Piel CP 750 Beryl plans clarification

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tenns

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Hello all. I'm working on digitizing the CP 750 Beryl using Solid Works with the eventual goal of building an updated version of the design. The plans for the main spar seem unclear regarding the rear shear web. When looking at the dwg it is difficult to decipher if the 3mm plywood is continuous from tip to tip or if it stops at rib station 9 and transitions to 5mm plywood. Based on the hidden line on the "straight" section of the spar I believe there is only 1 layer of plywood on the rear shear web which steps down from 5mm to 3mm but wanted to get others' opinions. I believe the spar design on the Beryl is very similar to the Super Emeraude so perhaps someone with a set of Super Emeraude plans could chime in.

Thanks in advance.

Tom
 

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rsrguy3

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Do whatever makes it stronger... I know there were issues with the cap spars ... you might want to get ahold of those service bulletins and apply the fix beforehand.
 

cvairwerks

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Looks like the faces of the spar have 3 layers on the front and two layers on the back side. 3mm from the centerline to the tip, 5 mm from the centerline to Rib 6 and 2mm from the centerline to Rib 4, on the front face. For the rear face 3mm, full span and 5mm from the centerline to Rib 6.
 

tenns

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Thanks for the feedback thus far. When I first looked at the plans my feeling was that the 3mm plywood went tip to tip with the 5mm layered on top but then as I looked at it I wasn't 100% sure. I should have gone with my first instinct and not second guessed it.

I've got the wing and tail surfaces modelled and the fuselage is underway. Still lots of work to do but I'd like to get started on wing rib jigs over the winter.
 

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cvairwerks

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Mcrae: Not running the 3mm full length would have been a significant deviation from 70+ years of normal spar construction. Everything I’ve ever dealt with, that had box spars, the innermost face layer went full length of the boxed area of the spars. My dealings have all been with Fairchild, Stinson and Lockheed products.
 

cvairwerks

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I’d suspect that either section view A-A or C-C would show it for sure. The hidden lines on the inboard end are really smeared and not crisp, so hard to tell for sure by that view alone.
 

tenns

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rsrguy3: I'll be building the fuselage out of steel tube. I live close to VR3 engineering so will be having them do up the fuselage kit.

In regards to section views A-A and C-C, unfortunately, they are unclear as well. I originally had it modelled with the 3mm going tip to tip but as I reviewed the drawing I thought the only clear view was the hidden lines in the 'Straight' section of the spar. The fwd shear web clearly shows 3 distinct hidden lines and the aft shear web clearly shows 1 distinct hidden line which would indicate there is only one layer in that area. I'll likely just run the 3mm tip to tip to be on the safe side unless I can find a better quality print that shows otherwise. The savings would be about 6lbs if it were 'stepped'; I'll have to find those savings elsewhere...Time to get to the gym.
 

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cvairwerks

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I know of someone that recently built one. I’ll see what I can do on finding his contact info when I get home from wrk this morning.
 

TFF

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On the plans at the root, I see the dashed lines to represent the three layers. Also I don’t think one would splice 5mm onto 3mm. That seems odd. You would want to reinforce the 3mm with the doubler, trippler.
 

chintonmd

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My plans may be a little more clear. On the rear face the 3 mm and 5 mm are scarfed together at rib 9. On the front face they are layered as the above post notes. The rib spar openings work out just fine like this. This is how I built my spar. BTW, as you know the spar drawing is very difficult to understand so a digitized version would be very helpful. For technical help, Avions-piel.com has a separate forum for the CP750. Most of the website is in French but they are comfortable with English also. Have you started building?
 
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