Subject: Cabane Strut Fittings

I am right in assuming that the 3/4 x 3 inch filler on the lengthened fuselage drawing is there to allow the cabane strut brackets to be set a little further back?? ( to aid the c of g probs?) Or is it there just to strengthen the area, with the bracket remaining in line with the vertical member? A cold Camper builder in need of re-assurance Paul Shenton

Hello Paul,

Although we have fitted our cabane bracket to the piece of wood labelled on the 1966 lengthened fuselage drawing as "3x3/4 filler for cabane strut fitting", we don't think it is actually meant to go directly on it. The drawing would be clearer if it said "doubler for cabane strut fitting". We wondered about this same point when building our fuselage because it seemed odd to have the bottom of the cabane struts further apart than the tops, but could see the benefit in that it lets the spruce cross member at the top rear edge of the front seat back meet the fuselage sides. We sought the advice of Alan James and Alan put his fitting directly on the filler piece. We ended up doing the same and from photos it looks as if about 50% of builders also do the same. Although we would put the fitting on the main strut if doing it all again, we have no concerns about it being on the filler piece as G-BUCO is so well proven.

Ironically we have actually put another filler piece or doubler to the rear of the actual filler piece to reinforce this area. An E-mail sent to Paul Prince is attached for additional guidance since it describes the only disadvantage of our arrangement that we're aware of - ie the Hal Danby style upper harness frame fouls the aileron cables. This is because the lower cross tube of the frame fits betwween the rear cabane fittings and these are further aft when you put the fitting on the filler piece. We hope that this all makes sense, but if not please feel free to ring us on 01252 542493 for more details.

We hope that your project is making good progress and we wish you a very Happy New Year, Chris and Fran

Extract from E-mail sent to Paul Prince a few weeks ago: "............We now believe we have found out why there is the clearance problem on this harness frame with our aircraft and not on Hal's. On the lengthened 1966 fuselage drawing there is an ambiguous note about a "3/4" x 3 filler for strut fitting". We took this to mean that the strut fitting goes on it, but another way of looking at it is that it backs up (ie it is a doubler to) the main strut which has the fitting bolted through it. If you do the latter, this obviously would place the plane of the frame further away from the two aileron cables. If the term "doubler" had been used on the drawing instead of "filler" it would have been clearer. A further influencing factor is that the more forward positioning prevents the cross member across the top of the front seat back from contacting the sides (ie there is no joint possible on a wood fuselage, however loads could pass through the ply top deck instead) and also the rear cabane strut is right on the edge of the coaming (awkward). Alan did the same as us (in fact I found some early notes where I'd asked Alan about this very point), but looking at photos you can see a mixture of positions on other Pietenpols. I guess that Hal has the more forward position, but I haven't confirmed this with him. Oh well - the joys of building!" ..................

CHRIS AND FRAN BARLEY'S FUSELAGE NOTES

(First published in AJ's Airborne reproduced with kind permission)

The majority of these notes were originally supplied to Jim Wills (probably circa 1996), following his request in the Squadron Newsletter for comments on the plans. We then subsequently supplied them to Tony Anderson. Unfortunately circumstances have meant that they haven't been widely seen, although some earlier hand written notes of ours have been circulating around some builders. We have always been very keen to pass on our experiences to other builders to help them, just as we were given fantastic help in the early days.

1. Drawing No 9 - Firewall Strut The front strut immediately behind the firewall contains some detail 11 3/4" down from the top longeron. The purpose of this detail is unclear. (I have discussed it with Jim Wills by phone and Jim advised it should be ignored, as it was associated with engine types other than the Continental series - ie Ford A or Corvair).

2. Drawing No 9 - Large Gussets Large gussets (21 1/2" x 5 3/4") are shown at the front, upper inboard faces of the fuselage sides. These seem to be particularly related to the Ford 'A' version "tray" and it is not clear whether they should be included on the Continental/other powered versions. Jim Wills advised by phone that they are not strictly required for Continental versions, but we decided to include them anyway, as do most other builders. They will help reinforce this area for fuel tank mounting if you decide to use a fuselage tank.

