TopModel Bidule 170 ~ build thread by JimD

[JimD]

Assembling the fin and stab proved to be interesting. The supplied hardware was a problem in that the two screws that attach the fins were not a good fit. It seemed like the diameter of the bolts was slightly undersized. We replaced them with socket head metric bolts and things went together perfectly. Then, when the diagonal braces were installed, one of the supplied bolts would not thread down into the stab. One side fit fine and the other side just did not fit. Once again, I went to my inventory of metric hardware and found the correct size socket head bolts. The side that the stock bolt fit into was fine with this new bolt, but once again the other side was a problem. Looking down into the hole, the threads in the T-nut did not look the same as the other side. Out of frustration, we tried a 6-32 bolt and it threaded right in!!!!! So, one side was metric and the other side was English! At this point, we decided to replace all of the hardware with 6-32. We carefully drilled and taped the metric side for a 6-32 bolt and all went well fortunately. The bolt and lock nuts at the fin joint were also changed to 6-32 hardware.



Hinges were epoxied in with West Systems G-Flex epoxy which holds extremely well and resists vibration damage.



Our rudder servos were mounted to the stab instead of the covers.



DuBro horns were used instead of the stock parts.



The supplied bolts are 1-1/2" long, but we changed them out to 2" long bolts for better control hookup geometry.

[JimD]

Here are the six plywood pieces installed plus hardwood triangle:



Next step was adding a tube for the rudder and elevator servo wires.



Covering was removed from the fuselage sides to gain access.



Plywood braces were cut to reinforce the bulkhead at the leading edge of the stab.





Diagonal balsa sticks were added along each fuselage side.

[JimD]

Looking at the backside of the main firewall where it attaches to the fuselage sides and floor reveal a shocking lack of gluing surface to keep that firewall in place as the 170cc engine cranks out torque.



The structure can be significantly strengthened by the addition of some 1/8" plywood triangles. Here we made paper patterns.





Then we used these to make out plywood parts.

[BobM]

Really looks great Jim ! Looking forward to seeing how it progresses.

Bob

[stevekremer]

That is very impressive Jim

Steve K

[Steve P]

Bidule Bling to the extreme!

[JimD]

ARF = Always Require Finesse

😉

[jgallacher]

These new ARF sure are a snap to assemble huh Jim.
Jim Gallacher

[JimD]

Every chain has a weak link, and the nose gear pushrod system is that weak link in the Bidule 170. The nose gear is massive and the wheel has a trailing arm suspension system. If the nose wheel is slightly turned (as it would be if you are holding rudder in a crosswind landing) it exerts a lot of force on the servo and pushrod when the nose gear touches the ground. Even taxiing, especially on rough ground, puts a lot of force on the steering system.

We set out to make a shock absorbing system for the steering that would be up to the task of the thousands of take offs and landings that tow planes are subjected to. Our design involves a double Bellcrank with springs between the two. A pushrod connects the nose gear tiller arm to the front crank arm on the right side. Double pushrods connect the servo output arm to the rear crank arm. The springs in between these two cranks allow the front crank to move a fair amount without transferring the shock of that movement to the rear crank. The springs also act to keep the nose gear centered after being moved off center by the force of contact with the ground.

As an added feature to protect the servo, the two pushrods are attached to the servo arm with an EZ connector but allowed to slip through this connector if there is a significant shock. Double springs act to center the pushrods in these connectors but allow for some slipping motion in the case of a sudden shock load.

I made a prototype out of steel parts to test the concept and then had Gunny fabricate aluminum parts using his CAD design programming skills and his CNC router. Here is the second prototype that will go into our plane.

[JimD]

StephaneR (aka French1) made us aware of the success of the Bidule design in France and that set in motion a group order from TopModel. After Len's Bidule 170 (with ZDZ-180 engine) went into service this summer, it became crystal clear that this model is the current segment defining aircraft for aerotowing. We really need to thank BobM for putting together the group buy through ICare that brought the first of these planes into the USA. Then we need to thank ScotS (Stew) for actually transporting them from Etienne's shop in Canada to us here in the states, and of course Stephane for the idea in the first place!

Bob has already posted extensive pictures of his build and modifications, but I am taking a little different path than either he or Len. This plane will no doubt be the subject of numerous build threads and every builder has their own ideas. This will be my take on the subject.

First is mounting the engine. We have opted for a DA-170 engine to power our Bidule. The engine needs to be spaced 1-5/8" out from the main firewall and we elected to build a plywood box spacer. This method has worked very well for us on numerous other models, so we are sticking with what we know. Here are our un assembled parts.

The box is 4-1/4" wide and 4-5/8" tall.



The sides were cut to 1-1/2" wide with the firewall inset inside these side pieces.



A second layer of 1/8" plywood was added to the front of the box.



We cut a center hole the same diameter as the one in the main firewall and inserted a cardboard tube that the ignition wires will pass through. The engine mounting bolt holes were used to secure the box to the main firewall while the epoxy cures.