New gadget- essence of a Shark

[Dave_Trible]

I had decided to decode a Shark at the Worlds to understand why the corner as they do.  I think I have the secrets mostly figured out but to aid the process I cobbled up this neat gadget to get to how the controls are configured.   It’s fun to play with and a little eye opening.

[Dave_Trible]

It represents a standard arrangement.  For example as configured
Elevator 10 degrees the flaps are 8
Elevator  20 flaps about 16
Elevator.  30 flaps 25
Elevator   40 flaps 32
Elevator   50 flaps 39
Elevator    60 flaps 45  I think this is what we are seeing on the Shark.   Anything more that 60 degrees you lose most all power or leverage over the surface and risk cam over.

[Paul Taylor]

I would think weight would be a big factor in how they can turn a corner.
I have handled a few Sharks and other Shark type of planes. I can’t get over how light they are even with a 6s battery on board.

But most of you have forgotten more than I know. 🤣

[Dave_Trible]

They are very light for their size.  I hear around 60 ounces for some.   Nats tail of the tape says more like 63-64.   We SHOULD be able to build balsa airplanes this light but making them stand up to grass fields can be tough.  One of the Mongolian Sharks shed it's landing gear on the new smooth pavement of the LPad during practice.   Basically it was an aluminum strut just glued to balsa ribs!   I looked inside one of Orestes older IC Sharks  fuselages long ago and was a very thin balsa with a thin veil of carbon outside.   The Canadian StarLight airplane uses a thin foam-maybe almost 1/16" thick with either carbon or glass bonded outside.   Obviously vacuum bagged.  The newer Sharks might be similar.

Dave

[EricV]

Your mockup looks interesting. I tend to try and stay around 1-1, but the design has a lot to do with it, with control surface areas, etc.

But my main comment is about your last post...We CAN build balsa airplanes that light, and it's not that hard. I'm not one to spend megabucks on balsa... 6 to 8lb wood is the norm for my shop... Yet, I still haven't had a 60 size pipe ship over 67 ounces come out of my shop yet with most coming out much lower in the low 60's.

For example: My last Nat's build, Katana, running a PA .75, 8 Oz metal tank and Aero pipe, the big Mejlik 75 prop 13.5" 3B (that's a big chunky prop!), carbon fuse landing gear, (with balsa wheel pants!) metal 2" spinner, using Klass Kote Epoxy paint and House Of Kolor Urethane clear was 64 Oz on the official Muncie scale said the tape on my wing tip which agreed with my digital home scale.

That wasn't because I skimped on finish either, as Katana sat on the 17 point row, my best Nat's appearance yet. And my Katana isn't exactly stock, with a slightly longer nose moment and slightly larger stab & tail moment, anticipating for the PA75, I cheated it up a bit to make things work the way I thought they should, so it's actually larger than a standard Katana. Turned out to be a good choice. I could easily knock that down to closer to 60 Oz dropping the plane down to a PA .65, with the smaller tank/pipe/prop/shorter LG/ etc etc.

If I went carbon fuel tank, carbon spinner, I could shave another couple ounces off of that, but then risk running nose weight. I usually adjust the nose and tail moment accordingly ahead of time depending on what I plan to run, so knowing your goals ahead of time and sticking to the plan is important. So, don't sell balsa home builds short, you can build them light, almost too light if there is such a thing. I chose to keep mine in its current config at 64 Oz, as I think anything lighter might actually hurt performance and trim, I like it just fine as it is.

Some basic suggestions/rules of thumb I try to stick to: Don't over-engineer, and don't get cute wasting time drilling holes either. Don't' skimp on structure on the front end, or you end up adding nose weight anyway, which adds no strength... go easy on epoxies, always wipe away excess glues, us CA where you can, and sand and hollow like crazy... Keep your fillets small. Fill with dope, not primer. Primer is heavy. I switched to white Klass Kote epoxy primer, as I use it as a blocking coat more than a filler. Oh, and don't be "One with the Gun" when you paint the thing... you don't need refrigerator white as a base coat, or it will weigh as much as one. LOL! Reverse mask your paint job, don't add colors on top of colors, that adds weight too. That's pretty much my mind set and it seems to work for even a has-been duffer like me.

You can out-build those buy and fly Sharks, don't let them get inside your head. You got this Dave! Looking forward to seeing what you come up with.
EricV

They are very light for their size.  I hear around 60 ounces for some.   Nats tail of the tape says more like 63-64.   We SHOULD be able to build balsa airplanes this light but making them stand up to grass fields can be tough.  One of the Mongolian Sharks shed it's landing gear on the new smooth pavement of the LPad during practice.   Basically it was an aluminum strut just glued to balsa ribs!   I looked inside one of Orestes older IC Sharks  fuselages long ago and was a very thin balsa with a thin veil of carbon outside.   The Canadian StarLight airplane uses a thin foam-maybe almost 1/16" thick with either carbon or glass bonded outside.   Obviously vacuum bagged.  The newer Sharks might be similar.

