What is a good "Contest Flying" model??

[ErichF]

I'm back, by popular demand, with a post about some good models for use in Precision Helicopter Aerobatics, aka FAI or Contest Flying. This is a second installment about contest flying that started with What is Contest Flying?
A common question in response to that post was: what is a good heli for contest flying? The current technology that goes into modern RC helicopters allows many options in setup for most of them. Some have more aerobatic potential than others, and some at the expense of stability. On the other hand, some have the versatility to be setup from one extreme to the other. The trick to setting up a contest model is in creating a model that will sit still in a windy hover, while at the same time be able to perform crisp, high speed aerobatics at the flip of a switch. While this post is not about contest setup per se, it will refer to some aspects of advanced model setup. These are items such as Delta, Flybar Ratio, Bell Ratio, Damper design, and spindle support. I will be discussing a few models that have proven to be great contest birds, and in so doing, will be detailing these features as they apply to those models. I will also illustrate the various setting positions as they apply to each model.
First, I will cover a couple 50s that can make great, entry level contest models for use in AMA class 1 or 2. These are the Kyosho Caliber 6, and the Hirobo EVO 50.
Kyosho Caliber 6

The current model in the Kyosho 50-size Caliber series has proven to be a reliable, stable model for practicing and performing precision aerobatics. The model has a belt-driven, two stage main transmission, belt driven tail, and high-quality plastic main frame. These features make for a smooth running, relatively quiet bird at lower main rotor RPMs. Fit a good quality Hatori and equivalent muffler, and you have a nice model with which to perform with. Both the YS50 or OS50 Hyper will provide ample power for great speed and tall verticals for an awesome presentation of the maneuvers.

The picture above shows the Caliber 6 Main Rotor head. You may note that the head mixer arms are a bit unique, and this design carries over directly from the flagship Kyosho model, the Caliber 90. Also note that there are two mixing options for the Bell Mixers to connect to the main grip pitch arms. These options set how much Bell input is mixed into the blade pitch. While there are no options for Delta or Flybar Ratio, the stock condition of this head is rather optimized for precision aerobatics, and the current geometry works as-is.

Above you see the new tail pitch mechanics of the Caliber 6, also brought down from the Caliber 90. This is also a unique design that has its roots in large scale, precision aerobatics airplanes - Pull-Pull rudder control. Rather than using cables, as in fixed wing rudder controls, the Caliber 6 uses two light control rods connected to a T lever and torque axle that drives the tail pitch plate. This setup allows the ability to tighten up the system and remove virtually all free play between the servo and tail control. The servo output shaft us balanced, just as in regular push/pull design elsewhere in helicopter control systems. The entire system allows for a bit tighter gain on the gyro, and more precise tail pitch control...important in precise hovering maneuvers and pirouettes.

Here you see the Caliber 6's two stage, belt drive transmission. The auto-rotation "one-way" clutch bearing is housed in the first stage pulley, rather than the main gear hub. This means the one way is subjected to only a fraction of the load encountered in other designs, as the bearing has mechanical advantage by way of the gearing of the second stage. The first stage belt drive absorbs engine power pulses, and smoothes out transmission from the clutch to the main gear. This system also has very low gear noise, as the pinion is operating at a much reduced speed compared to traditional single stage transmissions.
These features, along with the Caliber 6's standard push-pull controlled eCCPM controls, make the 6 a great model with which to practice and perform precision aerobatics. It's stable, fast, and reliable. Also, for those who prefer the advantages of a mechanical collective mixing system, the 6 can be fitted with a mechanical mixing tray.
Hirobo EVO 50

The next model I'll discuss is the Hirobo EVO 50 series. These helicopters have been on the market for some time now, and have "evo"lved into a very capable precision aerobatics model, as well as a nimble 3D model. This model is also available with mechanical or electronic mixing options. The EVO 50 is another mostly plastic composite model, which lends for a smooth, quiet bird. The EVO 50 employs a traditional, single stage transmission and belt driven tail.

