kenh3497

I've been working on a 90 sized Black Magic. I think I have everything re-scaled to an appropriate size. The wings,stab and fin/rudder is 87% of the full size and the fuse is 85% of the original. The only difference that I can tell from the E-version to the fueled version is a difference in the firewall.

Not that there is any difference between the 90 and the full size, but here are 90 size PDF's.

See post #6 for ready to go plans.


Ken

flywilly

My Feedback: (121)

Nice work! Thanks for sharing. I like the size; so I may have to build one myself.

kenh3497

Thanks FW!

I'm having some minor issues with the scaling/printing of the fuselage PDF. I think I have a handle on it but a fellow modeler who uses DraftSite much more than I do is checking me out. When the issues are fixed I think I'll be good to go.

I do need to get cracking on my foam wing cutting machine. It's just a copy of the feather cut rig but I see it as a vital piece of equipment for this project.

I'm hoping the YS 91 will have enough poop to haul it around.


Ken

kenh3497

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kenh3497

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kenh3497

FINALLY.... Success with the scaling issues I was having with the PDF's. Everything is as it should be now. I've made a few changes to get everything on two sheets. The wing sheet has templates for two sets of root and tips so both the top and bottom of the template guides can be cut and matched.

The fuse sheet has all the templates needed to build the fuse. Some of the wood sizes may need to be adjusted and I'm considering not using foam cores for the top and bottom. Just using a couple of extra stringers and sheeting. We'll see when I get to that point.

With all the above said as with any scaling job not all pieces of wood called out on the plans are appropriate . Use your best judgment and build to suit.

Use these plans as you see fit. If you see something that needs to be changed let me know and I will make the adjustment.

Ken

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kenh3497

Having no exposure to modern F3A airframes I was a bit shocked to see the size of the airframe. Now I''m second guessing myself if it is too large to be powered by a YS 91. Any thoughts from the collective. What weight should I shoot for?Than

thanks

Ken

maustin

My Feedback: (7)

Ken, just guessing RTF weight for a 90 size plane should be around 8.5lbs max. I had a World Models Excelleron years ago with a YS 120 on it and vertical was ok but not spectacular at 8.5lbs.

maustin

flywilly

My Feedback: (121)

Hi Ken,
I am guesstimating a length of around 67" and a wing area of around 800"square. These are pretty much the exact dimensions of the MK Skystar 90 (sadly, no longer kitted). I agree that 8.5 lbs is about the max. My Skystar weighed 8 lbs (or a little less) covered entirely in monokote and flew very well on 15% nitro. I think the Black Magic fuselage may be a bit larger fuselage (so, more drag); keep it as light as possible. Contest balsa, lightening holes where possible and minimal adhesive when sheeting the horizontal surfaces.
Good luck and keep us posted!
-Will
Of course you can always upgrade to a YS 115...

kenh3497

The fuse is 65 1/2 long and the wing span is 64 1/2. The fuse is about 11 or 12 inches deep at the canopy (without measuring) and about 5 1/4 inches at it's widest. To me it looks like a 120 YS would be a better fit. I may need to rethink this a bit?????

Ken

TFF

For a YS91 you probably need to make it a little smaller. I have had a couple of 90 Pattern planes. With a 90 twostroke they flew like a sport plane. I will say it was not the most powerful 90. YS110 fixed it so it could go verticle any time but not a lot of excess. A friends GP Venus II was nice with the OS120AX but even then it was not grossly overpowered. I know my 110 runs about 1" more prop vs the 91 at the same rpm and pitch.

kenh3497

I've been playing with the Black Magic 90 a bit on size. If I scale the fuse back to 80% of the 2M I get a 62 3/8" fuse tip of spinner to tip of tail. The wing at 82% gives me a 61 1/2 inch span and about 680 SQ. IN. if I include the fuse which I think is the correct way to do it. Otherwise each panel is 312 SQ. IN. The fuse is roughly 60 SQ. IN. The depth of the fuse is 10 3/4" at it's deepest. The YS 91 will fit within the cowl except for about 1/16 + or - a 1/32 or so of the valve cover.

This looks more workable to me and overall weight should not be as big an issue to hit on target. Or I could go as planned and put my YS 120 in the nose of my present version That is still a bit larger than I like though for transportation issues.