Dave

[Lauri Malila]

You can out-build those buy and fly Sharks, don't let them get inside your head. You got this Dave! Looking forward to seeing what you come up with.
EricV

Maybe, but can you build to that weight with same stiffness, precision and weight distribution? They both make a huge difference in how the model performs. L

[EricV]

Maybe, but can you build to that weight with same stiffness, precision and weight distribution? They both make a huge difference in how the model performs. L

Sure, why not... maybe even better. If you read all of what I wrote, I anticipated weight distribution. I needed no tail or nose weight for final trim on Katana. Sure, I tried it, and took it back out. I adjust trim with different weight components (lighter spinner backplates, Aluminum spinner nuts, wheel hubs, etc) not dead weight, when I can. From what I have seen, the Shark's, while consistent, are not 'all that". The control horns remind me of old Midwest units... soft horns etc... the L-Gear mounts weak. They don't hold up to vibrations well (see old DR powered Sharks, man if you missed the needle it was like one of those beds you put a quarter in)... No Lauri, I don't buy the defeatist stuff when it comes to outbuilding a Shark. They are VERY good and VERY consistently built, and that is something a lot of modelers may never achieve, but they aren't the boogie man of builds. Guys with skills like Trible and many others I've seen at our Nat's can match and surpass that build level with ease. At least that's my .02 cents adjusted for inflation. I will always cheer on the side of the builder.

EricV

[Ken Culbertson]

... was 64 Oz on the official Muncie scale said the tape on my wing tip which agreed with my digital home scale.

If that plane were electric it would have tipped the scales at 74oz.  72 if fueled.  Most sharks are electric.

Ken

[Brett Buck]

It represents a standard arrangement.  For example as configured
Elevator 10 degrees the flaps are 8
Elevator  20 flaps about 16
Elevator.  30 flaps 25
Elevator   40 flaps 32
Elevator   50 flaps 39
Elevator    60 flaps 45  I think this is what we are seeing on the Shark.   Anything more that 60 degrees you lose most all power or leverage over the surface and risk cam over.

     This is also what the Igor logarithmic flap linkage does, near 1:1 around neutral and proportionally more elevator as you deflect it further.

     Brett

[Dave_Trible]

     This is also what the Igor logarithmic flap linkage does, near 1:1 around neutral and proportionally more elevator as you deflect it further.

     Brett

That kind of struck me.   I think if you mess with this you can achieve about anything you want without the extra hardware.  Of course you'd have to make your own crank and horns (I do).  I'm thinking about making the block canopy on a new airplane removable so I can make all adjustments at the flap horn.   This will help keep the weight a lot closer to the CG on adjustment hardware and just use a straightforward elevator horn which is WWWAAAYYYYY back there compared to my current airplanes.

Dave

[Brett Buck]

That kind of struck me.   I think if you mess with this you can achieve about anything you want without the extra hardware.  Of course you'd have to make your own crank and horns (I do).  I'm thinking about making the block canopy on a new airplane removable so I can make all adjustments at the flap horn.   This will help keep the weight a lot closer to the CG on adjustment hardware and just use a straightforward elevator horn which is WWWAAAYYYYY back there compared to my current airplanes.

Dave

   It might be accidental/coincidental on the Shark, but there was a thread on SSW about 20-25 years ago with Igor and other notables discussing the potential desirability of changing the ratio as the deflection increased.

    Brett

[Reptoid]

     This is also what the Igor logarithmic flap linkage does, near 1:1 around neutral and proportionally more elevator as you deflect it further.

     Brett

There's actually nothing logarithmic about that set up at all. It's almost exactly 5 to 4 over the complete range. Pretty standard throws for an airplane that's not overweight

[Brett Buck]

No one asked, but I don't think the cornering has much to do with the control ratios. It's the ability of the electric to keep the speed up in the corners, which is vastly better than even really good IC systems. I think just about any current airplane can corner as tight or tighter if you remove flap*, but you can't do that reliably with an IC engine, because one really hard corner tends to wreck the rest of the maneuver. It's the same difference we found when we went from 4-2 break engines to tuned pipes (particularly the first-generation "12-3.2 and 12000 rpm" systems), this is just another step in the right direction.

    Brett

*you can remove flaps by changing the ratio of the deflections, or making the flaps smaller:

https://plans.modelaircraft.org/product/imitation/

   

[Ken Culbertson]

That kind of struck me.   I think if you mess with this you can achieve about anything you want without the extra hardware.  Of course you'd have to make your own crank and horns (I do).  I'm thinking about making the block canopy on a new airplane removable so I can make all adjustments at the flap horn.   This will help keep the weight a lot closer to the CG on adjustment hardware and just use a straightforward elevator horn which is WWWAAAYYYYY back there compared to my current airplanes.

Dave

This is Igor's method with split flaps driven by the bellcrank.  It mounts on a tray and is removable through a hatch in the bottom.  If you are going to do anything complicated, I suggest you make it removable.  Could just as easily go through the top.   I have used this setup on two planes and another more classical version on one.  It can vary with the length of the arms as to how much the ratio changes.  As Brett stated it starts on t 1:1 and in my case it is at about 2:3 at 20 degrees of flap and the elevator keeps going to 30 degreed with little movement of the flaps.

Brett is absolutely correct in that you can hit hard corners using electric and not run out of steam. 

