Canadair Sabre F.4 - XB673

[dennisp]

Thanks DT just a big beast to glass so this leg of the build is consuming mega amounts of time.

[dennisp]

A very busy week at the office so not a lot of progress, however work started in earnest again on Friday evening to try to recover some lost time.

The horizontal stabilisers

Before glassing the foam I added an additional layer of Du-Bro hinge tape to the inner and outer hinge tape that was fitted by the manufacturer, a little bit AIA insurance so to speak.

Work was also hindered by two small but very important parts that were missing in the kit which are the plates that go on the top of the horns, these are a must to spread the load and stop the horn being pulled from the foam. DT kindly found two from his stores at the TSW so we were able to move forward again.

You will also note that the HS-65MG servo’s have a grey body, this is two layers of electricians insulating tape wrapped around the body of the servo. So why do that?, well if you want to remove the servo later just cut the tape with the modelling knife and bingo one clean servo for future use with no glue and foam all over it.

Needless to say the alignment was not correct for the servo push rod and as I had decided early on to use the FF horns (as there is not a lot of foam for a alternative control horn mounting) a solution was required to get the alignment something like at right angles to the hinge. The solution as always came while “burning one” why not use a ball joint on a 2-56 threaded push rod as this would move the push rod out from the servo by about 1/8” when secured in place. I would suggest that you tap the servo horn holes with a 2-56 thread before you glue the servo’s in, as it is just about impossible to do later and tap all the holes in the servo horn so that you can adjust the push rod throw relative to the elevator movement.

You may wonder why this servo alignment is important, well if you go back to your school days and geometry then you will know that the hypotenuse of a right angle triangle is obviously longer than the base, so in our case an angled push rod will require more servo force to move the control surface the same amount as correct right angle aligned push rod. The F-86 is a big model and reasonably heavy and we are using small servo’s compared to the same size 40 or 46 glow model, so why add in problems build them out. I have somewhere a graph of typical servo forces on a model which I will try to locate, but do remember that the as the speed of you model increases the force increases in a non linear manner just like the dreaded drag.



Although the ball joint is not secured to the horn you see the off-set the ball joint makes, I should point out that there is a brass washer that has to be fitted between the servo horn and the ball joint which will be added when the push rods are finally fitted.



The exciting bit comes next fitting out and that is assembling the rear fuselage, I need to clear the bench again ready for this activity, so stand by for a progress report on this step later on this weekend.

[dennisp]

The rear fuselage join

I have to admit that I have been looking forward to this step after all the glassing, as per the destruction manual the first items to be fitted are the stabilisers a no drama task once you have made a slot for the servo lead to go into the fuselage where the original small hole was.



The next part is the real messy part of making holes in the foam for the all the cables and pipes to go through the fuselage, being that I had opted for an operational rudder the little slot that is the foam for the stabiliser wire was enlarged as I wanted to be able to use the extension leads “as is” rather than solder them to the servo leads. It also had to be just large enough to be able to pull the slack from the rudder servo extension once the fuselage is joined.

I actually gave myself more work (as usual) as I am using air up / down retracts and need to sets of holes in the EDF cover, not a lot of work but just a bit more mess.





Now check that we all the wires and pipes where they should be AIYO Ooop’s power to the ESC needs re-routing...



One more set of checks and then we are ready for the join..., trial fit the two fuselage halves are they a good fit still with all these pipes an wires..?, no glue in wing fixing plate blind nuts..?, all the wires and pipes where they should be..?, are all the servo’s working properly..?, now is the time to fix any problems.

OK good “go for glue” .... YES, now here is piece of important advice do not attempt to use 5 minute or even 30 minute epoxy for the join unless you are the bionic man and can work at the speed of light...!, there is a lot of foam to have epoxy brushed on and you want the epoxy to cure when the fuselage halves are together not while you are spreading the epoxy.

I used 90 minute epoxy which gave loads to time wipe any oozes of excess glue, tape hold the halves together and generally make it a nice and slow join.



