Pattern Plane Design Considerations
 

Hi,

Lately I've been trying to explore the basic concepts of pattern plane design. Can someone provide an overview of the latest trends in pattern design and the reasons why pattern planes have been designed like that?

Also how does root/tip ratio affect the pattern plane stability? I notice different ratios in well known planes that'why asking.

Looking forward to your replies,

Thanks and regards,
Nick

RE: Pattern Plane Design Considerations
 

Ahhhh what the heck. I'm going to post this with my first point being: These are MY opinions, right or wrong, and I don't have the time or energy to get into a big arguement. I would love a good debate on the matters, but if it turns nasty, I'm out. The question you ask seems like a very simple one, but reality is a lot different. So here goes.

Pattern plane design is centered around one concept: balance.

What you want is the perfect blend of neutrality in all attitudes of flight, inherent stability (EI it goes exactly where you point it in any angle of flight) and manueverability. if you design or set up a plane to be dead stable and straight, it may have trouble with snaps and spins and the like. If you set up a plane as a snapping/spinning monster, you may have to give up some of the stability around center.

Right now, something that is not discussed openly, or at least hasn't been, is that we in the US especially fly 2 entirely different types of pattern. Everything from sportsman to the FAI P sequence is what I would define as "pattern". The other type is the planes designed for the F sequence of FAI specifically. These schedules include many combined rolling/pithing/turning manuevers that the rest of the world never sees in competition. In short, a "real" pattern plane designed and optomized for the "pattern" schedules isn't necessarily the best plane for rollers and such. This is why you're seeing those silly looking T canalizers popping up. All it does is smooth the airflow from the spinning prop and direct it at the rudder/fin to neutralize some of the aerodynamic blanking that occurs with most wide body planes. If you have a large tall fuse and you throw it up on the rudder in KE flight, you wouldn't believe what that airflow is doing around the tail section. It's not pretty.

Now for the shocker.....almost all of the brand new cutting edge planes are designed specifically for the F sequence. (Duh?) But here's the catch.....a guy that can fly that huge monster on a level of the FAI Nats finals in the US has no problem dealing with what he's giving up in the P pattern. Most of these guys are so freakin good that it just doesn't matter, they don't really notice. Now take that same plane, hand it to a very accomplished intermediate pilot, and watch him fly it. in calm air he'll fall in love with it. Add a 25 mph crosswind and he'll wonder why he has his hands full. It's because he's flying a plane that was not really designed with him in mind. But since Billy Bad-***** flies it in FAI and is on the cover of all the magazines, he MUST have one because it must be the greatest plane he can get his hands on. Well it is, but not for intermediate.

So on to the design questions specifically. Let's begin with the wing.

A full 2 meter square plane with a full 2 meter wing was all the rage years back. But, people began to notice that snapping and spins were suffering a little. You had to really nail the set-up or they'd be hit and miss. Lots of zeroes. After a while people discovered that we simply had too much wing for the sequences we were flying, and that's in almost all classes. An 1100in wing is a kite. Good luck not zeroing a snap or spin here or there. if the plane was less than 10 lbs, spins breaks were really hard to get right.

Enter the new style of wing. About 4" or so total clipped from the span, and somewhere between 925-1000in of area. Less mass, less lift to break into a snap/spin, things got easier. Also the older style wings had a straight trailing edge. This made the effective sweep angle of the panels really significant. This really makes a plane roll easy, it snaps ok, but in turbulent wind it will throw your plane all over the place. So the sweep angles were lessened and the wings now carry more of a double taper. This makes the plane snap fairly easy all things being equal, and the effect of turbulence is lessened. It does make mix values increase slightly given the exact same plane otherwise.

Now add thicker wings and trailing edges. This allows the plane to fly more sbale at a slower speed, and the thicker TEs make the wing more stable, especially in turbulence. Thick TEs act like built-in expo, and this works on pretty much all surfaces.

As for the taper ratios, anything about 2:1 and you get incredible snaps but you shift the balance toward manueverability and away from stability. The design question is "how much". You'll find every school of thought out there, and they are all right (and all wrong too, depending on who you ask).

Dihedral is necessary to minimize roll coupling in KE flight. You can affect this to a large degree by where you locate your wing on a vertical plane. As in, how high the wing is on the fuse. the closer to center, the less dihedral you will need as a general rule of thumb. If you mount the wing really low you will have to use a lot of dihedral and that brings about other problems in certain conditions and attitudes. Too close to center and you're likely to get into some wierd mixing curves depending on the overall design of the plane.

Fuselage: Here's another area where things can get weird. "Wide body" fuselages are all the rage nowadays. But super duper width can really mess with the areodynamics around the tail section (see above about aerodynamic blanking). 6 1/2" is about right. Anything more and you have to get creative with the airflow. The Symphony is a good example of a really wide plane that uses curves and flutes to get the airflow right. And it's still not perfect, but it does a better job than most in that respect.

