With the very kind help of Steve Lange 🙂 – Lisez la version en français ici.
I will detail here every aspect of my Ahi Madstab modifications: drawings, construction, and setup. I hope you will try it, and like it!
In a previous article in French I shared a few thoughts about this, but I’ve improved my system and now I am satisfied: I’m able to perform multiple flips and experience no flutter at all while flying at high speed. You can download the PDF file and print it if you will be making your own pieces using hand tools, or you can use this .svg file for lasercutting (Note: you will have to prepare your own file for each thickness with copy/paste, etc.).
The photo gallery contains all the details. It is followed by some information on my transmitter mixing and settings. Finally, a small video shows the ability to flip and to fly fast without flutter using this madstab. Click the images to see the captions, which contain detailed explanations.
Feel free to ask questions using the comment section, below! This will help prompt me to share information that I might have forgotten to mention above.
Warning: This system is not suitable for gliders over 800g/30oz! Check out the madstab page by François for that… 😉
.PDF and .SVG files look like this.
Rudder: Cut the entire disk needed to 2 x 90° move. Separate the rudder flap.
Prepare a 1.5mm plywood reinforcement for the rudder joint, with holes for 2 small hinges.
Reinforce the rudder foot using 2 carbon or fiberglass rods, 3mm.
In order to be effective, these reinforcement rods must penetrate 7 or 8cm into the fuselage so that they reach the carbon reinforcements in the tail of the stock Ahi.
The 3 pieces of the madstab subassembly, made from 5mm plywood.
Ready for fitting.
Use strong glue to affix the subassembly in place.
Madstab subassembly in place.
Glue the 1.5mm plywood reinforcement to the fixed portion of the rudder.
The Ahi receives a layer of paint.
Yellow above, red below.
Elliptical control horn: adjust the diameters of the holes, making sure they match from side-to-side.
Glue the 3mm ellipse between the two 1.5mm sides.
Use the lowest-stretch thread available. Use a 1.8mm pushrod with a sleeve-style washer cut from the 3mm pushrod housing. Slide the thread into the sleeve washer and slide both thread and washer onto the control tube. Cut the tip of toothpick for use in a future step.
Use CA to glue the toothpick tip and the thread to the end of the elevator pushrod. Loop the string around the elliptical control.
Then tighten the wire, and glue wire + washer.
Here 2 sleeve-washers are used to improve the durability of the assembly.
Glue the counter-ellipse to freeze the thread-ellipse position.
Sharpen the end of the Ahi’s original pushrod so that it will slide into the control tube, which will then become the new pushrod end.
Glue pushrod and housing.
Right side. A larger carbon tube is added to the elevator joiner rod. This tube will provide sufficient offset to the stabilizer halves so that they do not interfere with the rudder pushrod.
The rudder pushrod must be mounted with the Z bend in the correct direction so that it will clear the cut-out for the Madstab.
I reinforced the rudder hinge line using Blenderm attached to the fixed part of the rudder.
Assembled! Right side. In the 6mm Depron empennages, the holes for the axis are made with a sharp round file for the 3mm, and a toothpick for the 2mm.
Left side details.
Below. There is approximately a 6-7mm gap between the fuselage and the stabilizer.
The servos. The elevator servo arm is slightly longer to allow more pushrod travel. This requires that you move the elevator servo as far as possible to the right side of the fuselage, in order to allow unimpeded travel of the servo arm. It may rub on the canopy otherwise.
Holes are made with an mini milling cutter in the fixed part of rudder. This allows the insertion of lead BBs to move the center of gravity rearward.
The 45° travel of the servo is almost enough. Nevertheless, it will often be necessary to increase adjust the elevator servo’s end points (EPA) to allow for full +/-90° travel at the madstab.
It’s ready 🙂
Center of Gravity (CofG): At least 85mm from the leading edge (LE) for positive and negative multiple flips, adjusting to suit your preference thereafter. To start more cautiously, try a CG of 75-80mm from LE, and then adjust to your personal preferences.
Transmitter Settings: You will need exponential! Personally, I prefer a custom curve in 3 segments as shown in the diagram below. Check your transmitter’s manual for more information on setting up custom curves.
Note: I configure my Taranis so that the trim setting is independent of the endpoint settings. Without this, a few notches of trim sometimes change the madstab’s position by more than 5 °. This can considerably soften flips, or even make them impossible.
Here are detailed shots of my setup, followed by a little bit of flying to demonstrates the ability to multiflips as well as high speed flight without flutter.
And just for fun, the 1st place video of summer 2017 Ahi contest on Facebook group « VTPR & Slope Aerobatics »:
Feel free to share your impressions and ask your questions using comments…
Enjoy the wind-powered-fun! 😉