Fuselage 5 (6.5 hrs)


In three words, today was big, long, and exhausting. With much help from several EAA members I aligned and drilled the main landing gear brackets. A shout of thanks is definitely required to Jack, Marty, John and Steve for their help today.

The first step was to move the fuselage off the rotisserie and onto the saw horses. I needed to do this for two reason. First, because it is necessary to level the fuselage both laterally and longitudinally, and second because plumb bobs do not work well on a moving and rotating stand.

I used the standard Van’s method for aligning the gear. And its difficult. Why? Because it turns out that all gear legs are not created equally. You may well have a slight twist in the gear!

The method that Van’s directs is for you to hang two plumb bobs from each gear leg. One as far out and another as far in as you can imagine. Ensure both sides are in the same position, and then ensure all four plumb bobs are in a straight line. You can see that approach below. Using a chalk string we checked, adjusted and double checked the alignment several times. We got it close but we couldn’t quite get it perfect.

Unfortunately, because of all the work, and very dirty chalk hands, I didn’t take many photos. However, the other step directed by the Van’s instructions is to ensure that the distance from the outer plumb bob to the centerline of the fuselage at the tail is equidistant. Van’s expects this to be within 1/4 inch. We managed to get both outer plumb  bobs within 1/16 of an inch. The four plumb bobs on the gear itself were nearly in a perfect line with one out of 4 being troublesome. In order to have brought that into line we would have had to accept a much larger disparity between the distances to the aft centerline. We got it as close as humanely possible and began to drill.  

First you drill the forward holes in the outer brackets, and the holes aft. After this you can drill the inner brackets. You can see the end result below.   

I have a lot of cleanup to do, and several more holes to drill, but the holes that needed drilling as part of the process of alignment are complete. The fuselage is back on the rotisserie.

I did a fair amount of research on the methods for accomplishing the alignment. Of all the threads I read, I found the following to be most useful. I have posted a link to discussion on Van’s Airforce below, as well as a copy and paste of the most useful comment in the thread.

FROM VAF: http://www.vansairforce.com/community/showthread.php?t=36025


 

FB26…

I think you have hit on a common problem with the RV-8 here, and I’d suggest you step back and consider the way ahead before you get that drill out 

From eMail correspondance between myself and Van’s:

Quote:
On a QB trying to attach the Gear Legs to the Fuselage.The inboard 7/16″ hole drilled from the Steel part already built in, and the bolt inserted. Gear can now rotate about this bolt for alignment.The necessary “plumb lines” attached to the Gear Leg LE Inboard and Outboard. However, to get the 4 plumb lines “in line” (as the instructions require) requires both gear legs rotated “aft” as far as they can go, and when the 803 weldments contact built in structure. The aft bolt is also inaccessible – I can file away material – and it just looks wrong i.e. I would expect the gear leg to fit reasonably centrally in the area provided.I have attached 2 photos hopefully illustrating the above.I am unsure if I have misunderstood the plans, done something wrong or whatever?!*!

Please could you clarify what the plans are actually requiring, whether I am going about it the right way etc. The following link seems to relate to a similar problem / query:
http://www.vansairforce.com/communit…ead.php?t=2013

Edited reply from Van’s:

Quote:
The plumb bobs do make sure that the axles are in the same fore
and aft position, but the other consideration is that the axles are
parallel to each other and perpendicular to the centerline.If there’s a conflict between the fore and aft position and the
parallel/perpendicular requirement, I would incline to favor
whichever one puts the legs more centrally in the skin cut out,as that
will result in better edge distance on the longerons. If that’s no
factor, give the benefit of the doubt to the p/p aspect as that
eliminates the need for shims. If one wheel is a little further forward
than the other it won’t affect anything.

Me again:

Quote:
However, that DWG and your comments above at least make clear what is to be achieved. Given what you say:* Axles Parallel to each other. See Photo below – I have clamped 2 pieces of angle to the legs (ensuring they are flush against the inboard faces of the legs in the axle area). The angles significantly diverge as you go forward – to an extent of ~2.5 degrees toe-out per leg! This would suggest they legs are angled far too far back… as you and I think. The plumb blob x 4 method is therefore not working – probably somewhere in the way I have set it up.

Reply:

Quote:
Using the angles is OK, but I
would shift them to the outside of the leg, not the inside, in case the
thickness of the end of the gear leg varies. Also, be sure to measure
from plumb bobs (fore and aft of the leg on the angles) to the
centerline of the fuselage, as well as from one leg to the other to
ensure that the axles will be perpendicular to the CL.The misalignment using the plumb bobs on the leg may be because
of variation in the upper bend causing a twist in one or both legs, but
as long as the axles are correctly oriented to the centerline it will be
fine.

Summary
Using the plumb blobs as per the plans has no logic in what you are trying to achieve, and/or makes some assumptions about the geometry of the gear legs.

The replies from Van’s to me make clear (and much clearer than the plans!) what you are trying to achieve in order i.e. 1 is the most important:

  1. The outboard face of the Gear Legs (where the axles will bolt) are parallel to each other
  2. The outboard faces of the Gear Legs are parallel to fuselage centreline
  3. The ends of the Gear legs are the same distance for and aft

I am aware of at least 2 RV-8s in the UK with some “interesting” gear issues. One operates off a hard surface, and the tyres wear in such a way that he has to rotate the tyres inside to out from time to time.
The second, when we do formation takeoffs, requires me to have a very low power setting until we get airborne when I suddenly need to add a bunch of power  We both heard a loud squeal off a hard surface recently as we got airborne – he heard it louder, so we assume it was him 

Both the above seems to suggest a toe in/out problem and I just wonder if the builders followed the plans and experienced the problems we (and you) got, but pressed on…

Thoughts welcome from others 

PS We have ~120 hours, and over 300 landings. Most are on grass, but I’d say 1/3 off concrete. No noticeable wear on our tyres, and certainly not uneven wear… so I think ours are reasonably OK 

Andy & Ellie Hill
RV-8 G-HILZ


 

 

 

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