Pizza?

[Tim Wescott]

Because:

• I went on an eBay binge a couple of years ago, and now I have too many OS III 15's and Enya 19's in my engine drawer, not to mention the McCoy 19.
• I like weird planes
• I have this flying field that's just a bit too small for the Atlantis

Lots of details yet to be determined.  CG (I lost the envelope, on the back of which was the calculation), wheels, where to put sheeting, etc., etc. are all yet to be determined.  And the spar notches are wrong, but can be fudged if you're doing it by hand.

And I have no clue for line length.

The basic design rationale is that an 18" diameter wing gives the same o/a wing area as a Sig Akromaster, only in a weirder-looking package -- so what could possibly go wrong?

Rib spacing is 1 3/4", elevator is intended to be 1/4" balsa (I could go with 3/16").  Wing tips could be 1/8" sheet for lightness, or solid balsa blocks, carved to shape, if you want to maximize appearance points for Expert Stunt.

I really want a pair of Calvin & Hobbs figures, to put in dual cockpits (there's a Spaceman Spiff episode...), but it appears that such things are unobtainium, at least on Amazon.

[Dave Hull]

Pizzaman,

Looks like a fun deal. Go for it!

But....

It's going to go like a bat out of Wuhan with a .15 on it at only 18".  My basis for comparison is a 14" disk that uses a stock Black Widdy. On 42' lines it moves smartly. Your fattish 'foil will help slow things down, but I would not expect it to be underpowered at your planned size!

I've got my cg at 23% and pretty happy with it there.

Structurally, I would tie the back ends of the motor mounts into a full spar, or even a partial-span spar so that you are not so dependent on a couple of ribs. Easy to simply move your front spar forward a bit to take care of this.

If you want it to fly better, cheat on the circular shape. Make it an ellipse. Any additional span would help. These are all drag machines; huge induced drag during any maneuver. In the vein of the Flying Flounder, etc.

So what could possibly go wrong, go wrong, go wrong....Reset. Looks like a great project. Abend. Reset. Looks like a great project, Abend. Reset....

The Divot


PS--If it was me, I put George Jetson and his wife Jane in the cockpit

[pmackenzie]

There is a Spaceman spiff here, but he might be too small:
https://www.etsy.com/ie/listing/661304148/spaceman-spiff-figure-calvin-and-hobbes


"Regular" Calvin and Hobbes 3D printable figurines can be downloaded here, they could be scaled to any size:

https://www.myminifactory.com/object/3d-print-calvin-and-hobbes-35230
https://www.myminifactory.com/object/3d-print-calvin-hobbes-wagon-81487

I usually put Calvin in control of my F3P models, not sure many who see them know who they are!

Pat MacKenzie

[John Park]

When I was a little kid (I mean really little), a fairly aerobatic 'flying saucer' model for the Mills 1.3cc diesel was quite popular in my neck of the woods.  It was called the Stooplate (designed by Len 'Stoo' Steward), and the original plan can be found on the Outerzone website.  It had a diameter of 15" and the ones I saw flew quite well on the feeble old Mills.  They would have gone like a dingbat on the more powerful 1.5cc diesels that were just becoming available.  The plan might give some indication of the CG position it used, etc. etc.

[Trostle]

(Clip)

Lots of details yet to be determined.  CG (I lost the envelope, on the back of which was the calculation), wheels, where to put sheeting, etc., etc. are all yet to be determined. 

(Clip)

I do not know if this will help very much on the CG question.

The Sassy Saucer was published in the May 53 issue of Air Trails and again in the 1954 Air Trails Annual.  Has a span (diameter) of about 26" for about 530 sq. in.  With a Fox 29, it flew "at about 75 mph.  The article states:  "The main point to remember in building Sassy is that the C.G. should not be any further aft than the position shown on the plans or the model will make like a wildcat.  The forward position is not critical and has varied as much as two inches in some models.  The further aft the CG is located the more sensitive the model will be, so the position depends on your flying ability."  (Italics as shown in the article.)  The problem here is that the CG is NOT shown on the plans.  However, the plans do show the bellcrank position and a moderate amount of line sweep.  It shows a 3" bellcrank with constant line spacing to the "tip".  The bellcrank is shown to be just less than 8" from the leading edge or about 31% of the diameter.  It could be assumed that the bellcrank position is at or near the desired CG.  This might give you a starting point.  The airfoil is not at thick as what you show for your "plate".  It shows about 9% thickness at the center line.

