Jason D
08-19-2009, 08:28 AM
Part #1
I became involved in competitive precision aerobatics about 4 years ago. For those that are unaware of this facet of model aviation – it is basically flying a predetermined set of maneuvers and having them critically judged and compared to other competitors. What this means is that we fly a “sequence” and see who can fly it the best based upon the judging criteria.
Competitive aerobatic pilots tend to try and gain every advantage they can over their fellow competitors and a big part of this is ‘trimming’ their airplanes to fly true. I thought I would take this opportunity to share with you all the trimming method that many IMAC pilots use to get their airplanes to fly as good as they possible can. For IMAC pilots ‘trimming’ involved much more than just getting their airplane to fly straight and level at a given throttle setting, but the results are well worth the effort.
The article below was written by Peter Goldsmith and orginally appeared in Model Aviation Magazine. Peter is the team manager for Horizon Hobby and has been involved with competitive scale aerobatics since the days of the Tournament of Champions in Las Vegas, NV. This article is geared to giant scale aerobatic airplanes, but nearly any model airplane can benefit from the techniques. If nothing else, the ideas presented below may at least lead to a better understanding of how to equip your next airplane.
The majority of the programming detailed below can be accomplished with a 6 or 7 channel computer radio fairly easily.
So what will this procedure accomplish: First and foremost – it allows your airplane to fly ‘true’ that means that when you use the rudder, you only get a yaw response, when you deflect your ailerons, you get a true axial roll and when you point your airplane straight up or straight down, it goes straight up or straight down. Second it allows you to focus on flying your airplane the way you want it to fly by not having to fight unwanted flying conditions.
With that:
Peter Goldsmith: How to reduce your flying workload!
One of my passions in life is to teach. After a long discussion with Mike Hurley after sharing with him how passionate I was to share my life’s aerobatic knowledge, we decided that a trimming article would be a great start. A properly trimmed model can reduce your workload in an aerobatic sequence by an enormous amount. I judged at the nationals this year and thoroughly enjoyed the experience. I was also impressed with the skills, especially in the lower classes when displayed by pilots trying to fly around a pour trim setup, I was truly amazes how tolerant people were. It drove me crazy to watch in fact. I remember bouncing out of my judging chair and saying to Mike, “boy” I need to help these people. Hence here I am typing away at my exciting pace of about 80 minutes per word in an attempt to help educate the great skill base that exists in the US scale aerobatic scene.
Like all good input, it doesn’t come from me, but more a summary of 25 years of meeting people who shared their thoughts on trimming with me, then melting them down to put into some kind of legible format that most can understand.
Servo and control setup
3D, and precision model trim typically go against each other. What I mean by this is that when pilots set up their new 40% something, they go straight for the big rates, 35, 40, and in some case 50degrees of throw. Anybody thought how this can affect the servo resolution, and more importantly the servo power.
Scale aerobatic events typically allow a separate aircraft for freestyle. Between 80 – 100% of the results at a scale aerobatic event comes from the precision elements - known and unknown sequences.
Please don’t misunderstand me, I love to watch free style flying, and admire the talent of the pilots that do it well. It’s innovative and has been one of the main contributors to the growth of Giant scale aerobatic aircraft. My point is: Why not have your free setup specifically for the free event, and then have a precision setup for known and unknowns sequences. I know for me personally having a model just for free style will be something I aim to do in the future. Having said that, a good alternative is to bias your setup more toward precision, which will no doubt improve your sequence flying (especially if you’re frequently fly events).
With my Cap, I use 1” horns on all surfaces with the exception of rudder which use 1 ¼”. I have 28 deg on aileron, 32 on elevator and 35 on rudder. For me, this is a good compromise for precision and free flying with the bias towards Free.
With 1” horns, and 1 ½’ distance from control hook up, I am getting slightly better that 1 to 1 ratio. More importantly I am getting closer to the maximum servo power and control geometry available. With 1’‘ horns my resolution is better, control slop is reduced, and servo wear is greatly improved. Another novel bonus is, I don’t need as many servos per surface. Give it a try next time you set up your aircraft, you may be surprised, in fact in some cases you may see no difference in control responsiveness by going to 1” horns, as with the better geometry you may be reducing your control blow back.