Ken

[Matt Colan]

No one asked, but I don't think the cornering has much to do with the control ratios. It's the ability of the electric to keep the speed up in the corners, which is vastly better than even really good IC systems. I think just about any current airplane can corner as tight or tighter if you remove flap*, but you can't do that reliably with an IC engine, because one really hard corner tends to wreck the rest of the maneuver. It's the same difference we found when we went from 4-2 break engines to tuned pipes (particularly the first-generation "12-3.2 and 12000 rpm" systems), this is just another step in the right direction.

    Brett

*you can remove flaps by changing the ratio of the deflections, or making the flaps smaller:

https://plans.modelaircraft.org/product/imitation/

 

And the electrics get to run small, incredibly light props so there’s no funny business in corners either! I joked with Paul one night that the next revolution in IC is hollow props. He just shook his head and said there ain’t no way!

[Dave_Trible]

This is Igor's method with split flaps driven by the bellcrank.  It mounts on a tray and is removable through a hatch in the bottom.  If you are going to do anything complicated, I suggest you make it removable.  Could just as easily go through the top.   I have used this setup on two planes and another more classical version on one.  It can vary with the length of the arms as to how much the ratio changes.  As Brett stated it starts on t 1:1 and in my case it is at about 2:3 at 20 degrees of flap and the elevator keeps going to 30 degreed with little movement of the flaps.

Brett is absolutely correct in that you can hit hard corners using electric and not run out of steam. 

Ken

Ken what does that WEIGH?  Are you going to build a 60 ounce airplane with that in it?

Dave

[Lauri Malila]

And the electrics get to run small, incredibly light props so there’s no funny business in corners either! I joked with Paul one night that the next revolution in IC is hollow props. He just shook his head and said there ain’t no way!

I have used hollow props, some years ago Yuriy produced them for Retro .60. They were ok, stiffer and about same weight as the wooden ones. But the problem was that they were nearly impossible to tweak, the skins would buckle.
Russians have used carbon skinned balsa props back in the day. With today's CAD/CAM techniques, it would be easy to mill whatever core materials and also really nice thin carbon flat tow tissues are available.
So, I see no problem with hollow props for IC, you would just have to do the root section a little differently than with electric props.
But is it all worth the trouble? I don't know. you could also save many grams just by using a wood propeller. The modern CNC-milled props are much better than what wooden props used to be, in both efficiency and repeatability.
In general I'd say that the game is lost, but if we want to compete against electric with IC, we should really start looking for lighter props, and also there is lots of improvement to be done with acoustics. L

[doug coursey]

It represents a standard arrangement.  For example as configured
Elevator 10 degrees the flaps are 8
Elevator  20 flaps about 16
Elevator.  30 flaps 25
Elevator   40 flaps 32
Elevator   50 flaps 39
Elevator    60 flaps 45  I think this is what we are seeing on the Shark.   Anything more that 60 degrees you lose most all power or leverage over the surface and risk cam over.

I GOT PRETTY MUCH THE SAME DEFLECTIONS WITH  1" on the flap horn and 3/4" on the elevator horn

[Dave_Trible]

I think one thing being lost here is elevator speed.  Look at the bell crank.  For 30 degrees of bell crank movement (the space is spell check -sorry) we are getting 60 degrees of elevator -a 2 to 1 ratio.  Most the handles I saw had spacing at least as wide or wider than the 4 1/2" crank,  some looked close to 6".  This means very fast control rates.   You could then really only control that with a pretty nose heavy airplane.   Then on most our style airplanes we get max turn around 20-25 degrees (assumption) of elevator applied.  We aren't typically using the full range available to us. The turn is complete before we get there.   With the Shark style setup the elevator and flaps are getting closer to full range in the same TIME period or less while still not needing more handle input.
As to 'dead on the vine' IC after a hard corner-maybe you need a RO Jett .76.

Dave

[Lauri Malila]

Dave, I don't think any specific engine brand stands out in corner quality (except maybe MB.77 as I do have a better thermodynamical stability than others ).
I think what Brett noted, has more to do with the fact that an IC engine gives an impulse once in every rotation, that's something like 110-170 impulses/second.
And an electric motor gives what, about a dozen/revolution?
It also disturbs a lot the perception of round manoeuvres because every change in load, a corner or some other sudden change in acceleration, momentarily changes the engine run either immediately (gas flow ballistics) or with a small hysteric delay (load/temperature variations).
Maybe we are all too used to that that we don't pay much attention to it but it's always there, and electrics don't have it. L

[Dave_Trible]

Lauri I knew I should have grabbed your extra engine when you weren't looking!

Dave

[Lauri Malila]

That's not a good long term solution. I think you'll need a radial engine. L

[Ken Culbertson]

I think one thing being lost here is elevator speed.  Look at the bell crank.  For 30 degrees of bell crank movement (the space is spell check -sorry) we are getting 60 degrees of elevator -a 2 to 1 ratio.  Most the handles I saw had spacing at least as wide or wider than the 4 1/2" crank,  some looked close to 6".  This means very fast control rates.   You could then really only control that with a pretty nose heavy airplane.   Then on most our style airplanes we get max turn around 20-25 degrees (assumption) of elevator applied.  We aren't typically using the full range available to us. The turn is complete before we get there.   With the Shark style setup the elevator and flaps are getting closer to full range in the same TIME period or less while still not needing more handle input.
As to 'dead on the vine' IC after a hard corner-maybe you need a RO Jett .76.

