I just finished making some modifications to my birds. Both received a new canopy and chin design in attempt to increase side and frontal area. It'll be interesting to see what difference the changes make
Next will come new wings and stabs to complete the make over.

Todd Schmidt

Looking good, Todd! Additional canopy area should really help slower rolling stability, and slower knife edge w/less rudder. Should decrease your workload on rudder a lot!

Hope to see those pretty soon!!

Todd,
Like the new look! Think you will be happy with the results... What are you thinking about on the wing/stabs??? Charlie Rock

Thanks Bob and Charlie,

It's always a pain redoing something thats already flying, but always room for improvement. I'm hope the larger canopy accomplishes exactly what your thoughts are Bob. Hopefully I'll be able to find out soon. I need all the help I can get to compete with you guys this year!

Charlie, the new wings will be similar to the last version. Same airfoil, but I'm increasing the span from 72" to 75". I'm also moving the tips forward a half inch. The stab is going to be replaced on the airplane pictured with the same stab thats on my newest plane. Its thicker, larger and seems to fly smoother. My goal this winter was to get both planes the same. Hopefully I haven't screwed them both up!

Hey Todd, the planes look good as usual. Its a Two Seater now? [8D]

Brian

Todd: I'm just glad you are moving up to Masters this year!

Yeah, me too.

Hey Brian,

Thats one way to look at it! Hows your new Impact coming along. I see your trying 4 stroke power this year!! If we're able to hook up in St Louis again I'll let you fly one of my planes again with the mods. I'm always looking for input and value your opinion.

ual767,

Masters? I'm staying in advanced again this year so Bob will have one less to whip up on this year. Yeah, I'm moving up so I can be a "Pasto Student". I'm sure Bobs going to teach me how to be happy at the bottom this year!! I think I've heard him say several times he likes "Fresh Meat".

I'll feed him!

Todd

Yah, RIGHT, Todd... as well as you're flying Advanced last year, and as miserable as THIS new Masters' is, there ain't gonna be "fresh meat"....'cept maybe those big dogs as they consume all of us "no flyin' SOBs" (me, mainly!)[]

But no matter the class, the Defiant has proven it's abilities BEFORE you improved it...

The Impact is done and flying, just working the bugs out. Yep, I cracked open the wallet this year for the YS 1.60. Its been a good running engine so far. Pickup my truckload of fuel next month.

I look forward to flying your plane again, enjoyed it last year, I might try and get to KCRC this year too.

Brian

Hey Brian what Prop are you running on the 1.60? What's up Todd?

17x12, turning 8150.

If you don't try at least, you will never know. Glad to see that you are looking at altrenate routes to achieve a goal. There's no question about having greater rudder effectiveness by increasing the lateral area at around the CG. If you don't go overboard on the size increase of the stab and wing, it should actually assist other maneuvers also (snaps and spins).

MattK

Todd, aren't you afraid making the wings bigger you might change for the worst the snapping ability? It seemed to snap fine and go into spins fine for you..just curious on why bigger for wing/stab setup...Charlie

Charlie,

The wing I flew last year on DEF2 (72") was quite a bit smaller than DEF1 (77") but did'nt snap as well IMO. However the wing on DEF1 would not drop into a spin as good as the smaller wing. The wing on DEF1 had the extreme swept tips which might have helped its snapping,

The new wing will be in between these two. Total wing area will be around 980sq in" The stab on DEF2 is the one I'm staying with, its still not real big and seems to be quite a bit smoother than the small stab on DEF1


Todd

Todd - you are correct about that airplane not snapping or spinning well....[sm=lol.gif]
Was that *THE PLANE* ????

Bobby, I remember the first pattern plane I had built, many years ago. It came after a series of other planes I was building for some gents, to make spending money in high school.

I took it down to the local field where this one ominous looking dude who talked ALL the time came over and demanded that the plane undergo the extreme scrutiny of the "Safty Officer". And the first test flight had to be done by the guy's son, who wore the title "Chief Test Pilot" on his cap. You can guess the rest. The son duly crashed my pride and joy and then blamed the plane and its construction.

Talking about adding insult to injury, that certainly left an impression. Story fits

MattK

Hey Todd,
Bob is already trying to get you ready to compete in Masters. Fresh Meat!!

Joe

Joe, stab size is really important.... as is being able to SEE THE AIRPLANE.....
C'mon up.... Masters' sucks so bad this cycle that I'll be the fresh meat, boys.

And I don't have a big stab....