This is one of those articles that Air Trails did that stated "... details may be found on 'AT" full-size plans."  One of the interesting "details" on the full size plans is the statement "The Saucer will perform the complete stunt pattern with ease and will do little stints like consecutive outside square loops about 12 feet square."

It will be interesting to see the progress/results of your endeavor.

Keith

[Tim Wescott]

Dave:

I'm planning on sheeting the center four ribs back to the spar.  I may also double up the center two ribs with vertical-grain balsa -- that should provide a nice strong structure (and if the motor bearers break out, we'll know I was wrong!)

Your 14" saucer has an are of about 154 square inches, which sounds about right or smallish for a Black Widow.  18" gives you 250, which does seem small to me, but then, that's exactly what the Sig Akromaster advertises.

Keith:

 Outerzone has plans for the Saucy Saucer that include the "furthest aft CG" -- it's actually close to my calculations (I found the envelope).  Outerzone claims a 25" span, which puts the area closer to 490 squares -- with that skinny airfoil and a Fox 29 tuned for speed, I could see it going 75mph.

I actually looked at just scaling the Saucy down, but I wanted a thicker airfoil and a rounder LE, and I wanted to figure out how to get those @#$% ribs into CAD (I ended up writing a Python script, but all it does is make that particular set of ribs -- and I still need to accommodate sheeting and fix the spars).

[jim welch]

Hey Tim how about this?

[jim welch]

More.... It is 25 inches and that's a k&B 35c combat motor with an 8x9 wood prop and 85 is a good speed. The bellcrank is 7.5 inches from nose on center of bolt, with front lead out straight out. 3 inch bellcrank with not a lot of elevator travel just like a fast combat ship.If you fly the pattern like s... it is perfectly fit to fly just as s..... as you do. he he he......sometimes when you push the second maneuver hard it falls outa the sky and rolls across the circle like
a manhole cover, a neat maneuver in a nostalgia slow combat contest.The things an aerodynamic nightmare which makes fun to fly sorta like the byslob without line tension. This is number 7 of 8.  jim

[Trostle]

(Clip)

Keith:

 Outerzone has plans for the Saucy Saucer that include the "furthest aft CG" -- it's actually close to my calculations (I found the envelope).  Outerzone claims a 25" span, which puts the area closer to 490 squares -- with that skinny airfoil and a Fox 29 tuned for speed, I could see it going 75mph.

I actually looked at just scaling the Saucy down, but I wanted a thicker airfoil and a rounder LE, and I wanted to figure out how to get those @#$% ribs into CAD (I ended up writing a Python script, but all it does is make that particular set of ribs -- and I still need to accommodate sheeting and fix the spars).

In my previous post, I determined the diameter of the Sassy Saucer from the magazine article where the plans provided a scale.  I just took a dive into my files and found the full size Hobby Helpers Plan # 553A that has the Sassy Saucer.    The length shown on these plans is 25 3/4",  and the span measures
25 1/4 ".  (The lines on the drawing are almost 1/8" thick.)  Apparently the magazine plans do not show an exact circle.  The area still will work out to be around 510 sq in.

I am not trying to make an issue of this. 

It would be interesting to learn the CG position you determined for your platter based on your calculations.

(For those not from that era, Hobby Helpers was the source for full size plans from the Air Trails magazine.)

Keith

[jim welch]

Hi Keith
The first one was from the 54-55 era when I was a kid. Club members built some with mixed success. Templates were traced and passed between members. Kinda like rumors, templates change as they are being passed around for years but the basics remained pretty close. It is (on this one) #7 25.5 wing span after finding close center of the not so round airframe...eyeballed the first time . 25.75 length with the difference being in the elevator not
a perfect circle. # 6 had an adjustable bellcrank  with adjustable lead outs and that was optimal for getting to the 7.50 center of bellcrank and lead out position for number 7. Engine offset was a disaster waiting for a windy day to manifest itself. Airspeed turns out to be the most important trimming tool because of the pointed leading edge and drag.