Dave

Dave, I am trying to solve this problem in a different way.  I am trying a 5" bellcrank with a rather wide flap pushrod hole and I have restricted the bellcrank to 60 degrees movement.  I get the same leadout movement from neutral to full up/down but it is much closer to linear than the normal setup where the bellcrank moves through nearly 90 degrees with little movement of the pushrod past 60 degrees.  The only thing that would be better is an exponential bellcrank.  I have one of those waiting for a plane to put it in.  In theory, an exponential bellcrank coupled to a logarithmic flap horn might produce the snappy controls and still give you smooth level flight and flats.   My problem in getting snappy corners in the past was the handles back pressure.  I fly with my fingers and the pressure of a big plane in a tight corner was forcing me to use more wrist which was just too slow.  I have cured that problem using canards and spades which both work extremely well - for me.  They are however complicated and are more a novelty to play with than a serious aid in top level competition.  The next limiting factor is the timer.  My planes routinely out turn the timer.  I use Fiorotti and have not used the latest one yet but I doubt he has made it any faster.  Getting the corner boost after the mid point in the corner is hard to deal with.  We used to compare engines among the top fliers at these big competitions.  Now I think it will be timers that we want to know what the winners are using.

Ken

[Brett Buck]

Dave, I don't think any specific engine brand stands out in corner quality (except maybe MB.77 as I do have a better thermodynamical stability than others ).
I think what Brett noted, has more to do with the fact that an IC engine gives an impulse once in every rotation, that's something like 110-170 impulses/second.
And an electric motor gives what, about a dozen/revolution?

   Thats one thing, but, the kicker is that the electric not only prevents it from slowing down too under load, but, restores the rpm, subject to the limitations of the controller. Any IC engine, the best you can do is have it sag under applied load, and limit the sag. A working feedback system, it sags, but then comes back. Igors new gadget also gets a head start monitoring the pitch rate, it starts trying to compensate even before the speed drops, in anticipation.

   So, you go into a very hard corner, as quick as it can, it starts fighting the speed loss, making all the aerodynamic effects keep working as they were, instead of hitting the corner and bleeding off speed for a long time, meaning V^2 varies less, so your inputs can be abrupt and large, and the airplane just keeps plugging.

This is the same effect we first noticed when we changed from ST46 to tuned pipes. And also why we started folding wings right and left, because you hold the speed better, it will corner harder, go that, and the aerodynamic loads by definition go up, astronomically if you take full advantage of it.

     Depending on your prop airfoil, there is "prop magic" that can help you, too, specifically, the "drag bucket" effect that, again Igor first noticed and immediately explained why certain engines and engine setups worked better with undercambered props and others needed flat-back.

   The aerodynamics of the Shark are perfectly good, but certainly nothing out of the ordinary. Its reasonably light, but the electric versions are certainly heavier in flight, and despite that, they clearly turn much better with electric.

      Brett

   

[Doug Moon]

   Thats one thing, but, the kicker is that the electric not only prevents it from slowing down too under load, but, restores the rpm, subject to the limitations of the controller. Any IC engine, the best you can do is have it sag under applied load, and limit the sag. A working feedback system, it sags, but then comes back. Igors new gadget also gets a head start monitoring the pitch rate, it starts trying to compensate even before the speed drops, in anticipation.

   So, you go into a very hard corner, as quick as it can, it starts fighting the speed loss, making all the aerodynamic effects keep working as they were, instead of hitting the corner and bleeding off speed for a long time, meaning V^2 varies less, so your inputs can be abrupt and large, and the airplane just keeps plugging.

This is the same effect we first noticed when we changed from ST46 to tuned pipes. And also why we started folding wings right and left, because you hold the speed better, it will corner harder, go that, and the aerodynamic loads by definition go up, astronomically if you take full advantage of it.

     Depending on your prop airfoil, there is "prop magic" that can help you, too, specifically, the "drag bucket" effect that, again Igor first noticed and immediately explained why certain engines and engine setups worked better with undercambered props and others needed flat-back.

   The aerodynamics of the Shark are perfectly good, but certainly nothing out of the ordinary. Its reasonably light, but the electric versions are certainly heavier in flight, and despite that, they clearly turn much better with electric.

      Brett

 

Sitting there watching flight after flight re-enforced what I had learned from my very short time in electric helicopter. The electric power is "always there" The ESC stabilizes the whole thing electrically within milliseconds and does it the entire time. Glo systems are fully relying on physics for needed changes. The electric anticipation/response will always be faster and more consistent.  There is no lag it's "always there".

Old glo helicopter pilots that went electric were excellent from the get go and would make huge gains in their flying very quickly. Electric guys who gave glo a run had to take a few steps back to learn how fly with the lag. It would take some learning for sure. Throttle vs pitch management etc. Hard heavy loaded maneuvers will drag the RPM off drastically and responses to get the RPM back would take forever vs electric where it's not even noticeable.

Stunt planes are doing the same thing. The ESC is running the show based on split second electronic inputs from the gadgets while actively monitoring the rpm constantly.

I also think the pocket hinges make a huge difference as well. The flying surfaces are not sealed and they roll on an axis that is aft the wing or stab TE. Where our traditional models have the flaps and elevators sealed and the pivot line is as close to the rear of the flying surface as possible. There is something there....

