Horizontal Stabilizer
Construction of the Hstab on and off the tail cone
Also includes two Vacuum Forming videos and a clever Clamping Method
Started 2/15/2015 and Finished 6/6/2015
Updated 7/27/2015
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I found the Hstab construction more time consuming and difficult than planned.  The elevator was fairly simple.

Construction of the Horizontal Stabilizer (Hstab) began directly on the fuselage.  Eventually, the assembly was moved to the workbench for precision work.  Ultimately, I was forced to final rivet the E-to-F section of the fuselage to ensure that the fit between the fuselage and the Hstab would be tight.

Multiple ribs were made before I was satisfied with the dimensions and shape.

A major GOOF required building a second right skin.  The GOOF was the result of adding a spacer to square the rear spar to the fuselage center line.  I thought the spacer would merely shift the angle of the rear spar by a few degrees.  BUT, it also made the right skin larger!  The size increase was small but as the future test pilot, I didn't want to find out what that would do to the flight characteristics.

Before completing the Hstab, I removed the Fuselage-E-to-F  section ... made a new skin ... and completed final riveting.  This was done to ensure that Hstab would be perfectly fitted onto the finished tail cone ... not too loose nor too tight to fit.

The Horizontal Stabilizer took longer to build than expected due to the need to finish rivet the Fuselage E-to-F section.  Making new skins for the right Hstab and the Fuselage E-to-F section cost about a day and one-half.

The start:  The bare Rear Spar and Inner Ribs temporarily installed on the Fuselage:

Very nice rear spar by Charles Snyder.  Note lightening holes and hinge doubler.  Hard to see, but the top part of the doubler folds back under the spar flange.  Hinges easily fit on top with no interference.  Crimped holes stiffen the structure.

I did not include lightening holes.

A temporary brace is installed to maintain the critical angle between the rear spar and the inner rib.

This is essential when the Hstab is removed from the aircraft for work on the workbench.

Ultimately, the skin will maintain the angle.

Hinge notation in RED is marked at the hinge point to avoid drilling any holes until the hinges are ready.  After the hinges are drilled and ready for installation, match drilling will be used.

Checking each side of the Hstab to ensure that the left and right side are at the same angle.

At this point, the front slot was still just a hole.  Later, I elongated the hole into a slot made extra long based on inputs from other builders.

Strangely, the angle was zero degrees.  On page 9 (left center low), the plans call out 3 degrees negative.  After your first test flight, you may need to make an adjustment depending on your weight, position of the seat and other factors.

Off the Fuselage and on the Workbench
The Hstab skin is easily formed using the vacuum process.

A 3/4-inch plastic pipe with three bleed holes spaced 120-degrees coupled with a shop vac and some cheap painter's drop cloth (plastic) does the trick.  The edges of the Horizontal Stab are taped together.  Gaffers Gaff Pro tape is the best to use.  Strong but doesn't leave any residue.

A mini-vac is used in the demo.
http://youtu.be/4V_Bvk1wB90 ... my video

The link below is a detailed video on Vacuum Forming for the Sonex wing.  Overkill but good. A little leakage won't hurt.  Iron pipe not required.  Clamping pipe to the table over the center line is a nice touch ... but taping the pipe to the skin works OK.
Sonex Wing Vacuum Forming

Workbench ready for Horizontal Stab.

Skinned Hstab with clamps on the left and the right stab open for drilling.  See details on Clamps below:

The skins really look nice with no Clecos.

In the enlarged image, you can that the skin is extra long and wide to allow for trimming of the skin to fit snugly to the fuselage.

The red arrow points at a spacer to achieve a rear spar perpendicular to the fuselage center line.  Ultimately, I determined the forward hole in the tail cone was1/8th inch forward.  The spacer moves the spar back 1/8th inch.  Thus; the stab skin will now be 1/4-inch larger!  GOOF!

The bare frame Hstab is moved from the workbench for a test fit on the fuselage.

Cleco spring clamps hold things in place in addition to two bolts and Clecos.  Back drilled the inner ribs to the rear spar.
My clamping Design
You need a method to clamp the skins around
the stabilizer frame without introducing kinks and scratches

Do you have three hands?   Two boards coupled with two binders require 3 or 4 hands to install.

Four clamps were devised for holding the skin tight to the ribs and spars.  A light bungee cord holds them closed.  The clamps were built using the wooden rib form for tight fit.  A fast and easy way to bend and hold the skin tight without creating any distortion.

I used Snyder's method of clamping on the Vertical Stabilizer but got tired of the fumbling required due to the lack of third hand.  Also, when installing or removing ... you have four parts to pick up or set down.

With my method, the entire clamp is essentially one piece.  Also, I found two clamps was enough as time went on and occasionly got by with only one clamp.

The plans call for a doubler located at the inner rib and the rear spar.  I also added doublers at the mid-spar ... First: to cover up some inadvertent holes ... GOOF ... and, Second: to beef up the connection between the inner rib and the mid-spar.

Note: the WWII PT13 Primary Trainer had similar doublers on their vertical stabilizer.

View of the center section of the riveted Hstab.

Enlarged trim slots can be seen.  I chose to place the inspection holes on the top for safety reasons.

WARNING: While I added doublers on the mid-spars ... one should be aware that adding strengthening material adds weight and may transfer forces to weaker parts of the structure.

Sliding the finished E to F tail cone in place to the horizontal stabilizer. (Not fully on.)

Bottom line ... it fits perfectly. 

Installing a new skin on the fuselage tail section (to replace the ugly, beat-up old skin) followed by the final riveting didn't change the dimensions.  Whew!

Red marks are a reminder to NOT rivet (holes for dorsal fin).

Elevator layout:  WARNING ... do not use my pattern.  I did not realize that my plans were incomplete (ended at page 18).  Additional plans contain the exact layout for the elevators.

Hummel Aviation offers a complete set of new plans for a nominal price ... or replacement single pages.

Elevator skins after forming on 4-foot brake.  The skin to the left has been additionally formed by the use of a 2x4 and brute force below.
As demonstrated to the left, errors in bend angle can cause the elevator surface to be concave or convex.  The flange-bends are critical.  A convex or concave surface may affect the trim or control forces.  Adjust the flange bend with your fingers until the part fits perfectly without any outside forces.  ... Don't depend on the end ribs to straighten the surfaces at the middle.

Hinge doublers are required at the outside ends of the horizontal stabilizer.  I drilled the clearance holes to ensure the pop rivet was fully seated.  A test rivet proved that the holes were necessary but I'm not taking any chances.

Trial fit and drilling of elevator hinges ... upper surface is clamped below to provide access for drilling.  Later when the elevator is removed, I will back drill the holes from the elevator spar into the upper flange.

Elevator is flipped up 90-degrees to allow view of the hinge doubler installed.


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