One of the biggest challenges I see pilots dealing with is surface blow back. With blow back, your snap exits will be all over the place, both entry and exits. Getting consistent flying is almost impossible. Every time your speed changes, you control response will change. Hmmm, I suspect a few lights just went on. Yep, could it be the fact that you consistently miss your snap exits is not due to your skills, but control blow back.
When setting up you servos, make sure you run the numbers. Do the math and figure out just how much power you are delivering to the surface. All servos are rated at inch ounces, that is at one inch from the center of the servo. A JR 8611 is 266 Inch oz on 6V. With a 2” horn they are only 133, and around 200 with a 1 ½” horn.
Years ago I was able to measure the forces on my Cap, believe it or not the ailerons required well over 30 lbs of force to deflect at 100mph. Now there are a lot bigger ailerons out there than mine. Please pay attention to this, it is crucial to consistent flying. If you have to use 1 ½” horns, or 2” horns, you will need more servos.
Sequencing your trimming
Many of the trimming articles I have seen over the years incorporate some kind of chart, graph - do this and this happens and so on. My concept of sequencing your trimming is simple. If you get your trimming out of sequence you will end up chasing your tail.
As with most things in this universe, for every cause there is an effect, same applies to trimming a model aircraft. So many times I see people test flying their aerobatic creation, flip the thing on it’s side and see what kind of knife edge mixing it may need. Thrust, CG, wing balancing and basic flight control trim can all effect knife tracking.
I can’t make this point more loud and clear, it is very important to trim you model in the correct sequence to make sure each adjustment has no effect on the previous adjustment.
You will see I have broken each element down, and there is an intentional order in which I recommend to trim a model. Model balance especially CG is the most important as differential, knife edge flight, and down line tracking will all be affected by the CG.
Next is dynamic balancing or wing tip weight. Next comes thrust angles, then aileron differential, and finally P mixing - knife edge tracking, roll coupling, down line track.
Oh…. if you change your propeller, you whole trim setup will change.
Balance
OK so…How do I know what is the correct CG for my model? If in doubt, read the instructions. Yep, chances are somebody from the TOC or similar has designed your aircraft and has determined over many flights where the CG should be.
For precision flying forward is better…but… too far forward can be a problem. I can not put in writing what is the best feel for each pilot other than simply stating - it is a feel thing. I can however, give you some symptoms of too far back and to far forward, plus some simple tests I do to check.
One of my favorite ways to determine the correct CG is spin entries. For precision flying I would expect you to be running between 12 – 15 deg of elevator throw. If you feel you need more than this, check your exponential it may be too high. Just as a starting point, 35% expo is what I call a linear feel. What I like to have with my expo is when at half stick, I get about 50% of the reaction of full stick, around 35 – 40% expo gives you this with modest control deflections. Ok, if that didn’t make sense - IF I have my stick at full travel, my aircraft will roll around 360-400 deg per second, about right for precision. Now when I only move my stick half way, I should be looking for 180-200 deg per second, make sense.
If when entering a spin, you model mushes, kind of slides into the spin with no real stall visible, you may be too far forward. Another sign of forward CG is excessive down elevator needed for inverted flight. This is not always the reason but is a sign.
Rear CG is probably easier to see for most pilots. Model is sensitive in pitch, unpredictable around the stall, climbs when on an inverted 45deg line are some I have noticed.
CG is mainly about feel, each person will have their preferences and each aircraft will have its preferences. Be patient, spend some time on this one; it’s important you are happy with your CG. I would recommend at least 10 – 15 flights before making the commitment to where it needs to be if it’s a new model.
Dynamic Balance
Ok, we are happy with our CG so the next thing is dynamic balance. This is really only relevant with wing tip weight as most other axis on a model aircraft are not affected very much by the dynamic effects of high g force loads. Having said that, your wings are. Just cause they both weight the same, and don’t carry any aileron trim doesn’t mean you can’t have a wing weight problem.