Above you see the EVO 50 main rotorhead. This design also uses a free-floating axle that supports the main blade grips. The Bell Mixer arms are supported by the flybar carrier (see-saw). There are no mixing options on either the arms, nor the carrier, so no options exist for changing flybar or Bell ratios. However, the existing geometry does lend well for a stable yet fast flying model. With a set of flybar weights, heavy-set paddles, and good blades, the EVO 50 is a formidable model for AMA class 1 or 2.
The main swashplate controls of the EVO 50 are all push/pull for slop reduction and servo balance. The rear fuel tank location also allows a more consistent balance throughout the entire flight. The low cost of the EVO 50, coupled with its long legacy of great support by MRC/Hirobo, make for a great long-term investment for contest flying. You can get EVO 50 parts just about anywhere, however you rarely need to buy many parts for a contest model. When I flew Hirobo X-Specs in competition, I never needed to replace anything except the odd bearing or ball links.
Next, I'll discuss a couple 90 sized helicopters that are great for flying in competition or precision style without the price of a top-end FAI machine like an Eagle 3WC or Caliber 90. These are the Hirobo EVO 90 and the Blitz Avro 90.
Hirobo EVO 90

The EVO 90 takes the 50 to a whole new level of performance, stability, and versatility. The new FFZ-III rotor head has a dozen possible setup combinations that allow the user to customize it to whatever feel and performance desired. The EVO 90 is also a mostly plastic-composite framed model. The transmission is the traditional, single stage pinion and main gear setup, with a multitude of gear ratios available.

Here you see the EVO 90's main rotor head. The FFZ-III head is very similar to the one on the 50, but as you can see, there are numerous tuning options for Bell Mixer ratio and Flybar Ratio. The mixing arms mounted to the flybar carrier have three mounting positions on the carrier. This adjusts how much influence the flybar has on the blade pitch. The mixing arms themselves have 4 mixing options, based on how the connections are placed on the arms. These tuning options alone equate to 12 different head setups in one system. Add to the fact you can install various hardness dampers, and spacers on the blade grip pitch arms to adjust Delta, you can have dozens of setup combinations. You can also see that there are two options on the washout arms, for adjusting flybar paddle pitch rate.

The tail rotor and control system on the EVO 90 is legendary. The octagonal cross section of the boom tube makes for a super rigid design. The double supported pitch plate eliminates most of the system slop, and lasts a long time without wearing out. The power in this tail system is tremendous, capable of insane pirouette rates. At the same time, this system is incredibly precise, allowing tight gyro gains without wag at high forward speeds. This tail is also belt drive, so you can start to see a pattern here. Many, if not most, models that are applied to precision aerobatics use belt driven tails. Maintenance is essentially non-existent, and in the event of a crash, repair bills are lower. I flew a pair of X-Specs for over three years, and never had to touch a thing on their tails, including the belt.

The swashplate control on the EVO 90 is also mechanical; however a CCPM (known as SWM in Hirobo-ese) option is available. The standard mechanical setup is interaction free, and very precise. The plastic swashplate that's standard will work for some time, but a high-quality, precision machined metal swashplate is available also. All controls are push/pull as well. The geometry in the system is very well balanced, and when setup properly, works very well with little slop.
Overall, the EVO 90 is probably the best bang for the buck when it comes to 90 sized models. It can use any 90 size engine on the market, with its multitude of available gear ratios. It will fly well with mid-grade servos such as Futaba 9252s or Hitec 6975s. The rotorhead now allows the use of up to 720mm blades without issue. The stock paddles with both weights installed are actually very well suited to precision aerobatics...in fact, I use them on my Caliber 90 contest model. The EVO 90 has proven itself in a number of contests worldwide.
Blitz Avro 90


The Blitz Avro 90 helicopter is the new kid on the block. Used by Dave Fisher to win the British F3C National Championships, the Avro has also proven itself a capable contest model. This helicopter uses a number of unique designs that we haven't seen before, as well as a combination of proven designs that have worked well in other models.

The Avro also uses a belt-drive, two stage main transmission. I find this system to be a hybrid of the Caliber 90 and JR Sylphide transmissions. The belt driven first stage is much like the Caliber 90 setup, while the helical main gear and one-way bearing design is much like that on the Sylphide. The Avro doesn't use push/pull on the servo output arms, but instead uses metal servo shaft stabilizers that mount to the servo itself:

This reduces the number of ball links that need installing and replacing when worn. This model also puts the fuel tank in the rear of the mechanics, which allows easy monitoring of fuel level, but more importantly reduces balance trim change as fuel is consumed. Also unique to this model is an ingenious new gyro sensor mount:

This mount isolates the sensor unit from mechanic's induced vibration, allowing increased resolution and efficiency of the gyro.

