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LarryM
Joined: 27 Nov 2007
Posts: 63
Location: Genoa, IL
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 Posted: Fri Apr 04, 2008 5:28 am Post subject: 6" gear extension |
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I finally got a chance to extend vertically my Grove gear by 6". I did so in order to have a better angle of attack for take off and landing, as the airplane would want to fly before the gear geometry would allow it to, similarly, the tail would always bang on before the wing was done flying. The change does make a difference. I can not tell you exactly how much, as it's been fairly windy, but, I can definitely get the nose up higher without hitting the tail. I do need to change my sight picture, as I have the tendency to hold the "old" angle so I don't slam the tail. I'm thinking that I can see (remembering that IAS is inaccurate at high angles of attach) about 5mph slower at touch down. Take off is also sooner, as the geometry will allow for lift off at slower speed.
The mod was quite simple, I just bolted a 3/4" piece of aluminum block to the axle holes. The same brake lines could be used.
larry
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wingnut
Joined: 11 Jan 2006
Posts: 356
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| Posted: Fri Apr 04, 2008 7:47 am Post subject: Re: 6" gear extension |
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Curious. The short field takeoff procedure that I was taught involved lots of forward stick to get the tail up as soon as possible. The idea being to minimize drag and maximize acceleration. I take it that you do it differently?
Also, on my Kitfox the AOA on the ground is about the same as power off stall when flaps are deployed. Thus, I too would bang the tail with flaps up. However, with flaps deployed, it stalls right into a three point landing. I take it that your kitfox behaved differently? Any idea what might cause the difference?
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Luis Rodriguez
Model IV 1200
Rotax 912UL
Flying Weekly
Laurens, SC (34A) |
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LarryM
Joined: 27 Nov 2007
Posts: 63
Location: Genoa, IL
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| Posted: Fri Apr 04, 2008 9:08 am Post subject: Re: 6" gear extension |
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I don't think that a single short field technique works on all airplanes. The Avid definitely takes off much shorter in a 3 point attitude. The nominal angle that the wing sat at was 10 degrees while in the 3 point. It now sits about 3 degrees higher. Bringing the tail up would reduce the angle of attach and therefore you would need more forward speed to develop the required to lift off. Ideally, a wing sitting in the 3 point should be at the stall angle of attack or higher so that you could bring the tail up. But, my experience in the Avid is that the take off run is the shortest with 3 point and full flaps. As far as landing, its the same thing in reverse. I don't know what the critical angle of attach officially is, but its more than 13 degrees. Try flying as slow as possible (at altitude). You will probably find full power nose way up 30+ degrees. Obviously, we can't safely land this way, but somewhere around there would be the slowest touchdown speed. Perhaps your tail is not effective enough to get the wing to the critical angle of attack without power, or even with power. I know mine wasn't. I did increase the tail surface and add VGs to the underside. I still have less effectiveness than I would like to see. Power on helps a lot to keep the air flowing over the elevator and is a noticeable difference. The wing wants to fly so much that to experience some of this, you have to get up early. That is while there is no wind or day time heating. The perfect clam of pre-dawn - I love it. Anyway, that's my 2 cents.........
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wingnut
Joined: 11 Jan 2006
Posts: 356
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| Posted: Fri Apr 04, 2008 10:02 am Post subject: Re: 6" gear extension |
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| Quote: | | Bringing the tail up would reduce the angle of attach and therefore you would need more forward speed to develop the required to lift off |
That all makes sense but I thought that the idea of lifting the tail was to enable the airplane to get to takeoff speed faster. Takeoff speed still being defined as the a speed at which the airplane will fly outside of ground effect regardless of attitude. When you get to that speed, then you drop the tail.