3. Drawing No 1 - Rear Seat Back The rear seat back is shown on the drawing as a 21 3/4" wide x 21" deep rectangle. Since it forms a vital jig when aligning the 2 fuselage halves we accurately pre-made ours to the dimensions shown and then used it to jig up and locate the sides. Unfortunately because the seat back is inclined within the fuselage the bottom edge needs to be slightly wider than the top edge, i.e. the bottom edge sits in a wider part of the fuselage than the top edge. If the seat back is pre-made as a proper rectangle it will not fit properly. (NB the references to bottom and top edges are true edges. Since the fuselage is assembled upside down on the building table, the true bottom edge of the seat back is actually uppermost!).

4. Drawings 1 & 3 & 47-003 - Ash Cross Member Drawings 1 & 47-003 call up ash cross members which are 2" x 3/4" in cross section. Drawing 3 calls up for a forward beam which is 2" x 1" in cross section with its ends tapered to 2" x 3/4". We followed the drawing 1 & 47-003 requirement.

5. Drawings 1 & 9 - Tailplane Mounting Drawing 1 gives a dimension of 18" between the end of the turtledeck and the end of the tailpost. Drawing 9 quotes 18 7/8". Since the tailplane chord is 18" we have made ours approx. 18 1/8" to allow a small clearance between the tailplane leading edge and the rear face of the turtledeck.

6. Drawing 1 - Fuselage Width Drawing 1 quotes 24" for the fuselage width, with the note that "all dimensions to outside of ply". However 47-004 sheets 1&2 imply that the fuselage is actually 24 1/4" wide across the skins. Ours has been made 24 1/4" wide, but we know of others which are 24". It probably doesn't matter much since the pick up points on the engine mounting are very flexible and can easily accommodate a ¼" difference. However, there is also a need to consider where the centres of the centre-section cabane strut brackets sit in relation to the fuselage longerons. With the centre-section brackets positioned as per drawing and the cabane strut centralised within it, a fuselage width of 241/4" allows a comfortable fit at the bottom end of the strut with the strut slightly favouring the outside of the pair of fuselage brackets. Plenty of space is then available for the outboard fillet of braze between bolt bush and cabane strut. With a fuselage width of 24" you may need to offset the cabane strut slightly in the centre-section brackets to get enough space for a good sized fillet at the bottom end. Not a problem, but something it's nice to be aware of.

7. Drawing 1 & 9 - Tail Thickness After Assembly No dimension is quoted for the thickness of the tail-post after joining the two fuselage sides together. Since the main beams of the tail components are all 1" thick at this point, logically it should be the same, but it is not dimensioned. We made ours 1" thick. If you vary the tail surface main beams (as some builders have done - we haven't), bear this in mind.

8. Drawing 1, 4 & 9 - Bellcrank Position Various dimensions are quoted for the position of the bellcrank above the bottom longeron lower surface ply. Drawing 4 quotes 9", drawing 9 quotes 7 1/8" and drawing 1 quotes 7". We are using the largest dimension to try and avoid the control cable to the upper elevator horn rubbing on the tailplane leading edge, as many do. Pietenpol G-BKVO cunningly uses an eye and rod arrangement to prevent this though, as on Tiger Moths.

9. Drawing 1, 4 & 9 - Bellcrank Mounting Consideration needs to be given to sanding the vertical strut surfaces flat where the bellcrank mounts. Since this would weaken the strut, we glued 3" x 1" x 1/4" ply plates at the mounting faces, before sanding. These ended up with a 1/8" x 1/4" wedge shape after sanding. We used a 3 foot piece of 6" wide Contiboard shelving with abrasive paper stuck to one face and a 2"x2" batten stuck to the other forming a stiffener and handle, as a sanding block.