I have seen a myriad of ways to test for wing weight trim. Loop’s, pulling to vertical, and so on. My suggestion is to think about the sequencing argument. If you do loops, or pull to a vertical up line, the engine thrust can have an effect, yet we haven’t got to trim our thrust angles yet. Think about it, what could you do to check you wing tip weight in flight that will not be affected by thrust?
What I do is put the model into a vertical dive (minimum of 3 – 4 seconds) and pull a hard corner at the bottom. No matter where your wings are in roll, when you pull to level, the wings must be level. Check this concept with your stick plane. It really doesn’t matter where your wings are but as you pull to horizontal flight your wings must be level.
If you attempt to pull a hard vertical FROM horizontal, you must be absolutely sure your wings are perfectly level. I don’t know about you guys but I am not that good.
If you go from vertical TO horizontal, not only will the engine thrust have no effect but your wings can be anywhere as you are on a vertical down line. Now when you pull the corner, the aircraft may be pointing in a different direction than you planned, but that is ok, as long as the wings are level.
When I was told about this procedure several years ago, it made a lot of sense. The only thing I would recommend - pay attention to is make sure you only use elevator through the corner.
Don’t be quick to make a decision, have a friend observe the proceedings, do many pull outs, make absolutely sure before you move on to the next step of trimming.
Thrust angles
OK, guys, it’s time to put aside aesthetics and get that engine thrust correct. I sure see a lot of spinners perfectly lining up these days. One of the biggest deterrents to adjusting for the correct thrust angles is the spinner won’t line up any more. That’s true. Once again, when building you model, pay attention to the instructions, chances are somebody has figured it out pretty close.
What I like to do (or use to do) is test fly the model before I paint the cowl. Once I am happy with thrust, I can make the appropriate cosmetic changes to complete the model before painting. Setting up the correct thrust angles is fairly simple. Well… it’s simple to identify, harder to adjust.
To be continued...
I became involved in competitive precision aerobatics about 4 years ago. For those that are unaware of this facet of model aviation – it is basically flying a predetermined set of maneuvers and having them critically judged and compared to other competitors. What this means is that we fly a “sequence” and see who can fly it the best based upon the judging criteria.
Competitive aerobatic pilots tend to try and gain every advantage they can over their fellow competitors and a big part of this is ‘trimming’ their airplanes to fly true. I thought I would take this opportunity to share with you all the trimming method that many IMAC pilots use to get their airplanes to fly as good as they possible can. For IMAC pilots ‘trimming’ involved much more than just getting their airplane to fly straight and level at a given throttle setting, but the results are well worth the effort.
The article below was written by Peter Goldsmith and orginally appeared in Model Aviation Magazine. Peter is the team manager for Horizon Hobby and has been involved with competitive scale aerobatics since the days of the Tournament of Champions in Las Vegas, NV. This article is geared to giant scale aerobatic airplanes, but nearly any model airplane can benefit from the techniques. If nothing else, the ideas presented below may at least lead to a better understanding of how to equip your next airplane.
The majority of the programming detailed below can be accomplished with a 6 or 7 channel computer radio fairly easily.
So what will this procedure accomplish: First and foremost – it allows your airplane to fly ‘true’ that means that when you use the rudder, you only get a yaw response, when you deflect your ailerons, you get a true axial roll and when you point your airplane straight up or straight down, it goes straight up or straight down. Second it allows you to focus on flying your airplane the way you want it to fly by not having to fight unwanted flying conditions.
With that:
Peter Goldsmith: How to reduce your flying workload!
