Landing gear question

[Will Weidner]

I have a question about the landing gear height.  On page 22 of the plans there is height of 17.5".  Is this the height when your using 20" BMX wheels, or Blackmax wheels?  Looking at pictures of XL's with Blackmax wheels, it sure looks like the gear is a lot taller than 17.5" (compare it to the 22" fuselage height).  17.5" would make sense for the BMX wheels.  I'm asking because otherwise the plans seem to be geared toward using the Blackmax wheels.  The BMX wheels are 20" OD, and the Blackmax are about 12.5" OD, so there would be an axle height difference of (20-12.5)/2 = 3.75".  It kind of makes sense that the Blackmax axle vertical dimension would be 17.5 + 3.75 = 21.25".  I hope one of you guys with your XL sitting on wheels can help.  Sorry if this is obvious to everyone.  Thanks.

[scottiniowa]

I have a question about the landing gear height.  On page 22 of the plans there is height of 17.5".  Is this the height when your using 20" BMX wheels, or Blackmax wheels?  Looking at pictures of XL's with Blackmax wheels, it sure looks like the gear is a lot taller than 17.5" (compare it to the 22" fuselage height).  17.5" would make sense for the BMX wheels.  I'm asking because otherwise the plans seem to be geared toward using the Blackmax wheels.  The BMX wheels are 20" OD, and the Blackmax are about 12.5" OD, so there would be an axle height difference of (20-12.5)/2 = 3.75".  It kind of makes sense that the Blackmax axle vertical dimension would be 17.5 + 3.75 = 21.25".  I hope one of you guys with your XL sitting on wheels can help.  Sorry if this is obvious to everyone.  Thanks.

Hello Will!
    you have noted some good things that must be figured out in accordance to your end desires.   I documented three different wheel heights and the effects here
  http://www.eaglersnest.com/forum/index.php?action=downloads;cat=11 

Hopefully that will direct you to the exact page and you will see three different down loads you can look over for this question.  Or go to <down loads> then <graphic aids by Scottiniowa> and then to the wheel height ones (1, 2 and 3) 
And as you have calculated, the wheel size effects the height by 1/2 of the difference in wheel dia.   i.e. 20" wheel is a center axle of 10" and a 10" wheel is 5", thus the actual height change is 5". 

 Some toss in different lengths of A frame gear legs (different from plans) thus changing parts of the equation.  Simple math does most of it for you.   In the end, Your physical weight, engine HP, airstrip conditions all ALSO lend themselves to   the take off and landing distances and speeds.

cheers

[Will Weidner]

Thanks, Scott.  I downloaded those files when I first came across them a couple years ago.  So the idea is to make the gear height based on how you want it to set on the ground?  And this is based on your individual preference?  Just seems like there should be a predetermined fuselage angle relative to the ground that works best for most situations.

By the way, thanks for putting so much stuff out there.  It's been really helpful overall.

[Dan_]

 So the idea is to make the gear height based on how you want it to set on the ground? 

I don't want to speak for builders who have made changes to their planes, but I think the idea for the change here is make the gear height based on how you want it to land.

In general in most airplanes, the higher you make the nose sit the harder it is to see out, but the slower and therefore shorter you can make it land (think full stall 3 point).   

If you always make wheel landings then you will want to keep it flatter sitting on the ground.

Make the gear to plans,  change it latter if you want...