Century Radikal G20 Review

Friday, January 15, 2010

James "sparx" Kovach
Specs (as reviewed)

Type: 50 Size Gasser Helicopter
Flying Weight: 10lbs 7oz/4,734 grams (fueled)
Engine: Zenoah 20cc
Pipe: Century Torpedo Slim Tunable Gasser Muffler
Fuel: 87 octane pump gas with 4/5 oz Quicksilver Marine 2 Cycle oil
Main Blades: Mavrikk 620 mm Widecord Carbon Fiber
Tail Blades: Stock and Pro 3D 92 mm Carbon Fiber
Electronics/Radio: TX - JR x9303 2.4ghz, RX - Spektrum AR7000, Cyclic servos - Hyperion DS20-FMD, Throttle Servo - JR DS537, TJ RevMax Rev Limiter, Gyro - CY Solid-G, Tail Servo - Futaba 9254, A123 2S – one for Ignition and one for Receiver/Servos

This is going the be the first in a series of reviews I will be doing on the Century Radikal G20 Helicopter. A Gasser engine is a different animal compared to a Nitro engine. The most notable differences are the break-in for the engine and how/when the engine will start making its best power. So I thought I would do a series of reviews covering the different stages of building and running in the Century Radikal. I also have some different things I want to try on the Radikal over the next few months such as different blades sizes, converting it to flybarless and possibly sending an engine out to have it modified.

This first part is going to cover the building of the helicopter, the first gallon of fuel through the engine and how it performs on the different gear ratios availble. This will give you an idea of what to expect should you decided to purchase it.


So what is the deal with a Gasser Helicopter? Why would someone want one? They are typically heavier than their Nitro counterparts. They are “fussier” when it comes to tuning the engine and are more vibration prone. Well, the answer is usually the same when you ask someone that is looking into putting together a Gasser Helicopter: Fuel Costs. We are not talking about half the cost of running a Nitro. We are not even talking about a quarter of the cost. It is not uncommon for someone to see savings of up to one tenth of the running costs verses a comparable Nitro helicopter. This cost savings is not just over Nitros, but Electrics as well.

Over the years there have been a number conversions around to change a 50 size Nitro helicopter over to a Gasser. All of these have been “home brewed” designs that mainly focused on how to get the bigger engine into the frame and the lower RPM that Gasser engines run at. Some have been good and some have been bad, but none of them really took off. Enter the Century Radikal G20. It is the first production 50 size Gasser to hit the market. The airframe and drive system were designed to cope with the different stresses that a gas engine will put on a model helicopter airframe, most notable, the large amounts of torque that these engines produce. I must say that from what I am seeing, Century has done a top notch job with the Radikal G20.


I am not one of those people that enjoys this part of getting a new helicopter. Some people enjoy the build and look forward to it, I do not. So I appreciate a model that goes together easy and quick. The Radikal G20 did not disappoint me.

The manual does a good job of guiding you through the build. If you take your time and pay attention to the text and the diagrams, you will not have a single issue with the build. I must confess, there were a few points when I picked up a part and though “now what am I supposed to do with this”. Each time it turned out that I had skipped over a notation or diagram that showed me exactly what it was for.

The fit of all the parts was as good as I have ever seen. Century has invested into some new CNC machines to produce their helicopter lines and you can really see how that is paying off for them with the Radikal G20. If two parts were meant to go together, that is just what they did. When I am putting two parts together, I am looking for a “snap together” fit. That tells me that there is going to be no play. With the Radikal G20, the parts did just that, they “snapped” together. Everything went together like they were meant to be. I am used to having my dremel, file and sand paper ready when I am building a helicopter. It just seems like those are “tools of the trade”. With the Radikal G20, I did not have to use those tools at all.

I did not time how long it took me to build the Radikal G20. I started it on a Sunday evening and had it finished up first thing Monday morning. It really does go together rather quickly. There are no complicated sub assemblies. It is really quite simplistic in its design. You can really tell they put a lot of though into the Radikal G20's design.

There is plenty of room for mounting all your electronics on the Radikal G20. One thing that will drive me crazy at times is when I run out of room on the “typical mounting spots” and have to start putting components on the sides. The Radikal G20 has 4 mounting spots for all the electronics. The front has an upper and lower tray. In the rear above the gas tank is another tray. Lastly, above the tail boom mount there is a tray for your gyro. Needless to say, I did not find myself putting any of my electronics on the side frames.

Mounting the servos was a little bit tricky. They provide you with those plastic “u” shaped servo nuts. With the upper radio tray installed, it was almost impossible for me to get the servo nuts onto the screws on the back side of the servos. I ended up taking that tray off to give me better access to the back side of the servos. When you are building the Radikal G20, I would suggest you do not loctite those particular screws until you are done installing the the front servos.