[Brett Buck]

Sitting there watching flight after flight re-enforced what I had learned from my very short time in electric helicopter. The electric power is "always there" The ESC stabilizes the whole thing electrically within milliseconds and does it the entire time. Glo systems are fully relying on physics for needed changes. The electric anticipation/response will always be faster and more consistent.  There is no lag it's "always there".

  Bingo!   There's *some* lag, that's why you have to use a Spin 66 but not a Spin 66 Pro. But to first approximation, that's the effect.

    Brett

p.s. The same thing is why you can use the high elevator/flap ratio, you don't need as much flap deflection to support a given turn rate. The airplanes, as flown, are either the same, or heavier, than IC airplanes. And, having flown a number of Sharks with IC and electric, the definitely fly differently with different power, and the IC versions were clearly overdone.

[Howard Rush]

I had decided to decode a Shark at the Worlds to understand why the corner as they do.  I think I have the secrets mostly figured out but to aid the process I cobbled up this neat gadget to get to how the controls are configured.   It’s fun to play with and a little eye opening.

It’s a three-dimensional problem.

[Howard Rush]

I have used hollow props, some years ago Yuriy produced them for Retro .60. They were ok, stiffer and about same weight as the wooden ones. But the problem was that they were nearly impossible to tweak, the skins would buckle.
Russians have used carbon skinned balsa props back in the day. With today's CAD/CAM techniques, it would be easy to mill whatever core materials and also really nice thin carbon flat tow tissues are available.
So, I see no problem with hollow props for IC, you would just have to do the root section a little differently than with electric props.
But is it all worth the trouble? I don't know. you could also save many grams just by using a wood propeller. The modern CNC-milled props are much better than what wooden props used to be, in both efficiency and repeatability.
In general I'd say that the game is lost, but if we want to compete against electric with IC, we should really start looking for lighter props, and also there is lots of improvement to be done with acoustics. L

We saw Andrei Yatsenko at a couple of contests last year. He was using a wood prop. He preferred it to a black prop because he could tailor the flexibility.  Wow. 

[Dave_Trible]

It’s a three-dimensional problem.

Hi Howard.   Yes I am aware there are other factors involved here.   I know I'm not tech enough to dig into that very far.  That's why for the most part I work Ozark style with basic test fixtures and field testing to seek answers to my dilemmas.   Sort of pass/fail methods.   I'm hoping what I'm learning here will just make my modifications to my designs work better.  To catch a Shark-

Dave

I know you know what Ozark style means-I know where you came from...

[Howard Rush]

I know you know what Ozark style means-I know where you came from...

He’s outing me.

[M Spencer]

Heres some drivle gfrom here . https://stunthanger.com/smf/stunt-design/the-best-stunt-airfoil/50/





Your Figure ( of deg. movement ) are about what mr rabe settled for on the sea fury & Mustang . as in 30 flap 37 elevator .

Id think its just that theyve put in the air time . Here ( Aus. ) you see them bounce & bobble , particularly first flight of the day .
But ' the story ' told is theyre pretty ' Hair Trigger ' as in , sneeze & they bounce - They go where you put em.
But blowing like stink they get blown like ***** anything else .  I think there maybe better ' gale ' airfoils .

Lack of control friction , relitive ridgidity , and light weight , seem to be their chief virtues . But you can wobble their tailplanes dead easy .

Another Thing , the SV II ' Appears ' smooth . This is likely true here . the blunter airfoils disquiseing minor ' bumps ' in the air .
But when ALL the airs bumpy , Id think the trad sharpish airfoils can ' fly clean ' . The issue is still the ' bounce / bobble , out of squares etc .

Another likely crucial factor is the Control Surface Ridgidity . RABE again . 5 layers of glass cloth ' gets it ' ridgid - Flaps .

Be intresting to see the Top six put through that flight trace // track program . to see wot actual they did . Holding a pencil on the screen -
Vertical Eight intersection consistancy accuracy repeat and hight loss from top thru into outside . AND the Sq 8 Vertical Leg wander ,
also Clover ' straights ' random seem to be a topic. If it were filmed thru a Hor. & Vert. grid wire fence , youd spot it .

[Steve Thompson]

"A working feedback system, it sags, but then comes back. Igors new gadget also gets a head start monitoring the pitch rate, it starts trying to compensate even before the speed drops, in anticipation."

'The ESC is running the show based on split second electronic inputs from the gadgets while actively monitoring the rpm constantly.'

One could conclude:

IC engines can be tricked into working, with limits.  Electronic controller/motors are AI and are "thinking" faster than the motor can physically react.

[Brett Buck]

"A working feedback system, it sags, but then comes back. Igors new gadget also gets a head start monitoring the pitch rate, it starts trying to compensate even before the speed drops, in anticipation."

'The ESC is running the show based on split second electronic inputs from the gadgets while actively monitoring the rpm constantly.'

One could conclude:

IC engines can be tricked into working, with limits.  Electronic controller/motors are AI and are "thinking" faster than the motor can physically react.