When I look at the cable and pipe duct at the front of the fuselage AIYO looks like Dr. Frankenstein’s knitting, but easily tidied up.

Next task is to fit the vertical stabiliser once the 90 minute epoxy has cured fully... so standby....

[dt8666]

that looks like a full size airbus wiring... aiyo... i am sure it will not be seen once you have all the fuse joined.

Very nice work..

[dennisp]

Thanks DT, the ESC mounting is a challenge especially for a Opto CC ESC but I think that I have a solution.

[SKYHOBBIES]

side track.... I am admiring your work bench... so very organise!!!

[dennisp]

Thanks Capt. according to the MOHA it is even nicer when there are no models on it AIYO....

[dennisp]

The vertical stabiliser fit to rear fuselage

The fitting of the vertical stabiliser proceeded with no real drama’s except the dorsal fin on the rear fuselage is lower than the front edge of the vertical stabiliser, AIYO some more MRO to get this correct later.

My list of little finishing tasks is getting longer everyday YOIKS..!, but I did anticipate this so I am sure that I shall use all of my contingency time in the build schedule the way things are going at the moment.



So with the major work completed on the rear fuselage it is time to focus on the front fuselage and see what has to be done there, especially with the mounting of the NLG retract.

Plan to start this tomorrow afternoon.

[dennisp]

NLG retract mounting block

As is my standard practice I decided to go for the classic “D” box mounting for the NLG retract, a few measurements were taken to see how and where I could fit the assembly as I particularly wanted to use the ¼ moon stiffeners that supported the original FF NLG. Consideration had to be given to the steering servo as again I wanted to avoid tubes for the steering wires.

So wood dust was created big time and a further beating of the MOHA’s broomstick for making a mess of the house but the NLG mount was completed.







With a completed NLG box the next step was the NLG leg, AIYO the standard Robart Robo-Strut is far too long, according to the instruction manual the NLG should be 165mm from the fuselage bottom to the ground I was over 250mm. You can shorten the leg so a check was made as to the minimum length you can chop and I was still at 180mm so drastic measures are no required.

First step is to determine how long the strut has to be with a 2” wheel, then it is disassemble the strut and halfway up the strut is a plug which has to be removed. The plug acts as buffer for the spring inside the leg if you look at the retract I have a buffer on the shaft anyway. You must also allow for the plug that goes in the end of the leg for the fixing of the strut to the leg. Moment of truth came and chop-chop leg shortened, plug shaft size drilled out to 5mm and time to reassemble...., once assembled I had a distance of 163mm to the mounting flange of the retract.... sheer magic or just good luck.



The next step is the one way ticket fitting the box in the nose.....

[dennisp]

Mounting the NLG mounting block (NLG MB) in the fuselage

My objective was to ensure that the NLG MB would sit inside a cut out on each side of the fuselage with foam support on all four side and as much as possible on the top, the original FF moon pieces being used to add additional strength for any upward forces from any assisted returns to planet earth with additional aid by Mr gravity.

The tail of NLG MB is to sit in slots each side of the fuselage to help spread the loads, lines were drawn as to where the chops had to be made and I decided to leave the chopping until today as this sort of work needs sunlight or at least my eyes need it.

Chopping completed and time to see if it all works, the fit on one side umm seems to be working....





Yep looks fine and I can use the FF half moon supports...



View up the intake so I should be able to use the FF plastic bit over the retract... that is a bonus..

Now the real test is the NLG MB parallel with the fuselage bottom, bubble on the fuselage and another on the NLG MB and my cutting skills with foam are getting better it is spot on...



Sorry I do not have a picture but the leg goes nicely into the cheater hole without any further chopping so that 165mm is a critical dimension if you are going fit alternative retracts to this bird.

Next steps are the fitting of steering servo and associated control wires, routing the air pipes and servo control wire to the cockpit avionics area.. coming soon...