Setting the head and servos up is pretty much the same as any other helicopter. Center your servos and get everything in the head squared up as needed. There were no oddities that I ran into . One thing I discovered while setting up the head and the servos was an easy way to get everything squared up where it needed to be. I touch on this in the walk around video. It is hard for me to put into words so be sure to check out the video.

All and all I must say I was not “annoyed” during the build as I often get. I would like to say it was a pleasure building it, but as I stated before, I really do not enjoy the build as others do. I will say after building the Radikal G20 that I had a lot of appreciation for how well the airframe was designed.

Flight Report

I know, this is the part you want to know about. It's heavy right? It is going to fly “like a pig”. There is no way it can fly near as good as a 50 Size Nitro. So come on, tell us already.

Well, let's just say that I was very surprised on how the Radikal G20 flies. It is not slow like I had thought it would be. It did not fly like it had a bowling ball strapped onto the skids. At first, I had a hard time seeing any differences between it and a Nitro 50. It flips and rolls nicely and pretty quick. In forward and backwards flight, it zips around with quite a bit of speed and tracks well with no tendencies to pitch up or down. It zooms up into stall turns with authority and seems like it is never going to stop climbing. Big power loops can be done with little effort. If you are into big aerobatic type flying, you will be not be disappointed. What I did notice that was different for this style of flying is that the added weight would carry the helicopter through this type of flying better.

I know you are now thinking, yeah right. There is all that extra weight. I cannot be just like a Nitro 50. Well, as I said, at first I could not “feel” the extra weight. It wasn't until I started doing things like Tic-Tocs, Rainbows or any other type of maneuver that has a hard direction change or a quick stop that I started to “feel” the extra weight. Now I am not saying that the Radikal G20 cannot do these maneuvers, it just does them differently. It is not going to happen with the same quickness and sharpness that you are used to with a Nitro 50. It is going to seem more “cushioned”. If you like doing a “smoother” type 3D, then you will not mind this at all. It is not a direct transition from doing “smooth 3D” on a Nitro to a Gasser though. You need to be ahead of the helicopter with the collective, in other words, “Collective Management”. If you are into the “hard/crack” type 3D, then I think you would feel the Radikal G20 is a little lacking when it comes to doing 3D.

I think the best way to sum it up is this. The Radikal G20 will do everything a Nitro 50 can right up to “hard/crack” type 3D, but it is “just about there”.


Currently there are 3 gear ratios that are available for the Radikal G20. Stock it is 6.0:1 and you can get upgrades for 6.4:1 and 6.9:1. At this time I have flown it with the all three gear ratios. I have not spent much time with the 6.9:1 yet, but enough to see how it is going to do. The 6.9:1 ratio is the one to use. My suggestion is to put in the 6.9:1 ratio and run the head speed at 1800 RPM. I know that seems low for the head speed, but as I talked about on InsideHeli, you are flying “on the torque, rather than the RPM” with Gassers. This is a hard concept to grasp. I was dead set on getting it running at 2000 RPM just like I do with my Nitros figuring that it what it was going to need. But in the end, I found that there was really no lose in performance when running at 1800 RPM. What I did get was consistent power throughout the flight.

The ratio of tail blade RPM to main blade RPM is 5:1 on Radikal G20. This is on the high side in my opinion. The stock plastic tail blades are 95 mm. I replaced mine with some carbon fiber 92 mm blades. With the higher RPM of the tail blades, I felt the 95 mm was not needed.

Kits are currently being shipped with a number of addendums. There are two that have been added recently that might not be in the kit if you get it from some shops. One of them is regarding adding a radial bearing to the top main shaft bearing block. This is to be installed in place of the thrust bearing on the main shaft. The other is a replacement for the stock tail pitch slider plate. With the stock pitch plate, the tail grip pitch is changed with trailing edge control. The replacement pitch plate will change this to leading edge. I would highly suggest doing both of these changes so make sure they are in your kit. If they are not, contact Century or your dealer and they will get them to you.

Getting air in the fuel is something you do not want. So to combat this, it is highly recommended that you install a felt clunk in the tank. These can be found online and also at just about any small engine shop. I found them at a local Ace Hardware. I think I paid $1.50 each for them.

Filtering your fuel is another thing that is highly recommended. It is best to filter it before the fuel enters the tank. What I have done is used one of the felt clunks on the gas can side of my pump. I also pass the fuel through a paper gas line filter that is used on lawn mowers. This way, the fuel is filtered twice before it enters the tank. Again, I found all of this at a local Ace Hardware store.