Where a large fuselage helps is in it's height. Given a conventional fuselage (with none of the T canalizers or weird strakes that Nat Penton is famous for) a fairly tall fuselage makes rolling manuevers easier, and you can perform them much slower than a skinny plane like a Prophecy for instance. Since slowness, grace and "constant speed" are the main goals of pattern flying right now, a tall fuse helps a lot and is very nice. However there is always a drawback......put that sucker in that 25mph crosswind and have fun with the most bizarre crab angles you've ever seen. Anybody that watched the Nats finals this year had a front row seat to exactly what I mean. Again, this might not be the best option for Joe Intermediate. But he'll fly it anyway....LOL

Also the genral shape of the fuse has a LOT of effect on how the plane flies. years ago drag was the key to slow flight. And I mean, big, ugly aerodynamic drag that borders on parasitic drag. Check out the old Smaragd for instance, have a look at the bulbous look of that plane. Drag city man!!!! of course in a high wind, you had to really work to make the plane penetrate and move along. That's probably not the best example of this, but since it spawned so many clones, I figured it's familiar enough to get the point across.

Now we have evolved a step further it seems. Somewhere along the way, we had another look at the japanese planes. These things were huge and sleek, but they didn't have all those abrupt cuvres and angles; the lines flow nicely....and so does the airflow. So now designers are heading back towards sleek, clean designs....just bigger.

Now for the real pickle: the tail section. This is what controls that plane in every weird axis it encounters except for the roll axis. Design here is more critical that one might think. We'll start with the stab since it's fairly straight forward. the area of the stab should be somewhere between 23-25% of the wing area. The larger the stab, the more stable the plane....and the harder it is to snap. The smaller the stab, the more agile the plane is.....and it is a little harder to lock in around neutral. So again, it comes down to balance. You have to find the right area. Also in direct relation is the moment of the center of lift of the wing to the center of lift of the stab. The longer it is, the less area you need, and the more stable it will be. the shorter it is, the larger it needs to be and it will be less stable around the pitch axis given the same design/balance/etc. Thickness is really personal choice, like the wing. A thicker stab is really kinda dead around neutral and gives a lot of drag, but get it too thick and other things suffer. Again, balance. Depends on the overall design of the plane and what you intend to do with it.

Fin/rudder: Here's the one place every one in the world is still trying to figure out. We've seen it all and it's still changing almiost daily. Small fins and rudders, large fins and rudders, HUGE rudders with counter balances, sub fins, you name it, it's being tried. Even boost tabs.

the rudder/fin is a direct relation to everything since pattern is very rudder intensive. ESPECIALLY the F sequence. Too much and it gets touchy around center but has oodles of authority. Here is where you'll find those 3/8" TEs on a rudder. And sometimes even bigger. This was unheard of by the general public until a couple years ago. Chad Northeast was the first one I remember using a rudder TE that large, but it does work well. Also remember that if you have a huge fuselage, your fin/rudder has to grow in exact porportion to that area of the fuse. If it gets too big, you have a severe kite on your hands in even the slightest of crosswinds. But that sucker will do some serious rollers!!!!! And again, not really the best choice for Joe Intermediate.

Another important consideration for the rudder is it's relative location to the wing and stab. Too much area on top and it will pitch HARD to the belly with rudder in level flight and KE. If you manage to mix it out, watch what happens with your stall turns......heh.

The trick here is to balance it with the entire plane, and I mean every single peice including the landing gear. If you don't believe landing gear affects trim and mix, fly the same plane with and without fixed gear and retracts. You WILL notice a difference on most planes.

Balancing the rudder/fin area is easily one of the most difficult part to designing a pattern plane. you can get away with something being a little "off" practically anywhere else, but it's amazing how much just a couple of square inches here and there affects how the plane behaves with pure rudder.

Construction: It still amazes me how much misinformation is out there about this subject. here's one of the most common myths in pattern: "Composite planes are lighter than wood planes". I'd need a bulldozer to move that pile of BS. Generalizations simply don't apply to what we do, especially ones that big. The TRUTH to that myth is simple....it depends on the plane and who builds it and makes it, and how it's constructed. We've seen every extreme on all sides of that issue. Totally built up wood planes, totally composite painted in the mold planes, vacuum sandwiches, wood formed composites, everything. It flat out depends on how the plane is built, period.

I'll give a couple of examples. Some poeple design and build really awesome wood planes, but they simply over build them. They use plywood where they should have used balsa, and use balsa where they should have used plywood. they use too much bracing and not the best material selection. Then they go and slap on a pound of paint. And they wonder why that plane is 11 lbs if they're lucky. This is/was how most wood planes were done in certain areas for a while, and probably how the myth got started in the first place. (Besides marketing, but I'm not even going there). Conversely with careful attention to detail and using composites in key places, and most importantly...material selection, you can fairly easily build a wood plane every bit as large as the biggest FAI planes at 9 1/2 lbs or less. I've done it myself, and am about to do it again. Although in my personal opinion I like the way my plane flies at 10 lbs better than at 9 1/2.

On the flip side of the coin is composite planes. By now I'm sure you've heard the expression "flying eggshell". Well, some are just that. Expensive ones at that. because if there is a REAL generalization, it's that a production composite plane will require much more engineering and attention to construction than a wood plane of the same design. the trick is you don't have to worry about it; it's already done for you. Follow the instructions of those very experienced and you will be just fine. Faster to the finish, too.