As I write this though, I think I see what I was missing. The point at which you can drop the tail and get in the air will be slower on your airplane because you can get the airplane closer to your critical AOA "with power on". which is much higher than the critical AOA with power off. I still wonder though, if you wouldn't get to that magic speed faster with the tail up.
| Quote: | | As far as landing, its the same thing in reverse. I don't know what the critical angle of attach officially is, but its more than 13 degrees. Try flying as slow as possible (at altitude). You will probably find full power nose way up 30+ degrees. Obviously, we can't safely land this way, but somewhere around there would be the slowest touchdown speed. |
That's only true if you land at full throttle. As I said, my critical AOA with power off (which is the power setting I like to land with) is more or less right at the AOA she sits at on the ground. I know that I have enough elevator authority to get there because I've hit that point on many occasions a tad too high causing her to plop down. All that is to say that it sounds like your critical AOA is still higher than mine even with power off and flaps deployed. Are you using VGs?
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Luis Rodriguez
Model IV 1200
Rotax 912UL
Flying Weekly
Laurens, SC (34A) |
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dave
Joined: 22 Sep 2006
Posts: 1382
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| Posted: Fri Apr 04, 2008 2:02 pm Post subject: Re: 6" gear extension |
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look at my videos on youtube, and you will see what Larry it talking about. I raise my tail on start of roll and then after 75 feet I hammer the taildown and it takes a few feet before I get the wings flying. I have mentioned and asked this forum about lengthening the main gear before and not much talk on it. GladLarry finally got it done with favourabel results. I would like to make a new set of gear higher by 6 to 10 " and get the higher AOA to cut Take off roll further .
Just watch this and tell me how yours compares http://www.youtube.com/watch?v=itqyBYxU0lU
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_________________
Realtime Kitfox movies to separate the internet chatter from the truth
http://www.youtube.com/user/kitfoxflyer
Hundreds of Kitfox Movies
Most viewed Kitfox on youtube
Most popular on youtube
Highest rated on youtube |
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wingnut
Joined: 11 Jan 2006
Posts: 356
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| Posted: Fri Apr 04, 2008 2:34 pm Post subject: Re: 6" gear extension |
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| Quote: | | look at my videos on youtube, and you will see what Larry it talking about. I raise my tail on start of roll and then after 75 feet I hammer the taildown and it takes a few feet before I get the wings flying. |
Lifting the tail at the beginning of the roll out is what I was trying to communicate. I understand now how being able to increase your AOA on the ground at the transition point is an advantage. But on the other hand, what's the advantage of dropping the tail before you reach takeoff speed? Wouldn't it work better if you wait until you actually reach take off speed and then drop the tail?
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Luis Rodriguez
Model IV 1200
Rotax 912UL
Flying Weekly
Laurens, SC (34A) |
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wingnut
Joined: 11 Jan 2006
Posts: 356
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| Posted: Fri Apr 04, 2008 2:43 pm Post subject: Re: 6" gear extension |
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Just took a look at the video. That's incredibly short. Looks like your tail comes up as soon as you start rolling. Takes my model 4 about 2 seconds to get the tail up and just under another 3 get get off the ground. Another thing I can't do is hold the plane back with full throttle. Brakes are too week.
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_________________
Luis Rodriguez
Model IV 1200
Rotax 912UL
Flying Weekly
Laurens, SC (34A) |
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wingnut
Joined: 11 Jan 2006
Posts: 356
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| Posted: Fri Apr 04, 2008 2:49 pm Post subject: Re: 6" gear extension |
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By the way Dave, what model Kitfox is that?
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_________________
Luis Rodriguez
Model IV 1200
Rotax 912UL
Flying Weekly
Laurens, SC (34A) |
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dave
Joined: 22 Sep 2006
Posts: 1382
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| Posted: Fri Apr 04, 2008 3:19 pm Post subject: Re: 6" gear extension |
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Kitfox IV , empty weight 570s Engine over 400 hours now ( 3rd engine)
It's not just what you got , it is how you use it !!
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_________________
Realtime Kitfox movies to separate the internet chatter from the truth
http://www.youtube.com/user/kitfoxflyer
Hundreds of Kitfox Movies
Most viewed Kitfox on youtube
Most popular on youtube
Highest rated on youtube |
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