Overall a fun airplane for a looooong time since 54-55 .
jim
PS # 7 is only about 7 years old and has been flown many times. # 8 is framed hanging in shop.

[Tim Wescott]

I got a CG range of 4 1/2 inches back from the LE to around 3 1/2 inches.

Only flying will tell.

I'm wondering if I build this if I should go up to 19 1/2 or 20 inch diameter -- I know the OS-III 15 was a hot engine in its day, but it's day was around the time I was coming out of diapers.

[jim welch]

Tim
The os is a real hot rod which is a good thing I  believe is a plus for a draggy saucer that has to fly pretty fast to be stable . Wing area helps the glide which needs help, but adds more drag. If you make the lead outs adjustable the bellcrank centerline won't be quite as critical
having experimented with the adjustable bellcrank model. You have to land these things pretty quick because the airspeed scrubs off quickly and control input in glide is like an airbrake. The differences  make fun though.
jim

[Tim Wescott]

Tim
The os is a real hot rod which is a good thing I  believe is a plus for a draggy saucer that has to fly pretty fast to be stable . Wing area helps the glide which needs help, but adds more drag. If you make the lead outs adjustable the bellcrank centerline won't be quite as critical
having experimented with the adjustable bellcrank model. You have to land these things pretty quick because the airspeed scrubs off quickly and control input in glide is like an airbrake. The differences  make fun though.
jim

I'm planning on adjustable leadouts -- and expecting that the flying quality may not be superb compared to anything with actual wings.

Mostly I want to get one of those engines in the air!

[Gordon Van Tighem]

http://pdkllc.com/wp-content/uploads/2015/02/DSC01619_edited-1.jpg

Pat King has some saucer kits, plans on his site show CG.

G

[pat king]

My Super saucer is a 22 1/2" diameter disk. I show the C.G. at 4 7/16" aft of the nose of the circle. The airplane flies and glides well with the C.G. there. I do not remember how I figured that one out. the airplane is an enlargement of the 14 3/4" diameter Jetco "Satellite Saucer" The plans for that one do not show a location for the C.G.
If anyone wants to go crazy, I have the 36" Area 51 saucer. That has over 1000 square inches of wing area.

Pat

[Tim Wescott]

My Super saucer is a 22 1/2" diameter disk. I show the C.G. at 4 7/16" aft of the nose of the circle. The airplane flies and glides well with the C.G. there. I do not remember how I figured that one out. the airplane is an enlargement of the 14 3/4" diameter Jetco "Satellite Saucer" The plans for that one do not show a location for the C.G.
If anyone wants to go crazy, I have the 36" Area 51 saucer. That has over 1000 square inches of wing area.

Pat

What motor does your Super Saucer like to fly on?

[Serge_Krauss]

This is always interesting to me. Tim has already responded to Dave on area; so we know that Dave's (14" span = dia.) has an area only 60% of the 18" Pizza's. My problem is similar, and I'm interested in your thoughts on appropriate engine sizes. About 15 years ago I drew up an unconventional plane that incorporates a large central area, and I'm getting too old to let this project languish much longer. I know from reading Bill Netzeband's material that he packed a lot of area into wings of lower aspect ratio for spans employed and the engine sizes used. I'll have to re-read those articles and probably do some computations of my own, but I am interested in what you guys think would  work best for normal lap times your saucers. I want to build a simple 1/2-A PoC model first.

