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Mar 14, 2021, 07:35 PM
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Big McDDD!!


I've been trying to learn 3D for the last year or so. I started with a QHOR 40, then a SPA3D and a SPA3DT. I had more success with the QHOR (Fox 40BBRC) than any of them. But I'm still not very good. I was looking for a better 3D trainer when I happened to see a Big McDDD video. It looked great, sounded great when I read Dave McDonald's instructions, and it is great!! What an improvement over the SPA3D and SPA3DT. I maidened it today, 5 flights in all. Hovered briefly on the 4th flight, caught a wingtip on the 5th flight and broke a prop (APC), but that was the extent of the damage. I was as nervous as a cat in a room full of rocking chairs the whole time. But it was a blast! My old Magnum Pro 45 with MCP seems to be a good match for the lighter Big McDDD, which came in at 4 lbs 4 oz. I think my SPA3DT weighed over 5 lbs.

Dave, I thought I read somewhere to turn the LE under 3 1/2 inches, so I ended up with a 20 1/2 inch wing chord - I guess that was wrong? And I just slipped some antenna tubing (instead of straws) onto the 2-56 control rods in the rear. Will that make them too stiff? Anyway, it's not perfect but it sure flies good. It's much more stable than the older SPADs. I broke so many props with those things I thought I'd have to quit the hobby.

Thanks, Dave!










mMM
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Mar 16, 2021, 08:28 PM
Pro Bro 415
Dave McDonald's Avatar
Congrats on the successful test flight! And really glad to hear you like the plane! The build quality in the photos looks good too!

Even after all of these years, the Big McDDD is still one of my favorite planes to fly. Just today I put three more flights on it.

I just measured the wing on my current Big McDDD and it's 19.25" wide with 4" tucked underneath. The other .75" is taken up by the height of the leading edge. If your wing is 20.5" wide, that isn't wrong, it's just different. It might even be better since yours has more wing area.

The goal of the straws over the 2/56 pushrods is to keep them stiff enough to avoid constant bending that becomes a nuisance, but still flexible enough to bend before the servo gear train strips. If the antenna tubing you used accomplishes that goal, then you are good to go. If stripping gear trains becomes a problem, then the antenna tubing is adding too much reinforcement. Different servos have different strength gear trains, so the reinforcement amount can be different. Use whatever applies to your servos.

Breaking props is just part of flying 3D with spad type planes. However the Master Airscrew 12x4 has proven to be much tougher than the APC 12x4. They still break, but not nearly as often. A Magnum 45 with a MCP should work fine with a MA 12x4.

Three suggestions:
1. Move the exhaust pressure tap from the mousse can up to the header flange. On top of the flange near the rear of the exhaust opening works best. This pressure tap location provides a more consistent pressure to the tank and improves the throttling accuracy. Just drill and tap the header flange, and screw in the pressure tap. (see photo)

2. Use bamboo skewers that run the full height of the vertical fin. One skewer on each side of each mounting screw. I use three mounting screws, so six skewers. This helps to keep the fin from folding over and permanently creasing. (see photo)

3. Screw and glue the horizontal and vertical fins to the fuselage. Goop, Shoe Goo, and Professional Welders all work great. I tend to use Plumbers Goop. This keeps the tail surfaces from shifting and changing the trim. Or worse, having a tail surface loosen or fall off during hard aerobatics. (Which actually happened today to a flying buddy on his Big McDDD because he forgot to glue the vertical fin. It ended up spinning all the way to the ground. No damage, but he's going to glue the vertical fin before the next flight.)

Please keep me posted on your progress!
Mar 17, 2021, 06:49 AM
Registered User
Thread OP

Big McDDD!


Hey Dave. I appreciate your comments and suggestions. I plan to build a second one. I have another Magnum 45 for it. They run very well with an OS 4BK carb. But I need another header. Does anyone know where I can get a header with 1.1 inch bolt spacing like the Mac's 2581 or 2582? Also have a TT Pro 46, which I think would accept a Mac's 2591 or 2592 (bolt spacing is 1.46, I believe).

Thanks.
Mar 17, 2021, 01:30 PM
Pro Bro 415
Dave McDonald's Avatar
I've been using the Macs headers with the standard offset on my Big McDDD and 3D profile planes. (2590) Every now and then they show up in the classifieds, but don't last long. You might try posting a want ad in the RC Groups Classifieds to see if anyone has one for sale.

The TT Pro 46 has the same hole spacing as the OS 46 SF, 46FX, 46AX, and even the OS 55AX. So any of the 2590 series will work. One of the guys on the probro site was building headers in this size. He still had some a month ago. Maybe he still has some to sell.
Finding a header for the Magnum 45 with the 1.1" hold spacing might be tough. If it was like the old OS 40/45 FSR the bolts pass through the header flange, then screw into threaded holes in the crankcase. But you never know what you will find by posting a classified ad.
Last edited by Dave McDonald; Mar 17, 2021 at 01:38 PM.
Mar 23, 2021, 03:49 PM
Call me Frosty
TheRealFrosty's Avatar
I was thinking of adding plans for the Big McDDD to the spadtothebone.org free plans page. My search for plans found a 2006 post on rcuniverse by you that contained a McDDD picture and this text:

Quote:
Sorry, but I never made any plans for the Big McDDD.

