Matronics Email Lists :: View topic - KF IV Distance from DATUM to center of wheel

Matronics Email Lists
Web Forum Interface to the Matronics Email Lists

Get Email Distribution Too! FAQ Search Memberlist Usergroups Register

Profile Log in to check your private messages Log in

KF IV Distance from DATUM to center of wheel
Goto page 1, 2 Next

Matronics Email Lists Forum Index -> Kitfox-List

View previous topic :: View next topic

Author Message

dcubj3(at)terra.com.br
Guest

Posted: Sun Jan 25, 2009 4:35 pm Post subject: KF IV Distance from DATUM to center of wheel

Hi!

 Someone knows which is the distance from DATUM  line to "center of wheel" in Kitfox Model IV ?? 

  

 See jpg attached of Highlander (www.justkitplanes.com)

 I need the same image of Kitfox IV, to find  answer to my question.

  

 Can you help me?

  

 Tks

 FD

 www.dcubj3.com.br

  

 [img]cid:EAA80A4E759F477B86BDBC9E17027B5B(at)compa563fded83[/img]

highlander.JPG

Description:

Filesize:

31.16 KB

Viewed:

594 Time(s)

eskflyer

Joined: 24 May 2007
Posts: 44
Location: AK

Posted: Sun Jan 25, 2009 4:52 pm Post subject: Re: KF IV Distance from DATUM to center of wheel

Need one more answer to answer your question . What landing gear are you using ? wide tall gear ?. Narrow gear?.  or the spring gear ?.  



ex718PD

New 3579erA

John

_________________
FLY FUN FLY LOW FLY SLOW
John Perry
Kitfox 2 N718PD
582 cbox 2:62-1 IVO IFA
1220 Full Lotus

Guy Buchanan

Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA

Posted: Sun Jan 25, 2009 5:22 pm Post subject: KF IV Distance from DATUM to center of wheel

At 04:30 PM 1/25/2009, you wrote:

  	  Quote: 	
		  Someone knows which is the distance from DATUM line to "center of wheel" in Kitfox Model IV ?? 

  	
I'll try this again, Francisco,



 At 03:15 PM 1/17/2009, you wrote:

  	  Quote: 	
		  I´d like to know if my spring aluminium (Grove Type) landing gear is in correct position.

 with this configuration, could be dangerous to land? 	


 Francisco,

         Sad to say it does appear that your landing gear are further aft than is typical with Grove gear. However, the only thing that matters are the numbers. My plane has its axle 1.875" (48mm) behind the leading edge when in the measurement configuration, which means the lower door sill / fuselage bottom is horizontal, and the plane is "empty". When in that configuration, 7.3% of the weight is on the tail wheel. (The tail wheel is 163" (4140mm) behind the leading edge.) Also in that configuration my CG is 13.68" (347mm) behind the leading edge. Let us know how that compares to yours.



 

 Guy Buchanan

 San Diego, CA

 K-IV 1200 / 582-C / Warp / 100% done, thanks mostly to Bob Ducar.    [quote][b]

_________________
Guy Buchanan
Deceased K-IV 1200
A glider pilot too.

Paul A. Franz, P.E.

Joined: 02 Dec 2008
Posts: 280
Location: Bellevue WA

Posted: Sun Jan 25, 2009 5:53 pm Post subject: KF IV Distance from DATUM to center of wheel

On Sun, January 25, 2009 4:30 pm, Francisco Drovetta wrote:

 	  Quote: 	
		   Hi!

 Someone knows which is the distance from DATUM line to "center of wheel" in Kitfox

 Model IV ??


	


For ease and safety in landing, the gear should be set as far forward as practicable.



The limit is usually dictated by the fuselage structure, that is, you can only mount

it to the forward limit of the fuselage. But in your case with what looks like a

forward mounted and heavy engine, weight and balance might be the limiting factor.



If you can supply the moment arms and weights of your existing setup, I can calculate

what happens when you move the gear.



I would need:



moment arm and weight of the main gear

moment arm and scale weight of tail wheel

moment arm and weight on main gear (empty, no fuel or oil) at tire contact point

moment arm for oil in crankcase

moment arm for fuel in tanks.

moment arm for occupants

moment arm for baggage



If the existing gear is not going to be used then I need the weight of the proposed

gear and location of it's c.g. relative to the fore and aft mounting positions.



 	  Quote: 	
		  

 See jpg attached of Highlander (www.justkitplanes.com)

 I need the same image of Kitfox IV, to find answer to my question.



 Can you help me?



