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FF2017 Int. Race Pace Plane: Beck-Mahoney Sorceress


Hostage Taker of Quads
Staff member
As many of you are aware, Wilsonman, here on the forum, has just closed the design phase of the FTFF 2017 International Air races, a competition to build scale "golden era racers" then race them in both a speed and endurance competition. If you haven't seen the build threads, do yourself a favor and go have a look :)

For the endurance competition, I've been chatting with Wilsonman offline, and we've hashed out a variant of All-up-last-down:

- Everyone takes off roughly the same time with the same sized battery pack
- Pilots fly the track at their own pace
- After the first lap is completed by the lead plane, a pace plane launches and flies the track at a reasonable pace

+ If you get "passed" by the pace plane or "land", you're "Down".

+ last competitor down, wins.

Looking over these rules and the plane I had chosen, seemed poetic justice to make it the pace plane. So I have entitled this build . . .

The March of Progress


The Beck-Mahoney Sorceress was a biplane that arrived on the scene about 4 decades late to rub shoulders with the "golden era racers", but the race heat she arrived in was becoming stagnant. Sporting some modern design concepts and a composite Aluminum skin/EPS core wing (yup, she's a foamy!) she not only performed top of her class, it's been argued the rules were changed at least twice to dull her overwhelming competitive edge. Despite the changes, she still won 3 first place in her class (crossed the finish first 5 times, but twice was bumped to last by the rules), 4 second place finishes and one third. Not a bad showing for a pretty girl like her over a 13 year career. Overall, Lee Mahoney designed a game changing airframe, and between he, Don Beck and Paul Deschamps, her advantages were clear enough to earn some coveted hangar space in the Smithsonian National Air and Space museum.

Noteworthy plane with beautiful lines.

She's also a fairly rare model, but not unique. Just this past year, Lockey over at RCG ran through the design in roughly 1/4 scale (at 16' span, she's not a big plane), and did a fine job of it. It's my understanding a cutout of the kit is available at "Hoosier Cutout Service", or you can contact Lockey directly for the plans. While this project will be a new build from the 3-views up, I can't say I won't recycle ideas from those who've gone before ;)

Otherwise, there are a few pics around from various scratchbuilds, but no other plan sets or kits I'm aware of. Rare, but not unique.

sorceress jp.jpg

So this is going to be a bit of a challenge for me. My design goals are:

- Build out a 1/6 "fun scale" Sorceress with details
- Altered to improve flight handling
- Repeatable plans for an high-intermediate/low-advanced builder primarily using common techniques
- Reasonable flight speed with capacity for a larger battery (I have no race battery limits)
- Demo-platform for some simple composite techniques
- Detachable wings for transport
- Capable of pace-setting for the Bixler Trophy contest.

Not a lot different than the standard build-off racer, with minor tweeks . . . but there are a few things this project is not:

- Designed to be easy enough that a beginner can build and/or fly
- Designed to be the fastest plane in the air
- Designed to be the most efficient plane in the air (seriously, I'm planning ahead to carry a bigger battery ;) )
- Repeatedly built to prove repeatability.

This isn't a typical FT-style design, and it's not being built to win, it's begin built to set a pace for a reasonably long period of time.

To unpack all that just a little . . . this all flows around two things I want form this plane -- build a sorceress for me to fly ( :D ) and demonstrate a simple composite molding technique.

As we get closer to it, I'll step through how to inexpensively build a molded foam/carbon spar in a one-time mold using simple materials you have on hand (ok, you have to mail-order the carbon, but most everybody has to mail order their electronics anyways :p ). For the purpose, it's probably overkill, and I'll show off some alternate techniques while I'm at it, but this is a chance to de-scary-fy composites.

I do see some significant engineering challenges coming, many of which, I have solutions, some I'm still stewing on:

- Wings: This is the core of aerodynamic design. There's a lot that TLAR can get you out of an airfoil, but if you truly want to create a high performance airframe, this shouldn't be ignored . . . In fairness, I'm not trying to make a high performance airframe, but I do want well behaved. Overall design is square-stagger-gull-with-constant-cord-symmetrical-airfoil . . . not the most stable of combos, but she is a racer. I plan on doing a bit more research before I lock in the airfoil . . .

- Spar: this is where the carbon comes in . . . but how to build it detachable? At 1/6 scale, 16' span becomes 32" , but it's a long ride to Ohio . . . More to come on that.

- Tail Feathers: Did I mention short coupled? The full-scale Sorceress routed the engine exhaust across the rudder to increase it's authority while keeping the size (and drag) down. I'll have scale exhaust ports, and might even use them to route cooling air, but I won't pretend to believe I'll get that advantage -- the tail will need to grow.

- Ailerons: located in the upper wing . . . but where to mount the servos? in the wing? route pushrods through to the fuse? still on the fence, but I might be picking up some more very thin servos.

- Battery bay: Did I mention I wanted a big one? I did? well . . . now I've got to fit one in . . . or two . . . we'll see.