Hey Joe

I think you should come up to masters tooooo! That way we both can have a laugh and Bob will have a full belly at every contest!

Bob, what do you think is important in stab size in relationship to the wing as far as thickness, span, and total area?

Todd

Todd, I wish I knew more about stab design... the only thing I know is Mike Harrison once was coaching me and pointed out that stab size had a tremendous effect on spin entry and slow speed stability...I never did get to follow up with him much.

It seems that more successful 'current' designs have a lower aspect ratio; not really a lot of span, but plenty of squares near the root. The three birds in my house right now appear to have same percentage thickness as the wings, and the same planform....and I have no idea why, unless it's to "make it look about right"

Stab size is important in terms of pitch stability. Depends entirely on the kind of flying one needs the model to do. For older pattern where a model essentially drew straight lines and curves with large radii, a larger stab produced smoother, more graceful flying. That is, larger stab as a percentage of wing area.

Present day patterns require much greater acrobatic ability from a design, with ability in both smooth lines as well as snaps and spins, in various attitudes. Smaller stabs will reduce the pitch stability of a model and allow it to perform far more aerobatically than the earlier designs could.

Stab thickness matters little as long as it is within reasonable window. Too thin and structure becomes unstable. Too thick for the chord involved, and desired crisp response maybe compromised.

Tail Volume Coefficient is a parameter that should be understood by anyone designing. In my experiments, TVC's within a certain window produce snappier, crisper maneuverability, yet straight lines and smooth curves are easily flown as well.

Fin/rudder size affects yaw stability just as a stab affects pitch. However, unlike the horizontal surfaces (stab vs wing), the vertical stab only has the fuse to stabilze plus the vertical component of the wing area(due to dihedral.) Older designs tended to have wings placed lower in the fuse which meant more dihedral and hence a greater vertical area component. We could get away with a pencil thin fuse and still have decent yaw effect because of the wing dihedral.

As wings were raised, they had to get flatter for reduced roll coupling. That tended to reduce rudder effectiveness, since the effective fuse lateral area was reduced. These models were extremely stable in yaw and had trouble performing crisp snaps and spins. Fuses required a deeper section around the cg to get improved rudder effectiveness again. That's where we are today.

It isn't that compex but I have oversimplified it.

MattK

Hey Matt,
Excellent post... It makes a lot of sense.
Todd, I've been playing around with the Masters schedule some and it's really a fun schedule. I wouldn't mind trying it. It would sure be nice if you could try it at a contest and if you felt you were in over your head, you could drop back a class.

Joe

Matt,


Your input is very interesting and greatly appreciated. One of my first "real" pattern planes was a SL1 that I flew for several years. This plane had a very large stab at 36" and was placed pretty high in the fuselage. It was one of the worst snapping/spinning planes I ever flew.

I do have trimming question for you or anyone else that can help.

The wing on the Defiants sets on the thrust line which I know is uncommon in todays designs. The wing has no dihedral and the stab sets 1/2" above the thrust line. What I like about this arrangement is how axial the plane rolls. It does have a slight pitch to the belly on rudder input, but from what I read most planes do. In advanced, I was able to get away with flying it this way, but this is something I'm going to have to correct before flying the new Masters pattern. What do you feel is the best way to correct this problem? Currently my wings are set at -0- incidence and the stabs .5 to .75 negative (leading edge down). Do I need to zero the stab and try a little positive in the wings?

Todd

Todd, if you have wing adjustability, increase wing incidence before you do any thing else. I am talking 1 to 1 1/2 degree positive, not just a couple turns on the screws. Do one thing at a time. Most likely the plane will require a bunch of down trim. That's okay. Observe the knife and start removing some of the negative from the stab. Eventually you will most likely arrive at a stab that is also positive relative to the reference line. The model will look like it is flying with the tail a little high possibly.

If no amount of tinkering with the incidences helps enough, then add a dorsal fin about 1 1/2" wide by about 12" long (triangle actually) from the base of the vert fin, forward. That will improve the character of the knife edge and you should be able to take out about half of themix you are using now.

Observe how the downline is affected. With the wing at about 1 degree pos, and the stab at about 1 degree pos your down line should be pretty close. Check your up line. If the up line pitches to canopy, add a little down thrust about 1 degree. Most likely it will not pitch to gear, but if it does, after an extended vert line, then you may have too much down thrust. But I doubt it.

Make sure you track all your changes so you can return to where you were.

Let me know how you make out

MattK