 Tks

 FD

 www.dcubj3.com.br


	




-- 

Paul A. Franz

Registration/Aircraft - N14UW/Merlin GT

Engine/Prop - Rotax 914/NSI CAP

Bellevue WA

425.241.1618 Cell

_________________
Paul A. Franz, P.E.
Registration/Aircraft - N14UW/Merlin GT
Engine/Prop - Rotax 914/NSI CAP
Bellevue WA
425.241.1618 Cell
425.440.9505 Office

Paul A. Franz, P.E.

Joined: 02 Dec 2008
Posts: 280
Location: Bellevue WA

Posted: Sun Jan 25, 2009 6:07 pm Post subject: KF IV Distance from DATUM to center of wheel

On Sun, January 25, 2009 4:30 pm, Francisco Drovetta wrote:

 	  Quote: 	
		   Hi!

 Someone knows which is the distance from DATUM line to "center of wheel" in Kitfox

 Model IV ??



 See jpg attached of Highlander (www.justkitplanes.com)

 I need the same image of Kitfox IV, to find answer to my question.


	


Check out the photo of Bruce Hoisington's Series 7 KF with what appears to be Grove gear.



<http://www.kitfoxaircraft.com/images/Recent%20Completions/BHoisington.htm>



It looks like the gear is mounted about where yours is, slightly behind the datum

(leading edge of wing).



-- 

Paul A. Franz

Registration/Aircraft - N14UW/Merlin GT

Engine/Prop - Rotax 914/NSI CAP

Bellevue WA

425.241.1618 Cell

_________________
Paul A. Franz, P.E.
Registration/Aircraft - N14UW/Merlin GT
Engine/Prop - Rotax 914/NSI CAP
Bellevue WA
425.241.1618 Cell
425.440.9505 Office

lcfitt(at)sbcglobal.net
Guest

Posted: Mon Jan 26, 2009 8:33 am Post subject: KF IV Distance from DATUM to center of wheel

I suspect that what Francisco actually needs is the location of the axle 

relative to the CG.  I think the easy way to approximate this is by 

tailwheel weight vs. empty weight.  My first Kitfox had a tailwheel wt of 44 

lbs. vs an empty wt of 704 lbs. - yes a heavy.  This gives 6.25% on the 

tailwheel.  From what I see in the pictures on Francisco's website, I 

suspect his emtpy weight in the 850 lb range giving a tailwheel weight in 

the range of  53 lbs.  This in level attitude.



Lowell



---

dcubj3(at)terra.com.br
Guest

Posted: Mon Jan 26, 2009 5:40 pm Post subject: KF IV Distance from DATUM to center of wheel

Mr. Lowell Fitt

Mr. Paul Franz

Mr. Guy Buchanan



Tks a lot for useful information.



Attached is excel file W&B of my aircraft info.



Tks



FD

www.dcubj3.com.br



---

PESO_BALANCEAMENTO_PU-KFV_FRANCISCO_DROVETTA02.xls

Description:

Download

Filename:

PESO_BALANCEAMENTO_PU-KFV_FRANCISCO_DROVETTA02.xls

Filesize:

25.5 KB

Downloaded:

531 Time(s)

lcfitt(at)sbcglobal.net
Guest

Posted: Mon Jan 26, 2009 10:06 pm Post subject: KF IV Distance from DATUM to center of wheel

Well, Francisco, I wasn't too far off with the empty weight estimate, and it 

should fly fine based on your W&B numbers, but the tailwheel wt. should be 

much heavier.  Since you have the spring gear, could you fabricate an 

extension that could be bolted to the gear at the axle attachment, extending 

the axle forward in increments until you get the 55 lbs. that you should 

have with that empty weight and that then would be your proper axle 

location.  You could then fabricate new attachment points for the spring 

gear or maybe use tube gear that would angle forward to the correct axle 

location.



Lowell



---

Guy Buchanan

Joined: 16 Jul 2006
Posts: 1204
Location: Ramona, CA

Posted: Mon Jan 26, 2009 10:39 pm Post subject: KF IV Distance from DATUM to center of wheel

At 05:39 PM 1/26/2009, you wrote:

 	  Quote: 	
		  Attached is excel file W&B of my aircraft info.



Tks


	


Francisco,

         My IV build manual shows a CG range of 10.7" - 14.8". The 

latter was changed by service letter to 16". Where did you get your 

numbers? Also, did you obtain your pilot location by weighing the 

aircraft with the pilot in it? When I did my W&B I weighed with and 

without pilot. I found the pilot location to be 15.8" behind datum. 

Finally, is it true that your aircraft is not really a Kitfox IV, but 

a copy? If so, I guess that none of this really matters, since it 

appears your plane flies just fine.

Guy Buchanan

San Diego, CA

K-IV 1200 / 582-C / Warp / 100% done, thanks mostly to Bob Ducar.

_________________
Guy Buchanan
Deceased K-IV 1200
A glider pilot too.

Paul A. Franz, P.E.