    Everything always will have limits, some are more limiting than others,

   IC engines were the only game in down for the first  60 years and are still viable after 80+, the definitive system has been around for almost 40 years. They are about as refined as they will ever get and we more-or-less know what all the limitations are. Electric has been viable since maybe the mid '00s, feedback control with this sort of control lead is now in pre-production and not widely available, and are working with a different set of limitations. Right now, it works about as well or better, for the most experienced users (to compare apples to apples). For the less-experienced user, you probably have to know less about electric to get a reasonably decent results, and you don't have 80+ years of "stunt lore" (AKA bullsh*t) to send you in the wrong direction.

     Brett

[realSteveSmith]

    Everything always will have limits, some are more limiting than others,

   IC engines were the only game in down for the first  60 years and are still viable after 80+, the definitive system has been around for almost 40 years. They are about as refined as they will ever get and we more-or-less know what all the limitations are. Electric has been viable since maybe the mid '00s, feedback control with this sort of control lead is now in pre-production and not widely available, and are working with a different set of limitations. Right now, it works about as well or better, for the most experienced users (to compare apples to apples). For the less-experienced user, you probably have to know less about electric to get a reasonably decent results, and you don't have 80+ years of "stunt lore" (AKA bullsh*t) to send you in the wrong direction.

     Brett

Would the current rules allow 'throttling' of an IC engine in the same way that the electric motors are being controlled?  Would this provide any improvement for an IC powered model?

I remember reading about Windy's Z-tron and how it was quickly outlawed.  But....that was long before the prominence of electric and all the current 'tricks' that the modern flight timers are playing.

[Brett Buck]

Would the current rules allow 'throttling' of an IC engine in the same way that the electric motors are being controlled?  Would this provide any improvement for an IC powered model?

I remember reading about Windy's Z-tron and how it was quickly outlawed.  But....that was long before the prominence of electric and all the current 'tricks' that the modern flight timers are playing.

   "Windy's" Ztron - actually Sergio Zigras' Ztron that Windy bought as an "off the shelf" item - was not "quickly outlawed", in fact, it was legal until the rule change cycle in (I think ) 2020 when we made anything but 2.4GHz illegal in conjunction with the AMA CL General rules. 30 years, long after Windy had stopped participating, is not "quickly". This is a (unfortunately typical) story Windy and his supporters told to make it seem like be was being persecuted.   Tom Dixon proposed outlawing it the very next rule cycle, but that never even got past the screening vote at the contest board - because absolutely no one aside from Tom seemed to have a problem with it. I thought it was pretty cool, albeit mostly useless to solve the issues we are discussing here.

     No one in stunt was ever "out to get" Windy, far from it, the event indulged him (and a few others) to a remarkable degree, sometimes to the  detriment of the event,  for decades.

   There are no current rules in the AMA that would in anyway restrict an on-board feedback control system on an IC engine. The problem with the idea is that response lag is an even bigger issue that IC than it is with electric. Right now, Igor's gadgets only work well using the Jeti Spin 66 controller, and not as well with the Jeti Spin 66 Pro, the issue being that the "Pro" responds too slowly. IC is far slower still, to even if you did do it, it would have to be so slow as to be not worth doing .

    The example that came closest to working was Scott Bair's coupled exhaust throttle, any time you deflected the bellcrank either direction, it moved a valve in in teh muffler that reduced the restriction. The bellcrank deflection was a stroke of genius, it is arguably an even better input to use than Igor's pitch rate in the new prototype controller "drag compensation" function discussed above, since over short periods it is effectively the first derivative of the pitch rate, even more lead than the measured pitch rate. The weak point was that even immediately changing the exhaust restriction was still too slow to affect the RPM and so it was less effective than many other means of indirectly controlling the speed.

   I note that this was in the *early 80s*, 40+ years ago, and used exactly zero electronics, strictly thermo-mechanical.

     Brett

[Trostle]

Would the current rules allow 'throttling' of an IC engine in the same way that the electric motors are being controlled?  Would this provide any improvement for an IC powered model?

are playing.

Please refer to the Control Line Precision Aerobatics rule book.

Paragraph 2.6:

"2.4GHz spread spectrum radio control signals may be used  to control retraction or extension of landing gear and/or a one-time irreversible engine or motor stop function.  Otherwise, all control of the model during flight shall be through the flying lines.  The retraction/extension of the landing gear and/or motor/engine stop function shall be under the sole control of the pilot and may not be operated by any other means than direct pilot control.  No other uses or any other means of wireless remote control are permitted."

Keith

[Brett Buck]

Please refer to the Control Line Precision Aerobatics rule book.

Paragraph 2.6:

"2.4GHz spread spectrum radio control signals may be used  to control retraction or extension of landing gear and/or a one-time irreversible engine or motor stop function.  Otherwise, all control of the model during flight shall be through the flying lines.  The retraction/extension of the landing gear and/or motor/engine stop function shall be under the sole control of the pilot and may not be operated by any other means than direct pilot control.  No other uses or any other means of wireless remote control are permitted."

Keith

    This does not outlaw on-board feedback control of the engine, or anything else for that matter, it refers only to wireless control. It does outlaw IR controls, but that happened decades after Windy had used it

     Brett

[realSteveSmith]

    The example that came closest to working was Scott Bair's coupled exhaust throttle, any time you deflected the bellcrank either direction, it moved a valve in in teh muffler that reduced the restriction. The bellcrank deflection was a stroke of genius, it is arguably an even better input to use than Igor's pitch rate in the new prototype controller "drag compensation" function discussed above, since over short periods it is effectively the first derivative of the pitch rate, even more lead than the measured pitch rate. The weak point was that even immediately changing the exhaust restriction was still too slow to affect the RPM and so it was less effective than many other means of indirectly controlling the speed.

