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Cruise Speeds model 5

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chris(at)southernskies.ne
Guest

Posted: Mon Oct 19, 2009 3:46 am Post subject: Cruise Speeds model 5

Hello Listers,



I always read with great interest but seldom post. My question is regarding Speeds. My model 5 -taildragger, Franklin 116 HP,high compression mod, 2 blade 76 inch magnum Ivoprop ground adjustable cruises at  85 to 90 mph at 75% power.

At wide open I can manage 100 to 105 mph at 3000 MSL. Checked with GPS many times.

Tried different pitch  settings and it only changes rpms,not speeds.

I often read about other Kitfoxes going considerably faster. 



Should I check the rigging? What part?  



Or is this just a slow bird, period?



Love the short field performance-other pilots raise eyebrows about my 800 foot strip that goes down (for take off) or up (landing) a hill,works fine for me.



Chris Bowles

Model 5 Outback

FlyboyTR

Joined: 04 Nov 2006
Posts: 215
Location: Mobile, Alabama

Posted: Mon Oct 19, 2009 4:40 am Post subject: Re: Cruise Speeds model 5

Chris,

I fly a Vixen (Series 5 nosedragger).  My power is a Continental IO-240 swinging a 68" Prince Prop.  Full throttle, straight and level at 1,500'MSL, will nail VNE at 140 MPH indicated.  My high end cruise, 6,000' MSL and 2550 RPM give me a TAS of 125.  My typical cruise is turning 2,300 PRM at 112-115 MPH TAS.



I have wheel pants on all three wheels, streamline lift struts, jury struts and horizontal stabilizer lift struts.  I do not have the typical large hose from the crank case breather hanging out the bottom.  It is internal and anything that drips, drips directly onto the exhaust pipe just before it exits the cowling (similar to some of the RV's).  The exhaust tip is cut at an angle that matches the cowling and only extends below the cowling about 1/2 to 1".  I had about 1/4" gaps between the wing and fuselage.  Closing those in ( rubber weatherstripping) gave me about 1-2 MPH on the top end.  I have the lift strut to wing speed cuffs that I haven't installed yet.  I may also want to consider the gas cap fairing...but really haven't read anything about that mods potential improvement.  Also thinking about a gap seal between the elevator and stabilizer...don't know. 



My hanger is open on two sides and the plane is subject to getting covered with dust, pollen, etc.  Mix that with a little blowing drizzle and the planes finish can get real nasty.  Strange thing is...the plane is 1-2 MPH faster when it's real dirty.  ...not sure if it's just trying to get away from itself...or if it has something to do with laminar airflow over the surface.  



Anyway...your speeds to sound a little slow for 116 HP and adjustable prop.  However...and everything being said...it is not a fast airplane and I think I am fortunate to get the speeds I'm getting.  Yesterday I was parked next to a friends new Jabiru (the large one with the back seats removed). Man...that thing is slick, clean and I'm sure much faster...sort of made my Vixen look like a wheelbarrow!      However, I love my wheelbarrow.  It's strong, it's agile and dependable. 



Can you tell us more about your plane (struts, cowling, exposed exhaust, spinner, wheel pants, etc?



Travis

_________________
Travis Rayner
Mobile, AL
Skystar Vixen, N-789DF
Continental IO-240, Prince P-Tip Prop
ADI-II Autopilot
AnyWhereMap Navigation with weather
www.enotam.net (My Flying Info Website)

FlyboyTR

Joined: 04 Nov 2006
Posts: 215
Location: Mobile, Alabama

Posted: Mon Oct 19, 2009 4:51 am Post subject: Re: Cruise Speeds model 5

Chris...

Another thought...

You said that your speed does not change with different pitch settings, only the RPM.  I'm having a hard time getting my arms around that one...odd???  I also have a Prince Prop that is slightly underpropped for my engine.  With that prop I can launch like an ultralight, climb like crazy, etc.  The problem is...I can easily run past redline on the engine, even in a slight climb.  With this prop...my top end is (with limiting the engine to redline, 2,800 RPM) is only about 115.  Cruise is WAY down.



You should be seeing a change in your speed envelope with changes in prop pitch and engine RPM.  It is possible to dial in too much pitch (no speed gains there).  Again... more details would probably help.



Travis

_________________
Travis Rayner
Mobile, AL
Skystar Vixen, N-789DF
Continental IO-240, Prince P-Tip Prop
ADI-II Autopilot
AnyWhereMap Navigation with weather
www.enotam.net (My Flying Info Website)

n85ae

Joined: 14 Mar 2007
Posts: 403

Posted: Mon Oct 19, 2009 9:00 am Post subject: Re: Cruise Speeds model 5

Series 5 with IO-240B, 74" dia. Sensenich, faired lift struts, no wheel pants,

I get 120-125 mph cruise at 2200 rpm, and can exceed 140 at full throttle

at 2800 rpm.



Three different variations of Sensenich tried, and with the exception of

climb performance cruise has been the same with all. 70, 72, and 74

diameter props tried. 74" gives best takeoff acceleration, and climb.



8.50x6 and 6.00x6 tires same thing, can't tell any difference in cruise.



