Ok, it's been a long time coming, but I think maybe it's time for a thread like this. In case you haven't noticed, there's been a recent ground swell in personal aircraft design. It's nothing new, it waxes and wanes. Right now it's on the upswing, and this is a great opportunity for every last one of us to learn and share knowledge. I'd hope we can remove the mystery and voodoo, and share our own thoughts about the question that drives new designers: why. We have a wealth of experienced people here, and I believe we have the opportunity to do something good.

In addition, I would like to lay a few ground rules for this thread.

1- no flaming. This means me especially, I'm the world's worst. Although I do it usually in a sarcastic and teasing manner, it has caused some hard feelings and flat out made some people angry. For that, I sincerely apologize. Troy and Tony, and others I know I have rubbed the wrong way: truce. I don't have to agree with you about everything, and you don't have to agree with me. But we should be able to voice disagreement, tease a little. and still avoid open conflict. I will give you the benefit of the doubt, and I expect you to do the same. I would however ask that any opinions be clearly stated as such, and if you believe it's fact, please back it up with something substantial other than personal experience. Personal experience falls under opinion. Can we do this, or do we just want a war? Please, keep it civil. Feel free to post as much and long as you wish, but check ego at the door and bring honest opinion and fact. All of us.

2- ask questions. What is the advantage of a double tapered wing vs a straight trailing edge? What is the purpose of thin wing tips? Why ist he rudder post slanted? How do I minimize pitching in the design? Admittedly while most of this is trial and error and varies somewhat from one plane to teh next, there are similarities and theories. Ask, learn, share, implement.

3- no political hijacking. Keep your agenda to yourselves.

4- share your design if you feel like it. Got a pic or drawing? post it. Ask for critique, and pleae those that are experienced, be dead honest and temper it with solution. "That's a dog and will never work" is unacceptable.

I don't expect this to be an explosive thread, but it's just an open door. It's up to you to walk through it and utilize something potentially educational and enlightening. I'd love to ask some good FAI pilots why they do some of the things they do, and get an honest opinion. Without feeling like they'll just be insulted because I asked in the first place.

Well, have at it or ignore it, it's up to you.

-Mike

Ok I'll start with a few generalities. These are my opinions, which I base in personal experience with both models and full scale aircraft. When something seems constant to both, it's worth forming an opinion.

Pattern planes are the ultimate balance. They are a trade off. if you want stability, you must give up some small degree of manueverability. That's pretty much a time proven hypothesis. It's bordering on law, and in full scale, it is law.

There is and never will be a perfect pattern plane. Anyone who tells you different is either misinformed and doesn;'t know any better, or is trying to sell you something. This comes back to my first though, that everything is a trade off. Every time you tweak some thrust, turn the incidence adjusters, add some mix, you're making one thing more nuetral and another more unstable. Balance is the key.

Set up: If you fly 100 people's different planes, you'll feel 100 different set ups. Pattern planes are a very individual thing. As an example: I have flown 2 airplanes that were set up by Troy Newman. (or at least that's what they told me, proudly I might add). Not picking on Troy, but everybody knows him so it's a good example to use. I think everyone would agree that Troy is a very good pilot right? To me, those planes were unflyable. I don't mean a little off, I mean "oh crap let me get this thing on the ground". After some adjustments on throws and expo, and a touch of mix, they flew great...to me. And I do fairly well in competition. I don't fly FAI, but I do fairly well. in both cases, the people in question said thier planes then flew much smoother. As a side note, niether of them fly FAI either. The moral? What works for one person in one class doesn't work for everyone. And that's not a knock on Troy ( I feel I have to add that disclaimer lately). That's just a fact. I'm positive if he flew my set up, he'd hate it.

Allright, feel free to either ignore this thread or enjoy it and use it. have fun, and be civil and learn, I hope to.

-Mike

{edited for better wording, I suck at that sometimes}

And now I'll ask a question.

