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DreamBird...

Posted By:
Martt Clupper
Homebuilder or Craftsman
59
Posts
20
#1 Posted: 2/2/2010 22:41:53

I've been drawing airplanes since I was about 12 years old (that was a long time ago!), and I'm still doing it even tho none of them have ever been built.

My newest I call DreamBird:


DreamBird-2.jpg 

Click the pic to see it bigger and read a little about it.  I'd love to hear your comments on it : )

Thanx.

Martt
AirPigz

 

 

 



AirPigz
Martt Clupper
Homebuilder or Craftsman
59
Posts
20
#2 Posted: 2/5/2010 21:50:35

I was really hoping for a some feedback on my little DreamBird... what do ya think?  Hot or Not?

Martt
AirPigz



AirPigz
Roy Etter
2
Posts
0
#3 Posted: 2/6/2010 10:20:50

I like it- very nice aesthetics.   I think the round engine is a good choice, too.

But I'm not sure that the physics are going to work out.  Mostly because you're going to have the weight of the engine and pilot/passenger forward of the wing...  now you could balance that with baggage behind them, but you're not always going to have baggage, right?  You might also wind up having to make the tail bigger so that you have enouh control authority.

Overall, very cool - but it would be a larger than average engineering challenge with the wing layout and getting a reasonable cg envelope worked out.  I'd be interested in how the x-plane model works out.



Ron Wanttaja
246
Posts
98
#4 Posted: 2/6/2010 11:02:38

A pretty design (I like the DH tail) but a couple of things occur to me when I look at it.

I'm not sure that nose will fit a Rotec radial in the area you have shown.  Hard to tell for sure without a scale, but the diameter looks marginal for a Rotec.  Remember, it's not just the diameter of the engine, there has to be a bit of space around it as well.

Second, the engine appears to me mounted too close to the cabin to fit the accessory case.  A radial engine is not just the "ring" of cylinders; there is a bunch of necessary hardware (magnetos, starter, generator oil tank, etc.) that mounts behind it.  Here's a picture I took of the smaller Rotec on a two-seat Fly Baby:

 
rad_mount.jpg

You can see most of the stuff I mention behind the nominal bulkhead in the center of the picture.  The silver tank with the yellow cap is the oil tank...it's gotta be pretty much where the picture shows, which would put it right about in the middle of your instrument panel.

You could encapsulate the accessory area in the cabin area, but implementing the firewall would be a bit more difficult, and getting at the items for service would be a real pain.  Plus, of course, it's taking legroom away from the cockpit.

The other way to fix it would be to move the engine even more forward...which would make a dicey CG situation even worse..

Another thing that doesn't look right is the cabin door position...the hinge line is just barely forward of the pilot's torso.  This will make getting out very difficult...the pilot will have to twist in the seat to slide his knees between the seat and the cabin sidewall far enough to get them to the opening.  Get in a 172 and move the seat forward until the door hinge is right at your belt buckle, then try to get out.  Couple that with a slanting taildragger stance that puts the cabin floor ~30 inches from the ground, and ingress and egress will be difficult.  About the only solution would be to make the fuselage wide enough that there's enough room for folks to exit by slipping aft between the front seats...in which case, you might as well move the whole door a foot or so further aft and get it away from the pilot entirely.  Take a look at a Gull-Wing Stinson, for example.  The advantage of this approach is that you can install engine controls on the cockpit sidewalls.

Big windows and thin door frames look great, but they don't leave room for the structure necessary to support that cantilever wing.  It's going to probably take more than just a hoop of 3/4" tubing.  Your "A" pillar (to steal a term from the automotive world) is exactly in the right place, but it'll have to be a bit thicker to hide the structure inside.  You could put some of the structure across the front of the cabin (like the tubing in a Cub or Stinson) but I really think that uglifies the plane from inside.  The carry-through structure inside the wing will be right near the center of your door, but probably wouldn't make ingress/egress any worse.  A strutted wing would help, but it'd be in the way of the door.

Have you looked at what the wing structure would have to be, to support those angled ailerons near the wingtips?  Looks to me that the outboard attach point would actually be forward of the nominal front-spar position.  This would probably mean you need to move the ailerons a bit inboard.  I'm a bit concerned about losing aileron control early in the stall process due to the thin chord of the wing, but a good bit of washout would probably take care of that.



Ron Wanttaja
Martt Clupper
Homebuilder or Craftsman
59
Posts
20
#5 Posted: 2/6/2010 13:46:46

Thanx Roy and Ron for some input, I appreciate it.  It also gives me the chance address your comments and show that I've actually thought a lot of these concerns thru already, tho I admit I like to think outside the box, and sometimes that works and sometimes it doesn't!

I've done several things to help with the challenge of moving the pilot and passenger forward enuf to get their line of sight forward of the leading edge of the wing.  The cabin is a little taller than 'normal' which allows them to sit in a slightly more upright position, effectively moving their cg slightly aft.  Keep in mind that my thoughts are to accumulate several cg shifting ideas here, so while the change in seating position won't make much difference, it certainly will help.

Also, the cabin area extends a little farther aft than would typically be found in a 2 place airplane, which helps in 2 ways.  It positions the baggage area a little more aft, and it makes room for the seats have more fore and aft travel than is typical, specifically to allow for acceptable entry/exit.  The door is mounted where it is to allow for a windshield to reach as far back as it does without having the 'A' pillar in the way.  That pillar often times winds up being seriously in the way of good visibility.  If the door was moved forward, the pillar would be right in line with the eyes.  So, move the door aft, stretch the windshield farther aft, and then use the sliding seats to make entry/exit work just fine.

The battery would be mounted in the tail, possibly waaayyy back in the tail to help with the cg.  Additionally, I've thought of a fuselage mounted fuel tank (none in the wings) that is mounted at an angle (with the last 5 gallons being positioned farthest aft.  That approx 30 pounds would almost always be in place to help with the cg.

I could be wrong, but these items all added up could make a pretty big difference in offsetting the change in the cg from having the people moved forward.  I've also made the horizontal tail a little larger to help in making sure that there's enuf flare power available when it's needed, and to allow for enuf down force in the situations when the variable weights aren't there (like that last 5 gallons or no baggage).

The wing has the forward sweeping trailing edge to effectively move the center of pressure slightly forward, again to help offset the people being farther forward. (I think I'm making sense here, but I'm really just a seat of the pants designer, feel free to tell me if I'm not making sense).

I've also envisioned the wing as having 3 spars.  If you notice, the position of the pillars around the windows lines up with 3 spar locations.  The 3 spars run out as far as the inboard end of the ailerons.  It then transitions to 2 spars.  The #1 and #3 spars extend all the way to the tip, with #3 being right along the hinge line for the ailerons. Seems to make for a simple and strong structure for the wing overall.

So hopefully you can see that the airplane looks the way it does specifically to address the primary goal of having the people's eyes forward of the wing leading edge.  I think that not only is that goal met, at least in general concept, but the overall look is fantastic!

Also, I drew the cowling to scale around the Rotec R3600 engine.  It may look a little small but I think that comes from the fact that the airframe is just a bit larger overall than would be typical.  The one area that would require some serious research is, as Ron pointed out, getting all of the associated components from the engine installation to fit in the compressed area of the front end.

But then, solving problems that at first glance seem impossible is part of the fun!

I look forward to more comments and input : )

Martt
AirPigz



AirPigz