Light Bar between float attach points, with 6" diameter flood lights

attached, same thing, no difference.



Jeff Hays

FlyboyTR

Joined: 04 Nov 2006
Posts: 215
Location: Mobile, Alabama

Posted: Mon Oct 19, 2009 9:51 am Post subject: Re: Cruise Speeds model 5

Jeff,

EXCELLENT numbers!  Wish I was getting that kind of cruise at 2200!  ...I though mine was pretty good...but...not any more.  



Travis

_________________
Travis Rayner
Mobile, AL
Skystar Vixen, N-789DF
Continental IO-240, Prince P-Tip Prop
ADI-II Autopilot
AnyWhereMap Navigation with weather
www.enotam.net (My Flying Info Website)

n85ae

Joined: 14 Mar 2007
Posts: 403

Posted: Mon Oct 19, 2009 10:17 am Post subject: Re: Cruise Speeds model 5

Oops, mistake.



Correction, actually 2200 rpm, is more like around 105, which is my normal

setting for not being in a hurry. 



2400 rpm is my 120 cruise setting. 



A lot of the time I throttle back to 17-1800 just for puttering aroung



Jeff

FlyboyTR

Joined: 04 Nov 2006
Posts: 215
Location: Mobile, Alabama

Posted: Mon Oct 19, 2009 10:21 am Post subject: Re: Cruise Speeds model 5

Still good cruise numbers for 2,400!

_________________
Travis Rayner
Mobile, AL
Skystar Vixen, N-789DF
Continental IO-240, Prince P-Tip Prop
ADI-II Autopilot
AnyWhereMap Navigation with weather
www.enotam.net (My Flying Info Website)

n85ae

Joined: 14 Mar 2007
Posts: 403

Posted: Mon Oct 19, 2009 12:02 pm Post subject: Re: Cruise Speeds model 5

Just a thought, but I think it might be relevant. I added 12 lb's ballast to the

tail behind the battery in order to get a more favorable cg. If you're nose

heavy and compensating with trim, or tail incidence, that may be creating

drag.



I made my own lift strut fairings based on some symmetric airfoil data

from the UIUC airfoil database, and cut foam cores, and layed up glass

over the cores. I'm not saying they are the best out there, but I think the

foils I'm using are pretty good, and the lift struts are a big drag contributor.



I honestly like the plane at slower speeds, so I rarely use power above 

2200 rpm level in any case. It just get's too much of the runaway

freight train feeling when going 120+. 100 is a nice speed for the plane.



Also I have a taildragger, so I don't have all the nose strut drag.



Regards,

Jeff

chris(at)southernskies.ne
Guest

Posted: Tue Oct 20, 2009 2:10 am Post subject: Cruise Speeds model 5

O.K. here is some more info then...



This is an "Outback"-tailwheel. I do have the lift strut PVC fairings. No gap seals. Exhaust pipes are hanging out the cowling by 2 inches.



No spinner. Just the ugly Ivo hardware hanging in the breeze. Bugs are washed off.



CG is a bit noseheavy but well within the allowed range.



I have very noticeable trim changes between climb and glide. For take off my stabilizer is trimmed pretty far "down"- that translates into the leading edge of the stabilizer up- in the upper 1/3 of the slot. Only a small adjustment is needed to change to cruise. 



For glide and landing that changes to plenty "up" trim- leading edge of stabilizer now in the lower 1/3 of the slot. I land with 50% flaps(short field coming in over trees) and need to tap the trim button a good bit more "up" after extending flaps. All that seems normal.



I have only 86 hrs in this model 5 so far- I had a model 3 before. The nose high attitude in the 5 is very noticeable -or is it just that big long cowling not letting me see straight ahead.



Have tried different pitches on the Ivoprop-giving it more pitch makes for lower rpms-and longer take off runs- but minimal speed increase.



It just feels like hitting a wall at some point and the plane doesn't want to go faster. That is why I suspected the rigging might be off? 



Wanted to ask here before I go through with this. I don't have a good level place to check the rigging-need to go somewhere else for that and enlist help of the A&P with the big concrete floor hangar...

Nothing but hills where my kitfox normally lives.



Chris Bowles

Taylorsville,NC 

Model 5 Outback

Franklin 235



--

FlyboyTR

Joined: 04 Nov 2006
Posts: 215
Location: Mobile, Alabama

Posted: Sun Oct 25, 2009 4:04 pm Post subject: Re: Cruise Speeds model 5

Chris,

As noted by Jeff, being nose heavy does make a difference in your speed.  I carry my tools and ground anchors, etc as far aft as possible in my luggage area.  It does make a difference...just how much will depend on how far forward your CG is.



Another easy place to check are the flaperons.  If they are trimmed to low, they will create a lot of drag and slow you down.  That would not require a level floor, etc.   Refer to your assembly manual and step through setting up the deflection on the flaperons.



Travis

_________________
Travis Rayner
Mobile, AL
Skystar Vixen, N-789DF
Continental IO-240, Prince P-Tip Prop
ADI-II Autopilot
AnyWhereMap Navigation with weather
www.enotam.net (My Flying Info Website)

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