On the question of drag, I'll disagree on the saucer's drag penalty. While low-aspect-ratio wings do generate their lift at higher angles of attack and pretty high drag, the saucers should not have nearly the drag of the Williams "Flounder." Back in the early 1930's Doc Snyder from South Bend, IN built a series of four low-A/R heal shaped planes, two of which were very successful (He flew family members all around the midwest and as far east as Washington DC). These planes had a high ratio of top to low speeds, were able to take off in short fields, and landed very slowly on low power (there are films on You Tube). The "Arup" S-2 had an aspect ratio of about 1.7, without the tip ailerons (as in photo below). NACA's Charles Zimmerman reviewed the Snyder patent application when it came in (common practice then) and was intrigued. So he researched low-A/R wings with Clark-Y airfoils, including circular ones. His first report was NACA TR 431 of 5/5/32. At that time they had not figured out all the effects of Tunnel wall interference and mountings on effective Reynolds Numbers, but the model chords (diameter for the circular model) were about 14".  These ranged from higher aspect ratios down to circles, which were simply "rectangular wings" with only the semi-circular tips remaining, graphed for all A/R's down to the circle (A/R = 1.27). Zimmerman later produced NACA TN 539 of 7/15/35 as a follow-up on low-A/R wings of distorted shapes and/or with slots. Both of these are well worth looking up on the NACA report server, where you can download PDF's. They are not difficult reading. I DO think though that the circular wings give up efficiency to the wings with straighter, less swept  leading edges. TR 431 is what you really want, and I believe it directly compares the basically rectangular wings (w/faired tips) to circular wings. I'll have to re-visit it, but I'm sure that it shows your saucer to be superior to the "Flounder." I am not saying that the circular wing is anywhere near ideal - just that it's not as bad as the Flounder.

What Snyder and, I think, Zimmerman found was that when the trailing edge is nearly circular, 3-D flow allows air to reattach over the aft  wing at high angles of attack, delaying the stall and reducing losses to vorticity.  The best of these wings have the trailing edge start to curve pretty far forward toward the leading-edge tip. Such wings do not wallow around like rectangular wings or consume so much power.

Zimmerman then went on to build his own "Zimmer-Skimmers" or "Flying Flapjacks", the V-173 and XF5U1, but Snyder's (and R.B. Johnson's) showed how safe and efficient these planforms can be.

[Trostle]

Hi Keith

(Clip)

 # 6 had an adjustable bellcrank  with adjustable lead outs and that was optimal for getting to the 7.50 center of bellcrank and lead out position for number

(Clip)

jim
PS # 7 is only about 7 years old and has been flown many times. # 8 is framed hanging in shop.

Jim

What is an "adjustable bellcrank"?

Kieth

[jim welch]

Keith 
Adjustable mount....bellcrank floor was about 3 inches wide with a slot cut in it front to rear
with bellcrank mounted on a threaded rod that protruded through the wing top side so it could be held with vice grips while the bottom you could used a nut driver to loosen the stud and move from front to rear of the bellcrank slot.Top planking had slot for the stud /bottom was a keyhole and slot for the nut driver. Allowed the bellcrank to move front to rear about an inch in both directions. Inboard ribs except tip were cut to clear the leadouts. Once it flew its best,
 built the next one with that measurement.


control horn was an rc deal that the 1/8 inch wire passed through the collar and was locked by a bolt so it adjusted easily to match the bell crank movement from front to rear. jim

[Trostle]

Keith 
Adjustable mount....bellcrank floor was about 3 inches wide with a slot cut in it front to rear
with bellcrank mounted on a threaded rod that protruded through the wing top side so it could be held with vice grips while the bottom you could used a nut driver to loosen the stud and move from front to rear of the bellcrank slot.Top planking had slot for the stud /bottom was a keyhole and slot for the nut driver. Allowed the bellcrank to move front to rear about an inch in both directions. Inboard ribs except tip were cut to clear the leadouts. Once it flew its best,
 built the next one with that measurement.


control horn was an rc deal that the 1/8 inch wire passed through the collar and was locked by a bolt so it adjusted easily to match the bell crank movement from front to rear. jim

Jim,

Interesting.

I am not wanting to start an argument here or to open old wounds.  However ---

The bellcrank  can be located anywhere.  What is important is the location of the leadouts relative to the CG.  Position of the bellcrank should be what makes sense structurally as well as having some alignment of the leadouts to the lines such that there there is minimum bending of the leadouts at the tip leadout guides.

I guess it would be useful to have an adjustable bellcrank if there is no idea where the CG might be so that even with adjustable leadouts, the optimal line rake and leadout postions may not be achieved without having the bellcrank on some sort of a for and aft slider as you explain.

What is the Mean Aerodynamic Chord of a disk/platter?  Whatever that is, I would think that the CG of a flying saucer should be no further aft than 25% or even 20% of the MAC.  I am interested because I have a bucket list project for a CL flying saucer, sort of modified, based on a sketch from a 1952 Air Trails.

Keith

[Dave Hull]

If you want other examples to inform your new design(s) you might look at the Vought V-173. I don't have an engineering text on it, but in looking at a spin test model, you can see the location for the balance attachment. I suspect that it is near the CG.

Photo and reference data from the NASA website:

https://crgis.ndc.nasa.gov/historic/File:NACA_22925.jpg

Just compare the stinger location from the side view with the plan view. And then some area estimates since it is not exactly circular. But the good news is that the prototype had well over one hundred flight hours on it, so they probably had the balance worked out pretty well by then.

I also noted that they used a symmetrical NACA section with 15% thickness.

One critical feature of the Vought design that I recall is that the direction of the prop wash offset (overpowered?) the spanwise flow off the "tips."  For such a low aspect ratio design this was thought to be really important. If you are adamant about retaining a circular planform, then consider putting a fence somewhere near 90% of the semi-span. Pimp it up so that the fence looks either real "military" or like a pair of swimming anchovies if you are going with the pizza finish motif.

On the other hand, you can always look to the Osborne platters, right? There has to be plans for them on the club website, likely with a CG shown.

My interest leads more towards building the Nutnik. It might be considered a cruciform platter?

Dave

[Dave Hull]

Serge,

I probably did not explain myself very well, so let me try to do better. For my 1/2A "platter"  which is actually a Dave Braun-designed Stop Sign and thus an octagon which may be approximated by a 14" circle, it has a thin semi-symmetrical symmetrical airfoil. It appears to be very efficient with about a 6% thickness. So in level flight, the AOA is negligible and it goes fast. Faster than you would expect for all that area. However, the induced drag during any type of hard maneuver is huge. The drag rise with AOA must be being affected very strongly by the planform, since there is little wrong with the airfoil itself in my opinion. High aspect ratio flying wings don't have this problem. Thus, the logical blame is on the super low A/R.

One other thought:  if you want a saucer to fly like a regular C/L airplane, then speed is what it takes. If you want it to fly like a BiSlob, or a Flounder, or.... then all the setup rules for those would apply. This would appear to be consistent with Jim's experience. I will say that one local guy built a Slob and seemingly wanted it to fly like an airplane. To get it to do that, he needed all kinds of power. We're talking OS.46LA power, not Fox .35 power. Again, super low A/R, no fences, blunt nose, and a wing gap that is smaller than optimal for aero efficiency. In other words, the area of the combined wings produced much less lift than you would normally expect because of the flow interference between the two.

I am puzzled about Jim's comment on engine outthrust on his platters. I think we need to have a common reference line before that conversation will make sense to me. Since there is no fuse or vertical stab, the key elements are actually the CG location, the center of the leadouts, the weight of the plane, the lines (size, diameter, length) and the flying speed. From this, you can draw the angle between the engine thrust line and the line rake coming out of the wing. Since there is no penalty for yawing the airframe, and it may be difficult to tell if it is flying with a bunch of yaw, screwing with the leadout guide is exactly like adding or taking away outthrust. With that thought in mind, a guide that happens to be too far forward directly results in uncompensated in-thrust. Which I took Jim to say was more exciting than really desired.

I hope the first paragraph makes clearer what I was trying to say earlier.

Dave

edit:  I looked up the plans, which show a fully symmetrical airfoil

[pat king]

What motor does your Super Saucer like to fly on?

The Super saucer has 397 square inches of wing area. It is for .25 to .40 engines. Dennis used an ENYA Model 5224B It was either a .29 or a .35, I don't remember which.
The 36" Area 51 has 1018 square inches and is for .60 to .90 engines.

[Dan McEntee]

  Ii always lusted after the Jetco kit of a flying saucer and finally snagged one at a decent price on evilBay after tracking the sales of several others that were just too ridiculously high priced. I got mine for a price I could afford at the time and the seller was obviously disappointed that he didn't make a huge amount of money that he did a really crappy job of packing it and shipping it, and it barely arrived in one piece as the kt was hanging out the end of the box! We had a little back and forth over the length of time it took for me to get the kit, shipping costs, and the negative feedback I left  for him afterwards. But in the end, another childhood memory acquired!
   The Jetco kit was supposed to be a .15 powered model, and I believe it was the same as a plan presented in Popular Mechanics? Does that ring a bell with anyone? I will have to check my plans stash to see if I have that.
   Pat's Super Saucer looks really cool and would be a perfect mount for Spaceman Spiff!!
  Type at you later,
  Dan McEntee