Rudder counter balance. Some say it's the way to go, others say it causes wierd things in certain manuevers. I'd like to know more about this, pros and cons. As much detail as possible. I know a few people have done some experimenting, and I hope they will answer with thier findings. With any luck, maybe we can find a good answer. The top designers probably already know this answer, but if you look, some top end planes have them and some don't. So what's the scoop? Anybody?

-Mike

The finer points of pattern plane design is something that many of us would find very interesting but and maybe I'm wrong, would have a great trouble actually contributing to. Folks could give an opinion based on personal preference, but I would think most would have trouble documenting any serious data. That's not knocking the post by the way it's just reconfirming your statement that everyone has their own personal quirks when it comes to setting up- trimming, CG, incidence, throws and flying style etc. What suits you, doesn't necessarily suit another. It's not the airplane at fault, it's the person behind the sticks. I feel if people, myself included, really could get a grip of that we'd be seeing quite a different picture.

So why do we get so many new airplanes? Well the schedules change, evolve would be a better term and designs, in theory change to for fill these new demands. I say in theory. There is only pilot/designer that, in my opinion has truly evolved his planes and thats CPLR and the Alliance-Synergy-Oxalys sequence. The great majority of the others seen to come out with a completely new plane, every couple of years or so. Surely things aren't changing that fast... so why the new designs? Because it's good business.... and we, as (hobby) pilots like new planes, new toys and new reasons to blame our bad scores on an "out of date" design; And that's even better for business!

If any of the worlds top ten pilots where to turn up at your average pattern contest equipped with a 4 generation old airplane, how do you think they'd fare.They'd probably win... by a long margin! I saw something similar with my own eyes 2 years ago at the Norwegian Nationals. The multi time, ex champ coming out of hiding and bringing an old Wolfgang Matt designed airplane, 12 years old or so. The P-03 was never flown better during that event...The snaps (and remember this airplane was never designed to snap (of course it was, all airplanes are) where things of utter, jaw dropping beauty. When asked what made this old design snapped so well, I was told that, at first it didn't...I just work and worked on them. It's not the airplane that makes the maneuver, it's the pilot. Enough said.

Huummmm bummer! Now where the catalog of the latest, new and exciting airplanes!

Alrighty.....I'm working on a Excelleron/Typhoon/Epsilon close to 2 meters want to be pattern plane. I'm ready to cut the cores for it and have a question about wing tips.
The wing tips on the Epsilon are very simple and light....one 40 degrees cut and an 1/8" cap.(pics).
I'd like to know if this kind of tip has bad habbits or should I stay with the traditional shape?

Is there a formula for the spacing of the wing and hor. stab? How do you know where on a 78"ish plane to put the CG. or hole for wing tube?

Doc -the slashed tip is a very old design trick -and properly used - works great.
It simply acts as dihedral
Most new pattern designs are very similar to stuff done over last 15 years - the large cowls don't really add anything- in the way of drag -tho they can screw up prop flow.
The best part is the increased torsional rigidity at front of the model
For those still using the shaker engines - this is a worthwhile - for an electric motor - not of any benefit.
However, the deep fuselages with increased forward lateral area, are good for the sequences and the lighter and stiffer the airframe , the better.
rudder hinge line sweep - a little does not hurt -
thrust line - matter of choice as the maneuvers stand - a bit above true wing C/L - good enough.
All of these, added together - tend to reduce stability - NOT making the plane unstable but making it more neutral.
The reduction in weight and improved thrust is critical
This allows the model to operate at lower angles of attack for any maneuvers.
Said differently, more constant AOA and speed - produces less difference in trim drag --which produces a plane that stays in the line desired. Up/Down etc..
And yes, we have tried all this for our own amazement .
Finally - nothing beats lots of proper practice time as the largest influence in flying pattern.

Dick - when are you going to write a book, or should I say treatise, on this subject. You've written loads on this subject over the years; including columns in at least 2 magazines (that I can think of) and numerous articles which have appeared in the K-Factor. Put it all together - we will buy it!!
I think Dick has more emperical expertise in the area of model aerodynamics than anybody out there. He's never been afraid to experiment and has taken the time to test lots of variations on theme. Just my opinion...
-Will B.