10. Drawing 1 & 9 - Seat Back Mounting As per item 9 above, the vertical strut faces where the rear seat back mounts need to be sanded flat with one another before trying to glue in the seatback. We set our fuselage sides to the correct plan-form before offering up the seat back (see item 11). The need for some sanding was immediately obvious. We used the same sanding block as in item 9.

11. Drawing 1 & 47-003 - Floor Ply Thickness Drawing 1 quotes a floor ply thickness of 7/32". 47-003 contains a sectional note giving the floor ply thickness as 1/4".

12. Seat Belt Attachments This is the most worrying of all the areas of uncertainty within the drawings. I discussed this issue in about 1994 with Francis Donaldson and he advised me to follow the advice contained in a back edition of Popular Flying ( Jan 1990 edition, page 28). This ultimately says that all systems must be approved by PFA Engineering. We've basically used this information and copied some of the arrangements used in G-BUCO. The only area that isn't yet sorted out is the difficult one ie the front seat upper restraint attachment point. An earlier edition of Aircamper 'Appenings and the letter from PFA containing Hal Danby's system will be a great help when it comes to finalise the arrangements. Unfortunately our fuselage was completely finished early in 1996 and we've recently discovered that our aileron cables coincide more or less with the position where the bottom cross tube of the Hal Danby designed harness frame will go. Hal didn't have this problem (discussed at Sywell 2000), but we're going to have to work out a way around it on our aeroplane.

13. Fuselage Side Planform To hold the fuselage sides in their correct plan positions we used blocks fixed to the building table to locate the true top longeron (fuselage being assembled upside down) and lengths of threaded rod to locate the true bottom longerons. At each point we used two lengths of threaded rod passing through wooden blocks to sandwich the longerons. A bonus was that it allowed the longerons to be eased apart to provide clearance for gluing and then closed up again a controlled amount. This avoided all the glue being wiped off and retained the accurate dimension. See photo and sketch for detail. Bottom Block Longerons Rod Nut Strut Top Longerons Block Table

14. General - Cutting Of Diagonal Braces The fuselage drawings 1 & 9 tend to indicate that diagonal braces may be cut to a point, whereas other references we have seen insist that they be cut to a double tip. Hopefully the sketches clarify, we've assumed both are acceptable though since it's the ply gusset provides the load path. Most of ours are double tipped though.

15. Centre Cabane Strut Fitting Dimensions Drawing 5 shows the aerofoil section and shows that the spars are on 28 3/4" centres (27 11/16" + (1 1/8)/2 + 1/2"). Referring to drawing 9, if the rearmost cabane strut fitting is positioned over the 3" x 3/4" doubler clearly labelled as being for this purpose, the centreline of spruce fuselage strut no 3 is actually going to be 28 3/4 " + 5/8" away. Therefore the two cabane struts will be closer together at the top than at the bottom. Whilst this probably doesn't matter, it does seem odd. A further concern at this same point is that the brackets securing the main cabane struts to the fuselage do not line up with the struts themselves. Therefore there will tend to be a turning moment on the brackets which appears undesirable, but most flying Pietenpols seem to have this feature and manage quite happily.

16. Drawings 1 & 9 - Rearmost Side Gusset No horizontal dimensions are given for the rear gusset which glues to the top longeron, bottom longeron and tailpost. We made ours 4.5 inches wide at the top and 7.5 inches wide at the bottom. This applies on the port side fuselage frame only. On the starboard side the whole of the last bay has a narrow plywood frame with a rebated lip to allow an inspection panel to be fitted.

17. Tailwheel Spring Mounting It is beneficial to incorporate an ash wedge into the apex formed by the lower longerons at the rear of the fuselage if a conventional leaf spring mounted tailwheel is to be used (as opposed to the drawn A-frame and coil spring type). We also added 1/8 inch ply on the bottom of the whole rear bay and on the top surface of the ash wedge. We were conscious of the need to minimise weight at the tail end and only did the minimum reinforcement considered necessary.