So far I am really enjoying the Radikal G20. It is a great flying helicopter and is easy on the wallet when it comes to fuel costs. I find myself saying “am I done with that gallon yet” instead of “burned another gallon already” like I typically do when I am out flying my Nitros. Do I think it will be a replacement for a Nitro 50. Well, that just depends on what you want out of a helicopter. If you are into smooth aerobatics and 3D, then I believe you will not be disappointed at all with the Radikal G20. I believe for most of the pilots out there, the Radikal G20 will be more than enough for you. Even if you are into the “hard on the deck 3D”, the Radikal G20 will make a great practice machine. With the little bit of extra weight, it will force you to manage the collective and this will carry over into your Nitro machines as well. Also, with the low running costs, you won't be spending 100's of dollars on the weekend practicing. All in all, it is a fun machine and I think just about anyone would enjoy it.

As I mentioned before, this is the first in a series of reviews I have planned for the Century Radikal G20. So be sure to listen to the show and check back here for updates as I get to play with the Radikal more.

Shows we talked about the Radikal G20

EPisode #73 (with Bill Meader from Century Helicopters)

Pictures and Videos

Century Radikal G20 Walkaround Video

First day at the field with the Radikal G20 Highlights

Bobby Smigh flying the Radikal G20

An InsideHeli Review Extra

Break in and Tuning

This part really had me on edge. The Radikal was shown off at an RC Show about a year ago. From that day on I spent quit a bit of time reading about Gasser engines. Well, let me tell you that what I read did not exactly have me feeling like this was going to be very trouble free. First off all you hear about are vibrations, vibrations, vibrations. If you do not tune your engine properly, they will turn into big vibration generators and rip your helicopter apart. Being that this is my first experience with Gassers, it did not exactly have me feeling all warm and fuzzy. But guess what, it wasn't all that bad at all!

First things first, you have to break in the engine. I followed one of Centurys Rep's suggestions to the letter, well for the most part. The first step in the break in is letting the engine idle for around 15 minutes. So you set your needles at the suggested 1¼ turns out on the low and 1½ on the high needle and then start it up and let it idle. You might need to fiddle with the low needle a bit to get a good idle, but odds are that these needle settings are going to be right where you need them for awile. To finish off the first tank after you do the 15 minutes of idling, you run the RPM up so that the head is spinning at around 1700 RPM. You do this with the blades at 0 pitch. You want to put a load on the engine, but you do not want it to be too much of a load at the same time. I used the Rev limiter I installed on my Radikal G20 to keep the head from going over 1700 RPM during this part of the break in. If you are not using a Rev limiter or governor, be very careful when increasing the throttle. There will be very little load on the engine so it will not take much throttle to get the head spinning around at 1700 RPM.

Ok, now you got that part done. Now guess what? You get to spend a tank or two just hovering. Oh, by the way, a tank will get you 15-20 minutes of run time. So if you are not a “hover master” yet, after these two tanks you will be. You should set your Throttle Curves or Governor/Revlimiter up so that you are hovering around 1800 RPM. Pick it up off the ground and hover. Pay attention to how the RPM comes up as you are going into a hover. The transition from idle to a hover should be pretty smooth. You may need to tweak your low needle some more at this point to get a good transition. Try to keep it on the rich side though. Also, one suggestion I would make is when you feel a need to adjust one of the needles, if you are unsure if you need to lean or richen the needle, always richen it first. If the situation gets worse then you went the wrong way. But it is better to error on the rich side rather than the lean side. Now back to the hovering. After you have had it hovering for a minute or two, now land and let the engine cool off a minute or two. Wash, rinse, repeat until the tank is empty. Oh, did I mention that with the cool down times that this will extend each tank of this part of the break in out to around 30 minutes? As I mentioned, you really should do this for 2 tanks, but if you are impatient, I am told one tank will suffice. I did 2 because I wanted to be sure my engine was broke in “right”.

