+ Reply to Thread
Results 1 to 9 of 9

Thread: Landing Gear Help

  1. #1
    Registered User bradyaero's Avatar
    Join Date
    Mar 2010
    Location
    Canada
    Posts
    67

    Landing Gear Help

    Hi,

    I've been designing a square tube ultralight and have been having a hard time figuring out how to create a light and cost effective main landing gear.

    I've settled on two ways that might work, the first is tubing with a central 'welded mount that the tubing fits in, with a cross wire for bracing (similar to challenger - see purple piece on drawing). The second is flat spring aluminum that bolts into a cross mounted piece of tubing.

    Any thoughts on what might work better or is there another method that might work better?

    Thanks for any suggestions!

    Landing Gear Help-landinggear.jpg
    'The Piper Cub is the safest airplane in the world;it can just barely kill you.'
    - Attributed to Max Stanley ( Northrop test pilot) -

  2. #2
    Registered User
    Join Date
    Apr 2007
    Location
    Northern California
    Posts
    328

    Re: Landing Gear Help

    Mounting the gear to that single square tube will result in very high torsional stresses, unless you somehow never land with more weight on one wheel or hit any bumps or such on the runway. With a structure that skinny laterally (side to side) there really isn't any structure to resist the moments generated by different drag loads on the two wheels trying to twist the gear around the vertical axis. Think about putting a long wrench on a small bolt and giving the wrench a push, with a small bolt it will just twist the bolt off, that is what you are trying to do with this setup. You have the same problem along the longitudinal axis (front to back), the gear as shown would wrench the lower member of the fuselage truss severely even with minor amounts side force or different weight on the two wheels at touchdown, bumps etc. If you look at trikes that use a similar single plain truss they commonly use a shock absorber from the axle up to the top of the truss, creating a triangulation. With the current design you just won't get the strength needed as the structure won't be stiff enough or strong enough to take it. You will likely need a bit more structure to tie the gear into the main structure, you could combine this with strut mounts for the wing possibly to gain some synergy in the structure.

  3. #3
    Registered User bradyaero's Avatar
    Join Date
    Mar 2010
    Location
    Canada
    Posts
    67

    Re: Landing Gear Help

    I agree with what you are saying, there will be a fairly large gusset bolting the main boom tube, engine support and secondary mast.

    I still need to figure out how to attach landing gear to the gusset. If I do a 90 degree bend on the gussets at the level of the main tube, I would then have a nice flat area to bolt to if I did a flat stock type landing gear - but if I try for a tube leg landing gear I still need to weld or bolt in some tubing as main landing gear support . It's a tricky thing to figure out, I sure don't want high torsional stresses on the main tube!

    Thanks for the reply!
    'The Piper Cub is the safest airplane in the world;it can just barely kill you.'
    - Attributed to Max Stanley ( Northrop test pilot) -

  4. #4
    Registered User bradyaero's Avatar
    Join Date
    Mar 2010
    Location
    Canada
    Posts
    67

    Re: Landing Gear Help

    fiberglass or aluminum flat legs bolted to gusset:

    Landing Gear Help-landing2.jpg
    'The Piper Cub is the safest airplane in the world;it can just barely kill you.'
    - Attributed to Max Stanley ( Northrop test pilot) -

  5. #5
    Registered User
    Join Date
    Apr 2007
    Location
    Northern California
    Posts
    328

    Re: Landing Gear Help

    You still have the problem that the piece of structure you are bolting it to is all of what 2-inches wide? There just isn't enough stiffness there. What I would suggest is making a small frame at that location that attaches to the main frame but pushes the connections for the gear off to the side several inches on each side and goes up to the top of the truss. This could be two triangles made of tubing or a bent up sheet aluminum structure. I would also create a similar frame in the longitudinal axis so running forward to the next truss connection. You could use the outside points of these triangular frames as both the attachment area for the gear and for any flying wires or struts for the wing. This would greatly reduce the stresses on the structure. I understand the allure of the single plain truss, it seems so simple, but it really lacks rigidity and strength in torsion and side to side. You can make it work like Goat gliders with wires to handle the out of plane forces, but that doesn't work well for the gear legs.

  6. #6
    Registered User bradyaero's Avatar
    Join Date
    Mar 2010
    Location
    Canada
    Posts
    67

    Re: Landing Gear Help

    The main boom is 3x3 6061 1/8 wall. The 3x3 would be expanded by 3" on each side of the gusset giving 9" of flat bolting area reinforced in the roll axis by 12" of vertical gusset. Yaw stability provided by 6" of width x .5 of uni-glass mix or an equivalent piece of spring aluminum. A cross wire to share forces between legs, and perhapse a triangulation wire from the main mast to each leg???

    Any hope of that working? As a proof of concept the Sandpiper or did it have issues?

    Thanks again DaveK!
    Attached Thumbnails Attached Thumbnails Landing Gear Help-sandpiper2.jpg  
    'The Piper Cub is the safest airplane in the world;it can just barely kill you.'
    - Attributed to Max Stanley ( Northrop test pilot) -

  7. #7
    Registered User
    Join Date
    Apr 2007
    Location
    Northern California
    Posts
    328

    Re: Landing Gear Help

    Don't know about the service history of that particular aircraft, but bracing the legs with wires in the way essentially gives you a rigid gear, so no shock absorption. They sort of did what I'm talking about by using that rather beefy probably welded up steel bracket which appears to be one piece with the gear leg leaf. See my rather crude drawing to get an idea of what I'm talking about if it wasn't clear. Landing Gear Help-20120110171026.jpg

  8. #8
    Registered User dino's Avatar
    Join Date
    Sep 2007
    Location
    florida
    Posts
    264

    Re: Landing Gear Help

    A small A frame like DaveK suggests.Landing Gear Help-img00149-20111031-1456.jpg

    Dino

  9. #9
    Registered User bradyaero's Avatar
    Join Date
    Mar 2010
    Location
    Canada
    Posts
    67

    Re: Landing Gear Help

    Wow that works! Thanks for the pics! So no matter what, triangulation will be required to carry the landing and takeoff forces adequately? I was trying to keep the design as clean as possible, but I see what you mean now.
    'The Piper Cub is the safest airplane in the world;it can just barely kill you.'
    - Attributed to Max Stanley ( Northrop test pilot) -

+ Reply to Thread

Similar Threads

  1. Q2 Landing Gear
    By Vector in forum Aircraft Design / Aerodynamics / New Technology
    Replies: 13
    Last Post: June 20th, 2011, 09:53 AM
  2. Landing in a taildragger vs a tricycle landing gear aircraft...
    By CALL911 in forum Rules and Regulations / Flight Safety / Better Pilots
    Replies: 50
    Last Post: November 11th, 2009, 01:37 PM
  3. BD-5 Landing gear?
    By K-Rigg in forum Aircraft Design / Aerodynamics / New Technology
    Replies: 5
    Last Post: September 15th, 2009, 08:58 AM
  4. Landing Gear
    By Alan Waters in forum Tube and Fabric
    Replies: 6
    Last Post: June 18th, 2009, 04:10 PM
  5. Landing gear
    By ZENO in forum Tube and Fabric
    Replies: 12
    Last Post: April 22nd, 2006, 04:56 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts