Here is a short article on how I've modified and tuned my Parkzone Radian to improve its performance and reliability.This popular training plane can greatly be improved with a few simple mods. Read the article and check out the photos after the jump.
The Radian (and Pro) is a fine plane, I tell new pilots to get one, fly it for a year, learn to tune it right, learn to thermal, learn to land it in your hand. When you can do all that, it's time to step up to a better plane.
Out of the box, the Radian is flyable for sure, but it certainly does not handle as well as it should, nor glide as efficiently as it could. Especially as compared to a Gentle Lady, Spirit, or Wanderer, all of which I have built and trained others to fly in the past. Some of the gear, its installation, rigging and flight settings are not what they could be.
This plane is being used as a demo e-glider for a DVD covering electric soaring essentials. The footage shot in my short video was just some test footage to see how the plane handling was effected by the onboard camera when mounted in different locations on the airframe. Could I have flown a stock radian under the goal posts, sure, no problem, I have the skills. Is it way easier to fly the modified version and do low passes and other speed maneuvers? Yes, much. Does my set up thermal better than stock? Absolutely.
I take any plane, new or used, foam or carbon, and run it through some basic set-up procedures learned over 23 years of flying with the best pilots and experience building a hundred or so planes. I check all the hardware, disassemble, remount, improve, then tune and program the radio to get to the 95% perfect tuning point before the plane ever flies. The techniques I and other top pilots use are taught on my DVDs.
The things I did to my Radian are not magical or high tech. The only money spent was on paint and a bigger prop to try. My main goal was to optimize the planes performance under power and gliding. I also wanted to improve reliability, eliminating any break points or failure-prone hardware. I also wanted to make the plane a bit more crash worthy as I will start training my 6 year old son on it. I had already flown both the Radian and Pro models, so I already knew the tuning issues that needed changing.
First off, the CG setting in the manual was going to be way off, and I just eye-balled the nice modern planform and figured the CG was about an inch off. Good, I can then add more structure to the tail group as I would need tail weight any way. I first put 3 strands of 12K carbon tow down the boom, see pictures. Used epoxy and made a nice dry layup, added maybe 6 grams, and this really helped stiffen the boom. A layer of 2.5mil box tape over that helped even more. There is still a weak point at the fin, not much foam there, lots of twisting force from the fins, which really hurts foamies at speed. Nothing worse than aeroelasticity in the elevator/fin when going at a fast L/D. Put in a plywood splint with epoxy, see picture for the approximate shape. This splint ties in to the keel in the fuse. Big improvement, as you can see in the video, minimal bending and twist even under G loads. Elevator stays firm, no pitch or yaw drift.
For the wings, wet sanded the foam with 400 grit to get off the nubs and polished up the LE a bit. Added 3M box tape around the LE and added 2 strips top and bottom. This smoothes out the foams roughness and adds much strength span wise. Having the smooth tape for the first half of the wing should really help keep the flow more laminar. 3 grams added weight per tape strip, well worth it. Tape also adds crush resistance for the whole LE area. Low temp film would work too, though much heavier. Paint is Krylon Fusion for red, cheap black stuff for the rest. Tape peals paint though.
For the elevator, the plastic hinges are going to fail, so I used a box tape hinge on the bottom span- wise. Tape gives more stiffness too, so added a strip top and bottom. The rudder hinges seem OK for now, I added some gap seal to the top hinge area, should help rudder response .001%. Will keep tabs on that hinge line though, its suspect.
Pushrod/servos: The geometry of the pushrods is not the best. Having huge arms on the servos is not good practice as it reduces the resolution and holding power of the analog servos. I have not remounted them yet, but might later. Moved the elevator pushrod to the next hole in, though I would like it in further. Melted the servo arm with a soldering iron at the hole to close it up to remove slop at the z bend. You can use CA at the hole too. Faired in the pushrod runs in the fuse with spakle, and used balsa blocks to support the pushrods at the aft ends to eliminate flex under load. (see photos) I also glued down the entire pushrod lengths with CA as the glue they use is sparse and does not hold well.