Joined: 02 Dec 2008
Posts: 280
Location: Bellevue WA

Posted: Tue Jan 27, 2009 4:11 am Post subject: KF IV Distance from DATUM to center of wheel

On Mon, January 26, 2009 10:01 pm, Lowell Fitt wrote:

 	  Quote: 	
		   



 Well, Francisco, I wasn't too far off with the empty weight estimate, and it

 should fly fine based on your W&B numbers, but the tailwheel wt. should be

 much heavier.  Since you have the spring gear, could you fabricate an

 extension that could be bolted to the gear at the axle attachment, extending

 the axle forward in increments until you get the 55 lbs. that you should

 have with that empty weight and that then would be your proper axle

 location.


	


That would be more difficult than just calculating the effect of moving it. Using his

spreadsheet numbers for weights and moments I could easily do that if I only knew the

weight of his main gear. That is the weight of the assembly that would be moved

forward.



My concerns are getting the proper allowable weight and balance envelope for his

particular airplane as moving the main gear forward will alter the CG. Ideally it

should be moved forward as far as possible. The limits would be one of:



1) practical forward limit for attaching the gear to the structure

2) forward CG limit

3) maximum allowable tail wheel weight.



I think normal conventional design is a tail wheel weight of 5 to 10% of the gross

weight. This might be limited by the tail wheel spring(s) or the tail wheel itself.

But, I think it could be much higher than 55 lbs. Certainly it needs to be higher than

the 15 lbs he shows now.



So, if you know the weight of the main gear assembly that would be moved or in the

case of changing gear types, the weight of the old and the weight of the new, I can

calculate new weights at the wheels for any new gear position. In fact, I could do it

in spreadsheet fashion so you could just plug in the new moment arm and get the

results.



I guess one could do it for plugging in both the weight and the position. For me it's

a matter of time available.



-- 

Paul A. Franz

Registration/Aircraft - N14UW/Merlin GT

Engine/Prop - Rotax 914/NSI CAP

Bellevue WA

425.241.1618 Cell

_________________
Paul A. Franz, P.E.
Registration/Aircraft - N14UW/Merlin GT
Engine/Prop - Rotax 914/NSI CAP
Bellevue WA
425.241.1618 Cell
425.440.9505 Office

propellerdesign(at)tele2.
Guest

Posted: Tue Jan 27, 2009 5:01 am Post subject: KF IV Distance from DATUM to center of wheel

Moving the gear a few inch forward will not move the CG much, it will add 

weight to the tail.



most taildragger have the main gear close to the leading edge of mean 

aerodynamic chord, just a few inch behind.



the main wheel should be so placed that a line from wheel axle to CG is 

15-25deg with tail up, meaning we need to know not just the cg in length but 

also height position.



Jan

---

Tom Jones

Joined: 12 Mar 2006
Posts: 752
Location: Ellensburg, WA

Posted: Tue Jan 27, 2009 6:29 am Post subject: Re: KF IV Distance from DATUM to center of wheel

 	  Quote: 	
		  Attached is excel file W&B of my aircraft info. 



Tks 	




Francisco, the primary issue I see in your weight and balance sheet is that the axle centerline is only 1.7 inches forward of the forward CG limit...assuming one degree forward wing sweep.



The 'Most adverse forward" on your sheet should be labeled 'Most adverse aft".  Doing some quick and dirty math with the 154 pound pilot, 30 pounds fuel and no baggage, I calculate a "Most adverse forward" CG of 12.0 inches and gross weight 1069 for your plane.  With these numbers the axle is still only 3.74 inches forward of the CG.



To compare, my Classic 4 axle center line is 2.5 inches behind the datum and the forward CG limit is 10.2 inches.  Axel is 7.7 inches forward of forward CG limit.



My actual calculated most adverse forward CG is 12.3 inches at a gross weight of 796 pounds.  The axle is 9.8 inches forward of CG.



Your plane will also have more inertia due to the heavier gross weight.  Just a little too much brakes or a gust of a tail wind and your beautiful plane will be on its back.



I would not taxi until this condition is resolved.

_________________
Tom Jones
Classic IV
503 Rotax, 72 inch Two blade Warp
Ellensburg, WA

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Tue Jan 27, 2009 7:45 am Post subject: KF IV Distance from DATUM to center of wheel

Lowell:



 I just ran a couple of calculations and I think he needs to move his main

wheels ahead to position 3.21 in. aft of datum to provide 45Lb. on the tail

wheel at empty weight.



I think all aboard will agree 15 lb is way too small a weight on the tail

wheel for a close to 900 lb. plane.  In the mean time he should keep his

feet off the brake pedals.



Just for the fun of it my calculations started with 

45lb on the tail (at)151.8in.  = 6831 an increase in moment at the tail of

4486.  This moment to be subtracted from the total of the main moments.

(3610.28+3573.85)-4486 698.13



I then subtracted the 29.55 lb added to the tail from the total of the front

wheels.  (437.08+432.67)-29.55=837.2



Finally 2698.13/837.2= 3.22  that is just about a full five inches forward

from where it is now.



Truth is because the landing gear itself has weight it will probably put

slightly less than 45lb. on the tail wheel.



Noel



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

lcfitt(at)sbcglobal.net
Guest

Posted: Tue Jan 27, 2009 8:07 am Post subject: KF IV Distance from DATUM to center of wheel

Paul,



That is the problem I find with math.  The typical weight if the Grove gear 

including fasteners and axle is 30 lbs and that was on personal inquiry from 

Grove.  In my head you would be moving a 30 lb. wt. forward about 10 inches 

or so by my guess - no math, just looking at my uncovered fuselage and where 

his gear is and where mine is.

Regarding the 55 lbs. That was calculated based on my tailwheel wt. vs. 

gross wt. and my airplane flew fine with full three point elevator 

authority.  Lynn Matteson said his tailwheel wt was in the 55 lbs. range as 

well and that was at 6.25%.  Maybe it is time for another survey .



Lowell

---

Tom Jones

Joined: 12 Mar 2006
Posts: 752
Location: Ellensburg, WA

Posted: Tue Jan 27, 2009 8:34 am Post subject: Re: KF IV Distance from DATUM to center of wheel

I did some "What if" computer weight and balance assuming 50 pounds for the landing gear.  With Francisco's weight and balance numbers the 50 pound gear can be moved to zero inches from the datum (at wing leading edge) and it moved the empty weight CG only about a half inch forward.  



I think there is room in the numbers to move the gear forward enough that the tail weight will take care of its self.

_________________
Tom Jones
Classic IV
503 Rotax, 72 inch Two blade Warp
Ellensburg, WA

propellerdesign(at)tele2.
Guest

Posted: Tue Jan 27, 2009 8:57 am Post subject: KF IV Distance from DATUM to center of wheel

If wing cord is same on BrazFox as Kitfox wheel should be at same distance 

from leading edge of wing.

(datum is something that can be placed any where, but is convenient to have 

on same place as other of same brand.



Jan

www.jcpropellerdesign.com



---

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Tue Jan 27, 2009 8:59 am Post subject: KF IV Distance from DATUM to center of wheel

C of G is fine for flight.  But only having 15 lb on the tail wheel means he

won't have to use very much brake to turn it on its nose.  

Especially on a short field landing.  One thing for sure he won't break any

tail springs.



Noel



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Tue Jan 27, 2009 10:10 am Post subject: KF IV Distance from DATUM to center of wheel

P.S. when nothing else works simple math does.  



Noel



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Tue Jan 27, 2009 10:11 am Post subject: KF IV Distance from DATUM to center of wheel

Re ran my calculations for a 65 lb tail wheel the answer comes out that the

main wheel should be .41 in ahead of the datum.  This maintains the current

C of G



Noel



--

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

Float Flyr

Joined: 19 Jul 2006
Posts: 2704
Location: Campbellton, Newfoundland

Posted: Tue Jan 27, 2009 11:44 am Post subject: KF IV Distance from DATUM to center of wheel

I just did a search on the web to try to get a handle on what the weight on

the tail wheel should be for similar configured airplanes, if not similar

weight.  I checked C-180s and Pa-18s They both have the tail wheel out under

the rudder. They were all around 5.5% of total weight on tail give or take

0.1% except for one Super Cub that was way down at 4.6% and that guy was

having problems with his W&B.



Going by that search, and limited data, I calculated the tail of the plane

should be around 48.68 lb. Give or take a pound or two. To get that weight

on the tail wheel without changing the CG would require the mains be located

2.31 in aft of the datum. I double checked the calculations and that

includes the movement of the weight of the mains.  I think he will be safe

by moving the mains 5" ahead.  His plane should have the same flight

characteristics but be a lot safer landing.



Any way we want to cut the grass I think we all concur that the mains are

much too far aft to be safe if any braking is to be used.  If he doesn't

mind loooooooong run outs and stays away from rough strips the gear that far

aft probably somewhat reduces the possibility of a landing loop as does the

far aft gear on a tricycle gear plane.



Noel

_________________
Noel Loveys
Kitfox III-A
Aerocet 1100 Floats

Display posts from previous:

	Matronics Email Lists Forum Index -> Kitfox-List	All times are GMT - 8 Hours Goto page 1, 2 Next
Page 1 of 2

Jump to:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum