Cable Fairings (Jan. 27th, 2007)

Had to chill out a bit from this control rod fuss. So I made these rudder cable fairings. This is not as easy as it looks. Thickness of the cable as well as the mounting points have to be taken into account to avoid any chaffing on the airframe. I spend the whole Saturday to build and install these gadgets.

cutout a bit too large.

 

the one on the right side fits better however this one is supported by only by three rivets. The lower three ones cannot be set because the longeron is in the way.

 

 

Kinematics (Jan. 21th, 2007)

This is a short movie of the elevator pushrod at bulkhead #3 while pulling the stick from the most forward to the most aft position. Surprisingly the pointer moves in a linear fashion, and not in an arc!

 

New Idler (Jan. 20th, 2007)

I have grinded the whole Saturday here and there to get the specified 25 up and 20 down degrees of elevator travel.

Hint

If you do this elevator adjusting (also addresses the aileron and rudder adjustment in the same way) DO NOT lay the Smart Level just on the elevator, lift up the thing and read the angle! This way you will NOT measure the angle as specified in the plans (don't ask how I know :-((.

The angle specified references to the symmetry axis of the aileron's cross section. Becasue the aileron cross-section is a triangle enclosing an angle of 10 degrees, half of this 10 degrees have to be added to the angle measured with the Smart Level. So you should read on the Smart Level:

Up = 20 degrees (this will determine how much I can pull the nose up in the landing flare - muchos importante)

Down = 15 degrees (the down travel is currently 20 degrees at my bird, but this is not so critical (I think). This can be reduced easily by shimming the end-stop)

 

This are the dimensions for the new-to-construct idler. The arm should be 81.7mm (if my calculation is correct). There will be no plastic bushings for pushrud support. The new idler will sit ontop of the bottom crosstie of bulkhead #3. In order to prevent bending of the crosstie I will reinforce this section with two more angles.

 

Simple Theory of Levers and Pushrods (Jan. 17th, 2007)

The elevator pushrod on both sides is connected to levers. The pushrod idler lever behing the seats and the elevator horn at the aft end of the fuselage. These levers follow a arc-segment when operated, or in other words the pushrod not only moves fore and aft but also up and down.

 

This very long pushrod should not be unsupported, because on heavy G-loads it will bend significantly. The Sonex plans show two vertical U-channels in the fuselage aft section. The U-channels carry two oversized holes where plastic snap-in bushings are fitted. The pushrod is guided through these two bushing-equipped holes.

Unfortunately this solution does not take into account the pushrods up- and down movement when operated.

This is the desired position of the pushrod: freely floating inside of the bushing.

 

And this is what you get when you follow the Sonex plans. There is only a single stick-position where the pushrod is friction-free. All other poasitions will either rub the bottom or the top part of the bushing - not a very elegant solution.

 

I'm not sure what to do here. Other airplanes designs use one or two more idler levers. Maybe I'll follow such a path. I think this excessive friction of the Sonex design will negatively influence the 'feel' of the elevator control

 

Elevator Pushrod & Rudder Cable Guides (Jan. 16th, 2007)

Before I installed the cable guides, I routed a string from the pedal to the rudder horn. The openings in the bulkheads seemed to be on the right place (surprise!). Then I installed the mounting blocks which I made from oil-filled nylon, a more up-to-date material than the bakelite suggested by the plans.

 

The elevator pushrod is supported by two vertical U-channels which are riveted to the bulkhead. I these U-channels have holes where two plastic snap-in bushings go in. This is a bit questionable because the pushrod dows not only move fore and aft but also moves up and down a bit casues by the arc the levers travel. To make things worse these holes are not exactly at the position where the plans show them.

Here you can see the bulkhead and the (black) elevator pushrod. I routed two thin strings vertically from the rivet locations where the U-channel is supposed to be riveted on. You can see that the rod will traverse this channel assymtrically. I asumed problems here so I drilled only a small pilot hole into the U-channel - nothing is lost here.

 

(Jan. 9th, 2007)

I posted this question to the unmoderated Sonex email list. Thanks to Tom Zelie who provided the answer. The link-rod ist installed the wrong way!

 

Control Stick Jam? (Jan. 8th, 2007)

Today I tried to fit the elevator control rods. Prpbably there is is another unexpected problen I ran into:

This is the situation where the stick is pulled about five to 10 degrees out of the vertival towards the pilot. The 'dual stick link rod' (C05-07) jams with the 'stick to idler pushrod' (C03-04). This can't be true.

 

Completing the Seat Reinforcement (Jan. 7th, 2007)

Implementing the Sonex Bulletin SB-003 took about a week. In the picture below you see the old part on top and the newly fabricated parts below.

The five additional U-channels are of my own invention. It took about 100 blind rivets of three different sizes to fasten the structure.

 

Now I can take a seat without fear to bend the underlying structure anymore. The additional channels and the 1x1x1/8" L-extrusion made the seat support rock stable.

 

Probably next step will be the disassembly of half of my large worktable. All the big parts are made now. The newly gained space will be used to install the empennage. Afte this the control rods for the elevator will be finally installed. After this the aft fuselage bottom will be fitted and temporarily fastened.

 

Positioning the engine (Jan. 4th, 2007)

For VW type engines with 'Diehl' accessory case (what I intend to use) the Sonex plans requests the whole engine to be brought forward for 35mm. This shall be accomplished with bushings.

Either I'm too dumb to unserstand this construction or it is wrong. In my understanding this cannot work, at least not with my engine hardware.

My rubber bushings got an inside diameter of 1/2". If 3/8 tubes go into this 1/2" holes the engine will wiggle around, this cannot be true.

So then this is what I intend to do:

 

Sketch of the whole 'shimmery'...

 

...and the real one

 

The real problem however is a different one: requested by my technical advisio I had to reinforce the rear fuselage sidewalls and bootom skin in order to prevent buckling. This made my fuselege heavier behind, so in order to maintain CG I have to bring the weight farther forward in front.

For a first try I made the spacer blocks 49.5mm instead of 35mm per the plans. This is just for safety because I cannot take a weight and balance in this state of completeness. Should CG too far forward the spacer blocks can be shortened easily (what is not so easy to shorten is the cowling because it has a conical form, bus this is still another problem...

To further complicate things, the Sonex plans show an engine length of 422,3mm (red encircled dimension above). This may be true for the AeroVee but it is invalid for my Revmaster. Because the Revmaster got a true pressure-lubricated front bearing the prop flange is farther forward then with the AeroVee (acually a good thing, because this allows for a nicer, pointen nose of the aircraft). The actual engine length of the Revmaster is 482mm, so my prop will be another 50mm further forward. Maybe this could be sufficient to completely avoid the spacer blocks.

But as said before, this all is pure guesswork. The spacers are made, if I don't need them - the better it is.

 

Reinforcing the Seat Structure (Jan 3rd, 2007)

Today I started the messy work

I used solid rivets on most places. These are easier to remove, however the drill may wander out of the center which will elongate the hole. This happened at a few locations. In order to maintain the strength I will insert a few extra rivets in-between the original positions.

 

 

This is the offending part. Before going into the scrap bin with some luck I can use it as a drill guide for the new part.

 

...when we're about reinforcing...

this horizontal crosstie is very flimsy and will buckle under load. So I will install this five U-channels (made fron 0.032" sheet). These will increase the buckling resistance significantly (however will not increase the weight much).

...will be continued

 

Seat Cross-Tie Service Bulletin (Jan 1st, 2007)

A few years ago, when I build the seat asembly of course I took a test seat (as probably all homebuilders do...). At that time I realized that the rear crosstie assembly was too weak. The flimsy sheet metal angles bent (even as I'm not one of the heaviest occupants (90 kg). I followed some conversation in the unmoderated Sonex email list. Other (heavier) pilots also experienced this weakness. However sone Sonex evangelists like Tony Spicer recommended to stay with the plans (as usual). So did I. This was a mistake!

In November 2005 a Sonex Bulletin SB-003 came out which recommended to reinforce this section with a solid extruded angle. This was almost five years after the first Sonexes were constructed and more than 100 were already flying!

So today I had a closer look on this mess.

The upper angle also contains the piano hinge where the seat slings attach. Of course also this hinge is for the scrap bin.

 

Simply drilling out all of the 50 (!) rivets is not possible, because there is no space for the drill (the other crosstie behind is in the way).

 

Another try with my angle drill. This angle drill is only made for occasional use, I hope it will not wear out after all the 50 rivets have been removed.

 

No luck with the angle drill. The drill wanders around even after centerpunching the rivet heads. Some rougher machinery has to be employed...

 

Two rivet heads grinded off. The damage on the metal does not matter because this part is for the trashbin anyway. Only question is if the remaining rivet can be pulled out from the other side.

 

The new part with drillguide made from old part

It is more than questionable if the holes in the new part will fit with the counterpart. From the rivet-removal the drillguide is quite worn-out. This is one of the most unpleasant tasks on my Sonex project so far.

 

Sonex Bulletin SB-003 states:

'Sonex,ltd suggests that SNX-F10-03 be replaced in all Sonex aircraft with a piece fabricated from 1"x1"x1/8" thick 6061-T6 Angle. This replacement part is installed in the same location and has the same fit and function as the original SNX-F10-03'

'Installing in the same location' is simply NOT possible. Why?

the 'old' angle was of 0.6mm thick material. The 'new' angle is of 3.2mm thickness. This brings the 'new' angle up 2.6mm. Which is -fatal- because the edge distance of the rivet holes can nomore be maintained

7.3 mm is a comfortable edge distance (which should be no less than 1/4" or 6.35mm). The new angle allows for only 5mm, which is not acceptable. What the f... to do now?

 

Ha! - Installing the angle -below- the right and left carrier angle?

No, Sir, also NO solution! because of the inside radius of the new angle the angle does not lie flat on this vertical crossmember. The crossmember itself carries several vertical stiffeners which cannot be shortened. So this again is a deadend road.

Looks as if I have to make two new ones of this carrier angles which brings the hole carboodle 2.6mm further down ('...installing in the same location'? - not in real world!).