Oddly Sized Piet Fuse

[Chris Clarke]

Hi All,

Been a longtime reader of this forum and am constantly inspired and motivated by the incredible builders/flyers here.

I'm beginning a Piet project that I acquired a few years ago. However, it has some fuselage dimensions that don't appear in any plans I have so I thought I would ask the group as to their thoughts.

First, the overall length of this Piet is 169". It looks like it was built primarily to the short fuse plans but gains length through a specific increase in dimension. From the firewall back to the first vertical support, the plans call for either 16 1/2" in the supplementary plans or I believe 12 1/2" in the short plans. This project however was built with that vertical support at 20 1/2" back from the firewall. So my first question is are there any support implications for the engine weight etc by having this support further back by an extra 4". Does it need any beefing up?

The second is that since they used the short plans for most of it, the pilots sit further back relative to the firewall for an airplane that is about 3 1/2" shorter than the long plans. This will move my CG rearwards. I have done some calculations using a weight of around 675 lbs with 25 lbs at the tailwheel. I think I can get this into a max rearward CG of 20" (at extreme case, 2 x weighty pilots, little gas) if I slant the wing about 4" after of vertical. The leading edge of the wing would likely be back about 13 1/2" from the firewall prior to slanting

Wondering who else has slanted that much and what our builders thoughts are on these two issues.

Thanks very much!
Chris

[Earl Brown]

Hi Chris
That is odd.
Do you have any photos?
Where are you located?

[Chris Clarke]

Hi Earl
I’m not at home now so can’t take a pic but here’s one that shows at an angle. The first vertical support you see on the right side is set back 20” from the firewall.
I’m located in Brampton, ON.
Chris

[danoliver]

If it was me, I would either fix it or just build a new fuselage. You’ll likely spend more time and effort trying to compensate for the odd size.
That being said, I’m pretty sure I’ve seen some pictures of Piets with long snouts on West Coast Piet. Maybe try and reach out to somebody that’s flown one that way.
I built my fuselage to the Improved ‘33 plans and slanted the wing back 3-1/2”. My leading edge is 11” aft of the firewall. I have a Continental engine on the mount from the plans. The W&B worked out good.
Also, the way you are describing the CG sounds like you kinda got it backwards. Extending the nose should move the CG forward. Try using the wing leading edge as your datum. Then, instead of thinking of it as slanting the wing back, think of it as slanting the fuselage forward .

[Richard Roller]

Piets tend to be tail heavy. On 34KP the engine (model A) was moved forward 7" to balance the a/c, short fuselage to the plans. This may be an attempt to help the tail heaviness. The main issue is not the pilots distance from the firewall, but his distance related to the wing. If the dimensions from the cabane attaches on the truss to the pilots seat back on the truss is to the plans, then it's a non issue.

[Chris Clarke]

Hi All, thanks for the thoughts. Yeah I understand the CG is from the leading edge of the wing. Since I don’t have a wing up to establish a position, the CG calculator I have uses distances from firewall and then you can input a theoretical leading edge position from the firewall and it does all calculations relative to that wing position. So playing with that this fuse can be in CG with a 3-4” shift of wing backward. Just not sure I like the extra space at front at this point although yes it could be to alleviate tail weight. Rick, yes the cabane strut attachment point is right on the vertical support behind front pilot seat.

[taildrags]

Just for the heck of it and for studying where things are relative to one another with the plane in the straight and level position, I've attached a plot of a CAD layout that I did of a conventional Air Camper pretty much by the plans (no brakes; Ford A engine mount; vertical cabanes)- except that I added the forward fuel tank that is on 41CC just to see where it fell relative to the axle, wing, and everything else. I don't think that a Ford can be installed with a fuel tank in that location though.

-Oscar

[Richard Roller]

The tank would be in the magneto bay.