So now that you are a hover master, now you get to become the master of flying circuits. For the rest of the first gallon, it is suggested that you spend it flying some nice and gentle figure 8's and such. Did I mention that with the Radikal G20 that you are going to get almost 13 tanks out of a gallon of fuel? I can see that look on your face now. About the same as it was on mine. You mean I have to fly out 11 tanks of fuel at 15-20 minutes each before I can start to really fly the heck out of his thing? Well, that is what is “suggested”. Well, I started off with the intentions of doing just that. I was told I could throw in some loops and rolls to “mix it up a bit”. Also those loops and rolls would put some load on the engine to help with the break in. You want to do as you did during the hovering part and land every couple of minutes to let the engine cool off. The idea here is to put the engine through some heating and cooling cycles. When you land, you want to have your temperature gun handy do make sure the engine is not getting too hot. You want it to be a little rich for the first gallon of fuel. Depending on the time of year and where you are flying, you want to get the engine up in the 200-220F range. If you find that your engine is running cool at this point, lean the needle up a little bit, fly around and check it again. If you are finding it is too hot, richen it up a bit. We really are not tuning the engine for “performance” at this point, you are just trying to keep the engine temperature in line right now. After the first gallon is when you will start to tune the engine for performance. I had a hard time restraining myself during this part of the break in. After about 4 tanks, I started flying the helicopter a little bit harder with each tank. If you find yourself doing that as well, you need to pay attention to the engine temperatures. Remember, you have not tuned for performance yet. So if you find you are flying it harder, makes sure you keep a close eye on those temperatures.

Remember when I said, “I followed one of Century Rep's suggestions to the letter, well for the most part”? Well this is where I deviated from what I was told a bit. I have this new helicopter, I want to see what it can do. Well, after 6 tanks of flying circuits, I wanted to start pushing it a little more. So I jumped up to the “tuning for performance” part a little early. At this point I had over half a gallon through the engine. When I spoke to the Century Rep about my intentions, he said go for it, just be careful to not go “too far”. I am not sure what “too far” is, but I must have not crossed that line. So with that said, now we need to get this engine tuned up.

Tuning a Gasser engine is a little bit different than tuning a Nitro engine. The concepts are the same, but the “tell signs” are a little different. When a Nitro engine goes lean, you can tell pretty easy when you start loading it up. It will sound different. As Bert Kammerer said on the show, “It will sound pissed off”. Well, I did not find the same with the Gasser engine. It really doesn't give you that “pissed off” sound when it is lean. What I found most difficult was that I really could not hear much difference in the sound of the engine when it was too rich or too lean. To me they sounded the same. I am sure with time that will probably change. What is different is how the engine reacts when it loads up doing things like full collective climb outs. If the engine is rich, the Head RPM will fall off as soon as you jam the collective and will just get worse as you continue to climb. If the engine is lean the Head RPM will start to fall off after the helicopter has been climbing out for a second or two. To me, both these conditions sound the same but it was easy to see the differences in how the helicopter climbs out.

Your low needle should be pretty good at this point. You should have tweaked it during your hovering tanks enough to get it pretty close to where it needs to be. Next up is getting the high needle “in the ball park”. I did this with a series of full collective climb outs. I had my high needle set at the 1 ¼ as suggested and found out at this point that it was a too lean. It was 35F so I should have known that I would need to run richer than someone else would in say Mississippi where it was 70F. When I did the first climb and using my past Nitro experience as a reference, I though the engine sounded rich when in fact it was lean. So I leaned it up a little bit and it got worse. I was a little puzzled at this point because it just seemed rich to me. But it got worse as I leaned it so I went with that. After a few more climb outs and adjustments, continuing to go richer, all the sudden the climb outs were smooth with no drop in RPM or power. I continued to richen it up until I noticed a change again. I did this because I wanted to see how the helicopter and engine reacted when it was running too rich. After I found that point, I leaned the needle up again to get a nice climb out and let it be.

At this point the needles are pretty close to where they need to be. The next step is to fine tune the high needle. To do this, I started flying the helicopter through big power loops, stationary flips, stationary rolls and a Tic-Toc here and there for good measure. During all this pay close attention to how the RPM of the engine and head are holding up. If you go into a loop and it “dogs out” at the start, odds are you are rich. If it powers into the loop but starts to “dog out” at the top, then odds are you are too lean. Same thing with Tic-Tocs. If it just “dogs out” from the start, you are rich. If you get two or three Tic-Tocs in and then it “dogs out”, then you are too lean. If you see these things happen, land and make small adjustments. Remember, when in doubt, rich-en the needle. Continue on with this until you are happy with how the helicopter and engine are performing.

Last thing to do is to get the hover/mid range tuned. This is going to be done with your low needle. Odds are with the tuning you did during your hovering tanks, this is going be pretty close already. But if you have made a big change on your high needle between then and now, you are going to need to adjust it again. So spool up into hover and listen to how it transitions. I have found that once you get a good transition, you really are pretty set with the low needle. It should be a little on the rich side and giving you a little bit of a “4 Stroke” in a hover. This is where I leave mine as I do not spend much time just hovering around, so I would rather it be a little rich.

In the end, after I figured out the “personality” of this engine, I am finding it easier to tune than my Nitros. If this is your first Gasser, just take the time to get acquainted with the engine and it will pay off in the end.