My two cent...a picture is worth more than thousand of words....

Great stuff so far.

Tph1, wing tube location is hit and miss. Honestly you can get in the ball park, but what type of engine you use, the shape of your wing, where you mount your servos, the construction of your tail, all of these things and a thousand more go into it. Then you have to fly the plane and see where it flies the best as far as balance. So on a totally brand new design, I'd say use a similarly configured model as your reference and then go from there.

Remember that moment=weight x distance, so one ounce in the tail will be equivalent to about 3 in the nose, as it affects balance. The balance position of a wing is somewhere between 25% and 33% of the total length of the plane, again using a number of factors that can push it a couple of inches either way. ALSO keep in mind that the further your stab from your cg, the more longitudinal stability you get with a given stab surface area, and the harder it is to snap.

These are VERY general statements, and meant only as a possible place to start and tweak from there.

As for why we constantly "need" new planes, I'm in total agreement. There's not a thing wrong with the one I'm flying now, but I want a new toy, and hope it flies even better. I know some properties I'd like to achieve so I designed them in, and we'll see if it works. Plus I just like doing things different to prove it can be done. In my case, it's a good dose of new style retro construction.

I also noticed Naruke's new 2 meter plane has anhedral stabs like the old Curares/Tipos. I'd love to hear from Dick about that subject, it was all teh rage for a while then *poof*...now Naruke is doing it again. What's the real scoop?

-Mike

Also I'd like to add how much I've learned from long conversations with Matt K lately. Yes there are some numbers and formulas to use, hopefully he'll chime in on a few things.

-M

If anyone has access to Lockheed or Northrop/Grumman software I have access to a super computer (really).

In all seriousness, personal experience and "feel" are very important. Clarence (Kelly) Johnson, could tell you from "feel" whether a design parameter was correct - from an airfoil to an engine intake duct.

Not trying to be a smart a*&. Just trying to encourage all types of input and discussion.

Best regards and good flying,
mike
New Patterniac

I agree Mike, after a while, you can just sort of look at it and at least get a gut feeling. It's developing that sort of feel that's key for people new at this, and they (we) all need a starting point, and then the guts to actually DO IT. The rest comes from the tweaking.

-M

Hi Mike,
Good idea with this thread! I had been thinking about asking about this very topic. How about some of your experience with the evolution of your Tempest? I'd like to know what flight charachteristics in the Typhoon you were unhappy with and the modifications you made to the design to improve them. What were the results of the modifications? This would give us a peek at real world design changes and effects, rather than theory.
Thanks,
Steve

Allrighty Steve, I'll give this a shot.

The T2k was a good plane in it's prime. QQ flew it to 6th at the worlds in 99, before he became "the man". So, it was definitely a competetive plane in the top levels of FAI when it was designed. QQ is also an awesome pilot, we can't discount that.

However, as the sequences evolved, so did the designs. I don't fly FAI so I can't tell you all of the specifics, but a larger plane with a smaller wing was needed. Well, it flew the newer sequences easier, so that's the way things have gone.

The T2K had an enormous amount of wing and stab area, and was a full 2 meters square. It had a major pitch to the belly, but it flew the new sequences better than say, a prophecy. What it didn't do well was snaps and spin breaks. With that much wing, you really had to wind it up in a snap, and that means you have to work 10 times as hard to stop it on point. It always seemed to be pointed in the wrong direction after a snap, the yaw was ridiculous to get it to snap well. With that much mass away from the CG at the wingtips, it made it hard to stop on track. In short, it was hard to get it going, then hard to stop it.

Also with that much wing area, spins breaks were difficult without a large amount of positive wing incidence. It just wanted to harrier in place. If you jacked up the incidence to make it break better, then it's pitch coupling and down lines became erratic. Also there are now inverted spins in FAI, and positive incidence makes this even more difficult to get a good break. getting a good break is hard enough without fighting the plane.