[jim welch]

Dave
I didn't run out thrust on mine others did. was talking of theirs , mine was straight on based on what I seen theirs do.
Mine has 2 vertical fins (rudders)  which serve as the tail skids also. This one has a landing gear and takes off from the ground nicely. The rudders do have a little off set in them also not a lot.
The bell crank is mounted at 7.5 from the leading edge on the center of the stud. I know It doesn't mater much where it was mounted from flying the adjustable set up. The front lead-out end up being square to the engine and center line of the airplane. That lead out is square to the front spar (just behind it)  Front vertical spar is at 6 inches from the front. Purpose of the adjustable airplane was to save everyone else an airplane trying all kinds of things that didn't work. The green head 35c was on pressure with a clunk tank that eliminated most fuel problems when flown fast it flew nice. The test plane was built and flown within 30 hours with the silkspan tightening up on the first flight. jim

[Tim Wescott]

That is just the wrong spot for the bellcrank -- but there's a fuel tank in the way of the "natural" spot!

Maybe I'll put it under the fuel tank -- there's certainly room vertically.

Edit: Drawing replaced with full size.

[Dave Hull]

Hmmm. The PDF that comes thru just shows the left rear quarterpanel. I would agree that's not a good spot for the 'crank--but I doubt that's what you have in mind!

There should be a ton of room just inboard of the tank. One of the few really good things about a low A/R flying wing is the large internal volume without drag penalty. The Universal Law of Fairness says you gotta get something in return for accepting huge induced drag from maneuvering.

Of course, engineers will find new gotchas even in the best "gifts." Just go look at the structural problems associated with the wet wing Navy A-12 stealth attack bomber. The weight growth and respin from that little gotcha may have been one of the biggest straws in the story of that particular camel's broken back story.

The Divot
"Awaiting new opportunities to leave holes in asphalt circles throughout Southern California"

[John Park]

The bellcrank  can be located anywhere.  What is important is the location of the leadouts relative to the CG.  Position of the bellcrank should be what makes sense structurally as well as having some alignment of the leadouts to the lines such that there there is minimum bending of the leadouts at the tip leadout guides.

We all (I hope!) know this now, but I remember an item in the 'Gadget Review' page of AeroModeller in the late 1950s showing a fore-and-aft adjustable bellcrank which its inventor confidently presented as an aid to learning C/L.  Your first flights were with the bellcrank in its rearmost position, making the model nice and docile to fly (everybody knew, of course, that the nearer the bellcrank pivot was to the CG, the more responsive the model was to control inputs!), and you moved it forward progressively as you gained experience.  There was no mention of altering the position of the leadout guides, or the CG or anything else but the bellcrank.  The magazine (whose editor was Ron Moulton, a noted C/L pioneer) evidently saw nothing wrong with this ridiculous idea, for which its inventor would have been paid the princely sum of five shillings (say, a dollar).  I don't know whether anybody ever tried it, but it took me many years to realise what nonsense it was.

[Tim Wescott]

Hmmm. The PDF that comes thru just shows the left rear quarterpanel. I would agree that's not a good spot for the 'crank--but I doubt that's what you have in mind!

There should be a ton of room just inboard of the tank. One of the few really good things about a low A/R flying wing is the large internal volume without drag penalty. The Universal Law of Fairness says you gotta get something in return for accepting huge induced drag from maneuvering.

My post has been edited with a proper full-sized plan.  My print-to-file utility likes to insist on size A paper.

I currently have it just inboard of the tank, but I don't like putting weight on the inboard side, and I don't like the degree of bend in the leadouts that'll induce.  I'm being overly picky for something that's definitely going to be a novelty.  But still...

[Dave Hull]

Well, ok--how about this? Thin down the wing to some reasonable thickness for a saucer. Then, put the tank where it's gotta go to make the motor happy. Put the 'crank on the outboard "wing" wherever the leadout angle makes sense for minimum bending. Get the pushrod out there two for more fake tipweight. Mark the leadout exit locations. Draw a line or lines across your tank where the leadout(s) will have to go thru it. Drill thru the tank and solder in "control ducts" just like the big boys use.

