Ed,

Why did Joe design it that way with 2 deg down thrust and ~1 deg pos on the wing?

Dirty Birdy Build...

The following posts are to provide additional perspective about the historically relevant Joe Bridi, Dirty Birdy. The work was completed the Fall of 2006.

My kit is from the last remnants of Joe's inventory featuring the built-up wing. I sent the wing plans, root and tip ribs to the new owners (circa 2006) of WING Manufacturing, to create a set of foam wings. WING, I believe, is now in Michigan and should therefore, have the wings available?

The photos show how I prefer to mount retracts (conventional) using a light plywood box which is glued into the wing prior to sheeting. The design provides for using the top sheeting, bottom sheeting and the foam to provide a significant amount of strength with weight LESS than a conventional 1/4" plywood plate and dowels. It is very important that the "box" fit very snugly for the most strength and least amount of glue. I add a 3" square piece of 3/4 ounce glass closth on the top and bottom of the box, between the sheeting prior to the sheeting process.

The cut-outs are made using 1/8" light ply templates and Sam Turner's KISS System...good luck finding this must have little gadget. The retracts are EZ- Supra for .60 size models from Central Hobbies. The 5/32 piano wire struts will be replaced with titanium versions also from Central Hobbies...much lighter.

Scheduled work shop time October 2008 - November 2008.

Rusty Dose
Team Futaba
Team YS Parts and Service

Dirty Birdy build...

This post is to provide an additonal perspective on building the Dirty Birdy. The techniques have been stolen, copied or adopted by me from many of you and in no way do I take credit for their origination.

Just as an earlier post described, my rear fuselage former was too short so I added a filler piece. The hole was cut with forstner bit.

The elevator pushrod is mounted to the rear, the rudder servo is elevated with 1/4" light plywood and will use cable for actuation. The elevator pushrod uses an MK item which puts the elevator pushrods on the outside of the fuse with very short rods driven by an arrow shaft. It is very tight, remains tight over time, requires no maintenance. Some builders have changed the drive pushrod to cables by fabricating a new horn.

The model will be powered by an OS .61 to meet the SPA rules by keeping the retracts down. The photo shows a white shim added to the left nylon engine mount for "right" thrust. The tank plumbing detail was executed prior to gluing the various top blocks in place. The Rossi .61 is shown with the Scott Anderson "Deception" canopy and the stock plastic canopy...it would be pretty cool...?

Rusty Dose
Team Futaba
Team YS Parts and Service

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My theory is that the old guys from that era were still designing models with reed flying setups. Old habits die hard. Another thing that is detrimental to model designing and thinking is flying full size planes. Many general aviation pilots can't shake their old habits when thinking of models, or designing them. That is one of the things that ruined many of Sig's earlier model offerings.

We fly models in an almost continuous circle, or stretched lines with quick turns. Full size aircraft (an older reed sets or escapement models) were designed to be stable and fly for extended lines. As a result, the models did not fly all that well. This is just me analyzing the situation and nothing more. No one has to agree in the slightest manner.

Downthrust is mostly used to defeat zooming when power is applied. This assumes that the model will climb because of an assymetrical airfoil, which is biased to provide lots of lift with increased airspeed, or a wing that has been canted with the leading edge going up (positive incidence). Again, this is a holdover from the days of yore and is totally unnecessary, in fact is detrimental to a model supposed to perform equally well whether upright or inverted.

It is also possible that downthrust was used to offset the drag of the fuselage above the wing, which will make the model move toward the canopy side of the model when in knife edge flight. Cancelling this move with downthrust is also accompanied by unintended consequences in other flight modes.

It all depends on which way you feel comfortable in compensating for idiosyncrasies that pop up after we make our "best compromise choices". If you don't mind holding a bit of down elevator in knife edge flight, then the downthrust isn't necessary. But be sure that you are going to be holding a correction some place else in another flight mode.


Ed Cregger

One of my most unforgetable memories is how precisely solid and stable Joe Bridi's Dirty Birdy seemed to fly through the pattern at Lake Charles in the mid '70s. Out of all the great flyers that I observed back then, those JB/DB flights left the longest lasting impression. He surely knew a secret or two about how to set up (and fly) an RC pattern ship. I'm gonna build my (at least the first one) Dirty Birdy to that spec.

It seems similar, to me, to the way B. Hebert advises to set up a plane with some 'triangulation' to create solid, predictable flight behavior. Works on planes on G3.5.

Terry in LP

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The beauty of modeling is that everyone can have it their way. I just love to speculate about history and their design concepts.

I don't suppose for an instant that I know a millionth as much as Joe Bridi. He is my design hero. Yet, I have improved upon his original specs "for my style of flying". I'm sure that if everyone builds their models absolutely stock they will have superb handling models.


Ed Cregger

Thanks for the photos BERUSTY. Your plane is looking good.


Ed,
I fullly understand your thinking and appreciate your post. I had already epoxied the firewall in place though so this one is going to be built stock. Like you said, it should fly great.

The attached photos show the tank top block that's been relieved a bit on the inside as per the plans. - I guess for fuel tank clearance.

I've got the rear top block glued in place.

Next will be the front top block and finishing out the nose. I'm going to save installing the rear bottom block until I get the pushrods in place.

Cutting the slots in the side of the fuse for the stab is going to take some time.

