Need some gear measurements

[akflyer 1427]

Howdy guys,

I am going to design and build a new and improved "bush gear" based off the gear I have now.  In reading up on it I have found that the stock kitfox gear goes straight down from the mount on the forward leg and the Avid gear is raked forwards 3 7/8".  I like to run at the back end of the CG range and I hate how heavy my tail is.  I would love to be able to pick the tail up with full down elevator and some power to get it out of the sand or snow.  Can someone who has stock kitfox gear post up and let me know if the front leg is indeed straight down from the mount or is it too raked forwards a bit.  I am thinking of reducing the rake on the gear and this should let me get the tail up a bit quicker and result in shorter take offs.  I may have to watch the braking with the double puck brakes so I don't decide to eat the prop.

Thanks

 

[EDMO 1078]

Leni, here is a photo of my KF2 when it was a taildragger with stock gear - maybe this will help?   If you look close, there are silver colored threaded rods sticking straight down from wing attach fittings.   I believe the front tube goes at a 90 degree angle from the longerons, although the gear shown at an angle don't show it well.   I have a gear set in storage.   If  someone could post the WB figures it would show where the axles are in line with leading edge datum.  I will look for that. 

OK - Don't have figures on KF2, but KF4 Classic sample page shows axle at 3.20" from leading edge.   You could compare that with your Avid WB figures.   But the KF4 may be including the 1" plastic leading edge?

Edited 22 Jan 2017 by EDMO

[Dusty 126]

 

I have a Highwing  gear and std  kitfox gear,I have also found with a rearward c of g the tail takes too long to get up. Moving the gear rearward would be an improvement,I wouldn't worry too much about sticking your prop in the dirt (try sitting in your plane and getting a helper to lift the tail till the prop contacts the ground!)

When your mods are done I would be real keen to hear how much improvement this makes.

cheers

[tcj 150]

Kitfox Classic 4.  The center of the axle is raked forward 3 inches from the front of the front leg at the front mount.

Edited 22 Jan 2017 by tcj

[EDMO 1078]

tcj,  Does your WB show axle location different than the 3.20" behind leading edge that the KF4 sample page shows?  EDMO

Edited 22 Jan 2017 by EDMO

[tcj 150]

Centers of the front axles are 2.5 inches aft of the wing leading edge.

Weight and balance Spread Sheet.xls

[EDMO 1078]

Centers of the front axles are 2.5 inches aft of the wing leading edge.

Weight and balance Spread Sheet.xls

Do you have the plastic leading edge extension or is that from front spar?  Thanks, EdMO

[Av8r3400 1178]

Centers of the front axles are 2.5 inches aft of the wing leading edge.

Weight and balance Spread Sheet.xls

Do you have the plastic leading edge extension or is that from front spar?  Thanks, EdMO

 

Classic IV = Improved Riblett Airfoil = Extruded leading edge.  This is a given.

Standard Grove Gear places the axle right on the leading edge, +/- 1/2".  My custom gear placed the axle 2" forward.

Edited 22 Jan 2017 by Av8r3400

[lostman 198]

Centers of the front axles are 2.5 inches aft of the wing leading edge.

Weight and balance Spread Sheet.xls

Do you have the plastic leading edge extension or is that from front spar?  Thanks, EdMO

 

Classic IV = Improved Riblett Airfoil = Extruded leading edge.  This is a given.

Standard Grove Gear places the axle right on the leading edge, +/- 1/2".  My custom gear placed the axle 2" forward.

Larry, I take it you would be able to get on your brakes pretty hard and not worry about rolling forward right? How do you like this gear placement?

[akflyer 1427]

Thanks guys.  I have got it drawn up to have the center line of the axle 2" in front of the forward mount.  I think this will take a tad bit of weight off the tail but still allow you to brake just about as hard as you want.  I know with the rake on my gear there is no way I am going to nose over even locking the brakes up with the double pucks.  Its about impossible to taxi with full power and brakes and keep the tail up with the rake I have now. 

 

The gear is also extended 3" to give a better AOA.  Will see how it works out on this set, if it needs to be changed then its easy to do.  The pull on the cabanes is much closer to a cub and not going straight side to side as others have done, I dropped the center point down 4" to help spread the pull.  Cad work is 85% complete and should have it finished up tonight!

