I have been flying pattern planes for a few years now and am wanting to design my own onw, there are some questions I need answered first to help with my planning, it's going to be a 2m x 2m job with a YS140/160 up front, fixed landing gear with plug in tail andn wings.

1) can I use a straight forward symetrical aerofoil.
2) Do I need dihedral - if so how much
3) do I need wash out - if so how much
4) is there a set distance between nose to leading edge, and chord lenght, and tailplane position

I understand what all these mean I just don't know how to implement them into a pattern plane so I can have good flying qualties.

If anyone can help that would greatly appreciated

foofydoo's the dog that chews my wreckages

I have a good friend who just completed his 1st composite version of his personal design. Everything is his own design and I mean everything. The labor of love took over 2 years and it is a thing of beauty. Its the smoothest plane I have ever personally seen fly.
He had over 500 hours in hand carving the plug alone.
He went through 3 stages.
1 was a boxy design to flight test the tail moment, wing design and all the basic flight characteristics.
2 was a balsa version of the model
3. is the finished version, a composite fuselage, with foam core wings that are glassed and all of it is custom painted. The wings are so light you wouldnt believe it. If you seriously do it and do it right you will be sick of it by the time you actually make your 1st flight. But it was a joy to see the look of satisfaction on his face as the plane lifted off and flew out.

I know his wing is symmetrical and there is a tough of dihedral in it. All of the wing incidence and tail moment rationale that went into the design he has talked to me about goes WAY over my head.. GOOD LUCK!

do you have a web address so I could have a look at his plane, sounds very interesting and useful.

No I Dont, but heres a mailing address to get on the NSRCA discussion forum where he and the rest of the pros frequent. I believe his name comes up as BuddyonRC. Its kind of a pain because its not a mesage board its an email exchange, but a lot of the top pattern guys in the US frequent there and can probably answer any technical questions you might have. They are a very open and talkative group, I get about 30 new messages a day. Just email this address and ask to be added to the discussion board in the subject.

[email protected]

PS
Im going to the Houston Warmup this weekend. Keep an eye out, if I dont forget I will post some pictures including his plane.

Hey, lets define designing your own.
If we're seriously designing, we would be using our own aerofoil, our own gyometry with regards the wing and stab placement, trust and rudder line angles and a million other things... the knowlege of which only comes from many years of competitive flying.
Why bother doing this?

There are several excellent diagrams, side views and PDF format instruction available over the net of many of the lastest production designs. You can see the aerofoils, the measurement etc etc...copy them! Use your artistic talent for doing subtle changes to the shape, modifying it to you personal taste and building technique. This isn't copying, it's just being smart and doesn't infringe any copyright as long as you don't start commercial production.

This is absolutley the best starting point as there isn't any correct aerofoil shape etc...it's all personal. Take the Synergy for example.
That has a real thick aerofoil that in the hands of a certain Frenchman can perform like magic... yet everybody that I know, hates the aeroplane as is... and have produced there own wings with a far thinner foil at the tip. One, a worlds competitor has even made a new stad, again featuring a thinner section to suite his style.

A fun project thats done by many. Start looking.

Hey there FOOF

Washout? No... you want upright and inverted flying qualities as similar as possible.
Symetrical section? Yes......., see above (Airfoil selection can alter the snap roll characteristics significantly. You don't want an airfoil that requires an AOA of 25 degrees before it stalls... this will result in snap rolls totally killing any speed or heading you may have had)
Dihedral? Maybe... Use dihedral to eliminate YAW induced roll. (Adverse roll, more dihedral, proverse roll, less dihedral)
Total fuselage length? 78.74" long. Minus 3.5" for spinner. Using "NORMAL" motors and construction techniques, set location of wing on remaining fuselage to achieve UNBALASTED CG.
Tailplane position? Located so that there is no (or minimized) YAW induced pitch. (Pitches down with rudder, lower stab, pitches up... raise stab)

Other things to think about.... How much vertical area below stab/fuselage (Subfin?), Thrust angles, taper ratios, control surface sizes, Exhaust system accomodation, Cooling inlet, cooling exhaust....... a system of compromises for sure!!

I would suggest that you first at least fly several of the current popular models. This will give you an idea of what there is to improve upon. With no concept of what you are trying to make better, you will more then likely just come up with what is already out there. If you want to just make a Pattern plane that looks cool.... then buy a wing and tail set and make a new fuselage.

There is certainly alot to think about when designing a plane. I followed the idea mentioned by bla bla. By observing what works, you can be somewhat confident that the plane will behave well in it's first prototype version. It may not be perfect, but it will be a starting point.

As for me, I derive a great deal of satisfaction from drawing, cutting, building MY own airplane. However, there are many really great, inexpensive pattern kits and arfs out there.

