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Tech Talk - Tricycle to Tail-Dragger Conversion

by Greg Doster, Safety Officer, Macon Aero Modelers

  Tail Dragger Conversion

            If anyone has ever had a prop dig in the dirt taxiing you trainer down the runway or your airplanes seems to have a mind of it's own while taxiing then you are not alone. Tricycle gear and grass runways just donít mix too well. I have converted several high wing trainers such as the Hobbico Avistar, Tower trainers and the Hobbico Hobbistar 60 to tail dragger configuration with great success. After using both types I really can not see the need nor do I have the desire to ever go back to a nose geared airplane again. The following article is based on my experiences and reflect my opinions on this subject. Some may disagree and that's o.k. This is to allow those that want to have a more enjoyable experience with a tail dragger trainer flying off of a grass runway such as ours at O.T.X.

            This modification will take a little time and thinking to get it right. It's really not that hard. Purchase good quality landing gear components and pay close attention to servo geometry.

           Pros and Cons of each type of landing gear:

     NOTE: This is solely my opinion.....

            Tricycle gear --- Pros:

  1. When adjusted properly provides good ground control of the aircraft.
  2. Nose gear will maintain safe distance between ground and propeller when plane is upright.
  3. Allows smooth rotation to nose up attitude once adequate ground speed is obtained.
  4. Three point landings with tricycle geared planes look pretty cool.
  5. Works best on asphalt runways.

            Tricycle gear --- Cons:

  1. Nose gear gets weak after a few hard landings due to weight of engine being directly over it.
  2. Eventually will weaken from side to side allowing prop to dig into the ground and stall engine on tight turns.
  3. Most nose gear could be designed better, being more rigid and robust.
  4. You will constantly have to adjust nose gear to make aircraft track correctly.
  5. slack in pushrod assembly due to length of pushrod.
  6. More drag on rudder servo if nose gear pushrod is not free and smooth in it's travel.

            Tail Dragger --- Pros:

  1. Great ground control on grass runways and asphalt runways.
  2. Very cool scale looks when Tail rises once ground speed provides lift on tail surfaces.
  3. Allows rudder to control yaw once tail lifts off of ground.
  4. More robust, trouble free.
  5. Allows you to use your creative skills when installing.

            Tail Dragger --- Cons:

  1. Must be set up correctly. or at least pretty close.
  2. Vertical center of gravity must be kept as low as possible. As close to stock ride height as possible.

            "This will help prevent ground looping."

            Converting tricycle gear to Tail Dragger Configuration....

  1. Re determine CG and mark on underside of wings. If the airplane has been flying correctly at the current CG then just find the current CG and mark it on the underside of the wing.
  2. You will need to purchase or fabricate a tail wheel assembly and a Main Gear for the project that is for the size of the airplane. Make sure it is the right size for the application. Try to keep the same ride height as the old mains. Remove nose gear from Engine mount.
  3. Mount the tail wheel to the fuselage. The tail of the fuse is pretty solid at the end of the fuse so no additional "beefing" up is necessary. You must determine the best way to link the rudder pushrod assembly to the steerable tail wheel.

            This can be accomplished 1 of 2 ways.

  1. If the aircraft is new and not yet assembled you can link the actual rudder to the steerable tail wheel before the vertical stab and rudder are installed. This way greatly reduces drag on the servo for the rudder and no additional pushrods are required.
  2. If the aircraft is already assembled then you have to add an additional pushrod from the rudder servo to the tail wheel assembly. Exit the pushrod on the opposite side of the fuselage that the rudder pushrod exits. This will allow you to use the other side of the servo arm to push when the other side is pulling. Kind of of a push-pull configuration. When the rudder servo is pushing the rudder to one side it will be pulling the tail wheel to the same side.
  3. Remove the old Main landing gear. Determine the best location to mount a Durra Gear landing gear assembly. This needs to be no further back that the leading edge of the wing. Line up the axle center line. Try not to get too far in front of the wing. A good range would be from the leading edge of the wing to 1 inch ahead of the leading edge of the wing.
  4. Once the location is determined you must beef up the inside of the fuselage where the gear will mount. This can be done with 3/16th inch aircraft ply wood. use 30 minute epoxy to secure to bottom of fuselage. Try to keep added weight to a minimum without sacrificing strength.
  5. Once dry turn fuse over, working from bottom, determine wheel tracking by measuring from the tail wheel bracket to each main axle centerline to get everything centered up. mark and drill holes thru bottom and recently installed plywood former. Install blind nuts on inside ply floor and install gear. Recheck measurements from axles to tail wheel and adjust if necessary.
  6. You will need to trim out the steerable tail wheel to match the rudder. This is easily accomplished if you used the additional push rod method. It is a little more tricky if you used a mechanical link system. You have to bend the tail wheel wire to get tracking close.
  7. Now recheck the CG of your airplane. Rebalance it back to where it was before if necessary. Try to move the battery around to get the CG right before you add any lead. It really should not be too far off.
  8. Take offs and landings are much easier on a tail dragger when flying off of grass. With tricycle gear the nose gear is very weak. This make taxiing very difficult because the nose gear will bend easily after just a couple of hard landings. Unless you are solely flying off of asphalt runways then tail draggers are the ticket. Be sure that you do not mount your Main Gear too far back on the fuselage. If you do the aircraft will be more able to tip over on the nose upon landing. Not to mention it is more likely to ground loop with you. It just needs to be about 2.5" to 3" ahead of the CG to put most of the weight behind the axle centerline.

                       If you have ever seen someone try to take off a piper cub for the first couple of times this is apparent. A shorter wheel base (so to speak) make the aircraft more easy to ground loop. A longer wheel base prevents this. Don't go too far forward with the main gear location because it will look funny.

 

           Greg Doster

           Safety Officer

           Macon Aero Modelers, Inc.

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