 

Edited 22 Jan 2017 by akflyer

[Av8r3400 1178]

 

Larry, I take it you would be able to get on your brakes pretty hard and not worry about rolling forward right? How do you like this gear placement?

Yes.  Especially in 3-point there is no issue getting on the binders hard.  The new plane, with the larger elevator, allows for harder braking up on the wheels, too.

[zadwit 105]

There is a formula that aircraft designers use for TW aircraft. The determine the aft CG loaded for flight, level  the aircraft and draw a line vertical thru the CG. Then they measure 12 degrees from the CG forward and that line shoujld  not go thru the axles center line. If it does, it make the airplane very tail heavy and hard or nearly impossible to control. Ironically I read this in Design for flying by Dave Thurston, aeronautical engineer and a few days before I read it I was talkeing to Dean Wilson about trouble with ground handling on my Ridge Runner 1. Guess what, the Axle center line is 20 degrees maybe a little more ahead of the Datum, with plane loaded aft CG ready to fly on the Ridge Runner which is why it is such a squirrel on the ground. The Main gear axles are 8.75" fwd of the WLE on the Ridge Runner 1. When loaded to most fwd CG the angle from CG to axle is 10 degrees but it will never be there bevause the fat pilot is 22" aft!!!! so most of the time the wing CG is at the aft limit of 16 inches.........

The tail is slow to come up even with a 503, a bigger engine than designed.. and it wanders all over the runway. Does not want to go straight. The closer the axle centerline is to the loading flying CG, the more stable ground handling, easier to nose over, but tail  comes up quik.  Partly at Play on the PA-180150 is the engine is canted down on the mount, the engine is powerful and so the thrust line is above the axles quite a ways which all adds to lifting the tail quickly.  COnverted Tri pacer to tailwheel were terrible  on skis because you could not get the tail up out of the snow so takeoff runs for very long. The PA20 was not as bad because it had more down elevator travbel,, a lot more down travel.

 

Same problem  on the TexasTail Dragger Cessna 150, the gear so far fwd impossible to pickup the tail on takeoff so in the snow a real problem....

I have not measured the angle on a PA 18 but I looked this info up. Datum is Wing Leading Edge (WLE)

Axles centerline is 2" aft of the datum. Level the plane  and the axle will be 2" aft of the WLE, the CG  is still farther aft,

CG range is 10.5" to 20" aft of the WLE on PA-180150

YOu would need a scale dwg of a pa-18, mark the CG location fwd and aft, then draw a line 12 degrees thru the CG at the wing down towards the axles and see what it measures..

 

 

Edited 19 Nov 2017 by zadwit

[zadwit 105]

[zadwit 105]

On the Ridge Runner 1 the axles centerline is so far forward of the all up loaded CG that if you try to lift the tail on takeoff,it will try to eat you!!!! and had eaten many a test pilot......

[zadwit 105]

When I talked to Dean Wilson a few months ago about placement of the axle centerline on a tail dragger he had some interesting info.

He said when the JN4 Jenny first came out, it had no brakes and on tail wheel, only a tail skid so the axle center line was placed real close to the loaded flying CG. This worked fine until brakes were installed then the planes started getting nosed over so the axle centerline was moved forward. He told me about the 12 degree angle. IF you level the plane, drop a plumb bob thru the CG on the wing and then measure off that vertical line forward 12 degrees is about all you want . More than that makes the plane hard to control on the ground.

A lot less and you are prone to nose over... There has to be  a happy medium especially if operating on skis, plus wouldnt it be nice if you had more precise control on takeoff without the damn plane trying to Eat you all the time?????!!?

[akflyer 1427]

Thanks for that info.  The gear project stalled out due to various personal issues, but I will run the numbers and see what I come up with.  I am with you on the need to be able to get the tail in the air especially when on skis.  Right now even with full down elevator I cant get the tail off the ground till about 30 MPH.  On skis that sucks ass in a big way!  It also acts like a big anchor flying off the sand beaches.  A larger wider tail wheel is a band aide not a fix.