My own designed prototype is nearly ready to fly and to this point I have enjoyed the learning process during all of the work to get to this point.

www.geocities.com/markhunt_2000/INSIGHT

Big Ned, I'll see you at the Houston meet on Sat. and I will have my INSIGHT with me...almost ready to fly...cant wait...

Excellent Flyintexan!

I will be flying a Red and Yellow Prophecy, and my Buddys will be flying a Green, Red and White Patriot and a brand spanking new custom plane called the Eagle 1. If you make the rounds Im sure you know them, they have been in the pattern business for a long time. Seeya Tomorrow

Mike
www.MidCountyRC.com

dihedral depends on where you place the wing, low down you need some, mid wing none. I would go mid wing, fairly thick fully symmetrical section, (better for 3D and constant speed aerobatics) double taper, no washout, slightly thicker section at the tips. Tailplane slightly above wing, 25% of wing area, fin and rudder 14% of wing area, I would build the nose extra long and at the last minute cut it back to balance the plane at about 33% of the root cord. 30% if you want more pattern type flying. Make sure your body has enough depth for KE. wing and body the same length.

The main thing is too keep it as light as possible.

Why the difference in dihedral in mid and low wing?

its to do with stability, a high wing behaves as if it has dihedral (even if its straight) a low wing behaves as if it has anhedral (even if its straight) a good rule of thumb for a low wing, that is tapered to the tips, is to set the top surface of the wing straight.

what does the taper have to do with dihedral and if the wing is straight across the top is that considered dihedral if the tips have a slimmer profile?
thanks for humoring my ignorance on this subject

More than just stability, it has to do with roll coupling to rudder movement. A trainer like the Kadet will bank and turn with rudder control only, no ailerons. We have a guy at a local field who likes to fly big high-wing gassers on three channels (again no ailerons). He cranks the rudder, and the plane both yaws and banks. He cranks both rudder and elevator, and the plane does a full roll (more like a barrel roll).

In a pattern plane, you want to reduce and ideally eliminate all roll coupling to rudder. A high wing, or mid-wing with a little dihedral, will have proverse roll coupling. Not desirable. A low wing with insufficient dihedral will have adverse roll coupling, which means right rudder will roll to the left. I started pattern flying a Superkraft Cap 232 Sport, which is a low wing model with the only dihedral being in the taper of the thickness of the wing from root to tip--flat from tip to tip on top, but angled slightly on the bottom. This plane had a terrible adverse roll, which I finally learned to mix out on my computer TX. I would give right rudder, and the plane would roll and dive to the left. Drove me nuts until my instructor told me what was going on.

Another design feature that acts like dihedral is sweepback on the wing leading edge, which acts as positive dihedral. You'll see a lot of pattern designs with mid-wing placement and swept back leading edge. This enables neutral roll coupling to rudder and works like positive dihedral in both upright and inverted attitudes, whereas dihedral in the spar would be positive when upright but negative when inverted.

For anyone who has made endless test flights and modifications to arrive at a legitimate, reasonably neutral pattern ship (which leaves me out), it is a bit amusing to talk about "designing a pattern plane" with little understanding of the many subtle trade-offs and inter-relationships involved. You can design a plane that suits your fancy, fly it, and be very happy with it. But if it's not dynamically neutral, or very nearly so, it doesn't really pass muster as a pattern design.

If you want to fly a plane that looks the way you want it, that's great. Good adventure, good learning exercise, lots more interesting than knocking an ARF together or building someone else's kit. But if you want to score well in competition, buy a Zen or any other proven winner. If you want to appropriate an existing design and modify it to your taste, that's OK too. Happens all the time. Find a plane that points well, copy its airfoil, moments, proportions, everything that can be measured, then customize it for your powerplant, build it light, finish it the way you want, then fly it. Great project!

Advice from folks who suggest modification based on a proven design is good. That's how we do it whenever possible. Starting with a known airframe we change one thing...evaluate...change something else...evaluate...and so on. It's possible to start from scratch but unless you're very lucky you should to be prepared to build more than one prototype. That's our experience. It requires expert knowledge to troubleshoot a scratch design not to mention a healthy dose of reality check and perseverence to admit, "This version ain't it - back to the drawing board for another try."

Lee Davis
[link=http://www.piedmontmodels.com]Piedmont Models[/link]

After reading all of your replies Ive decided to buy a new pattern plane, the Lorenz High Society. Probably going to copy the fuselage design as I think that is such a beautiful plane and just modify the wing sections and planform, thanks for all your help and advice, haven't given up on designing my own, still have many years for that.

I only design my own now when I want something that is not available, like a .25 size 3D or a big old electric, or something really light. When I see what goes into a proper design by Chip Hyde or CPLR I know I could not improve on something like the Synergy for example.

I only buy top designs and kits that are built light and strong and keep away from these tip stalling, KE coupling, badly glued, way too heavy, mass produced planes.