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Schempp-Hirth Standard Cirrus - 3 Metre span

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GaryBridge1
Posts: 16
Joined: 17 Mar 2020, 13:22
Location: Devon

Re: Schempp-Hirth Standard Cirrus - 3 Metre span

Post by GaryBridge1 »

In preparation to build the wings, I cut out all the ribs (28) in all for each wing. Ribs 1 to 3 have a 1/8" ply doubler. I noticed that none of these ribs had the cutout for the brass wing joiner, however the Root facing rib (top of photo) does have the cutout. So using the plan, I've been able to cut these out on ribs 1 to 3, taking into account the 2 degree dihedral and then glued the balsa ribs to the 3 ply ones.
2020-04-15 11.34.58.jpg
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Then, I cut the Wedges from 1/8" Spruce for supports of the brass wing joining strip. My trusty Japanese saw is excellent for the fine cut required.
2020-04-15 11.08.32.jpg
2020-04-15 11.10.27 (2).jpg
2020-04-15 11.11.35 (2).jpg
2020-04-15 11.12.57.jpg
Also cut the brass wing joining strip and dry fit over plan.
That should sort the dihedral out. :D

GaryBridge1
Posts: 16
Joined: 17 Mar 2020, 13:22
Location: Devon

Re: Schempp-Hirth Standard Cirrus - 3 Metre span

Post by GaryBridge1 »

Starboard wing built, with spruce spars. Next stage is to sheet the under side with 1/16" balsa, from the main spar to the rear, requires removal from the board and turning over.
2020-04-18 10.03.42.jpg
2020-04-18 10.04.36.jpg
2020-04-18 10.04.43.jpg
2020-04-18 10.04.49.jpg
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Peter Balcombe
Posts: 1218
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: Schempp-Hirth Standard Cirrus - 3 Metre span

Post by Peter Balcombe »

Just a thought Gary, but why not sheet the upper surface first whilst the bottom is still in position?
If you do the bottom first then you will need to ensure that the sheeting attaches to all the undercambered areas.
Peter

GaryBridge1
Posts: 16
Joined: 17 Mar 2020, 13:22
Location: Devon

Re: Schempp-Hirth Standard Cirrus - 3 Metre span

Post by GaryBridge1 »

Hi Peter, On the plan, notes are quite sparse, but it does list an order of tasks to complete the wings. So I've just followed that and gone ahead with sheeting the underside first, to the rear of the main spar. It went well with no unforeseen problems. What I found a bit unusual with this plan for the wings, is that there aren't any jig tags on any of the ribs. So the only way to ensure the ribs are in the correct position, was to make sure the upper and lower spruce spar, were at 90 degrees to the building board all along the wing span. I managed that by cutting a few pieces of wood with a 1/4" slot and placing them at intervals along the plan. Here's a photo of the sheeting done so far and one of the simple jigs I made to keep the spars perpendicular whilst gluing the ribs in place. Once the glue had dried, it was then a simple matter of adding the 3rd spruce spar at the front, which slotted into every rib easily without any fettling, giving me confidence that the ribs are correct. Would sooner have jig tabs though?
2020-04-19 14.46.32 (2).jpg
2020-04-19 14.49.20.jpg

Next on the list was the vertical grain webbing, which all went in place nicely forward of the main spars.
2020-04-19 13.44.48 (2).jpg

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Peter Balcombe
Posts: 1218
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: Schempp-Hirth Standard Cirrus - 3 Metre span

Post by Peter Balcombe »

Gary,
It doesn’t really matter how you do it as long as the skins are attached to the ribs etc., but most importantly, the wing has the correct incidence all the way along.
You need to make sure that you have the correct amount of washout built in (if any- as identified on the drawing, usually at the tip end trailing edge area somewhere). The top & bottom spar edges will not necessarily be perpendicular to the bench.
Make sure that this is correct/wing TE jigged, before you attach the top skin which will then ‘lock-in’ any wing twist - intended or otherwise.

GaryBridge1
Posts: 16
Joined: 17 Mar 2020, 13:22
Location: Devon

Re: Schempp-Hirth Standard Cirrus - 3 Metre span

Post by GaryBridge1 »

Appreciate the advice Peter. There is wash out toward the end of the wings, which looks right.There is no mention on the plan of putting an intentional twist. It did mention; however that prior to gluing the vertical webbing, it was a definite requirement to have the lower and upper main spars at 90 degrees to the board. So I've been quite conscious of not getting any twist at all. I'LL try my upmost to jig the wing prior to putting any top sheeting on.

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Peter Balcombe
Posts: 1218
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: Schempp-Hirth Standard Cirrus - 3 Metre span

Post by Peter Balcombe »

Hi Gary,
The intentional twist is the washout often applied at the tip end which twists the TE up a bit to reduce incidence & avoid the tip stalling before the rest of the wing (tip stall). :)

GaryBridge1
Posts: 16
Joined: 17 Mar 2020, 13:22
Location: Devon

Re: Schempp-Hirth Standard Cirrus - 3 Metre span

Post by GaryBridge1 »

Okay, understand. The washout is achieved on this model by the shape of the outer ribs, which effectively gives a slight twist, although the spars remain at 90 degrees.

GaryBridge1
Posts: 16
Joined: 17 Mar 2020, 13:22
Location: Devon

Re: Schempp-Hirth Standard Cirrus - 3 Metre span

Post by GaryBridge1 »

Having built both wings and sheeted the bottom of each to the rear of the main spar, my attention turned to installing the brass wing joiners in each wing and through the fuselage. I realised quite quickly that the spruce wedges I'd cut from 1/8" Spruce for supports of the brass wing joining strip weren't quite right, even though I'd used the plan drawing. So I re-cut some more, making sure that the 2 degree dihedral was maintained on each wing.
2020-04-26 17.41.13.jpg

Having repeated the same on the port wing, time for a test fit on the fuselage, before I commit to gluing the wedges in.
2020-04-26 17.37.01.jpg
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Starting to take shape, so it's on to sorting the ailerons/fitting of aileron servos and air brakes next. :)
Last edited by GaryBridge1 on 04 May 2020, 18:10, edited 1 time in total.

GaryBridge1
Posts: 16
Joined: 17 Mar 2020, 13:22
Location: Devon

Re: Schempp-Hirth Standard Cirrus - 3 Metre span

Post by GaryBridge1 »

Managed to fit the Air Brakes and Aileron Servos into each wing.
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Also glued in balsa hinge blocks and balsa support strips along the ailerons. When the top sheeting is complete, I'LL be able to cut the ailerons away from the wing prior to shaping and hinging.

2020-05-04 13.41.12.jpg

Next steps are to position the brass tube in each wing for the incidence pins. Then I'LL be able to sheet the top of the wings and forward of the main spars with 1/16" balsa. Just waiting on a delivery of brass tubes and steel piano wire. Whilst waiting I'LL finish off planking the fuselage and position the snakes for Rudder and Elevator. :)

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