But realize the down side of a composite plane is that it is (generally) much more fragile). And the lighter the plane, the more fragile it is. As a general rule of course. One rough landing and that gear and half the fuse bottom is gone. And if you're lucky the tail won't whip and snap the fuse right behind the canopy.

Does this mean to avoid composite planes, or that they are inferior? Not at all. They are just so different that you can't compare them to a wood plane, and in most cases, to each other. there are really good ones and ones not so good, just ask a lot of questions.

One last note about design. And this one sums up everything in a simple package. There is no perfect plane. As long as we sue a spinning propeller, there never will be either. Designs will always flow, change and be tweaked. Because what works well today might not be as good tomorrow. Every designer in the world is still learning. We try new things. Some things work well, some don't, some are fads, some are butt ugly but fly like a dream, some are gorgeous but fly like crap, some are obscure and outfly everything....but everything out there today, yesterday and next year will benefit from trimming and some form of mixing. Anybody who tells you different is simply ill informed. That does NOT mean some designs can be flown very well with none at all, if the mixing and such are minimal enough (what we all strive for). But given time, you WILL find conditions in which something is a bit of a problem and should be addressed in some way.

There's about 10000000000000 opinions about all of this, and this is just one. I am really tempted to just hit delete and shake my head and let it go, that might be the best course of action in truth. But there is so much BS and misinformation out there, I feel sort of obligated to shed some blinding light on the darkest secrets of pattern design and construction. If you've read this far....man you must be bored!!! But take it for whatever it's worth to you. It's your money, your time, your hard work, use it/spend it/deal with it however you like. Just watch out for the hype. If a plane is touted as "perfect" and not a single defect is noted, beware.....somebody isn't telling the whole truth or simply hasn't tested it enough. There's no such thing as a "bad" pattern plane, some are just better at some things than others.

Most of all, HAVE FUN guys!!!! Fly whatever you want and ENJOY IT. Any plane can be made to do whatever you want it to if you're dedicated and determined to spend the time to make it do exactly what you need it to do. I hope that answers a few questions and I hope at least a few of you benefit from just one thing I typed today. No matter what it is.

RE: Pattern Plane Design Considerations
 

Wow, Troy Newman should be proud of me!!!!! That's a long post.......

LOL

-Mike

RE: Pattern Plane Design Considerations
 

I'm sure some would debate a few of the items mentioned. But I for one can't find any fault with your final conclusion!
Good job.

RE: Pattern Plane Design Considerations
 

I hope they do debate! (And not argue or insult on a personal level as can happen sometimes). Because every last one of us, especially me, is still learning, testing, forming opinions, trying new things, and come this time next year we could see things in a totally different manner. I reserve the right to change my mind [8D]

If somebody goes through the trouble to explain something I want to read it, and see if my mind gets changed. I want what we all seek, the perfect plane and the perfect flight! It's like golf in a way.....you'll never see that perfect plane or flight, but the fun is in the pursuit of it!

-Mike

RE: Pattern Plane Design Considerations
 

I agree with almost every bit of your (Magnum+!) Opus Mr Hester!
But my (Tall FAT) Leviosa is SO much better at the rollers than my (Tall thinner) Abbra!
And, as you say,74" of wing at 14oz per side snaps much better than 76" at 16 oz.

RE: Pattern Plane Design Considerations
 

There's more to that than JUST the fuse width though, I bet. If the Leviosa is really good at rollers, it's probably a combination of things, and also HOW the width is distributed and shaped.

We could write huge books on this stuff, this is just scratching the surface.

And yep, the less mass in the tips the better for snaps and spins. if you ever feel like it do an experiment to see this clearly demonstrated: Take 2 sets of wings, identical shape-wise. Same plane. One, build normally. Fly it. On the second set of wings, honeycomb the tips and take careful steps to lighten the end of that wing as much as you can without it getting weak. Now install those wings and fly it. You'll be absolutely amazed at the difference!

-Mike

RE: Pattern Plane Design Considerations
 

Good post Mike. That´s why I never got with that Tempest :-)

I still find my "old" Desire just fine for the Advanced schedule.

RE: Pattern Plane Design Considerations
 

I bet that the Black Magic is very close to that perfect balance.

Vicente "Vince" Bortone

RE: Pattern Plane Design Considerations
 

Mike
Thanks so much for the discourse on design. There should be a place where such valuable information could be collected.

RE: Pattern Plane Design Considerations
 

Yeah, the Tempest was an attempt to put a band-aid on a shotgun wound to the skull. I had great luck with mine, and won a lot of contests with it. But I knew it was never going to be any better than it was, and then the parts disappeared....and that's why I designed the Black Magic from the ground up.

The prototype Black Magic was awesome from the word go, but an FAI finals plane it was not. Dean Funk is currently flying it in intermediate, and if he gets some practice time, watch out....because I flew it again after all of this time, and I can't say I've ever felt a plane better suited for intermediate. Ever. Imagine a Prophecy that rolled with almost no rudder.....

