Extreme Gear Moment Arm

For general discussion of the Just Aircraft family of aircraft.
Includes: Highlander, Escapade, Summit and SuperSTOL.

Moderator: scubarider2

Extreme Gear Moment Arm

Postby FredHoffman » Fri Dec 01, 2017 9:21 am

Anyone know if the highlander extreme gear and standard gear have the same moment arm. I had the plane leveled and measured the other moment arms such as my tailwheel which is far from stock but forgot to measure the main wheels. From eyeballing it it looks close to the same but without going through jacking it up and leveling again I can't be sure. The manual gives an arm but the drawing shows the standard gear.

My initial calculations using Just's main gear data show in GC with one person(150 lb) as well as two heavy people (like me), bags and full fuel. I thought that was pretty lucky.

Fred
FredHoffman
Seasoned Member
 
Posts: 88
Joined: Fri Mar 23, 2012 8:57 pm

Re: Extreme Gear Moment Arm

Postby Tralika » Sat Dec 02, 2017 11:16 am

Fred,
I have Extreme Gear and I used the same Arm as the standard gear when I weighed my plane. I did not take a measurement to confirm the axle was the same dimension as in the manual. Now that I read your post I wonder if I should have. I'm confident the Arm is unchanged but that's not the same as being sure. The way to get a definitive answer is to call Just. Are you going to call or do you want me to?
John Nealon
Wasilla, Alaska
Highlander Extreme #191
mykitlog.com/jnealon
Tralika
Veteran Member
 
Posts: 216
Joined: Thu Oct 08, 2009 12:49 pm
Location: Wasilla Alaska

Re: Extreme Gear Moment Arm

Postby SheepdogRD » Sat Dec 02, 2017 10:32 pm

Seems like the extreme gear should be different. The legs are all thicker wall, larger diameter, and longer, plus there's an extra leg. I'd expect it to be additional weight, further aft.
Richard Holtz
Highlander N7340Z -- Ms. Tonka -- in gestation

If just enough is really good, then too much ought to be perfect.
User avatar
SheepdogRD
Veteran Member
 
Posts: 690
Joined: Tue Nov 30, 2010 5:41 pm
Location: West of Atlanta, GA

Re: Extreme Gear Moment Arm

Postby Tralika » Sun Dec 03, 2017 10:39 am

The Extreme Gear legs certainly weigh more. That extra weight is accounted for when the airplane is on the scales. The issue is the location of the axle relative to the air frame so the correct Center of Gravity can be determined. I used the published 8 3/4" forward of the leading edge of the wing when calculating my W&B. Now we need to confirm that is correct. I'd like to hear what the folks at Just have to say but there's really no excuse not to lift up the tail, level the plane, drop a plumb bob off the wing and measure it.
John Nealon
Wasilla, Alaska
Highlander Extreme #191
mykitlog.com/jnealon
Tralika
Veteran Member
 
Posts: 216
Joined: Thu Oct 08, 2009 12:49 pm
Location: Wasilla Alaska

Re: Extreme Gear Moment Arm

Postby moving2time » Mon Dec 04, 2017 11:19 am

Without having both gear it is impossible to tell for sure but from photos it appears that the heavy duty gear locates the axle of the main gear in the same location. That is the critical measurement for the weight and balance. Obviously the weight is different and the third leg is going to add a touch more weight to the tail. It appears that the first two legs of the heavy duty gear are identical in plan and should lay over the standard gear plan. The third leg is added to that plan. The factory can easily confirm this though.