One of my passions in life is to teach. After a long discussion with Mike Hurley after sharing with him how passionate I was to share my life’s aerobatic knowledge, we decided that a trimming article would be a great start. A properly trimmed model can reduce your workload in an aerobatic sequence by an enormous amount. I judged at the nationals this year and thoroughly enjoyed the experience. I was also impressed with the skills, especially in the lower classes when displayed by pilots trying to fly around a pour trim setup, I was truly amazes how tolerant people were. It drove me crazy to watch in fact. I remember bouncing out of my judging chair and saying to Mike, “boy” I need to help these people. Hence here I am typing away at my exciting pace of about 80 minutes per word in an attempt to help educate the great skill base that exists in the US scale aerobatic scene.
Like all good input, it doesn’t come from me, but more a summary of 25 years of meeting people who shared their thoughts on trimming with me, then melting them down to put into some kind of legible format that most can understand.
Servo and control setup
3D, and precision model trim typically go against each other. What I mean by this is that when pilots set up their new 40% something, they go straight for the big rates, 35, 40, and in some case 50degrees of throw. Anybody thought how this can affect the servo resolution, and more importantly the servo power.
Scale aerobatic events typically allow a separate aircraft for freestyle. Between 80 – 100% of the results at a scale aerobatic event comes from the precision elements - known and unknown sequences.
Please don’t misunderstand me, I love to watch free style flying, and admire the talent of the pilots that do it well. It’s innovative and has been one of the main contributors to the growth of Giant scale aerobatic aircraft. My point is: Why not have your free setup specifically for the free event, and then have a precision setup for known and unknowns sequences. I know for me personally having a model just for free style will be something I aim to do in the future. Having said that, a good alternative is to bias your setup more toward precision, which will no doubt improve your sequence flying (especially if you’re frequently fly events).
With my Cap, I use 1” horns on all surfaces with the exception of rudder which use 1 ¼”. I have 28 deg on aileron, 32 on elevator and 35 on rudder. For me, this is a good compromise for precision and free flying with the bias towards Free.
With 1” horns, and 1 ½’ distance from control hook up, I am getting slightly better that 1 to 1 ratio. More importantly I am getting closer to the maximum servo power and control geometry available. With 1’‘ horns my resolution is better, control slop is reduced, and servo wear is greatly improved. Another novel bonus is, I don’t need as many servos per surface. Give it a try next time you set up your aircraft, you may be surprised, in fact in some cases you may see no difference in control responsiveness by going to 1” horns, as with the better geometry you may be reducing your control blow back.
One of the biggest challenges I see pilots dealing with is surface blow back. With blow back, your snap exits will be all over the place, both entry and exits. Getting consistent flying is almost impossible. Every time your speed changes, you control response will change. Hmmm, I suspect a few lights just went on. Yep, could it be the fact that you consistently miss your snap exits is not due to your skills, but control blow back.
When setting up you servos, make sure you run the numbers. Do the math and figure out just how much power you are delivering to the surface. All servos are rated at inch ounces, that is at one inch from the center of the servo. A JR 8611 is 266 Inch oz on 6V. With a 2” horn they are only 133, and around 200 with a 1 ½” horn.
Years ago I was able to measure the forces on my Cap, believe it or not the ailerons required well over 30 lbs of force to deflect at 100mph. Now there are a lot bigger ailerons out there than mine. Please pay attention to this, it is crucial to consistent flying. If you have to use 1 ½” horns, or 2” horns, you will need more servos.
Sequencing your trimming
Many of the trimming articles I have seen over the years incorporate some kind of chart, graph - do this and this happens and so on. My concept of sequencing your trimming is simple. If you get your trimming out of sequence you will end up chasing your tail.
As with most things in this universe, for every cause there is an effect, same applies to trimming a model aircraft. So many times I see people test flying their aerobatic creation, flip the thing on it’s side and see what kind of knife edge mixing it may need. Thrust, CG, wing balancing and basic flight control trim can all effect knife tracking.
I can’t make this point more loud and clear, it is very important to trim you model in the correct sequence to make sure each adjustment has no effect on the previous adjustment.
You will see I have broken each element down, and there is an intentional order in which I recommend to trim a model. Model balance especially CG is the most important as differential, knife edge flight, and down line tracking will all be affected by the CG.