That is what I identified as fixable with the same fuse. The other problem is it needs more side area with the knife edge and point heavy schedules both in FAI and masters now. That is something I couldn't fix with the Tempest, and why I moved on, but let's stay with the Tempest.

First I moved the wing up to get it closer to the thrust line. This made it roll a little more axially and require less aileron diff. next I changed the wing to a 74" wingspan, and moved teh center of pressure more to the center of the plane away from the tips. This makes the plane snap like no other I have flown. It's effortless. Also I gave it more sweep, which translates to more dihedral and better stability inverted. I also swept the tips forward some. The down side is that for it to behave as I want, it has to be flown a tad tail heavy. Otherwise it does try to pitch to the canopy in down lines. Everything else is groovy, and I could play with thrust and mix and go that route. It may be a better approach, I think. But it snaps so well and tracks fine, I mean I 10d and avalanche at my first contest with a grand total of 9 days practice on the advance sequence, it's just that easy.

Also I reshaped the tail and gave it a bit of sub fin, and movedt he stab up to try and neutralize some of that pitching effect. It did just that, but as I made the plane more tail heavy, the pitching became noticable again, so I mixed it out with about 4%. To me that's acceptable. Over 10 isn't, and 30 CERTAINLY isn't.

I also gave it more area for the elevators and ailerons to make it more responsive. In order to keep the plane tracking right, it requires super high end servos to nail centers. This is not a problem for me, I use them anyway. And I love the response I get from the plane if I want to play, so I left it that way.

Anyway that's how I got to the Tempest. I had tried a standard T2K with clipped wings, and I liekd it so that's what made me go this route. Today though, because of many things and availability of parts being primary, I decided to break and do something totally new.

I hope that doesn't sound TOO nuts, that's what I was thinking at the time. It seems to have worked well, but if I am in error I HOPE somebody will correct me, that's what this thread is for.

-Mike

This is my dream's thread....

Thx for take your time, sure I'll learn more every time...

Mike, the way you got to the Tempest is amazing; I was always concern about wing and stab up or down move and effect on plane....

Doc, a friend tell me that wing tip is like trainer tip; it make the plane stable, as Dick say, make dihedral job

tph1, I was trying to get a formula to CG placement too without find nothing about; I guess it's a very personal parameter for every plane and designers have to play with it to match the plane they want, all around the engine; I'm newbie to design, just trying to learn, and maybe I'm making all wrong, but with Extra I'm building, must move CG rearback about 2" for balance, from wood prototype CG placement; I think it will loss longitudinal stability like Mike say and will be very "wild" tail for me (better than unflayable), but since it's a project, I take the risk and see what happend; I'll post the results.

I have Typhoon 2000 and Patriot 3D plans, and CG are in diferent place; distance between wing and stab are diferent too, not to talk about aifoil, engine-wing spacing, double tapered wing vs a straight trailing edge, etc.... too much numbers to work for me at this moment

Mike, I think this was discussed on the nsrca list a few months ago, but my experience confirms that making the stab smaller makes it more sensitive/effective near neutral.

Adam, do you think so?

It could be 100% correct, I don't know yet, trying to learn. In my theory, if you take a stab of the same size and move it away from the CG, it will make the plane more stable. However if you decrease the area and make the elevator area more sensative, you will get more response while retaining the stability. Whatcha think? Sounds like a winner to me. It sounds like you would effectively increase the stability while simultaneously increasing the manueverability, IF you got the numbers right on your areas and moments. In theory that is.

See, that's why I LOVE this stuff, nobody knows for 100% sure yet, it's all a new frontier, and we're all watching/learning/listening......always.....

Ok here's one for ya. We have a plane, and it's nice and stable in level flight. It has anhedral stabs and we're about to pull into our first high G vertical. We have a crosswind. We start back on the elevator stick, but something happens. What is it? We begin to enter a stall turn and slow the plane. All of a sudden the plane begins to act strangely, porpoising with the wind when we slow to speed. What do we do?

This is a good and relative question because it is based off of true performance, I would love to know the input of better pilots than myself.

