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jmbrooks(at)ctc.net
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 Posted: Tue Apr 04, 2006 2:30 pm Post subject: Another Porcupine Kolb (thanks John H., I like the name) tak |
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I recently installed modified Jack Hart designed vortex generators on the Firestar II 503 I build and have flown more than 450 hrs over the last 10 years. I used aluminum trim as material and a die similar to the one Jack describes on his web site. The modification was to leave a 3/16" flat on the top edges and add a 1/32" radius on the back corners. This produces vg's that are not as likely to damage someone practicing Kolb worship (washing).
The vg's were installed on the wing 11" back from the apex of the leading edge (measured along the camber of the rib) centered in the valleys. They were bonded to the fabric (Poly Tone paint) with GE 102 silicone adhesive. No vg's were installed in the valleys inside the prop arc. An additional 7 vg's were installed on the bottom of each horizontal stabilizer, evenly distributed between the tip and the last inboard rib of the elevator, 2.5" ahead of the hinge center line.
The following report is a compilation of 3 flights on 2 different days totaling 1.5 hr: I weigh about 280 lb when dressed for the weather present at the time of testing so the Firestar had a take off weight of about 640(me+30lb fuel+330lb airplane). Conditions for the test flights on both days were 50 deg F and no surface wind. After making 8-10 take offs and landings plus numerous touch and goes I can report that the take off roll seemed unchanged (130') although the altitude at the far end of the 5000' runway went from 800' AGL under similar conditions to 1000' AGL with the vg's using the 50 mph climb speed I normally use.
The stall speed dropped from 40-42 mph to 34-36 mph. My CG is at 29%. Before the vg installation the airplane always stalled the elevator first. This stall was characterized by the elevator stick pressure suddenly dropping, the wings staying level at the point of the stall and the ailerons retaining authority through the stall with a very noticable drop of the nose. After the vg's the wing is now stalling, characterized by the retention of the elevator pressure, the nose dropping and the slight dropping of a wing, 4 stalls (engine idling) yielded the right wing dropping twice and the left wing dropping twice. The stall with the vg's is less severe, losing less altitude than prior to the installation. A slight reduction in back pressure breaks the stall and recovery is immediate.
I have over 650 hr in certified airplanes as PIC. In fact, I owned the PA-12 that Homer Kolb was a partner in back in the late 50's and early 60's. 10 years ago I learned that wheel landing was the best method for me in the Firestar, though I've always preferred three point landings in the other airplanes I've flown. I had difficulty judging and maintaining the correct attitude for a three point landing, even with elevator gap seals installed. The additional 3-5 mph of the wheel landing made the arrivals much more consistent. I was very pleasantly supprised when my first landing, using the same stick pressure I previously used for wheel landing, yielded a very nice three point landing. I have three pointed ever since. Speed and power on final dropped from 50mph(at)3000rpm to 45(at)2500. As I gain confidence with experience I may find that landing at idle may be possible. I will approach this point with care as I have dinged the gear before.
The best and most fun imporvement in the flight characteristics has been in the lower end of the envelope. Before the vg's the low end of comfortable flight was about 50 mph. Below that speed it was difficult to maintain a constant altitude and speed without considerable concentration and continuous correction. Now cruising at 45(at)4600, while enjoying the scenery without concentrating on flying the airplane, is as easy as it was to cruise at 55(at)5000 previously. I feel this to be a real improvement in the fun factor.
I consider the addition of the vg's to be one of the best modifications I have tried on this airplane and a true improvement to a truly fine airplane.
John Brooks
FSII 503
Oakboro, NC
(As my Father-in-law always said "The center of the world."
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John Jung
Joined: 10 Jan 2006
Posts: 108
Location: Surprise, AZ, USA
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| Posted: Wed Apr 05, 2006 7:09 am Post subject: Re: Another Porcupine Kolb (thanks John H., I like the name) |
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John B,
Thanks for taking the time to share what you learned about VG's. I found it very interesting. As more of us follow the lead of the VG pioneers on the list, and report results, we all stand to learn.
As much as I like my Firestar II, one disappointment was the 40 mph stall and the lack of ability to fly with friends in Quicksilvers. Even my original Firestar had a 35 mph stall, and could not fly with slower ultralights. Now, with VG's and a 30 mph stall, I can fly with ultralights again.
| | - The Matronics Kolb-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
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_________________
John Jung
Firestar II N6163J
Surprise, AZ |
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