      Brett

I have some experience with exhaust throttles in model boats.  They typically responded much quicker than a carburetor.  I'm surprised (not doubting you....just surprised) to learn that even the exhaust throttle wasn't responsive enough to be an effective speed control mechanism. 

[Brett Buck]

I have some experience with exhaust throttles in model boats.  They typically responded much quicker than a carburetor.  I'm surprised (not doubting you....just surprised) to learn that even the exhaust throttle wasn't responsive enough to be an effective speed control mechanism.

  It is perfectly reasonable to question, this was just the analysis of the time. But it could have been wrong. Anybody who tried the same idea with a carburetor quickly gave up, it was *glacially slow* for the sort of thing we are talking about, same with swing-weight carbs (which Igor and other people also tried) as a speed regulator.  I might actually try that on the new Skyray, but my expectations would be very low. It works pretty good without it!

      Brett

[Dave_Trible]

So to continue the thought.  A few years ago I had Igor build for me an accelerometer and electronic stuff to to use on IC.  Dub made me a special "carb"-not really,  a simple rotating valve to fit on RO Jetts and a remote needle assembly.   Never got a plane built to use it (yet) but if this new thing coming down the pike can be made to think ahead of a corner why couldn't it do the same for IC?   The settings might be different but the application should be the same...no?   Next question:   are we at a place where many other events went-to their demise-   making things too complicated and expensive for most?    Might it be time to think about more restrictions?   Just food for thought.

Dave

[realSteveSmith]

  It is perfectly reasonable to question, this was just the analysis of the time. But it could have been wrong. Anybody who tried the same idea with a carburetor quickly gave up, it was *glacially slow* for the sort of thing we are talking about, same with swing-weight carbs (which Igor and other people also tried) as a speed regulator.  I might actually try that on the new Skyray, but my expectations would be very low. It works pretty good without it!

      Brett

Have you considered variable pitch propellers? 

I've seen (from a distance...magazines, etc) several model airplanes outfitted with the variable pitch tail rotor from a model helicopter, in place of a fixed pitch airplane prop.  I do know that more basic model helicopters use a fixed pitch, direct drive brushless motor as a tail rotor (like a model airplane).  This provides adequate performance but the variable pitch tail rotor provides a much higher level of tail control due to the much faster response.  There would be lots to work out with a setup like this but it should be capable of near instantaneous speed control .... even faster than a direct drive electric motor that has to accelerate/decelerate the prop disc. 

Just a thought...

[Brett Buck]

So to continue the thought.  A few years ago I had Igor build for me an accelerometer and electronic stuff to to use on IC.  Dub made me a special "carb"-not really,  a simple rotating valve to fit on RO Jetts and a remote needle assembly.   Never got a plane built to use it (yet) but if this new thing coming down the pike can be made to think ahead of a corner why couldn't it do the same for IC?   The settings might be different but the application should be the same...no?   Next question:   are we at a place where many other events went-to their demise-   making things too complicated and expensive for most?    Might it be time to think about more restrictions?   Just food for thought.

Dave

   Too much lag and it goes unstable, which limits the possible response speed. You can only add so much lead, a corner takes 1/4 second. It doesn't know you are going to do a corner before you start to move the controls.

     Brett

[Brett Buck]

Have you considered variable pitch propellers? 

  Yes, that was another thread from 3-4 year ago, it also has the interesting characteristic that a larger moment of inertia of the rotating assembly actually helps instead of hurting. That's why the prop mass on electric is so critical and they are mostly hollow to save weight - to get it to work, you have to be able to spin it up/down as fast as you can, that is a direct function of the prop moment of inertia. With variable pitch, the tendency would be to lose speed rapidly as the pitch goes up, having some angular momentum to oppose that reduces the RPM loss.

  The trick is making it stay together through the extremely violent maneuvering and the torque impulses from the engine.

     Brett

[Reptoid]

So to continue the thought.  A few years ago I had Igor build for me an accelerometer and electronic stuff to to use on IC.  Dub made me a special "carb"-not really,  a simple rotating valve to fit on RO Jetts and a remote needle assembly.   Never got a plane built to use it (yet) but if this new thing coming down the pike can be made to think ahead of a corner why couldn't it do the same for IC?   The settings might be different but the application should be the same...no?   Next question:   are we at a place where many other events went-to their demise-   making things too complicated and expensive for most?    Might it be time to think about more restrictions?   Just food for thought.

Dave

Food for thought;
     First; I don't believe you will ever get an IC engine to respond like an electric. It's not the controller, it's the electrics ability to provide instant response at full torque.

     F2B and AMA Precision Aerobatics are the only two events in FAI and AMA that allow electrics to compete with Internal combustion engines in the same classes.
     Electrics are a huge advantage from the start of building all the way through to flying in competition.