The main rotor head is also a departure from what most of us have seen, specifically in the spindle support/damper design. Rubber inserts, captured by a top plate, support the blade grip spindle, as opposed to o-rings or cups. Also, there are a number of Delta offset positions on the grip pitch arms, and six bell mixer options. There are no flybar mixing options, however. This can be adjusted with using different length flybars, more or less weight, and various types of paddles, though. Last, but not least, this head is standard all metal, requiring no upgrades for longevity or precision.
The tail drive on the Avro is a torque-tube driven system, with the traditional single-point pitch plate. The tail grips on this model are aluminum.
The Blitz Avro tops the list in price among these models, but it's still half the cost of an Eagle 3 or Caliber 90. You get some new designs with the best of other designs, all rolled into one, neat package. I believe we will start seeing this model entered in many contests in the near future, due to it's innovative design and quality vs. cost aspects. Also, this is a model you can compete with all the way up to F3C...a model you can grow with.
Wow, that's a lot to absorb. Of course, there are other models on the market that would also do well for precision aerobatics, and if you have specific questions regarding other models you may be interested in, feel free to post them here.
If you are interested in seeing what makes for a top end contest machine, I posted a build on my Caliber 90 HERE. While such a machine is rather expensive, it's actually in line with the average cost of a quality IMAC plane, or even a contest-quality pattern plane. The quality of such a machine's design and fabrication is top-notch, and in the minds of many die-hard contest pilots...is worth the expense. However, such expense is not necessary to enjoy the sport of precision aerobatics, and so I hope this post has illustrated that with proper setup, a good model can be had for a reasonable cost.
Erich

[Thrasymedes]

Great information Erich, keep them comming, I'm ready to learn more. Will look over the build thread.

[Thrasymedes]

Also, here is some really good documentation of a Blitz Avro build, part of the research I did to try and make a final desicion...

http://www.scalereplica.com/workbenc...enu/blitz-avro

[WillJames]

Great info Erich. Thank you.

[mysticmead]

thanks Erich!! lots of good info to digest...

[Thrasymedes]

You've mentioned a couple of times about delta, and Bell and Hiller mixing options. You also mentioned good geometry for contest flying. Would you care to elaborate a little on what that good geometry would be, and how it differs from a typical 3D setup? For those of us who have machines that were designed more for 3D from the factory, I think it would be good information.

Thanks in advance..

EDIT:

Also, I just loaded Pro Engineer on my home laptop, and my first project will be to design a set of aluminum bell and hiller mixer arms with multiple mixer holes for the Trex 600, to replace the current non-adjustable ones. If succesful I plan to use the first set along with the adjustable Quick UK swash that has set screws to preload the bearings. This combo along with a metal head should hopefully prove fruitful. If so, I will post full engineering drawings here on Heli Freak, with tolerancing, that anybody should be able to take to a machine shop and have made. Talk about a budget FAI machine!

Now onto my next question, what do you think these rubber bands are used for? This is a pic of Scot Grays 2007 Sylphide.

[ErichF]

OK, the ins and outs of those terms will have to be discussed in yet another article. Look for it in the near future. I will give a brief synopsis though....

Delta - the relationship of the blade grip pitch arm relative to the flybar feathering axis. If the pitch arm ball joint is directly above the flybar, or the centerline of the rotor head, this would be considered neutral Delta, or zero Delta. If, on a leading grip pitch arm, the ball is located on the grip side of the flybar, the Delta is positive, or "correcting" Delta. In this case, should a wind gust cause the blade to rise, the geometry of the correcting Delta would tend to take out blade pitch as the spindle, grip, and blade tilted upwards. The result is a positive, dynamic stability. The worse the blade excursion, the more the Delta influence, and therefore the harder the blade is brought back in track. The opposite, negative or uncorrecting Delta, works the other way. This setup is often considered for full-fuselage models, where the wind will work against the body more than the rotor disk. In that case, if the body is pushed to the side, inducing a roll into the wind, the result of the negative Delta is a countering force to raise that side of the disk, and bring the fuselage back to the original attitude and stop the model from drifting into the wind.