About the closest thing you'll find is an edited photo of the McDDD, and a text description of how to convert it into a Big McDDD.

Study the photo of the McDDD shown below, then make the following modifications to convert it to a Big McDDD.

1.) Build a SPA3D wing exactly like Tattoo's plans. 36" span, with 4" ailerons, but use half length wire spars.

2.) Use a 36" U-channel for the fuselage.

3.) Add 1" to the width of the rudder (5" total).

4.) Add 1" to the width of the elevator (5" total).

5. Increase the height of the vertical fin and rudder to 10" tall.

6.) Set the distance between the rear edge of the ailerons and the leading edge of the horizontal stabilizer to 10".

7.) Adjust the balance with an empty tank to 6.75" back, plus or minus 1/4".
Is this still correct? I could create a new image with the altered dimensions or something like that to add to the spadtothebone.org site. Or maybe there is a clean picture from the same angle of a Big McDDD that I could add dimensions to, but I have not found one yet.

-- Kris.
Mar 24, 2021, 08:21 AM
Registered User
Thread OP
Kris, FWIW, the latest info on the Big McDDD that I found is over on the Profile Brotherhood site, posted by Dave (as McDDD). I hope Dave doesn't mind my posting these links. The latest is Dec 2015: https://www.theprofilebrotherhood.co...p?f=23&t=38328. And there's another one from Dec 2013: https://www.theprofilebrotherhood.co...my+son#p751776. If you'll comb through those two threads, I think you'll have the complete picture. And I'm sure Dave will add any missing details when he looks at this.

A tip on engine mounts: the best material is PP (polypropylene), not HDPE (high density polyethylene). The older Walmart cutting boards were PP - it's the stuff that kinda melts behind the blade when you cut it with a band saw. It's translucent; you can see your hand through a 1/2 inch thick piece. It's not as brittle as HDPE and slightly lighter in weight. Screw holes too close to an edge of HDPE will crack, but not in PP. I actually tapped my mount above for 6-32 socket head screws and didn't even use nuts. They won't budge. Of course you can also use sheet metal screws. You can find 1/2 inch thick PP sheet at freckleface.com. It was about three bucks for a 6 x 12 inch piece last time I bought it. You can break one of these mounts (typically at the engine cutout) in a very hard impact. I've only broken one, and I think it was caused by sawing past the corners of the engine cutout with the band saw. Now I drill holes in the corners before sawing and end up with slightly radiused corners in the engine cutout. Of course, you should also drill pilot holes for all screws.

I hope this helps!
Mar 26, 2021, 12:53 AM
Pro Bro 415
Dave McDonald's Avatar
I’m on vacation now, but I have no problem with creating some updated plans for the Big McDDD.
Mar 29, 2021, 01:57 PM
Call me Frosty
TheRealFrosty's Avatar
That would be awesome
Jul 10, 2021, 01:19 PM
Registered User
Bump for one of the best flying spads ever!
Sep 19, 2021, 10:54 AM
Registered User
Time to build a Big McDDD I guess, nose planted my lil' McD and broke the carb on my TT 42
I have a selection of 46's, fx, tt pro and Ax 's.
Sep 19, 2021, 11:35 AM
Pro Bro 415
Dave McDonald's Avatar
The OS 46AX will be the best choice from the three options you listed. The TT Pro 46 is a close second, but just not as powerful. I've never been all that impressed with the FX version. Either way a Master Airscrew 12x4 is the best overall prop. The APC 12x4 actually performs better, but is too fragile for use in a Big McDDD.........unless you have an unlimited supply of them.
Sep 19, 2021, 12:07 PM
Registered User
Do you recommend the OS F plug on the AX 46? Or can I get by on the #8
Sep 19, 2021, 01:25 PM
Pro Bro 415
Dave McDonald's Avatar
The OS #8 works great in the 46AX. I've never seen a benefit of using an F plug in a 46AX, or any other 46.
Oct 06, 2021, 10:43 PM
Registered User
Went for an ill fated maiden. I just don't have any luck in my old age, cannot complete more then a tank of flying without issues, on any model. While starting it, snapped the servo wheel holding the rear part of landing gear. Thus the zip ties. 2nd dead stick i cartwheeled and twisted the U channel.
However it flew better then the small mcddd.
Screwed up and made 4" rons' rather then 5.
Back to the drawing board as they say
Oct 07, 2021, 12:33 AM
Pro Bro 415
Dave McDonald's Avatar
Congrats on the maiden flight!

Several years ago I ended up changing the landing gear wire design to two individual gear legs. That way if one gear leg breaks, only one gear leg needs to be replaced. See photo for updated design. Note each gear leg has a 90 degree bend at the end that passes through the motor mount to keep the leg from twisting.

The 4" ailerons work OK, but the 5" ailerons will improve the roll control at slow speeds.

HOWEVER........instead of building another wing with 5" ailerons, I'd suggest modifying the one you have to use two separate aileron servos. That way you can increase the throws on the 4" ailerons, and also reduce the servo load compared to using a single aileron servo. Later on if you build a wing with 5" ailerons, I'd highly recommend using two separate aileron servos.


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