Building:
     They can be built lighter-Little to no vibration, No need to be fuel proof, no building or trying to find an unobtanium fuel tank, Far more readily available spinners, a complete power package can be purchased including programmer and anyone who can read and follow instructions can set it up

Trimming:
      Battery can be moved to adjust CG, No change in CG during flight, Engine RPM for level lap speed infinitely adjustable, Boost in maneuvers infinitely adjustable, Flight time fully and easily adjusted without effecting other parameters. You can readily buy the exact power system you want/need from a single source and batteries/chargers are readily available locally or easy internet order

Regular flying and competing;
     Take apart transport have no worries about Dogs and sniffers at airport security or customs detecting fumes, No starting problems, no glow-plug issues, no fuel procurement issues when traveling, no variations in engine run from altitude density, Absolute repeatability in engine run, No worries about under or over run times, 100 % repeatable run time with 100% warning before shut down, absolute repeatable speed and boost adjustments for wind if wanted/needed

     I am not suggesting that one couldn't win with either, but having built, trimmed, and flown both and being fully capable of making either work perfectly, I'll say this: It's far less work and far easier to do with an electric and have less issues that could cost you points

[fred cesquim]

then just go with the gear that delivers the best performance and provide steady performance to flight skills
as in every high tech sport athlets take advantage of the material to boost the performance of their skills within rules
F2B deals with shape of the pattern , i dosen´t matter with what kind of plane or engine you achieve that
if we start rulling things not related we will be back to Noblers and fox 35.
even run the risk of having a empty competition if epower goes south

[frank williams]

I think that a piped IC system can respond as quickly as an electric system.  A pipe responds within one piston revolution.  (granted the electric ESC is working at fractions of revolution)  The pipe has the ability to alter the power curve of the IC engine.  Some pipe configurations work better than others.  I think this is what Doug is feeling for the first time with the ES Composites pipe.  The power curve shown below is vertical.  All pipes change the shape of the power curve.  The steeper the curve, the quicker the response to engine load

[Brett Buck]

I think that a piped IC system can respond as quickly as an electric system.  A pipe responds within one piston revolution.  (granted the electric ESC is working at fractions of revolution)  The pipe has the ability to alter the power curve of the IC engine.  Some pipe configurations work better than others.  I think this is what Doug is feeling for the first time with the ES Composites pipe.  The power curve shown below is vertical.  All pipes change the shape of the power curve.  The steeper the curve, the quicker the response to engine load

   The big difference is that even with a governor-only electric system, the response to load is second-order instead of first order like even the best IC systems. Electric sags due to the step function load, but recovers, IC sags and stays sagged until the load is removed. Better/sharper local slopes of the power curve only affects how much is sags, which is the effect everyone feels, but to first approximation it cannot recover until you remove the load, or at least in any reasonable amount of time. It *might* overshoot later due to thermal effects, but that is not helpful during the cornering.

    Brett

[Dave_Trible]

I might add that there were a few IC Sharks at the Worlds.  They appeared to my eye to keep up in corners with the electrics.   I can understand at least in theory the idea of the electrics.   I'm still not at all sold that it is that consequential in practice. 

Dave

[Ken Culbertson]

but if this new thing coming down the pike can be made to think ahead of a corner....

I am very skeptical that anything we can afford to put in a timer can do this.  I can accept that he may have gotten better at knowing that the plane is in a corner but thinking ahead?  IMHO, for boost in a corner to have any value it has to come near the apex of the corner, and I don't see how an accelerometer can react fast enough to do that.  I think that a sensor that detects pushrod movement as an input might help,

Ken

[Brett Buck]

I am very skeptical that anything we can afford to put in a timer can do this.  I can accept that he may have gotten better at knowing that the plane is in a corner but thinking ahead?  IMHO, for boost in a corner to have any value it has to come near the apex of the corner, and I don't see how an accelerometer can react fast enough to do that.  I think that a sensor that detects pushrod movement as an input might help,

Ken

  "Thinking ahead" is a sort of misnomer. The technical term is "lead" (pronounced leed), meaning it is using the rate of change of the controlled parameter. instead of just the current value of the controller parameter. It's not actually thinking ahead, if you are flying around in level flight, it doesn't and will not ever know that you are going to be moving the controls in the future.

     It is looking at the, in this case, pitch rate, and as soon as you start moving the controls, it sees the rate, which in short order will lead to increased drag, and increasing the power anticipating the drag/speed reduction that will inevitably follow. That, as opposed to just sensing the fore/aft acceleration (which directly corresponds to the change in drag) and then when it sees it start to slow down, then start cranking itself up. By that time it is already slowing down.

   The additional lead in the system compensates for some of the "lag" inherent in cranking the motor up, and having the motor/prop spin up. That's also why reducing the prop inertia is so important - spins up more quickly, same with the controllers, Spin 66 (regular) has a "fast response" mode that the Spin 66 Pro (I think) lacks.

    To Frank's earlier point, while you can certainly control the engine RPM more effectively with different pipe magic (increasing the partial of torque WRT RPM at the operating point), there is nothing like any "lead" in it, and aside from things like Scott Bair's bellcrank "sensor", there really can't be. There is also considerable lag at low frequencies due to thermal effects - when the engine comes under load, it slows down to the extent necessary to supply the required torque, but also, while doing it, heats up, which is a relatively slow process, and "hangs on" for a while after the load is removed. That's more or less how a 4-2 break works.

     Brett