The clamps they use at the control surface ends ARE junk. I broke both of them tightening them down. Horizon should know better than to use parkflyer hardware on a 2 meter. As you can see in the pictures, I used snap links either glued/crimped or epoxied to the pushrods. Far more reliable and stiff. There are other larger hardware connectors you could also use. I moved the elevator horn more inboard to get a straighter run and smoother movement. You have to reinforce the elevator area to do this, there is not much foam to clamp into. I CA'd the two horn halves along with the screws, its strong now. Really helped eliminate double neutral in the system. My elevator system is rock solid and centers perfectly, even with the long arm on the servo. Elevator feel/centering is so critical to good gliding.
I put the plane on the tuning table and measured for wing twist (foam twists easy) and decalage angle with Robart meters. I cover all of this tuning stuff in the Performance Tuning DVD. http://www.radiocarbonart.com/produc...ailplanes.html Wings checked out fine. Nice. However, the decalage angle (stab to wing incidence) was about 2 degrees or more. You could see the big angle just by looking down the boom from behind. This is the main issue with the Radian, built in massive up trim. This is contributes to the ballooning at motor run and during soaring flight when any speed is built up.
Check out the photos, fixing this is easy, describing it is not. Unscrew the plastic stab mount, its 2 pieces. re-insert the female end partially (shorter stubs) and rotate the front upwards, the measurement of the bottom of the plastic mount to the old embossed area molded into the fin should be 6-7mm, which gets rid of about 2 degrees of angle. You need to slice a piece of foam out of the top of the stab mount hole to fit the mount back in, and drill a new hole for the front screw stud. See photos. Reassemble the mounts with some CA or hot glue. You will have to trim the rudder clearance hole a bit so the horn clears at full deflections. Remount stab, cover gaps with tape. Takes 5 minutes.
Still needed some tail weight, so a 1 oz lead hunk got inserted into the foam under the rear skid. This got my CG about an inch back from the 'factory' setting. An inch is a huge amount of CG shift even for a 4 meter plane. My plane flies hands off, and will free fly for long periods. It is not pitch unstable, yet does not pull up in a dive test. It is sensitive to the lightest energy changes in the air. The elevator trims flat at a medium L/D glide, and a few clicks up give it minimum sink. The trim settings are set to flight modes, I have a third mode for speed penetration. With the down thrust of the motor, (which is there to counter the forward CG and decalage pull up tendency) I needed to mix a bit up up elevator with the motor switch, but just a bit, it now climbs at a 45 angle hands off, instead of with the stick jammed forward like with the stock set up.
For you guys putting a 2100 pack in the nose, if its shifting your CG forward and you are already at the factory setting, you are just making trim even worse.
If you are scared to change CG, get a 1/2oz piece of lead, and tape it to the boom just in back of the wing. Slide it back a bit each flight and feel how the plane changes. Keep going back as you learn. CG changes will only help things so much, you need to change the decalage angle to get things rocking. CG is a personal preference, but extreme nose heaviness kills handling and thermal finding. You may need to reduce the total elevator throws in your radio if the elevator gets too sensitive as CG goes back. If you watch the video closely, you can see how little elevator input the plane needs to maneuver. (rudder too)
I did change the prop to a 11-8, which did improve the climb, though at the expense of run time. Battery is a Gen Ace 25C 1300, great price and they get good reviews, they are actually 25 C packs. The stock prop is just fine, I am impressed with the stock motor system, this they did right. With the bigger prop, 200 meter ALES is no problem. The receiver is a JR 921, overkill, but that's what was in the spares box. Having a fail-safe set up is nice though, no fly-aways on this baby. My all up weight is 29.4 oz. If I used a smaller (850 25c) pack and was able to get it mounted more aft, I could shave about 3 oz off the plane, but it floats just fine. I still may shift the servos to optimize the arms/resolution and make the elevator a digital, but I have other things to do, it flies sweet as it is.
Post questions here, or call me, the number is on my site, happy to chat. Paul Naton Radio Carbon Art Productions