Bell Ratio - This is the ratio introduced by the Bell mixers located on the flybar carrier or blade grip pitch arms. This controls how much direct cyclic authority is sent to the blade grip, and is countered by the flybar (Hiller) input. Traditionally, higher Hiller ratios are used for more precise hovering and stability in fast forward flight. A higher Hiller ratio means that the flybar has more influence on direct blade pitch than the swashplate. A downside to using high Hiller ratio, is that it subtracts from your overall pitch range. Using too much can limit your pitch range so much that you don't have enough to get the -10 to +13 range typical of contest models. This is why some models have longer mainshafts, in order to get the required pitch range with a liberal amount of Hiller ratio.

Flybar Ratio - This ratio is the influence of the flybar on the Bell Mixers. Generally, the farther out the Bell mixers are on the flybar carrier, the higher the flybar ratio. You use this adjustment to balance the head response in the wing for hovering. Too high a flybar ratio, and the model will tend to drift into the wind. Not enough, and the model drifts downwind.

To answer your question: The bands as used there are to pre-load the swash linkages against the servo. One caveat of push-pull systems is that you can take up slack as the ball links or bell crank bearings wear in, but not servo gear lash. This band will preload the linkage system against the servo gear lash, making for a more precise system with greater resolution and no deadband.

[Thrasymedes]

Originally Posted by ErichF

To answer your question: The bands as used there are to pre-load the swash linkages against the servo. One caveat of push-pull systems is that you can take up slack as the ball links or bell crank bearings wear in, but not servo gear lash. This band will preload the linkage system against the servo gear lash, making for a more precise system with greater resolution and no deadband.

That, quite frankly, is awesome to know. I handn't thought of doing that, but it should work. When I get my new swash on with preload adjusted, I will give this a try and take it for a test fly.

Thanks for the great information again. I'm sponging all this up..

Also, would it be possible to have so much delta that the heli actually induces so much pitch correction so the heli would fall, or lose altitude, or pitch too much in a wind gust?

[ErichF]

Originally Posted by Thrasymedes

Also, would it be possible to have so much delta that the heli actually induces so much pitch correction so the heli would fall, or lose altitude, or pitch too much in a wind gust?

No, we're talking a degree max, usually just fractions of a degree in pitch. Delta is measured in millimeters. Plus it all happens in a fraction of a second, just like your tail gyro. You only see the resulting change in stability, not the actual response.

[Thrasymedes]

In the models you have listed above, both 50 size and 90 size, how much consideration should be given to disk loading? The Caliber vs 06 is listed to have a 2962in^2 disc area, and a product listed weight of 10.90lb, giving 271in^2 per lb. Is this a typical goal ratio, and what relevance would this have on disc loading for someone chosing a 50 size contest model?

Thanks,

Norman

[ErichF]

Hmm, I've never broken down the numbers for disk loading before. We usually just look at what blades feel best for the type of setup we do. Lot's of guys are running the 720 Rotortechs on their 90s. This would make for lower disk loading than say 690s. For me, I need all the help I can get for autos, so i prefer the longer, heavier RT720 Scott Grays. Others may be fine with autos, and want a shorter blade for higher loading in hover.

[Thrasymedes]

Thanks Erich, and also for your patience in talking through the effects of delta. Ok, so now I'm going to ask a hypothetical question, then I will bow out a little and hope this proves a good discussion for others.

I know there are probably a lot of people who have read this, find it interesting, but have recently purchased another type model. It may be a Trex 700n, or a Thunder Tiger 30, or an Aurora, or a Trex 500, or a Senergy. They've just laid down a lot of money, but would like to try their hand at this contest flying. They may like the list you provided above but with economic times they are not in the market to by another heli soon, or take a loss trying to sell the one they have.