Question: Are the weights taken with the plane leveled out so the tail wheel scale is elevated to support the tail in level position or is it done with all scales on the ground? I have never done this so I am not sure because all I have ever seen is people weighing their aircraft with all wheels on the ground. This is probably detailed in the FAA documents but that is way to much work to look up. Clearly the location of the main gear axle is critical to the weight and balance no matter how you calculate it. :) Thanks. Joe B
moving2time
Veteran Member
 
Posts: 203
Joined: Fri Oct 15, 2010 5:42 pm

Re: Extreme Gear Moment Arm

Postby Tralika » Mon Dec 04, 2017 12:03 pm

When weighing the plane it must be level front to rear and side to side. On the Highlander/Super STOL you use the airframe headrack above the doors/panel to determine level. If you can get your hands on a set of digital scales it will make the job pretty easy. The scales are used in the auto racing industry and can be rented. Not cheap but much easier and more accurate than using balance scales. You can download the FAA Weight and Balance Handbook (FAA-8-8083-1B) for free. Lots of information in there but Chapter 3 is the meat and potatoes for actually weighing the plane. Also, the EAA has free Hints for Homebuilders instructional videos available on their web page. After you weigh the plane and determine the empty CG you'll have to calculate the W&B for the Lightest Load, Heaviest Load, Most Forward CG and Most Aft CG. That report will go with your paperwork that you give to the DAR during your inspection. I watched the videos and read the W&B Handbook before I weighed my plane. It's not difficult but something you want to get right.
John Nealon
Wasilla, Alaska
Highlander Extreme #191
mykitlog.com/jnealon
Tralika
Veteran Member
 
Posts: 216
Joined: Thu Oct 08, 2009 12:49 pm
Location: Wasilla Alaska

Re: Extreme Gear Moment Arm

Postby Tralika » Mon Dec 04, 2017 12:16 pm

I just got off the phone with Jac at the factory. There is no difference in the arm between the standard gear axle and the extreme gear axle. The extreme gear is just two inches longer. Now I'm confident and sure.
John Nealon
Wasilla, Alaska
Highlander Extreme #191
mykitlog.com/jnealon
Tralika
Veteran Member
 
Posts: 216
Joined: Thu Oct 08, 2009 12:49 pm
Location: Wasilla Alaska

Re: Extreme Gear Moment Arm

Postby FredHoffman » Mon Dec 04, 2017 5:29 pm

John,
Thanks for making the call! Saves me jacking the plane up again! ............and possibly putting a hole in the fabric ! I was very nervous with the plane leveled and up on the scales. Looked to me like it could roll off and create some major damage.

Fred
Last edited by FredHoffman on Mon Dec 04, 2017 5:36 pm, edited 1 time in total.
FredHoffman
Seasoned Member
 
Posts: 88
Joined: Fri Mar 23, 2012 8:57 pm

Re: Extreme Gear Moment Arm

Postby moving2time » Mon Dec 04, 2017 5:34 pm

Thanks John. I had a feeling that weighing the plane for the weight and balance had to be done with the aircraft level. Forgot about the length difference in the extreme gear. From photos it appears that the front leg of both of the stock and extreme gear is vertical which is why I figured the axle would be in the same location. I'm guessing that since it is vertical the length of the gear doesn't affect the weight and balance. Either way, it has been confirmed by the factory.
moving2time
Veteran Member
 
Posts: 203
Joined: Fri Oct 15, 2010 5:42 pm

Re: Extreme Gear Moment Arm

Postby Tralika » Mon Dec 04, 2017 8:01 pm

I felt the same way about having the tail propped up so high when I was weighing the plane. I had the tail propped up so the plane was level many times during the build process but most of the time the main wheels were not mounted and the axles were resting on dollies that did not move easily. I made a four sided wheel chock mounted on a small piece of plywood for the tailwheel. I used that on my Workmate portable workbench and it was always very stable. I was able to put that on the scale and then zero the scale before I weighed the plane. I didn't have wheel chocks on the main tires when they were on the scales. When the plane was on the scales I rocked it back and forth a few times and it didn't move much. Even so I was glad to get that tail wheel back on the ground.
Attachments
DSC04123(1).JPG
John Nealon
Wasilla, Alaska
Highlander Extreme #191
mykitlog.com/jnealon
Tralika
Veteran Member
 
Posts: 216
Joined: Thu Oct 08, 2009 12:49 pm
Location: Wasilla Alaska


Return to Just Aircraft