What plan is this? ~58" span
 

A friend passed away a couple years ago and I have a partially finished plane of his which I am thinking would make a nice winter project to finish up. I dumb thumbed my Sig Kougar a couple years back and I think this plane might be a nice replacement. The wing is tapered on the leading edge and about 58" in span. as you can see from the fuse picture it looks as though the glass cowl has been cut to take a piped motor of some sort. I would probably not got that route but until I know what it is I'm going to be hard pressed to know what he CG is and what the preferred power range would be. The mount looks like it would take a 45 motor or small case 60. The plan is set up for fixed tricycle gear.

Thankshttp://www.rcuniverse.com/forum/atta...mentid=2054588

Chris,

that is a Dirty Birdy 40 and the correct engine for it would be a side exhaust 45-46.

The cowl looks like it is simply cut for an upright engine installation (hard to tell from the sole angle). DB40's were not designed to use a pipe over the fuse top. Instead, a proper canopy should be fitted and it can be obtained from Keith at Park Flyer Plastics. If you want to pipe the engine which is certainly appropriate, you should use a pipe on the side of the fuse.

You make reference to a "plan" but I assume you are talking about the model. If you have the actual build/design plans, it will tell you all you need to know. I'll look up the CG distance and post it later.

I hope this helps.

David

Definitely a Dirty Birdy as Doxilia said. I've never seen one with a glass (plastic?) cowl but I've only had the .60 size DBs. Well, I did have the 1/2A Baby Birdie too but that doesn't count I've got a DB in the next room on charge to fly tomorrow even as I type this.

Dirty Birdies are fantastic airplanes! Do be sure to add the canopy, and a nice long one. I've seen many flown without the canopy but the reduced side area will severely affect rolls and knife edge performance.

One of my all time favorites!

Dave

Guys thanks for the replies. I don't have the plan. What I think I will do then is pull the engine mount and rotate it 90 degrees so the head comes out the right side. I will fill the cowl with foam and then glass over the hole to fill the hole in the top.

I do have two long canopies. I think this thing should be a great flier. Do you think its worth putting a servo in each wing for the ailerons?

Any idea of what the control throws and CG should be on this?

Thanks for the help!

Engine mounted upright is standard on a Dirty Birdy. Any standard sport engine with side exhaust and stock muffler should be fine. A modern .46 will make this thing scream.

One aileron servo vs. two is pretty much a personal choice. I find the little extra weight is worth the bonus of not having to mess with torque rods, worth the extra stiffness and worth being able to use your computer radio to get throws to match exactly. But I rarely fly smaller than .60, mostly .90 or larger. The larger planes tolerate the weight of an extra servo much better. On my .40 size planes, I usually use a single aileron servo. With careful setup it works every bit as well as dual servos and saves you a little weight at the cost of having to install and adjust torque rods.

Do you have the wing? If it's already built, I'd definitely use it as it's built.

Like I say, it's builder's choice on that one. But to quote a great builder "Lightness is next to verticalness."

Either way, you'll love the Dirty Birdy.

Dave

Chris,

I agree with Dave. I'd keep the cowl as is and install an upright 46 side exhaust engine with a pipe down the side. If you side mount the engine, you will have to run the pipe under the wing which is also doable but just requires that little more time to setup and break down as you have to remove the pipe each time you mount or unmount the wing. Most DB's were built with either upright SE engines with pipe down the right side of the fuse or RE engines side mounted again with the pipe down the side.

I'd also suggest you fit the engine so the cowl and spinner ring match after which you can permanently install the cowl and blend it into the fuse. You will have to paint the cowl but with a blended cowl/fuse joint, you might as well glass and paint the fuse, fin and rudder as well. I would cover the wing (especially if it's framed up rather than sheeted foam) and stab to keep it light.

As for the canopy, in order to keep it authentic, I do suggest you use the appropriate DB canopy. It can be had (thanks to the generous help of fellow modellers who provided the originals for reproduction by Keith) for $7 from PFP here:

http://parkflyerplastics.com/cart/in...roducts_id=608

I also do strongly recommend putting one servo per aileron in the wing panels. There is no weight penalty these days as you only need to use mini (note, not micros) servos for the ailerons. A good fit is a Spektrum A5030 or a Tactic TSX25 - both great little digital servos. Besides, the shallow fuse makes using a single center mounted servo a little inconvenient as you have to manage the torque rod connections and make sure they don't interfere with the tail servos and rods. Twin aileron servos nowadays is simply a no brainer.

I'll check the CG tomorrow (~5" from the LE at the fuse side) but you'll be surprised how far back it is. All DB's and UFO's have CG's far back due to the strongly tapered LE and straight TE. Throws are small about 1/2" up and down on elevator and 3/8" up and down on ailerons. Full rudder deflection either side. Clearly setup up dual rates as well.

Dave,

the standard BHE DB40 and DB20 (Tweedy Bird) kits came with glass cowls. Only the 60 was designed around a built in wood cowl.

David

Thanks for all the great info. Glassing the fuse etc is a piece of cake. I just need to figure out the strut lengths and I think I'm good to go. More research last night seems to indicate the CG is about 5.5 to 5.75 inches back. I do have canopies.

Thanks again.

Chris,

I just measured the CG location off my plans and it is located 5.80" from the LE of the 11-3/4" chord at the fuse side. A better reference might actually be from the TE of the wing since it is straight. This distance is 5.95" (5.80" + 5.95" = 11.75").

David

Hi Chris,

thanks for your PM. I thought I'd reply here for continuity of the thread and for future reference including others who might be building this classic.

I set mine up to clear an 11" prop allowing an inch (1") of clearance. For this the distance of the main gear wing bottom to ground is of 4.62". With retracts, the gear is setup so the nose gear spans the full length of the tank/retract bay with a 5.2" retract radius using a Robart 602 mechanical gear. The actual radius depends a bit on the depth at which the gear base is mounted but the distance from the bottom of the fuse to the ground on the nose is 4.57". Note that the base of the fuse at the nose is a little higher than the base of the wing at the main gear position - hence the difference in height between the 4.62" mains and the 4.57" nose. If you only plan to turn 10" props, then you can make the gear a tad shallower or use these measurements and gain 1/2" of ground clearance - not a bad idea.

This puts the DB proud on its legs so you should aim to use 5/32" struts whether fixed or retracts. Naturally, the bird looks that much cooler with retracts and is the right thing to do on a classic such as this one. With retracts you'll also need to use smallish wheels so that the nose retracts completely. I set mine up with 2" mains and 1-3/4" nose. If you use fixed gear, you could increase these by 1/4" each and reduce the strut length correspondingly.

Incidentally, wing airfoil is NACA 16% thickness.

I look forward to seeing your progress!

Cheers, David

David,

Once again thank you for the information. I imagine I will do some work on the DB over the weekend. She is currently built as a fixed gear plane so no retracts.