ISON Tandem AirBike Builder's Log

January, 2001 -- Flaperon Solutions


This is gonna be a short one, folks. Perhaps it will make up for some of my previous verbosity.


I mostly took a break from the project during January, while waiting for some results from Chris Heintz regarding the Junkers aileron retrofit. This gave me some time to do some virtual airplane building, which you can see above. I started fantasizing about putting a 75hp HCI radial on the Tandem, and it wasn't long before I was scanning a photo of the HCI from the February Kitplanes and doing a little virtual swap with the Jabiru on Alex Boone's Tandem... Looks fabulous on there, doesn't it? I'm gonna visit the HCI shop in Missouri soon and check out their engines in person.


Most new builders start pulling staples from their first rib per the instructions, discover what a pain in the butt it is, and then ask if it is really necessary. Here's the answer -- 10 oz. of staples pulled from my ribs, or 5/8 lb. In a project where we are trying to save grams at every opportunity, this is some significant weight-savings. The staples add almost no strength to the epoxy bonds, and about all they contribute is weight and a corrosion risk, so off they go. Makes your gussets look like hell after they're dug out, though.


Yes, this photo is reprinted from last month. I just wanted to start this section with a visual aid.

After not hearing from Chris Heintz for a month, I finally got him on the phone. Apparently he had some FAA-related fires to put out in his own business and had to go out of town for two weeks. He doesn't expect to get to the nuts and bolts of my project until the latter part of February, but at least I got some questions answered which will allow me to recommence construction on my wing.

I found out that the Junkers flaperons are lifting surfaces -- just like the wing -- and 100% of their area contributes to the area of the wing. Remember this chart?:





31'-4" (stock) Plain (stock) 141 sq ft - 6.4 lbs/sq ft
31'-4" (stock) Junkers 162 sq ft +15% 5.6 lbs/sq ft
33'-10" Plain (stock) 152 sq ft +8% 5.9 lbs/sq ft
33'-10" Junkers 175 sq ft +24% 5.1 lbs/sq ft
28'-10" (clipped) Junkers 149 sq ft +5% 6.0 lbs/sq ft

I've updated the chart to reflect the true increase of area due to the Junkers. What this tells me is that the way I'm headed (extended wing plus the Junkers flaperons) is gonna give me way too much wing area and therefore too low of a wing loading. It might climb like a bat outta hell, but it would not be much fun to ride on a bumpy day. So, I have decided to cut my spars back to the original wingspan of 31'-4" (oh fun). With the Junkers surfaces this will still amount to 7% more wing area than I would have had from merely extending the wing alone, so this seems to fit well with my mission profile.

I also added a new row to the chart above, showing a clipped wing Tandem with Junkers flaperons. If a builder was to remove one outer rib bay on each wing panel and add the Junkers, he or she would still end up with 5% more wing area than the stock configuration. I bet with the shorter wing it would be a maneuverable little critter, too!

In my phone conversation with Mr. Heintz we also briefly reviewed a concern about the Junkers surfaces adding loads to the rear spar that it wasn't designed to handle. He said he doesn't see this as a concern, as the loads from the Junkers brackets will be transferred via the hinge ribs around the rear spar and to the front spar. He said that Wayne's ribs are very nicely designed, and this shouldn't be an issue. I still can't connect all of the dots in his logic, but I will be revisiting this with him soon to make sure that this issue is resolved to my satisfaction. Perhaps there will be a slight reduction in maneuvering speed with flaps deployed, but since I'm planning to be flying 30mph or less when I have full flaps deployed (towing gliders) I'm not too concerned about that. I never liked landing Cessnas with flaps deployed anyway -- perhaps I'll feel the same way about the Tandem and only use the flaps when I'm towing or doing a short-field operations.

I'm in the process right now of getting pricing and lead time info from Zenith for the flaperon kit. There should be lots more to report in the next update.


There are three simple rules for making a smooth landing.
Unfortunately no one knows what they are.