And here I am 2 years later, still tweaking......but really really close to exactly what I want. The V2 is a killer plane, MUCH better than a lot (if not most), but I'd go nuts if a winter went by and I didn't take it up a notch.....

And that's what all of this is about, the relentless pursuit of something better. And better. And better.......

Always learning.....

-M

RE: Pattern Plane Design Considerations
 

Some would say it is......just not for FAI F without a canaliser. So, I'm busy making a kewl one to go on them. It's been tested and it does really carve through the rollers. Without it, it sort of skids through the "S". With it, it's fine. if you don't ever fly the F sequence, you'd be hard pressed to find any real faults. It has a few mixes, but they're not high or strange. I've flown it without mix and could at the drop of a hat, I just prefer to really spend the time trimming.

I'd say it's better than most, especially for sportsman through the P sequence. That's what it was specifically designed for. But perfect? No, just really good. Good enough for certain. And some people say it does a few things better than any other plane out there right now. I'd tend to agree. So far......

-Mike

RE: Pattern Plane Design Considerations
 

Dang Mike, I can't read that much in one sitting LOL.
Emory.

RE: Pattern Plane Design Considerations
 

Dear Mike

Thanks for the answer and your time. It is seems that a good pattern plane is the one you have spent lots of time on to improve it via aerodynamic enhancements or mixing. According to what you wrote no plane is perfect and even if it's perfect for Mr Joe Intermediate may not be for Mr George Master. It all comes to personal preference and flying style. The questions had to do with the general rules of "thumb" being followed nowdays in pattern design.

I am really impressed by the Japanese designs I simply like the looks of them (Zeque is the most beautiful pattern plane I've ever seen), but some of these models are only available by OXAI and are very expensive. You can get some wood kits though but I do not have the time for construction, I would like to dedicate my free time on training and improve my flying skills.

I would like to get a 2x2 ship this year as bigger flies better, the most probable candidate is CompARF Integral. What do you think of it with respect to design?

Looking forward to your advice,

Thanks and regards,
Nick

RE: Pattern Plane Design Considerations
 

Ok, I'll simplify.

General rules of thumb:

Long moment from wing to stab

Tall fuselage, 2 meters long

Wing span about 74 inches long with double taper and conservative sweep angle, 2:1 taper ratio, about 950 in square average, about 1/4" thick TE, slightly swept tips

Rudder/tail: Large. Very thick TE on rudder.

Fixed gear

More streamlined look overall, canopy more forward than in years past

And that's about as general as it gets ;) From there, go nuts, try everything.

As for what I think of the Integral design......ask me again in about a week...... :D I have no opinion other than from a distance it looks promising. I'm not an expert, I just share opinions for whatever they're worth here and there. I realize that the one I might see is in it's infancy so I am not inclined to be very critical....but if it is awesome, I'll say so!

-Mike

RE: Pattern Plane Design Considerations
 

Heya Mike,
As far as the lower classes go... That old Aurora carved a line as well as my Angel's Shadow and probably a little better with the gusty wind. It doesn't fit into the current design thinking at all. There are a bunch of older planes out there that are as competitive as any other new plane for nowhere near the cost of the RTF composites. The newer designs offer the agility to roll your way through the "S", etc. So for folks out there looking to be as competitive as possible in the lower classes, I'd shy away from some of the new fat-n-funky planes. They just don't lock on as well as some of the older ships. You give up some stability when you add agility. Besides, some of these planes are just plain U-G-L-Y. But everyone knows that I like the slick looking planes better anyway. :-p

The real trick is find a plane that you really like to fly and like the way it feels in your hands. When you are comfortable with your plane, you are going to fly better.

Joe W.

RE: Pattern Plane Design Considerations
 

Joe I'd have to agree with 100% of what you said.

The only place I'd see a disadvantage (and this is just my personal take on it, after just climbing through all the classes with wide body style planes) would be possibly size with some of the older planes. And then only in the wind. Up until last year, intermediate had been won every year with an older style sleek plane. Boxer 60, Carerra, Prophecy....because that particular pattern requires smooth lines and tracking and round radiuses and not a whole lot else. let that wind get howling and the guy with a sleeker plane has an advantage in that class all things being equal.

At local contests sometimes the competition can be REALLY tough, and if the wind lays down, a guy who is well practiced with a larger plane seems to have an advantage in presentation.

Advanced, who knows, it's different every year. But AC won it with an Ariel last year!!!!

Tell Ryan he must bring that Aurora next weekend. He has no choice in it, he just has to and that's that :D I need to see it up close. I'll tell you all the details then.

-Mike

RE: Pattern Plane Design Considerations
 

Good grief, you do not want to see that plane up close. It's a 20' plane for sure! (You need to be 20' away for it to look good). We have all gotten so comfortable flying these larger planes for so long, many have forgotten just how well the older designs fly. I'm sure Ryan will bring it to Tangerine though... If not, we can send him home to go get it so everyone can have some fun with it. Fixed gear no less (a crime punishable by death, but when there just aren't any of these planes around anymore, we do what we must...)

See you in a week!