As you know, a lot of these models driven in the average US market have been desinged geometrically for 3D, mine included. What are the biggest things they could look for in their helis, weaknesses, points of improvement, setup that could help them take the model they already have and get started, with maybe having aspirations to purchase a Hirobo EVO 90 or another one of your recommended models listed above down the road. I don't mean specific to a model or even brand, but general points of taking a 3D heli to a more FAI approach, though it may never fully be ideal for FAI, it might get them started, and then who knows, maybe next spring they would be in a position to get a Caliber 6.

Thanks,

Norman

[warpspeed]

Man talk about perfect timing! I'm right in the middle of building an Evo 90 with a goal oriented more towards precision than 3d. Excellent write-up and I too appreciate the information on delta's. Looking forward to more.......

Plz pardon the interruption!:o

[ErichF]

I've seen a number of Trex 600s, both electric and nitro, used in some contests. They actually do pretty well, with a few items taken care of in the setup. These items are actually pretty common among most of the helis you listed here, among others.

Trick one: Servos - Use the smallest servo arm that will allow you a total pitch range of -10 thru +12, at least, on a CCPM machine. For a mechanical mix model, use the smallest servo arms which will allow at least 100% end points, and bring the swashplate to full deflection without binding at the corners. The idea is to use the entire range of motion of the servo in order to maximize resolution. To do this, the servo must move as much as possible for a given input. Given this technique, you should use servos around 0.18 speed or better, but have at least 70 oz of torque. There is no sense in using high resolution servos with the end points set at 50% because you put 2 inch arms on them.

Trick two: Dampers - Install the softest dampers available for your model, and experiment with shims to tighten it up as needed. Some of the models on the market have pretty hard dampers now, and lower head speeds used in hovering maneuvers will induce a wobble, or mast bumping. Soft dampers also allow Delta to do its job, and helps absorb wind gusts into the rotor system.

Trick three: Flybar weight - I remember back in the '06 Nats, Nick Maxwell used at least three clamp on 20g weights on each end of his T-600E flybar. He didn't want to change anything else on his model, so was relying on heavily weighting his flybar to make the model behave in hover. It seemed to work pretty well for him, but he's also a stellar pilot. Your mileage may vary. Together with these other tips, adding weights to your flybar will increase the gyroscopic stability of your rotor system, helping both in winds and fast forward flight. Weights are added to taste, so get a few sets and experiment. As for the paddles, use the stock paddles with all weights installed. If your machine comes with light, unweighted paddles, you can fit paddles from other machines. Raptor 50 or Hirobo EVO 50 stock paddles are good choices, as are Kyosho 50 paddles.

Trick four: Blades - The blades are where the rubber meets the road, so to speak. Here, you want blades that are symmetrical, have decent weight, and are well balanced chord wise. A blade with an aft center of gravity will bite and fly aggressively. A trick to see if a blade would be good for contest flying is to do this: Find a hex driver that fits easily through the blade bolt hole. Tie a washer to a piece or string or thread a bit longer than the blade, and tie the string to the driver. Then, measure the distance of the blade bolt hole from the leading edge. Towards the end of the blade, make a mark an equal distance from the leading edge. Next, insert the driver through the blade bolt hole, and let the blade and string hang together. Look at the relationship of the mark and the string at the end of the blade. If the mark is more than 2-3mm ahead of the string, this indicates an aggressive blade, as the blade will lead in the grip when under load. Alternately, if the string and mark line up, or the mark lies behind the string as it hangs, you have a dynamically stable or neutral blade. I have found Radix 600 blades to be great for all-around flying, and auto very well. Rotor Tech makes some 610 FAI blades that should also be very nice flying.

Trick five: Pitch curves - Pitch curves are all about how a helicopter feels and performs. Most 3D setups have identical curves for each flight mode, all centered around 0 degrees. In my contest models, I still follow the basic rule of 90s at 0 degrees when doing the initial setup; however I have different pitch curves for hovering and aerobatics. For hovering, a 1/2 stick hover really affords you the stick resolution and precision needed to maintain altitude without bobbing up and down. If you are used to 3/4 stick hovering, it will feel odd at first, but the idea is to open up the range of motion on the collective stick, where 3/4 stick hovering doubles the stick sensitivity. This makes it more difficult to control the model's altitudes in hover, especially when the wind is blowing. Most modern radios have a condition delay which slows the transition between pitch curves, so that when switching from hovering flight modes to aerobatics modes, the model drop is less pronounced. Generally, you don't switch into aerobatics flight modes until you have started your climb out and have the collective stick at the top. In this case, the transition is transparent. As you probably assumed already, we generally run a -10/0/+10 or similar pitch curve in aerobatics modes, with 0 at center stick. This is much like a 3D setup. This allows you to easily find 0 degrees in vertical lines for stalls or push-overs. It also makes rolls feel more linear on collective.