I kept thinking about side mounting the engine, and I decided to go ahead and make the modification. I removed the firewall and made a new one. In doing this I discovered that the firewall is also cut incorrectly. It's the right width, but the one supplied in the kit is cut square instead of rectagular as shown on the plans. So, now all is good. The firewall is the correct dimension and the engine will now be side mounted.

I've got the nose block beveled and installed. I need to fit a piece to the upper nose block to fill the hole that would normally be filled by the upright engine.

At this point I'm trying to decide if I should build a hatch to get to the tank or just open up former #2. I wont fit the chin block or tank floor block until the wing is done. I want to be able to access the front side of former #2 when I drill for the wing dowls.

Rusty:
That is a nice set up. I'll be doing essentially the same set-up with one additional item; and that is to honeycomb the wing and add some CF reinforcement via a balsa-CF-laminated spar on each wing section top and bottom. I can guess at removing about 0.5 ounces per panel. This may not sound like much, but it is removing weight from the outer most portion of the wing, keeping the mass of the wing closer to fuselage. This allows fore better snapping and roloing manuevers, it stops instantly.
I'll do a little build thread on hoeycobing. I too did not imnvent that system, but copies from others.
I do this on my AMA pattern planes presently.

Crashlander

Easily will hold up to an 8 pounder. If you are not comfortable with that, then save yourself some weight as follows:

Cut the steel struts leaving about 1" stub. Epoxy carbon tubing directly over the stubs. Cut the carbon tubes to length desired and also glue in a set of aluminum axles to the bottom. You will save about 3 ozs total and will make the gear actuate easier with the typical retract servo

MattK

An even better solution to the KISS is the Hot Knife. This is a simple handle with a 5" long rod that gets heated hot enough to melt foam. You only need to work from one side of the foam and really don't need templates. A 12V 1A supply is required to drive it. If I remember right, I bought it from CST.

It's nothing more than a length of nichrome wire, insulated with ceramic insulation and inserted into a 1mm stainless tube. The distal end of the tube is crimped directly onto the NiCr. The proximal end's insulation is passed through the tube without grounding out. That's the trick. The electrical connection is made between the proximal end of the NiCr and the stainless tube, to complete the circuit. Extremely simple idea and extremely functional

MattK

MattK

Matt:
Does the CF hold up to rough landing such as landing on grass.

Orlando

I wasn't aware of them. I found a quote on the website:

"As a rule of thumb, titanium has only three fifths the weight of the steel used in steel struts. So if your steel struts weigh in at 60 grams a pair (roughly 2.12 ounces), you can cut 24 grams off the gross weight of your plane by simply switching to titanium struts of the same diameter and length. Yet, while saving weight, you also add a lot of durability and strength to the landing gear."

Only catch is they're $17.95 a piece.

Tom

They also bend, and, once they are deformed, throw them awayexpensive.

Crashlander

So they're not worth it in your view?

If you fly off a grass runway that is not like a golf course, I would say no. Once they bend and you try to straightened them out (which btw yo cannot) they will always bend at the least bit shock.
Smooth runway, that is a different story.

Orlando

Pattern, even classic pattern, is about flying skills. It is not about who can spend the most money on a model.


Ed Cregger

Yes. The steel coil takes the abuse. The carbon tube that works well for this is a .160 ID x .230 OD. Various sources carry the size. A short aluminum sleeve ca'd at the carbon ends will maintain integrity. Probably not needed but I use it. I also use the ally sleeves on the carbon pushrods

MattK

Interesting Matt.
I'll have to try that on my DB.

Thanks.

Orlando

P.S.
Can you make Tangerine this year. It's going to be a good one.
All types of pattern to be flown.
SPA and BPA flying head to head.
AMA and F3A. You can fly any combinationof SPA, BPA or AMA/F3A.

Someone mentioned a 40 size DB. Anyone know where to get plans for it? I know RCM has the 60 size.

Thanks,
Jim

Uncle Willies is selling the ".40-.60" size plan. Enter this number is the serch box on the auction site. 270272449089

Although the specs for the .60 are:
Dirty Birdy 60

Wing Span: 64.25 inches
Wing Area: 688 sq inches
Engine Size: .50 - .60 (2 Cycle)
.60 - .90 (4 Cycle)
Est. Weight: 7.75 lbs
Symmetrical Airfoil


And the Uncle Willies plan specs are:

64" wing span. Power .40 to .60 size motor. Weight: 7.00 lbs to 8 lbs. Symmetrical Airfoil. Wing Area: 675 sq. in.

So is the Uncle Willies the .60? Anyone have specs on the .40?

My theory is that if you were able to go back in time and check Joe's original models, you would find that they differ from the specs shown today. Master pattern pilots seldom shared their flying secrets, and especially back then.


Ed Cregger

DB 40 Specs.

Wing Span: 58 inches
Wing Area: 565 sq inches
Lenght: 50.5 inches
Engine Size: .40
Symmetrical Airfoil


Here's a couple of photos of a DB 40 I built around 82.

Sounds like good ol' "Uncle Willie" is ripping off RCM, which still has rights to the plans. Too bad, since RCM has always kept their plans reasonably priced. Thanks for the info, but I think I'll steer clear of "Uncle Willie", whoever the heck he is.

Nice DB 40. I gather the .40 size was kit only - no published plans.

Jim