Joe W.

RE: Pattern Plane Design Considerations
 

I'll bring the rope, I assume there are strong, high branches nearby...

-Mike

RE: Pattern Plane Design Considerations
 

I have a question for you gurus out there.

Considering that, excluding sportsman & intermediate sequences, pattern planes spend about as much time inverted as upright, I've always wondered why they seem to be tuned more for upright flight? Specifically I'm thinking about the typical layout:
- wing position below thrust line
- positive dihedral on main wing
- positive incidence on main wing compared to tailplane
- right thrust on motor/engine

With the exception of the first, all of these seem to be "wrong" for inverted flight. What am I missing?
--Derek

RE: Pattern Plane Design Considerations
 

OK, first off, let me say that was very good summation of basic aerodynamic design you gave there Mike, my hat's off to you for putting all of that down. Now, I think I have a couple of responses for checksix, feel free to correct me if I'm wrong. Most of what he seems to have asked about can be summed up in a very simple response: the airplane still has to fly. Most pattern airplane wings have fully symmetrical airfoils (or extremely close to it). Bernoulli's principles (which are the basis for airfoils) show that a fully-symmetrical airfoil will not generate lift. The only way to achieve lift therefore is to raise the angle of attack of the wing (angle of attack = angle between the airflow over the wing, and an imaginary line drawn from the leading edge to the trailing edge). Now this change in angle of attack can be achieved one of 2 main ways: having the airplane maintain a nose-high attitude, or increasing the incidence relative to the thrust line (not realtive to the tailplane). Since a nose-high airplane does not present well to the judges, and really looks like it's just hanging from the prop, the positive wing incidence is put in. The right thrust is built-in to counter the effects of what is called P-factor. This a phenomenon caused mainly by 2 things. The easiest to visualize is a the rotation of wind around the fuselage caused by the spinning propeller. This wind strikes the vertical stabilzer on the same side (left, pushing it to the right) whether or not the airplane is inverted or upright, and always causes a left yaw whether or not the aircraft is upright or inverted (just remember when you're inverted, the left yaw pushes the plane to the right when viewed from behind). This vortex is present in all modes of flight, but is more pronounced at higher PRMs (during takeoff, acceleration for vertical maneuvers). The second cause of P-Factor is the fact that when the airplane is pulling towards a more vertical attitude (through a radius), the propeller's angle of attack increases momentarily only on the downward half of the rotation, causing it to create more lift on one side (yes, your propeller is two wings rotating). Conversely the angle of attack decreases on the upward side, causing it to create less lift. This happens whether or not the airplane is inverted or upright, but unlike the vortex created by the propeller's rotation, this increased pull causes the aircraft to yaw to the left when upright, and to the right when inverted. The amount of right thrust put into most modern aircraft attempts to balance the need for it in the upright radii, and for takeoff, with the lack of it's need for inverted radii (since the two effects that cause P-Factor almost cancel each other out). If our aircraft were never flown inverted I can guarantee you would see a whole lot more right thrust to eliminate the need most people have for rudder mixing with elevator. Since I choose to fly my airplane rather than programming the radio do it, I require right rudder during any radius I fly... it's just a fact of life. Well, I hope this helps explain the last two points you asked about, checksix. As far as the dihedral and wing position, perhaps Mike can offer some insight into those, because I frankly don't really know the answers and would just be guessing.

RE: Pattern Plane Design Considerations
 

Nope, that's pretty accurate.

Keep in mind what I wrote originally is a very VERY basic generalization (I hate that) of the "why" of it all. So many othert hings can be done to achieve the same results. However, if you change one thing, in general you may have to change everything else to match it.

Just as a fast and dirty example, if you were to make the general statement "a 74" wing snaps better than a 78" wing". All things being equal, true. But if the tip chord of the 78" wing is small enough, it may indeed snap better than the 74" wing. However, you might run into serious tip stall if your taper ratio gets too wild, and that opens yet another can of worms.

That's why there aren't any real books written on just this subject. There are simply too many variables.

I'm afraid right now I don't have the time I had a few days back, I'm preparing to travel to Florida for the Tangerine contest this weekend and trying to TCB and actually get a day's practice before I leave....so, I'll have to leave it at that for now...

-Mike

RE: Pattern Plane Design Considerations
 

In very basic terms(all that I understand ,really), the dihedral bit is easy.
With a low-wing design, flying upright, you'll need a little bit of dihedral to minimise(ideally to cancel out ) roll when the rudder is applied.
When the same model is flying inverted, effectively it becomes a high-winger--and then it will need a little bit of anhedral for the same effect.
In the far-off olden days,with one-piece wings and no mixers, it was common trimming practise to have a hacksaw and some 5-minute epoxy in the flight box---if it rolled against the rudder, you landed, cut a little wedge through the top of the wing centre, increased the dihedral a bit, glued it back together, and tried again....