- Landing gear: fixed or spring? it's own aluminum mount or tied into the wing? tail wheel? Might need to go one club over to use their plastic landing strip.

- Skin: Planning on mylar tape . . . but that's a lot of covering. If it's worth doing . . .

Well, that's enough to open the thread. Hopefully I'll get a chance to pull it up in sketchup and start the basic structure and layout . . . while I finish my current build (good gravy, I haven't touched it in almost a month!) . . . and build a trailer . . . and build a DLG pod . . . and . . . well, it's going to be a busy build season ;)


Hostage Taker of Quads
Staff member
Thanks Wilmracer!

hmmm . . . looks like the Museum/owner has mounted a fairing over the rear exhaust :p . . . and the owners repainted her. Grrr.

In fairness, that may have been the scale paint scheme under Don Beck. I don't have any pics from then, so can't confirm. I was really hoping to get better views of the paint she raced with in '70 . . .


Ah well, I'll take what I can get. The pics look about what I need, and I can piece much of it together from these and others I have. If you can catch a shot from tail on and 20 or so degrees off tail to the left and/or right, that should cover the remaining blind spots, but otherwise, I can wing it ;)


Hostage Taker of Quads
Staff member
Very pretty. And probably not a deathtrap. But I have personally wondered if a biplane can go fast enough?
From Wikipeidia:

  • 190.48 mph, qualifying heat record, 1970 Reno Air Races
  • 189.723 mph, championship race record, 1972 Reno Air Races
  • 202.153 mph, championship race record, 1976 Reno Air Races
For her class, those are respectable speeds for back-in-the-day. For other classes? Well, that's why they race in classes ;)


I build things that fly (sometimes)
If you can catch a shot from tail on and 20 or so degrees off tail to the left and/or right, that should cover the remaining blind spots, but otherwise, I can wing it ;)
I'll see what I can do. When Joshua, Patrick, and I were there we met the folks that work at their archives. They made it sound like we would be able to go in and get info from them. In the next few days I'll try to sneak over and I'll ask what they have. Perhaps they have some photographs or even plans.
Excellent choice CraftyDan! I have been keeping an eye on Lockey's work on this plane for a while now. I just have too many things going right now to start building her. Looking forward to your build!


Hostage Taker of Quads
Staff member
Over a week since I've last touched this :mad: . . . let's see if I can remedy that . . .

Finally finished brushing up on my sketchup skills (aka -- wrapped up the design on another project that uses it), so took some time last night to dice up the 3-view in GIMP and import/scale/align the views:

Fullscreen capture 1122017 120711 PM.jpg

The only object drawn at this point is a single line 32" long for the scale wingspan (16' = 32" at 1/6 scale). I'd drawn a 34" line to set the scaling on the side elevation, but found it agreed pretty well with the fuse length in the plan view.

These 3-view plans are fairly good -- you have to be careful that all three panels are in agreement with each other. It's easy for the sloppy draftsman to simply hit the high points in one axis and not go back and make sure they align in the other two views. In theory, any two of the three panels contains all of the primary information for the object (some detail is still needed from the third, but it's surprising how little) so you can cross check between the panels to verify they're correct . . .

Which led to noticing this:

BMS-skp - SketchUp Make 2016 1122017 123701 PM.jpg

The mis-allignemt here is between the wingtips from the plan view and the forward elevation view -- the plan view is about 1/2" longer on the right wingtip than the forward elevation. The center of both plans are aligned, and the left tips line up pretty well . . . so one of these wings is longer than the other :eek: If gone unnoticed, discrepencies like this might cause some consternation later on, but I've got two things working in my favor . . .

1- the forward elevation was made from a half-elevation that was flipped and spliced together -- I know which of the two is symmetrical and which one is off.

2- ABUSE symmetry. Wherever you have symmetry, only draw 1/2. If you need both, you can always mirror it over later. This discrepancy would have never been a problem since I'd never draw the right wing . . . I'd copy and paste it form the other side.

In any case, it's worth a few moments to move a couple of the panels up and down the axis to verify all the marks line up in the other two views.

A bit of quick work, to draw out some lines for reference, complete the boxes for Sketchup to draw the polygon surfaces (this also double checks all the reference lines lie in the same plane) and we're up to this:

Fullscreen capture 1122017 123151 PM.jpg

Decent profile, but still not completely descriptive . . . One thing of note with this set of plans are the cross-sections provided. Those are next.

So next is more dicing in GIMP, import/scale/align . . . and I should get a good representation of the fuse. Connect the dots, then look for good ways to simplify.
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Hostage Taker of Quads
Staff member
Being designer, builder, and owner has it's privileges ;)

In all seriousness, Dunno, but probably. When I offered to build the pace plane, the offer came with the expectation I will provide a pilot as well. Unless she's completely unruly (possible, but we'll see), I was expecting to pilot. Otherwise, I might hand over the controls with a better twitch than I have.