18. Rear Bay Dimensions The drawing showing the lengthened fuselage gives no width information This has to be obtained from the original fuselage drawing instead. We chose to keep the bay widths the same ie on the lengthened 1966 fuselage, the first vertical strut forward of the tail post, where the width of 5.5 inches occurs, is 19 inches from the tailpost rather than 16.5 inches. The knock on of this though is that the standard tailplane brace wire fitting on the underside of the fuselage is not the correct dimensions as it now fits on a narrower fuselage width. Others have simply kept the bay widths at various stations the same as for the original fuselage. We don't think it matters either way, but it's worth being aware of this point. On the underside of the fuselage immediately forward of the rear bay the original fuselage drawing shows an extra crossmember. We haven't incorporated it, thinking that it is only associated with the A frame tailwheel mount. If you are using a leaf spring tailwheel assembly it is neater to coincide the spring's attachment point with the brace wire attach bracket. A single bolt can secure both, and if it passes through the ash wedge mentioned in item 17 a good solid attachment results, with no weakening of the fuselage caused by having 2 holes close together. It does mean that the brace fitting is further aft than drawing, but this is unlikely to be a problem since it tends towards the upper brace wire arrangement, where the brace wires meet at the top rear edge of the fin.

19. Fuselage Frame Nodes On our aircraft, all the spruce member nodes in the cockpit area of the fuselage side frames are filled with spruce wedges, not just the ones where the undercarriage mounts.

20. Control Column to Bellcrank Cables We have fitted a twin pulley assembly at the bottom edge of the rear seat, aft face to guide the cables through the change of angle that exists here. A very small depression (1/8" deep) was sanded in the seat cross strut at this point to allow the cables to sit higher up than would otherwise have been the case. This prevents the cables rubbing against the top of the control column torque tube rear bearing housing and keeps the cables in firmer contact with the pulleys mounted at the rear of the torque tube. Greater cable tension would have achieved the same result but gave an unpleasant over-centre feel to the elevator control and felt to be overloading components unecessarily.

21. Coaming Reinforcement When making the coamings from 1/16 inch ply, it is worthwhile adding a 1/16 doubler to reinforce the lip that projects rearwards from the plane of the instrument panel. This avoids any damage occurring through knocks when getting in and out of the cockpits. I can confirm that you will hurt yourself rather than damage the aircraft (my elbow is still tender 2 weeks after thumping it into such a reinforced edge).

22. Cockpit Area Skining If you use an 8ft X 4ft sheet of ply cut through the middle for the two sides, it would be best to check that it will be deep enough. It may be necessary to ensure that the skin stops at the bottom longeron lower surface and lap the floor piece over it, rather than overlap the other way. This is because the ply panel may not be quite deep enough otherwise (you will need it to be 24 inches deep, and a 48 inch wide panel cut in half will be slightly too shallow). Using scarfed GL1 ply panels cut in half shouldn't be a problem as they are typically 50 inches wide (just under 25 inches when cut in half).

23. General Areas Where Lack Of Information Exists · Bear in mind the need to consider fuselage water drainage requirements. You need to anticipate where water may gather and provide drain holes. Particularly tricky areas are the lower tailpost areas and where the turtledeck meets the top fuselage surface. We've put drain holes in all our lower fuselage side frame gussets and in front of all cross.members in skinned bottom fuselage areas. · Access panel requirements are important considerations. We embodied a rear fuselage side panel below the tailplane (see item 16 above) and panels below the bellcrank assembly, similar to G-BUCO. · Advice is needed by novice builders on the required grain direction for ply panels. This appears on the supplement drawings but isn't on the older drawings. It's not always that obvious and a mixture is seen on the flying examples. · When fitting in a large fuselage fuel tank it will be necessary to design in extra structure to take the new loads. We elected to retain the original model A type tray and vertical wall (in 1/4" ply) on which to sit our intended tank. The large front internal gussets were also retained for this purpose to help spread the loads into the fuselage frames.