RE: Pattern Plane Design Considerations
 

Derek,

I'm no guru, but you have made a wonderful observations. Unfortunately, many of the things you list are there as tradeoffs for aesthetics, or tradition. If you toss out the aesthetics and tradition, you can eliminate many of the things you list and get much closer to an aircraft that is much more attitude independent. The caveat, is that you get an airplane that no longer fits the mold and while it may be beautiful to some, for other maybe not. The attached pictures are of a line of planes originating with the green one, The Voodoo Express. Mine is the yellow one, and the other is a smaller version flown at YS63 at 4.5 lbs...

Mine (the yellow one) has the following traits:

- Wing is on the thrustline
- No Dihedral
- No Up/Down/Left/Right thrust

The tradeoffs made in mine for upright flight are

- stab is 1/2 degree negative incidence for zero elevator input in upright flight. (Otherwise upright flight would require holding some up elevator)
- fuse area is shifted downward at the tail to provide a drag force in pitch that counteracts the negative stab incidence in knife-edge flight.
- rudder and vertical fin area are shifted upward to provide a roll force that counteracts the rolling force caused by the assymetrical fuse area distribution.

A number of folks on and off RCU have flown the Voodoo Express line of planes and should be able to attest to their neutral stability, and unique flight characteristics. Beleive it or not, the Voodoo Express's are incredibly smooth in the wind even with very light wing loading due to their high taper ratio wings and side area that is concentrated near the CG that provides very little moment for the wind forces to affect the attitude of the plane.

You can see the influence of the Voodoo Express in the Pentathlon that flyintexan has just introduced. He has tried to balance the tradition and aesthetics with many of the aerdynamic qualtities of the Voodoo Express (and payed homage to Nat Penton, the Voodoo Guru, with a tip of th ehat in the nane of tha plane). His design is a really great synergy of the two concepts and even though it is unproven on battle, I look for it to be a force to be reckoned next season in the hands of some capable pilots.

Richard

RE: Pattern Plane Design Considerations
 

Mike, I'm glad that you did not hit the delete key as it was an interesting article to read, thank you. I have an observation to share about aerofoils as there has not been a lot said in that area. A few years ago in Australia the model to have (before all the ARF's) was a local kit called the Cyclone. When I first saw one I couldn't help but notice that the aerofoil section was quite different. It's high point on the aerofoil was almost flat for about 1.5 inches, like someone spent too much time with a sanding block in one place. The owner said it was suppose to help the model retain it's original direction after a snap roll.?? This was a model that had been developed over may years by a builder as wooden models and the design was evolved and refined before the fiberglass kit was made and it enjoys a good reputation. Matt

RE: Pattern Plane Design Considerations
 

I'll bite.... WHY, exactly, does a 74" wing snap better than a 78" wing? Is the snap in the stall, or in the rotation? Where does wing area/planform come into play... or leading edge radius? And yes, I do know that I've asked the million dollar question. (FWIW, I've got some great slo-mo video of a 45 inverted downline negative snap with my 3D.) Personally, I feel the answer lies in the power; how much kinetic energy is the model carrying when it ceases to actually fly, compared to it's drag, which is not totally dependent on wing span. Most current 2M planes with the 160DZ will snap way better than an Atlanta with an OS61 (pre-Hanno). The Atlanta (Aurora knockoff) is much smaller than 2M. So, what's the deal? (If you survive this one, we can discuss upline/downline 'snaps')

Just when you thought you had gotten off lightly, Mike!

Brian

RE: Pattern Plane Design Considerations
 

Everything comes into play Brian. Taper, thickness, tip sweep, tip shape to a small extent, location of high point, balance (critical), thickness of trailing edges, airfoil shape, wing loading, tail volume coefficients, and one of the most important but usually overlooked aspects, mass.

You can't be that specific and that general at the same time.

LE radius has an effect on snap entry especially. But more important is the shape of the airfoil from the LE to the high point of the wing. If it's fat and rounded, it won't break as fast as a sharper airfoil. Hoever, as another general rule, sharp LEs tend to fly better at faster speeds. So a snap tends to be fast and violent. If you take the same plane and slow it down too much, which might be an excellent speed for another model, the snap might mush or wallow. There's a million ways to do snaps. Everyone has in thier mind what a snap looks like, and it's usually different.

Wing span is just one part of the total equation, which is why I said "all other things being equal". Same airfoil, taper, high point, balance, wing loading, the one with the shorter wing will snap slightly cleaner simply due to mass and newtons laws of motion.

Ok let's talk about wing rake. Again using a general set of parameters, more rake in a wing makes it more stable in a roll, and is effective dihedral. However, it has some issues with turbulent air, which is exaggerated by a sharp LE. What else is there involved? How much is too much and where does it begin to induce serious roll coupling at hard angles?

This is where planform comes into play. Why are all of the current designs using less total rake but more taper?

Also talking about snaps, the tail areas and moments come into play BIG TIME. the larger the stab, the harder it is to snap (for instance) what you have to find is exactly enough stab to make it stable enough to fly straight, but agile enough to break into a stalled condition and recover quickly. Any more and the scale shifts. What effect does stab thickness have if any?

Just sumpin to chew on.

-Mike

RE: Pattern Plane Design Considerations
 

Ahh one more thing about LE radius and snaps.