I'm just doing my part to help find the "best plane" . . . by running down the slower beasts in the heard.


Maneuvering With Purpose
Being designer, builder, and owner has it's privileges ;)

In all seriousness, Dunno, but probably. When I offered to build the pace plane, the offer came with the expectation I will provide a pilot as well. Unless she's completely unruly (possible, but we'll see), I was expecting to pilot. Otherwise, I might hand over the controls with a better twitch than I have.

I'm just doing my part to help find the "best plane" . . . by running down the slower beasts in the heard.
You're not going to race your biplane?

Edit: Doh! I see now. The biplane IS the pacer. I thought you were going to race that beast.
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Maneuvering With Purpose
I was expecting to pilot. Otherwise, I might hand over the controls with a better twitch than I have.

I'm just doing my part to help find the "best plane" . . . by running down the slower beasts in the heard.
By all means! Go for it and don't be shy. My dad was a horrible pilot. Crashed waaaay to much for waaaaay to long. Painful to watch. Never caught on until he got out on the glider slope. After that he was "competent plus". And at some point he wanted to race.

When they started the Quickie 500's we were early adopters with "Toads". And my dad got out on the course, but flew about as conservatively as humanly possible. Ran rich, took off last to stay out of traffic and managed to make it around the course without any cuts. And without crashing.

Not crashing and not cutting are items one and two on the list of racing fundamentals. After that you just get around as best as you can.


Hostage Taker of Quads
Staff member

Sliced and diced the cross-sections and inserted them in. Alligned and scaled . . . and these leave a bit to be desired :(

BMS.skp - SketchUp Make 2016 1162017 100332 PM-001.jpg

Just from a quick glance, I can already tell that section F (second to last) is lacking -- by that point, the rim between the cockpit fairing and fuselage join, so to have it showing on the section . . . bad signs.

Pressing onward, I traced out the sections using as few points as would follow the line well, then connected neighboring points to create the sidewalls . . . then nudged the points on the cross-sections to get the lines to match the photos :p

Which brings us to:

BMS.skp - SketchUp Make 2016 1162017 100506 PM-001.jpg

If you look carefully , Section C and F were way off -- F extending a ledge that wasn't there and C creating an odd bulge at 2 and 10 just forward of the pilots seat but the remainder weren't bad.

Fullscreen capture 1162017 100610 PM-001.jpg

Copy/paste/flip and we have a whole fuselage. Notice that the windshield isn't modeled -- the 1970 version had an open cockpit, so all I have to model at this point is the dash and the rear cockpit bulkhead. The cockpit will be a piece of plastic later . . . possibly molded, but might just be cut and glued into place. we'll see.

On to the wings . . .

Still haven't picked an airfoil yet, but we can set the profile for them to start defining where they go, a rough idea of the space they consume, and how they tie-in to the fuse.

We start by creating a copy of the plan view directly above the fuselage and draw out the wing profile on it:

BMS.skp - SketchUp Make 2016 1162017 101029 PM-001.jpg

Turn off the top plan-view and move the wing down to line up with the two elevation views . . .

BMS.skp - SketchUp Make 2016 1162017 101315 PM-001.jpg

Easier said than done. They don't agree :p Time for TLAR and in this case the side elevation looked better. wing goes to the winner . . .

Next repeat the process with the top wing by creating a flat projection of the wing (remembering to lengthen the lower span to match the '70 dimensions). copy that down . . . in this case I sided with the forward elevation and moved it down to align with the bend in the gull. Projected the inner gull-panel using the forward elevation, found where it intersected with the fuse and extended a horizontal middle section to join with the other wing half:

BMS.skp - SketchUp Make 2016 1162017 101423 PM-001.jpg

One thing to note here . . . it's hard to see, but there's a slight dihedral in the outer wing panel in the forward plan view. How slight? Sketchup calls it 1°. Not sure if that's an error in the diagram (the upper wing is dead level, within the margin of the pixelation) error from the draftsman (by 1°?), or something in the real airframe . . . but this bird needs all the help she can get.

Dink around a bit more and now she has wing struts:

BMS.skp - SketchUp Make 2016 1162017 101521 PM-001.jpg

A bit of copy-n-paste and a little cleanup, and all but the tip of the nose and the tailfeathers are laid out:

BMS.skp - SketchUp Make 2016 1162017 101611 PM-001.jpg

Quick look down the gullet shows a decent expanse between the wings for a battery, a good space forward the lower wing for a motor, and less and less space the farther aft you go . . .

BMS.skp - SketchUp Make 2016 1162017 101808 PM-001.jpg

Still need to profile out the tail feathers, but this low-polygon model is a good start for pre-placing parts (motor, ESC, Battery, Servos, RX) contemplating internal structure (Firewall, hatches, wing tie-downs . . . ) and contemplating simplification . . . There's no way we're folding along that many triangles, so some things are going to flatten out a bit, and some things will become turtle decks -- this is a good starting point for defining that.