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bigboyzt0yz
Joined: 29 Jan 2008
Posts: 29
Location: Centeral Maryland
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 Posted: Sun Feb 17, 2008 11:29 pm Post subject: Kitfox IV speed Range |
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I was thinking about changing my 70 hour 912UL for a 912ULS so that it has a greater top speed cruise. I was wondering is it better to ad all the fairings to the struts and rods on the whole plane? Along with Wheel pants and Spring gear to clean it up a bit. Or do I keep the same motor and add a in flight adjustable unit to the current prop drive. What is the expected flight speed for the plane in general? I know the Vne is listed at 140 Knots and with a Sport Pilot ticket you are not supposed to fly over 120 knots. so is there a limit to how fast that air foil shape is expected to go. My plane is 675 Lbs and has a 80 hp so where is the brick wall for how far you can really go? (The 701 kinda maxes out at 85 MPH with the tall airfoil) I do like flying slower looking at all the sights below, but some times you just want to get there sooner and so far this plane will do both pretty well. Along with being able to get into some pretty short fields.
I will be flying (next year after we build the plane together) with a friend that has a Sonex on order and is going to put in a Jab. 3300 in it. Or just tell him to deal with the fact that he will have to just fly slower or leave later.
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Lee Fritz in Owings Mills Md. 2002 KitFox-IV Classic/912UL/Warp drive taper tip/100% Complete ( Extras Strut fairings08, Grove gear09,) 300 hrs since Aug 07 "Have your feet on the Pedals and keep reaching for the sky". |
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propellerdesign(at)tele2.
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| Posted: Mon Feb 18, 2008 12:49 am Post subject: Kitfox IV speed Range |
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Lee,
going from 80 to 100 hp will gain 7,7 % top speed, but the climb will be a
lot better.
If you have a sport license your plane isn't allowed to have in air
adjustable prop.
Fairings gain more speed and reduce fuel burn at cruise, (getting there
faster or flying with less power at same speed)
Jan
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Fox5flyer
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| Posted: Mon Feb 18, 2008 4:19 am Post subject: Kitfox IV speed Range |
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Lee, the basic rule of thumb is more power will give you better climb, but
usually not much difference in speed. To get more speed you need to reduce
drag.
Reducing drag is a lot cheaper both up front and in the long run. It
usually has no effect on slow flight or stall characteristics, but increases
speed and reduces fuel per mile traveled. Your gph stays the same, but
enroute air time is reduced.
Deke Morisse
Mikado Michigan
S5/Subaru/CAP 355+ TT
"The aim of an argument or discussion should not be victory, but progress."
- Joseph Joubert
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Guy Buchanan
Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA
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| Posted: Mon Feb 18, 2008 9:39 am Post subject: Kitfox IV speed Range |
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At 11:29 PM 2/17/2008, you wrote:
| Quote: | I will be flying (next year after we build the plane together)
with a friend that has a Sonex on order and is going to put in a
Jab. 3300 in it. Or just tell him to deal with the fact that he
will have to just fly slower or leave later.
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This subject is currently being intensely discussed on the
Lancair list. In general:
1. Speed varies with the cube root of power. E.g. double the power,
get 26% more speed, or in the linear realm, to increase speed 1%,
increase power 3%.
2. Speed varies with the square root of the drag. E.g. half the drag
gives 41% more speed, or in the linear realm, to increase speed 1%,
decrease drag 2%.
3. Perhaps Jan can chime in with a way of quantifying the value of a
variable pitch prop, but the way I look at it is that you get to
cruise at max speed, but at a lower RPM. In other words, if I fly my
fixed pitch at 5800 rpm at a certain speed, then I'll be able to do
the same speed at 5000 rpm with a variable pitch prop.
The bottom line being that you probably get the most bang
for the buck with #2, drag decreases, followed by #3, the prop,
(assuming you're not Light Sport,) followed by #1, horsepower
increases. As for bang for the effort, switching to a variable pitch
prop is probably the easiest, followed by swapping to the S, followed
by drag reductions.
