The Parkzone BF-109 is an interesting product.  Like most scale warbird replicas, it does not have the most forgiving flight characteristics, and it has a couple of quirks.

I’ve flown mine about ten times now, and I would say that landing smoothly is the biggest challenge.  One tip I can immediately recommend is to pull BACK as soon as the main gear contacts and the wing has stopped flying.  If you don’t pull back, the tail likes to float and the model tips forward onto it’s nose.

I wanted to fly the BF-109 a few times before trying the flap option, and after dumping the 109 on it’s nose a few times this weekend (plus 2 good landings!) I was ready to give it a shot.

The gray tape that covers the aileron servo wires does not survive being peeled back gracefully.  Plan to get some new tape in a similar color before you start.  You will also need a servo Y adapter, a pair of sub micro servos (I used HXT-900) and the pushrods and stuff that came with your kit.  The manual says you need to buy the linkages for flaps, but everything I needed came in the box of my BNF example.

The first brain teaser is how to make the flaps work, considering that the Ar500 is only a 5ch reciever.

On a DX6i, the answer is to plug the Y harness into the ‘gear’ channel on the reciever.   Then go into the flap setup in the DX6i, and set the flaps to 100% down.  Most airplanes need some down elevator to prevent the model from ballooning up when you apply the flaps, but this particular model does not with 1/2″ of flap travel.  I set the correction value to 0, and it stays level, hands-off.

Next, you need to mix the flap channel with the gear channel.  I put this on Mix1, set it to active and 125% down.  Lastly, I reversed the gear channel from the ‘SETUP LIST’, ‘Reverse’ menu.

The mechanical part is pretty easy, too – Place your servos, route your Y harness, and mount the control horns as per page 14 of the manual.  I left my RX powered up so I knew the ailerons were centered as I set it up, and cut the flaps out as per the recommendations in the manual.

With the clevis connected to the third hole on the flaps, and the flap->gear mix set to 125%, I’m getting about 13mm of travel from the flaps when deployed, which is close to the PZ recommendation for half flaps.

My DX6i only has a 2-pos flap switch, and I decided to leave this at the more conservative setting until I have had a chance to fly the model.

Wrapping up the modification, I moved the clevis from the outer hole to the second from the bottom on the ailerons, and overdrove the aileron servos a little bit to get the PZ recommended 3/4″ (19mm) travel out of the ailerons.

This morning, the Winter storm that has been hitting Northern CA took a break, so I rushed out to the field.   I didn’t use the flaps for takeoff, but I flew around with them and did a bunch of approaches.  The flaps do slow the model considerably, and it takes out some of that low-speed wing tipping that everybody is noticing.  Again, there is no elevator correction required at 1/2″  flap travel, I wonder if it will be required when I dial the flaps up to 3/4″. 

It will be a few days before I figure it out, because in the gray skies I got disoriented and had a little mishap.  Thank God Horizon has spare parts in stock…

Please don’t take my numbers as Gospel, and I hope this article helps some folks wrap their head around the custom mix they need to do in the DX6i.

- Eli

**Update 10/26/09 – Crash repairs consisted of a new fuselage and wing

In this iteration, I put the clevis on the inner hole on the flaps and ailerons, and over-drove everything to 125%.  This yields 1″ of flap travel, and just over 1″ of aileron travel.  The aileron roll rate is quite manageable, and there is still no need to dial in an elevator correction with the flaps. 

My 109 on approach with flaps deployed

The flaps slow the model down, but the tip stalling is still there and you still need to land under power.  An experienced pilot friend of mine suggested that I cock each aileron up a few degrees to see if that tames the stalling a little, and I’ll be trying that this week.

Keep the shiny side up,

- Eli