bikefair
Joined: 25 Dec 2007
Posts: 6
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 Posted: Sun Dec 14, 2008 10:40 am Post subject: Kolb high thrust line. |
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Gretings fellow flyers.
I have been enjoying the reading of the posts, mostly I sit on the sidelines and “look” through the window of the postings.
Reading the topics I am stirred up to comment on one of my fears, that is giving advice on flying technique and in particular the latest one on take off procedures.
I suppose that my recent poor performance has brought me to the position of relearning some things, which has been a good thing, and in particular the review of reading all the postings has been a value.
I recently changed my plane from a Poorboy to an Ultrastar and the takeoff power is quite different so I got into a bit of a scare several times because my bad habit of holding the stick back and taking off with lots of thrust available. A big engine like a 503 with a 70” prop made a lazy pilot out of me and I frequently violated the rules of common sense because with lots of power you can transition from not flying speed to flying with a steep takeoff angle and climb out and hardly realize you are doing it. WWEEEEEEEEE, lots of fun but potentially dumb! This has the potential of putting me in the position of no thrust with steep angle of attack (and quickly no airspeed), if this happens close to the ground (under 100 ft) it may do more than just bang up my plane…ouch to me…
When I started back flying an Ultrastar (this is my second Ultrastar) I quickly saw that my tactics were wrong. Now I was flying a 50” propeller with UL202 35hp, in the air this is adequate power and is a good flying plane but is marginal on a 700ft runway, I don’t like being marginal and it scares me. A good portion of the problem lies in my poor takeoff procedure as holding the stick back on this plane actually slowed down the takeoff, increased the takeoff roll and the plane staggered into the air. I needed additional lesson from an instructor and review to get straightened out. This turned out to be quite nice flying plane, the engine ran flawlessly but the marginal performance (50 inch warp drive with adj. Experiments showed it was pitched very close to optimum) still it left me discontent for this runway has obstructions and I have sold the airplane and am now building a 1993 Firestar kit that was not finished. This is my second firestar (1st one 1991 rotax 377) and I had a mark III (1997 rotax 503).
The point of my comment is that I seem to acquire patterns or habits that meet the experience necessities of the plane I am currently flying and in so doing my judgment and comments to others becomes skewed, that means I prefer to be careful when giving advice as I have lost the objectivity of view required for folks who have an other frame of reference from their last flying experience. The safe way out of this for me is to recommend them to an instructor; never-the-less these pages of comments are great and with that in mind allow my summarization of what I remembered differences in Kolbs.
Ultrastar procedures. 1000 to 1200 ft. runway is adequate (unobstructed preferred), throttle up, stick forward or neutral to pick up the tail, take off roll is shortest with the wing angle of attack at close to zero until flying speed and gentle ease back on stick to lift off in ground effect or close to that height (ground effect generally one wingspan range of ground height) and let speed build a bit before entering climb out angle and rate. A great flying airplane, no handling surprised and it generally just does what you tell it to, very nice landing approach control. 35hp. UL202 has limited power as compared to some of the other Kolbs but is well suited to the plane, if a landing go around is required there is the need to recognize it early and add power soon enough if obstructions are part of the equation. My take off’s are 500ft range for the best short ones and 700ft isn’t long enough if I’m doing it wrong. This is my experience with the two Ultrastars I have had, others may be better pilots or have other variables of weight and power that give different results.
Firestar and Mark III. My experiences as I remember them were similar with these models as far as takeoff and landing are the subject, generally they are the same configuration. I have flown (owned) the short cab Firestar, flown a borrowed Firestar 2 long cab, and owned the Mark III. I have not flown a Firefly that has the most in common with the old short cab Firestar, the Firefly has a 22ft. wing and a flaperon control mixer. I will use the Firestar in general as a descriptive airplane subject as the high mounted engine configuration is present in all of these models.
The Firestar’s need a modified procedure and awareness from many other airplanes, particular to Firestars is there high thrust line. Tractor airplanes and pushers with the prop thrust line even or below the line of the wing have much less of the tendency’s that Kolb Firestars suffer from. My opinion is that they SUFFER from this feature as well as have the benefits of getting the prop high enough to allow efficient prop length (and the additional benefit of excellent aircraft fold up ability with the engine and prop out of the way of the folded wings), this is a reasonable trade off as Kolb sales have demonstrated.
The down side of this high thrust line is substantial and should not be (in good flying practice) safely ignored.
The 1st issue of high thrust line is adding power at takeoff, with the stick at neutral a quick throttle to full will put the Firestar on its nose often with damage, this is not a tendency present in most other aircraft. In order to compensate for this resultant action I hold the stick full back at early power addition and early roll for takeoff, but then I need to more neutral the stick as the tail becomes effective and in control, if the stick is left full back you encourage early takeoff and hard climb right into early flight, this is potentially dangerous and unnecessary. A safe and normal takeoff does not include a risky maneuver like early hard climb, this is special procedure for short field obstructed takeoff and good pilot judgment will try to avoid that. It takes a bit of practicing combinations of adding power more slowly and stick position for reasonable lift off speed and speed addition at low angle of attack before climb out. I notice that practice is what I need to keep from bobbing down the runway trying to balance that high thrust line and input stick control power issues, in actual application I tend to get lazy and just blast off with the stick too far back and allow the engine to haul my dumb butt up.
The 2nd issue of high thrust line is quick throttle changes in flight will result in nose up with quick decrease power and nose down tendency when quickly adding power. The tendency is not serious in normal flight with altitude but certainly can be an issue during the landing cycle. The first answer here is not get caught in a situation when large power setting changes are quickly required, the faster you make those throttle changes the more pronounced the result. In particular note that on approach if you find out a bit late that you need to adjust the glide path angle a throttle adjustment will complicate the issue and without experience (practice) you are in for a surprise. I will stick my neck out here and say that the most common “BAD” landing incidents here is an approach that is judged for correction late in the cycle and a quick power addition will drive the aircraft right into the ground, this has “damaged lots” of Kolbs.
How does that ring with you guys.
Well that was a mouthful anyway, hope it was enjoyable if not viewed as accurate. Jim
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