Guy Buchanan
San Diego, CA
K-IV 1200 / 582-C / Warp / 100% done, thanks mostly to Bob Ducar.
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Guy Buchanan
Deceased K-IV 1200
A glider pilot too. |
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dave
Joined: 22 Sep 2006
Posts: 1382
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| Posted: Mon Feb 18, 2008 10:12 am Post subject: Re: Kitfox IV speed Range |
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Kitfox is a high drag airplane.
In flight prop might help a small amount but if you go coarser to a lower rpm like you stated. 5800 to 5000 - i can tell you that your power curve drops off quickly below 5800 rpm with your stock exhaust. Plus with the Skystar exhaust mod which cost all 582 drivers about 5 hp.
So if you are cruising at 5800 rpm at 90 mph and drop to 5000 with a courser pitch , I think will will not have enough power and will likely slow down and see lower EGTs as you lug your engine down. 582 likes to run 5800 to 6000 rpm with the stock exhaust. I can tell you that with my last few tuned pipes I have made that I am getting a few more HP and better performance with less rpms giving the same numbers as I was getting with stock setup. eg now at 5600 same as I was doing at 6000 rpm + approx
I have a new Inflight prop here GSC with WARP blades that I will try in the spring unless it sells before. List is about 2200.00 http://www.hoverhawk.com/gtaprop.html this one has nickel leading edges ( 240$ option) . I will let it go for 1800$ plus shipping right now.
| Quote: | if I fly my
fixed pitch at 5800 rpm at a certain speed, then I'll be able to do
the same speed at 5000 rpm with a variable pitch prop.
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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
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propellerdesign(at)tele2.
Guest
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| Posted: Mon Feb 18, 2008 2:39 pm Post subject: Kitfox IV speed Range |
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An in flight adjustable / constant speed prop on a slow (relative) plane
will gain some increase in climb, on a fast plane, it will make a big
difference. on a fast sleek plane with low power it will make all the
difference in take off and climb.
I am not sure how fast a Kitfox is with 912 80HP is, but lets say that This!
kitfox is doing 110 mph SL WOT at 1200 lbs.
with a fixed pitch 68" diameter prop it have a initial climb of 700 fpm.
with a constant speed prop 68" it will climb 940 fpm.
34% better.
With 912S 100 Hp and fixed pitch 960 fpm
100 hp and CS prop 1270 fpm
Assuming all the rest remain the same, I didn't check for different gear
ratio. max speed? 119 mph.
Propeller efficiency at 110 mph 77,5%
so total drag is 80 * 76 * 0,775 / 49 = 96 kg (212 lb)
Say you have total 60 feet (18 meter) of wingstrut
drag from faired struts will be 4 kg or 4% of total (plus interference
between strut and wing/fuselage)
Round tubes? 4 times more or so, that will eazy make a difference of 15
miles.
Jan
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Guy Buchanan
Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA
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| Posted: Mon Feb 18, 2008 5:49 pm Post subject: Kitfox IV speed Range |
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At 10:12 AM 2/18/2008, you wrote:
| Quote: | In flight prop might help a small amount but if you go coarser to a
lower rpm like you stated. 5800 to 5000 - i can tell you that your
power curve drops off quickly below 5800 rpm with your stock
exhaust. Plus with the Skystar exhaust mod which cost all 582
drivers about 5 hp.
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Sorry for the confusion Dave, I was talking 912 RPM, not
582. (Yes I have a 582, but know some of the 912 #'s.)
Guy Buchanan
San Diego, CA
K-IV 1200 / 582-C / Warp / 100% done, thanks mostly to Bob Ducar.
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_________________
Guy Buchanan
Deceased K-IV 1200
A glider pilot too. |
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dave
Joined: 22 Sep 2006
Posts: 1382
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| Posted: Tue Feb 19, 2008 4:01 am Post subject: Re: Kitfox IV speed Range |
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| Quote: | Sorry for the confusion Dave, I was talking 912 RPM, not
582. (Yes I have a 582, but know some of the 912 #'s.) |
That makes better sense !!!! 
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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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