr 2000 hour guy in a variety of A/C. So, I took to the task and here is how it went:
With the Kolb assembled at the airport and thoroughly inspected, I first made a high speed taxi run that turned into a short flight. Man, is that thing twitchy in pitch and I over-controlled most of the time. pitch. The first run was 75%length of the runway at 10-20 feet, Porpoising most of the way about 5+ feet. Deciding it was too risky to learn how to fly the thing near the ground, the next run was a takeoff. I had planned at a 60MPH climbout, but couldn't get the airspeed and it quit climbing when I tried. I finally had to settle to climb at 40MPH indicated. The left wing was heavy, requiring a constant fairly strong holding against it. If I could have found a stable trim position, I'm sure it would have peeled off sharply to the left, if I let go.
When I reached 1500 on the climb out, I made a 180 back dead over the airport (A very safe place). Arriving at 2000 I leveled off to go into power-off stall tests, which happened at 35 indicated. I did two in succession. I followed that with power-on stalls, which also happen at 35 indicated, There is not much warning prior to either of the stalls, except a strong tendency to want to drop one or the other wing (spin time). It took a little dance on the rudder to keep it straight through the action. These stalls were done clean, no flaps.
Next I wanted to see what cruise speed was and play with the trim. Well, at level flight I indicated only 45. I lowered the nose and could hear the wind whistling furiously, despite I my head set on (it was competing, maybe louder than the engine) but I only indicated 50 MPH !!! Something wacky there. That's when I decided to come back in. In the descent I tried 3 notches of trim (that's where the springs take a hold), but really could not relax my grip on the control, because of the left roll tendency. I think trim would have caused considerable nose up. The approach at 40 MPH was dandy, but I plunked it down in a three point attitude despite carrying a little power. It didn't bounce back up, but I got into a bit of over control on the rudders, snaking down the runway, while tangling with those dang heal brakes which I really had no intention to use. An old habit dealing with rudder bars was taking over, when the Kolb has only rudder tilts. Because it got late, the A/C needs some attention first, I quit to also sleep on the adventure. We therefore put the Kolb to bed at the tie-down.
Prior to next flight, 3 things need attention:.
1. Pitot/Static system exploration/fix
2. lateral trim correction, an easy fix with flap adjust (I think)
3. Trim spring changes, they seem awful strong
Because of other commitments, a continuation report may have to wait two weeks.
Herb,
Mark III, 246KT
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neilsenrm(at)comcast.net
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| Posted: Tue Aug 11, 2009 6:45 am Post subject: Kolb Mark III first flight report |
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Hgraff
Do you have a MKIIIC or MKIIIX
It appears your plane has some problems that need to be fixed. First locate a good static source. Most people fine a good source a few inches under the fuselage. The stall speed seems about right but it is a bit unusual to have a wing drop. Cruise speeds are normally 70-75 for the MKIIIC and 75-80 for the MKIIIX but engine prop combinations can significantly effect these speeds.
Then fix the roll trim. Make sure the wings are correctly aligned. As described it is doubtful adjusting the flaps will be enough. At best performance will be negatively impacted. There are optional brackets sold by New Kolb that allows one to adjust the angle of attack on each wing. Get one for each wing you may need both.
Check the rudder pedal adjustment. They normally don't get tangled with the brakes.
Assuming you used the stock trim springs they should be fine. Make sure the tail cables are tight.
You may not be the best test pilot for this plane. High time GA pilots normally have the most trouble flying these planes. Kolbs are very light high drag airplanes. The high thrust line causes large pitch changes with power changes. They are not at all difficult to maintain level flight (pitch). Ground handling is normally closer to a good nose dagger than a tail wheel air plane.
Don't attempt to fly at low levels without considerable experience with power/pitch changes. Fly the plane off grass strips, it makes the plane even easier to control if you have numb feet.
As always worth what you paid for it.
Rick Neilsen
Redrive VW Powered MKIIIC
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John Hauck
Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)
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| Posted: Tue Aug 11, 2009 6:55 am Post subject: Kolb Mark III first flight report |
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First thing I would do is install a correct rudder trim tab, after I installed a good slip/skid indicator or a yaw string.
A lot of roll problems can be corrected with a good rudder trim tab, on a mkIII.
john h
mkIII
[quote] Do you have a MKIIIC or MKIIIX
It appears your plane has some problems that need to be fixed.
Rick Neilsen
[b]
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John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama |
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JetPilot
Joined: 10 Jan 2006
Posts: 1246
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| Posted: Tue Aug 11, 2009 9:04 am Post subject: Re: Kolb Mark III first flight report |
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The description of your first flight seems downright scary, and not typical of a nice flying Kolb. Your description of the Kolb being very pitch sensitive does not seem right, the pitch is light, but not what I would describe as oversensitive, my wife can hold my Kolb right over the runway level for 5000 feet without porpoising, even when she was just learning to fly. It was always my intention to replace the spring trim system with an electric servo trim tab system on my Kolb, but the spring trim system is so perfect, it was just never worth the time or the money to change it over. Your trim being so oversensitive is not normal, as is the pitch being so oversensitive, I think you should check the CG to make sure you are in limits.
The hard roll tendency is dangerous, you need to re rig the wings. Kolb can sell you the adjustable rear wing attach brackets and your roll tendency can be fixed with a few washers. It MAY be possible to fix a hard roll with flap adjustment as you describe, but it will be a horrible way to fix your problem and will result in a poor flying airplane. BTW - The way the flaps sit on the aileron tubes cause the flap trim solution to be OPPOSITE of what most people think it should be  ... Be very careful to adjust them the correct way, with hard roll forces the stick, the aileron tubes will spring twist and no matter how far you move the stick over you could have an uncontrollable roll on your next flight. I can overemphasize how dangerous this could be !!!! Do not try to fix the roll by adjusting flaps, take the time to fix it as it should be fixed. Only extremely small roll trims should be done with flaps once the wings have been fixed as close as possible with rear attach brackets.
The stalls do not sound right to me, my Kolb does not drop a wing in the stall no matter how badly my wife tried to screw it up during training. My wife tried 1. Pulling the stick all the way back once the nose started to drop 2. Putting full power instantly once the nose started to drop 3. NEVER used the rudders properly during her first stalls, she just corrected any roll with the stick throughout the stall. The stall series in my kolb is so docile, my wife never believes me when I tell her how dangerous accidental stalls can be... Your description makes me wonder what is wrong, check that CG again !!! Check out some videos of my Kolb MK III Xtra Stalls at:
http://www.youtube.com/watch?v=kWMRUPH39gM
Lastly your speeds sound WAY off, check them with a GPS. 40 MPH is a dangerously slow climb in a Kolb, as you said 60 MPH is perfect and what I use. I could live with 55 MPH and not be to scared, but anything below that is just bad. One last thing, that Hirth engine is a horrible and unreliable engine, it will very likely get your hurt one day, you should have a Rotax on there, but that is your choice....
I am glad you did not hurt yourself on the first flight, and very glad you did not do a second flight ! You have some things to fix, properly setup, the Kolb is a very stable, relaxing airplane to fly.
Mike
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_________________
"NO FEAR" - If you have no fear you did not go as fast as you could have !!!
Kolb MK-III Xtra, 912-S |
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