Next is dynamic balancing or wing tip weight. Next comes thrust angles, then aileron differential, and finally P mixing - knife edge tracking, roll coupling, down line track.
Oh…. if you change your propeller, you whole trim setup will change.
Balance
OK so…How do I know what is the correct CG for my model? If in doubt, read the instructions. Yep, chances are somebody from the TOC or similar has designed your aircraft and has determined over many flights where the CG should be.
For precision flying forward is better…but… too far forward can be a problem. I can not put in writing what is the best feel for each pilot other than simply stating - it is a feel thing. I can however, give you some symptoms of too far back and to far forward, plus some simple tests I do to check.
One of my favorite ways to determine the correct CG is spin entries. For precision flying I would expect you to be running between 12 – 15 deg of elevator throw. If you feel you need more than this, check your exponential it may be too high. Just as a starting point, 35% expo is what I call a linear feel. What I like to have with my expo is when at half stick, I get about 50% of the reaction of full stick, around 35 – 40% expo gives you this with modest control deflections. Ok, if that didn’t make sense - IF I have my stick at full travel, my aircraft will roll around 360-400 deg per second, about right for precision. Now when I only move my stick half way, I should be looking for 180-200 deg per second, make sense.
If when entering a spin, you model mushes, kind of slides into the spin with no real stall visible, you may be too far forward. Another sign of forward CG is excessive down elevator needed for inverted flight. This is not always the reason but is a sign.
Rear CG is probably easier to see for most pilots. Model is sensitive in pitch, unpredictable around the stall, climbs when on an inverted 45deg line are some I have noticed.
CG is mainly about feel, each person will have their preferences and each aircraft will have its preferences. Be patient, spend some time on this one; it’s important you are happy with your CG. I would recommend at least 10 – 15 flights before making the commitment to where it needs to be if it’s a new model.
Dynamic Balance
Ok, we are happy with our CG so the next thing is dynamic balance. This is really only relevant with wing tip weight as most other axis on a model aircraft are not affected very much by the dynamic effects of high g force loads. Having said that, your wings are. Just cause they both weight the same, and don’t carry any aileron trim doesn’t mean you can’t have a wing weight problem.
I have seen a myriad of ways to test for wing weight trim. Loop’s, pulling to vertical, and so on. My suggestion is to think about the sequencing argument. If you do loops, or pull to a vertical up line, the engine thrust can have an effect, yet we haven’t got to trim our thrust angles yet. Think about it, what could you do to check you wing tip weight in flight that will not be affected by thrust?
What I do is put the model into a vertical dive (minimum of 3 – 4 seconds) and pull a hard corner at the bottom. No matter where your wings are in roll, when you pull to level, the wings must be level. Check this concept with your stick plane. It really doesn’t matter where your wings are but as you pull to horizontal flight your wings must be level.
If you attempt to pull a hard vertical FROM horizontal, you must be absolutely sure your wings are perfectly level. I don’t know about you guys but I am not that good.
If you go from vertical TO horizontal, not only will the engine thrust have no effect but your wings can be anywhere as you are on a vertical down line. Now when you pull the corner, the aircraft may be pointing in a different direction than you planned, but that is ok, as long as the wings are level.
When I was told about this procedure several years ago, it made a lot of sense. The only thing I would recommend - pay attention to is make sure you only use elevator through the corner.
Don’t be quick to make a decision, have a friend observe the proceedings, do many pull outs, make absolutely sure before you move on to the next step of trimming.
Thrust angles
OK, guys, it’s time to put aside aesthetics and get that engine thrust correct. I sure see a lot of spinners perfectly lining up these days. One of the biggest deterrents to adjusting for the correct thrust angles is the spinner won’t line up any more. That’s true. Once again, when building you model, pay attention to the instructions, chances are somebody has figured it out pretty close.
What I like to do (or use to do) is test fly the model before I paint the cowl. Once I am happy with thrust, I can make the appropriate cosmetic changes to complete the model before painting. Setting up the correct thrust angles is fairly simple. Well… it’s simple to identify, harder to adjust.
To be continued...