A smaller LE radius will allow the wing to snap at lower angles of attack. this can be good or bad, depending on the degree and how it's done. What that also allows is for a plane to break into the snap more shallow and recover cleaner....in theory. It also makes the wing a tad unstable in certain conditions, and that depends on a number of other things as well.


-Mike

RE: Pattern Plane Design Considerations
 

Where is Dick Hanson on this discussion? Dick, you out there?

sc

RE: Pattern Plane Design Considerations
 

Similar questiom.Where is Dean Papas in the discussion?:)

RE: Pattern Plane Design Considerations
 

Probably trying to keep poop off thier shoes ;)

Because this whole subject has as many different answers as it has questions. But somebody has to try...

-Mike

RE: Pattern Plane Design Considerations
 

Xeretai Niko,
Kitaxo kai yelao!
Both for the rest of us on the forum, and because my Greek is household rather than technical: I will switch to English.
There are way too many design issues for us to talk about in just one forum, and when I can't really answer a question completely, I choose to keep my mouth (keyboard?) shut.
But you called me out, so here I am. I promise not to give you the answer to "Life, the Universe, and Everything" in fifty words or less.

Pattern design is a tricky business with only a few good rules, and lots of conflicting theories.
On top of that, the behavior of airplanes is very non-linear: even a amall aesthetic change to an existing airplane will sometimes produce large changes in how it flies.
and other times, dramatic changes accomplish nothing.
At best, the experienced designers have collected more "rules of thumb" about what not to do.
After that, we are all slaves to fashion, and will spend lots of time trying to trim out the designs we drew just because they were pretty.

There are Pattern designs with the stab very close to inline with the wing,
and those where the stab is much higher and "out of the dirty air" as the proponents of this school of thought say.
There are examples of both kinds of design that fly very very well, and there really is more than one way to solve the design problem.
If you are eager to learn it all, then you are going to have to build a few airplanes, or at least one with all plug-in feathers, and a simple fuselage with many wing and stab tube holes!
In the meanwhile, you might choose to pay a flattering compliment to a proven designer, and steal ... okay, borrow the "numbers" of a successful design.
The wings, tail, and thrust-line placement of a proven design can provide a skeleton around which you can draw something you like.
Then start making small changes and see what happens.
Here's an interesting one for you: the Oxalys is obviously a very successful design, but all of the ones I have seen needed lots of rudder into UP elevator mix in order to fly properly. Why? It turns out that the canaliser (or "flow straightener in English) greatly helps this problem on some designs, and does nothing for others.
Why not start out with the Oxalys skeleton and see what changes with a different fuselage shape.
My pet theory is that the Oxalys suffers from a strange airflow when it is yawed: the air separates around the tall canopy and then turns toward the belly aft of the canopy.
In my opinion, this is the cause of the strong pull to the wheels with rudder, and a fuselage shaped more like a fish will not suffer this problem. So will one with a spine that stops the cross-flow.

I have designed more than just a few really good airplanes over the years, and still have more questions that answers !
Later I will attempt to answer your question about taper ratios.

Yia,
Dean Pappas

RE: Pattern Plane Design Considerations
 

Wow, I'm on the same page with Dean! Cool!

Funny, but that's exactly how I designed my first plane. I took some basic measurements that I knew were sound, drew a straight line on a piece of paper....made tick marks where I wanted specific measures, and connected the dots. And that's where it started. By now it's really changed a lot, but I had to start somewhere.

Refining is an ongoing process, and you're never actually "done". That's one thing I think people don't quite get about pattern designs, is that they are not static. They are dynamic. Even the gurus are just more experienced and have just simply tried more things over the years. Some work, and as Dean mentioned, some do NOT work....but on a different design, the thing that didn't work may be just the ticket. And that's the problem. You can't just change wings on a plane and expect it to fix everything. You have to change or at least slightly tweak almost everything. The better the plane flies in actual testing, the less tweaking is needed. But we are a bunch of perfectionists, seeking perfection knowing full well it's unattainable. But along the way some darn fine pattern planes get made!!!

I have a question, one that I'm pondering right now. How does the thickness of a vertical fin/rudder come into play? It seems in general that a thicker one may be better for some of the current designs, but I'm wondering to what degree. Of course, I have about 5 different fins and rudders made to play with and see for myself ;)

Yeah....I'm just the crazy one that posts this stuff knowing how many people are either not interested or completely disagree. I just hope it helps somebody out there.

-M

RE: Pattern Plane Design Considerations
 

Hi Dean,

It was a great pleasure to read your answer to my question. I used to read your articles in Model Builder magazine during the very early stages of my involvement with R/C.

Now that I'm older :) I still have lots of questions, that I hope to be answered here.

Actually I don't own an Oxalys, I used to have the smaller version, so it is not possible to test the model. I thought that the T canaliser's role was to direct the airflow towards the tail and make the rudder more effective. I did not know that there were pitch coupling issues with that model.

To be honest I like the designs that have the canopy towards the engine cowl, like Oxalys, Integral, Evolis etc. in older designs the canopy used to be further back. Do you think that Oxalys' tendencies are due to a wrong location of the canopy?