So, these are five things you can do with ANY helicopter setup. These globally consistent items are easy to do, and rarely cost anything more than time to complete.

Hope this helps,

Erich

Originally Posted by Thrasymedes

I know there are probably a lot of people who have read this, find it interesting, but have recently purchased another type model. It may be a Trex 700n, or a Thunder Tiger 30, or an Aurora, or a Trex 500, or a Senergy. They've just laid down a lot of money, but would like to try their hand at this contest flying. They may like the list you provided above but with economic times they are not in the market to by another heli soon, or take a loss trying to sell the one they have.


Thanks,

Norman

[Thrasymedes]

That's fantastic information Erich!

We all do appreciate your efforts and knowledge you're spreading. I did look through your Caliber 90 vs 6 build, and I must say that is very nice heli. I like what I see in the Sylphide too. Definitely some precision stuff.

Thanks

[ErichF]

Originally Posted by Thrasymedes

That's fantastic information Erich!

We all do appreciate your efforts and knowledge you're spreading.
Thanks

Thanks, I'm just paying forward a wealth of knowledge I have learned from sport and industry icons by attending contests. No one keeps this stuff to themselves. I've been flying helis for 20 years now, but I have learned more in the past 4 years than previously.

[Thrasymedes]

Speaking of delta, I'm currently in the section of my ASA book that talks to this subject, and more specifically to full size helis, in regards to the effects of a Delta-3 flapping hinge or a offset pitch horn on the blades. See picture, sorry, you will have read it sideways. The book is assuming counter-clockwise rotation, as with full scale. Now, our model helis don't have flapping hinges, but the blades can move up and down like a hinge by the feathering spindle helt into position by the dampeners. According to this book, my Trex 600 offest pitch horn on the grip would be on the wrong side, rotating clockwise, in order to have the same stabilization effect as a delta-3 hinges in an oncoming wind? Is this not correct?

[ErichF]

The example in that pic would be positive, or correcting, Delta offset. Your Trex 600 has negative, or uncorrecting, Delta Offset:




It's not much, but it is negative. This is part of the reason the Trex 600 has the 3D "pop" that people comment about. So, as the blade lifts, either by wind or cyclic input, the cooresponding rise of the grip/spindle actually introduces MORE pitch to the grip.

The good news is, you can actually mod that head pretty easy for flipping the grips over and having correcting Delta. If you're at all familiar with the old Raptor 30 "grip flip mod", it's basically the same thing.

[Thrasymedes]

Originally Posted by ErichF

The example in that pic would be positive, or correcting, Delta offset. Your Trex 600 has negative, or uncorrecting, Delta Offset:




It's not much, but it is negative. This is part of the reason the Trex 600 has the 3D "pop" that people comment about. So, as the blade lifts, either by wind or cyclic input, the cooresponding rise of the grip/spindle actually introduces MORE pitch to the grip.

The good news is, you can actually mod that head pretty easy for flipping the grips over and having correcting Delta. If you're at all familiar with the old Raptor 30 "grip flip mod", it's basically the same thing.

You read my mind, when I put on the UK swash I am going to flip them over to positive. I think I'm going into overload, but I'm learning a ton!!!

When I pull them off I my have a friend in a machine shop drill and tap a couple of extra holes in the blade pitch horn to have 5-10mm positive delta adjustability, being that I'm using the metal blade grips.

[ErichF]

Originally Posted by Thrasymedes

When I pull them off I my have a friend in a machine shop drill and tap a couple of extra holes in the blade pitch horn to have 5-10mm positive delta adjustability.

All you need to do to vary your Delta offset is to shorten or lengthen the ball on the pitch arm. Going farther from or closer to the spindle will only affect your pitch range and rate.