No reason not to add all the finesse you can stand, even on a "for fun" project. Just pick a bit later project completion target date and get to it!

The Divot

[Tim Wescott]

I say that 15% is a perfectly reasonable thickness for a saucer, although even if a little ol' class-A ship may be personally responsible for the death of a balsa tree.

[Tim Wescott]

I have an engine!

[Dan McEntee]

  After hearing that video and your other thread about prop and venturi, I'm really interested in how this goes forward as to if you will have complete plan available or not. I have already mentioned that I have the Jetco saucer kit and I'm sure I have some of the other magazine plans for saucers  but this may be a better approach to one than the older designs. I'll look into Pat King's offerings also. I loved that photo of his in his post. I also have some of those older OS .15's also. I'm enjoying watching this!
  Type at you later,
  Dan McEntee

[Tim Wescott]

... complete plan available or not ...

You do realize that I start these little efforts in CAD because it's easier for me than grease pencil on butcher paper, yes?

[Tim Wescott]

Dangit Dan, this is now resembling actual work.

And all the detail makes the file bigger, which sooner or later is going to use up all of Sparky's disk space.

EDIT: I've put much more detail into the plans, and I'm calling it good.  I realized I left out the sheeting, then said "screw it, it's good enough, it's a little model, it should be light".

[Tim Wescott]

See changes to my last post.  I'm calling it good for now.

If you're worried about strength, move the bellcrank mount plates up and down to just inside the spars, extend them forward to the bulkhead, and make the bulkhead out of plywood.  That should make a nice rigid box.

[Serge_Krauss]

Dave, thanks for the details and discussion. Experience counts. However, you might still enjoy reading TR 431. Also, I don't know how the low-A/R 6% wing reacts regarding stalls or separation. Zimmerman does give induced drag coefficients for the saucer shape, compared to higher A/R wings with the same "tips." Again these are for the classic Clark-Y, rather than symmetrical sections that would have higher drags for a given lift. Cool discussion!

[Serge_Krauss]

Someone must have edited a post above, because I remember him mentioning an unidentified plane in a 1952 Air Trails, but can't find the reference. I was going to ask whether he was referring to Roy Clough's slotted saucer, because that FF model was my favorite of all gas models I built when young. The original was powered by an infant Torpedo .020, but mine had a Cox and flew out of sight and was lost one day about 55 years ago, when I over-filled it. I promised myself I'd build another. but haven't, although I ran across my templates. I was curious about whether this was the referenced model and, if so, what you intended to do with it. CL?

SK

[Dave Hull]

Well, Serge, I guess there are at least two missing posts.

I didn't post about a 1952 design, but I did post about my observations after a brief read-thru of NACA TR431 per your suggestion. It is also lost in the ether. Nice to know that there is ether out there, but it would be better if we could get the dang stuff into a can so we could make up some decent diesel fuel....

Good luck with your saucer hunt,

Dave

[Serge_Krauss]

What is the Mean Aerodynamic Chord of a disk/platter?  Whatever that is, I would think that the CG of a flying saucer should be no further aft than 25% or even 20% of the MAC.  I am interested because I have a bucket list project for a CL flying saucer, sort of modified, based on a sketch from a 1952 Air Trails.

Keith

THERE's the AT quote! So Keith, are you thinking of the "Clough saucer" or another? Re, your question...

I just remembered your mentioning the MAC - 'woke up thinking about that. Several years ago, I derived the MAC's of several wing plan forms (straight and swept versions of straight-tapered, elliptical, and parabolic), as well as their positions and some comparisons. No one was interested, when I offered to send a copy of the file, and since there seemed such animosity toward things mathematical. I just quit contributing that sort of thing.

The interesting thing about elliptical forms is that they are easier to analyze than usual wing forms with straight leading and trailing edges and taper. Since circles are just a simpler ellipses, it's not difficult to find their MAC's. I tried to draw the diagram, but my eyesight sort of wrecked that effort. So I used Microsoft Office Tools to draw a circular wing, which is pictured below. For the circle, you can get the MAC by just multiplying the radius by 16 and dividing that answer by Three pi (3 x pi). You can find the quarter chord point of the MAC (assumed approx. aerodynamic center) by dividing that answer by four. For a circle, the distance outboard on the wing is the same as that answer). Then you can find the point on the root chord corresponding to that point by subtracting that answer from the radius. That will tell you how far back from the root leading edge the a.c. is. SO...