Regards,
Nick

RE: Pattern Plane Design Considerations
 

Wow, much has been discussed since I last chimed in, and I am definitely out-classed with the likes of Dean Pappas and Mike Hester in here. Having not done much design myself, most of my opinions are based on theory, some mine, some borrowed, and some learned just by observation. I just felt like chiming in on a couple of things that were mentioned, but not expanded on much. First is the thought that some have that the horizontal stabilizer needs to be out of line with the "dirty" air coming off the back of the wing. Now from what I've seen of airfoils in wind tunnels, there isn't much turbulence on the back side of the wing as long as the ailerons are not deflected, especially symmetrical airfoils. If the air becomes turbulent while travelling across the wing, it kills lift. On most modern pattern designs the ailerons begin so far out on the wings that only the last inch or two of the stab would be affected by the turbulent air coming off the wings. Therefore, my feeling is that having the horizontal stab in line with the wing is not necessarily a bad thing, but whether or not it is needed there is another question, and has a lot more to do with the vertical placement of the wing on the fuselage. The next thought I wanted to throw out there is in regards to Mike's comment regarding vertical stabilizer thickness. My feelings on the vertical stab were seeded by Bryan Hebert and a conversation we were having as I compared my Genesis to his Shinden, and he got me thinking on the subject of the vertical stab's airfoil. He feels, and I agree after much pondering, that many designers overlook the importance of the fact that the vertical stab is a flying surface, which means that at certain attitudes of flight it will act just like a wing, generating lift (knife-edge flight, snaps, spins, or lateral lift anytime rudder is applied). He pointed out that one of the flaws of the Genesis was the extremely thick leading edge on the stab that then has a constant taper back to the trailing edge. If you were to turn this stab on it's side and imagine it as a wing, well, let's just say that dog won't hunt. Now, if viewed as just part of the fuselage, it looks just like it is part of the airfoil created by the fuse, but unfortunately the stab sticks out into the air all by itself, and will not be very effective under certain conditions. Now, that being said, in my opinion the thickness of the vertical stab is not that big of an issue, as long as it has an effective airfoil, and affects asthetics more than flight. As Mike correctly pointed out earlier a thick leading edge on a wing will decrease the angle of attack needed for the stall as you enter a snap. This principle can be applied to any airfoil. In other words, the vertical stabilizer with a very thick leading edge will stall easier, especially when you don't want it to (slow roll, snap roll). When an airplane is performing a snap roll, or a spin, only the wing is stalled, and the horizontal and vertical stabilizers are flying the airplane. If you lose control (stall) on either one of these surfaces during the maneuver you either end up with an ugly (sometimes zeroed) maneuver, or even worse a very expensive pile of splinters (or glass/composite materials). OK, my wine is starting to kick in and I can't keep a decent train of thought anymore, so I'll stop here, and leave these opinions to be eaten alive by Dean and Mike. Have at it, guys!

RE: Pattern Plane Design Considerations
 

Oh, and as far as I can remember, the answer to "Life, the Universe, and Everything," aka the "Ultimate Question" is without a doubt 42. I've thought about it for quite a while, and it's 42.

RE: Pattern Plane Design Considerations
 

If you are really keen of trying something else that is different -but works -- start with a lot more power -
a 22-24" prop - on a light spark ignition2 stroke setup
these are now extremely smooth runners and the big prop really makes speed control easier
you just dial in speed at will - slower or faster --

RE: Pattern Plane Design Considerations
 

Dick, how about diesel? From my understading, diesel has a very consistent torque curve, allowing larger props to be swung. Similiar to electric dont you think? larger props, slower rpms, more consistent throttle response, no need for special tuning.. etc

your thouhts?

Chuck

RE: Pattern Plane Design Considerations
 

the diesel engines used as model engines run on ether and oil and really lousy as throttlable powerplants -
I tried a conversion years back and the inability to control point of ignition made it not suitable .(compression controls ignition)
Glow engines are a step up from these and tho the nitro "softens " the critical nature of the glo engine - it is still -in my book NOT the ideal engine
the new generation of spark ignitions is really getting good and on alky and a tiny splash of nitro - are extremely smooth runners . The problem--is thay use lots of fuel -compared to gasoline .
a lightly stressed , large displacement, mildly tuned, two stroke , spark ignition is -in my book the best possible setup.
It is all a compromise -- Don't compare these to converted weedeaters --
If you have not actually ran these and flown them -don't be too quick to dismiss em .
40cc engines seem about right for the current 5 k weight limit-I did a few models with this and I thought they were terrific - others said they were grossly overpowered when they tried em - but that was -at the time -the objective. Noise and vibes wer also a problem -I think I am close to correcting these last two problems - A new ignition system is on the horizon and the carbon fibre exhausts are working extremely well.
By the way Ed Skorepa is doing the carbon fibrework (I won't touch that stuff) the ignition is a Czech design- the engine a lightly modified ZDZ rear intake /rear exhaust.
OR you can go with electric motors - The power curve of these is the direction we are trying for.

RE: Pattern Plane Design Considerations
 

i would love to go electric but the batts are killers.

Chuck :)