Anyways, I love this stuff. Keep it all coming all of you, especially you FAI guys (like you ADAM!!!!) cuz I want to ask you all some pointed questions soon, thanks a billion for even spending time with us!!

-Mike'

I wish Nat Penton would post in here....the "Voodoo Guru" allowed me to fly his plane (image 1) after the LARKS meet last Fall. It is the most neutral thing I have ever flown...period. He is a true aerodynamics thinker and tinkers constantly with new theories. His use of an anhedral stab is partly to keep at least some area of the stab in clean (or cleaner) air in all angles of attack. This design also includes flow straighteners that reduce the effects of torque, etc. This plane has zero engine thrust...not sure of other incidence numbers on stab and wings...they are probably at or near zero. Oh yeah, he is also a master at building light...70" (approx.) wingspan, 78.5" length, 8.5 lbs., OS91fx. The voodoo express is strangely stable in all axes.

I hope to build one of my own sometime this year...see 2nd image.

Some people are all about parasitic drag????...I thought, what if we were to mate this with nature's aerodynamic model of the raindrop? See 3rd image.



Where are you Mr. Penton?

This is a great forum.

-Mark

Okay. But let's not forget that aesthetic appeal is also a design criteria.

so what your sayin' is.....

It looks more like a cruise missle than an airplane?

I've seen it fly though, very cool. Just odd looking.

-Mike

This is a little bit off topic and is more a root cause thought than a definitive design idea. IMHO, the single most important thing that impacts the pattern aircraft designs is the maneuvers that they must perform and the space allowed for them. Looking at the post above you all may be headed for some real goofy looking aircraft if pattern continues on the same path it is on now. No pun intended, but is it possible that the pattern fraternity has somewhat “boxed” themselves into the current designs? Would it be helpful if the pattern rules were influenced so you could have more creative designs, e.g. more space (dump the box), larger more graceful maneuvers and faster more beautiful looking aircraft? I’ve always felt that high performance R/C aircraft should (and some still do) perform more like full scale jets than an Extra or a Yak, etc. If you go to a full scale air show and watch the spectators the most boring thing for them is to see the Extras and Yaks doing their little tight in patterns with smoke. I’ve seen people fall asleep! Just some out of the “box” thinking! Change is good and always brings out the best creativity.

Great stuff Mike, thanks for taking the time. I have a couple questions about your Tempest mods:

Moving center of pressure inboard....this is done by increasing the chord at the root and/or decreasing at the tips?
Swept the tips forward.......Why? This moves the COP forward?
Increased sweep for more dihedral and inverted stability..... Not sure I understand. Are you talking about swept back as in jet fighters? Seems opposite of swept tips forward. Or does this mean greater difference between root and tip chord?
Why don't all pattern planes have the wing located on the center line/thrust line for axial rolls?

OK, thats more than a couple of questions! I want to make sure I understand so I can compile this info into my "Little Book of Truths"

Umm, just one more teeny question. Do the majority of pattern planes use airfoils from the same family? ie. NACA 0012, 0013, 0014, etc? Or are there as many different airfoils as there are airplanes? How about changing airfoils from root to tip?

Oops, thats even more questions!
Sorry, I'm starving for knowledge!

Thanks for the info and help.
Steve

8178,

there are a couple of things a play here. first, you would not want to fly so far out and wide (big box) that the judges cannot see your manuvers and judge them correctly. second, is the design of the sequences. with sequences that are complex and have many manuvers within a figure the desire is to give yourself plenty of time between manuvers so that you are not rushing into the next one and present them with a nice even pace. make sense? sorry to jump in on this one, but why do some people associate pattern airplanes with speed?

what I am interested in with this thread is learning what combination of design alows for the slow downline, draggy flight. I have heard many comments the fuse design has nothing to do with it (or very little) but what does? is it wing design, wing loading, wide fuse, wide flying surfaces (tail surfaces), 3 or 4 blade props? or just what is the combination of all of these that work? then I guess that if it is too draggy or light then it won't snap properly? interesting reading and its been fun following so far.

Hubb