ISON Tandem AirBike Builder's Log

February, 2001 -- New Parts


In the ongoing saga of adapting Zenith flaperons to my Tandem wing, I found out that the CH701 surfaces are only 122" long, and are made up of two skins which are 72" and 50" long. But the Tandem wings are 184" long, so the stock CH701 surfaces would only be about 66% span on the Tandem.

I sent Chris Heintz three drawings showing the options that were most apparent to me:

  1. Stock CH701 122" flaperons on the Tandem's 184" wings (66% span)
  2. 144" flaperons made up of two 72" skins (78% span)
  3. 184" full-span surfaces made up of some stock and some custom parts.


This drawing shows option B, which Mr. Heintz chose as the best option based on aerodynamic considerations, control system convenience, and cost considerations. We're going to align the surface with the root of the wing as shown on the left wing, so that the existing flaperon mixer/pushrod system can be directly attached to the new surfaces. This will keep the complexity, weight and cost to a minimum. Keep in mind that this plan involves trimming my oversized wing panels back to the stock wingspan. (Also note the assumed hinge locations I marked with an H on the flaperons, for discussions below. Click on the drawing for an enlargement.)

When I asked Chris if he was comfortable with the roll authority I will get with the flaperons not going all the way to the wing tips, he said the Junkers-style ailerons are "very effective" and this arrangement will make "a very good airplane." My drooped tips are not shown in the drawing yet.


My approximation of how the Junkers-style
flaperons will look on the Tandem wing


My next move was to visit Zenith Aircraft Co. in Mexico, MO, and make my final decision regarding going this route. After seeing the parts and deciding to go ahead with the purchase, I was surprised to find that all of the parts I needed were in stock and I could take them with me if I wanted (or pay another $80 to have them shipped to me). That was a no-brainer -- I'm anxious to get this project back on track and make some visible progress.


At long last, I have parts in my shop for the new flaperons. Here you can see four pre-bent and pre-drilled 72" flaperon skins stacked together, four C-shaped spars, ribs, fiberglass tips and misc. hardware. Not shown are the hundreds of rivets needed to assemble these parts.


Zenith's pre-shaped flaperon ribs


I'm now trimming my wing spars back to the original length of 184" and beginning assembly of the right wing while I wait for engineering drawings from Mr. Heintz. This will include instructions for making flaperon hinge brackets (like the ones in the photo below) which will attach to the existing wing ribs.

I was amazed at how lightly these brackets seemed to be attached to the CH701 wing. Just a thin aluminum angle on each side, riveted to the wing skin (and probably to ribs on the inside) with eight blind rivets. If this is all the security that is required, attaching these brackets to the Tandem ribs should be a simple matter.


This photo shows the root end of the CH701 flaperons, and the method of attaching the pushrod. On the front (right) of the control horn you can also see an auxilliary hinge point, which is simply a pin attached to the fuselage side which projects through the control horn. This helps transmit the motion from the pushrod into the surface without immediate twisting losses. Unless my first hinge bracket will be located at the root of the wing (instead of my assumptions in the drawing above), I may need to attach a simple structure to the fuselage between the flaperons to support hinge pins like this.


This is the flaperon's mid-point, where the two skins are joined. The outer half of the surface is joined at a lower incidence, apparently to cause the outer portion of the wing to stall after the inner portion. I assume I'll be doing the same.

Underside of the flaperon mid-point


Fiberglass tip on the CH701 flaperon


Meanwhile, John has his scratch-built fuselage pretty far along, Robert has a lot of wing progress to show for himself, and Bill is putting us all to shame with his blindingly fast progress. I'm very pleased to have Bill paving the way for the installation of my 582, though. I'll leave you this month with a photo of his 582 installation in progress:


The propeller is just a big fan in front of the plane
used to keep the pilot cool. When it stops, you
can actually see the pilot start sweating.