MAC length = 16R/(3 pi) = about 1.7 R
MAC/4 = 4R/(3 pi) = about .424 R
a.c. distance back from root leading edge: x' = R - 4R/(3 Pi) = about .576 R
Distance of MAC outward from Root = 4R/(3 pi)  = about .424 R (same as MAC/4, for a circle)

I suppose a conservative version of the a.c. could be found by just going back .424 x R from the actual leading edge.

The diagram shows something else that some internet sites get wrong. Unlike straight-tapered wings, the MAC is not the same length as the local chord at its location; it is shorter. If you put the MAC at the location where it matches the local chord, you can get a ridiculous answer. Also, you would have to have a very large taper ratio to get a straight tapered wing to have the a.c. as far inboard as an elliptical half-wing (Taper Ratio T = .376). I put the top of the summary page for elliptical wings in a separate picture below. You can see that the equations simplify to what we have above:

MAC = approximately .85 x Root Chord. For a circle, that's about 1.7 x Radius.

d = .424 x Radius, for a circle

The third equation is big, because it includes sweep. For a circle it is just x' = R - .4244R = (1 - .4244) x R = about .576 x Radius

So you can get any of the three things you might want to know about the circle by just multiplying the Radius by some number. "Simpler" Wings take a bit more work.

One comment on the whole things about MAC's. These are really mean geometric chords (calculated without regard to actual air flow and pressures). They are just based on the idea of lift being the same at each point on a wing's surface, which is not true. We know by experience that the lift of a chord-length sliver of wing at some point out for a symmetrical wing section is about .24 to .25 of the way back from its leading edge. So we make up for that first assumption by considering the aero center of the wing to be at the quarter-chord point of the MAC or, better, the MGC. That gets us pretty close, but tip losses actually move the a.c. and thus the MAC inboard a bit.  This works well as a benchmark for determining longitudinal balance though and we choose c.g.'s relative to this point. The convenient thing though is that you can find the point where these imaginary, equal lifts are centered simply by cutting out a cardboard scale planform of your wing and finding where it balances, because the lift and thus weight increments are directly associated with weight.

Well, if I've unsettled anyone by posting equations, 'sorry. As always, it's a FWIW.

SK

[Ara Dedekian]

Someone must have edited a post above, because I remember him mentioning an unidentified plane in a 1952 Air Trails, but can't find the reference. I was going to ask whether he was referring to Roy Clough's slotted saucer, because that FF model was my favorite of all gas models I built when young. The original was powered by an infant Torpedo .020, but mine had a Cox and flew out of sight and was lost one day about 55 years ago, when I over-filled it. I promised myself I'd build another. but haven't, although I ran across my templates. I was curious about whether this was the referenced model and, if so, what you intended to do with it. CL?

SK

     Here's a Sassy Saucer and a Clough Flying Saucer that were left behind in our club field house. I repaired both to flying condition without plans and found the Sassy Saucer quite stable and capable of most maneuvers. I've flown it in a 15-18 mph wind. Perhaps a pro could get it through the pattern. The dimensions are a 26" circle.

    With a Fox 35 the muffler was needed for ballast. The airfoil is 1-1/2" thick. The two crosses behind the tank show the leadout connections to the bellcrank and the bellcrank location. The leadouts (bent from storage) exit straight out.
   
    Ready for flight as shown, the CG is 6-1/4" back from the front leading edge.

     Ara

     P.S. Serge, you were right. Your mathamatical analysis gave me a giant Excedrin headache and as hard as I tried, couldn't get through it. But I'll go back to it and try again when I recover.

   

[Serge_Krauss]

Thanks, Ara. It's good to see that old saucer again. I have to build and fly another before I'm done! Your c.g. seems to agree pretty well with what the equation would suggest. Remember that the result is simply that you can find the predicted aero center just by multiplying your radius (13" for your saucer) by .576 and then deciding how much forward of that point you want to locate your c.g.

SK