Ken

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kenh3497

I was just looking at a Mytho S 50e thread. That plane is the same size as my proposed 80% B.M. It is also rated for a "70 glow" engine. I assume a 70 YS. Now I'm very confused. Some say my 85% B.M. is to large for a 91 YS, yet the Mytho calls for a smaller engine and is the same size as the 80%. Ya I just said that twice

Would the Mytho with a 70 YS be under-powered??? I'm beginning to understand why there are so few pattern planes available in the smaller sizes.

Ken

TFF

I think when it comes to something that is for sale, the manufacturer goes for the safe number. Not a pattern plane but my old "U Wish it Could Do 3D" 46 was way underpowered with a 46 or 70 engine but they were worried that people would overspeed the planes and they would blow apart in the air. I put a 60 two stroke on it and it was ok. 60 size need 90s. 90s need 120s. The pilot has to know to use the throttle and not hall around doing speed passes, which is not what the average modeler does.

flywilly

My Feedback: (121)

Hi Ken,
Regarding engine sizes: the YS 70 is currently available (In a 'DZ' version, too) and has great power-to-wieght. The YS 91 (AC or FZ) has not been manufactured for more than a decade (maybe not even this millennium); so manufacturers don't even give it consideration. The YS 91 in the Mythos would probably be a great combination, heavier, but more power. The reduction in size you mentioned for the Black Magic would ensure plenty of available power from the YS 91 you are planning to use. The linear dimensions of new pattern designs (length, span) have not changed in 20 years but the total volume, especially of the fuselage, has increased significantly and as a result the parasitic drag of the airframe has increased dramatically; so either more power for a given sized model is required or a reduction in size of the model (your solution). For comparison: the mid-sized version of the Runaround (66" length, 820"sq. of area - designed more than 20 years ago) would fly great on your YS 91. Your 85% Black Magic would probably need a YS 115 to have the same performance as the Runaround. BJ Craft has produced several '70' sized models. You can go to their website and check them out. Typically about 59 or 60" long with wing area in the 620-680"sq. range.

Anthony-RCU

My Feedback: (2)

One concern is wing area. A general target for pattern planes is 100 sq"/pound or a little less. I would think your target would be in the 800 sq" range

kenh3497

Just about where the 80% B.M falls. When I first saw the 85% plans my first thought was "This is a 120 size plane".

Now we're learning something useful!

OK! Thanks for the input. The 80% plane has a wing area of 680 " sq., so I'm in the ball park there. I might shorten the fuse just a tad???? to make a "square" airplane. The wings and tail surfaces are currently at 82% so will leave them alone. FWIW, the YS 91 on that Xcelerator plane I had did a pretty good job of hauling it around. It was all of 10 pounds, with (I think) a 64 inch wing span and about 700ish sq inches. Like was mentioned, parasitic drag is the enemy, or not depending on your point of view. I don't think a lack of power will be an issue. I just need to have flying speed.

Thanks again!

Ken

mercura

Well done on your work so far. I would leave all the length in the fuzz.
Todays 2m planes tend to have wing span shorter than fuzz.

Dave

kenh3497

Thanks....

But, all I'm doing is rearranging the size of the parts a bit. ALL the credit for the design needs to go to the original designer of the Black Magic. I'm thankful to have the opportunity make a smaller version.

Part of my "struggle" with the sizing is the fact I've had no exposure to a modern F3A airframe so have nothing to reference to. It has been a trip for sure. Of course we are hardly out of the driveway. The real journey will start when the first piece of balsa is cut.

Ken

TFF

What is funny is the wing panels are exactly the same size on my old Quest 90 and my old Focus. The difference is the Quest are joined in the middle and the Focus has a wing tube through the fuselage. By numbers the Quest is less by the width of the Focus fuselage area. Fuselage is about 10" longer on the Focus. The fuselage volume is what is hard to scale as the drag per size of the plane goes up the smaller it gets. The Strength of materials is where bigger helps, too. The frailty can't shrink either. If you shrink the frailty, the 90 size will be so fragile you could not touch it. the 90 size plane will be heavier per volume. Still I like 90 size as a plane and I think the bottom two classes of pattern should encourage these size planes to get more people in. That comes down to the judges not having prejudices which is hard, because if they can't win it is a moot point.

Smooth Pilot

The judges should not have prejudices and the performance of the maneuver is the primary point. It doesn't matter what the size or even what the plane itself is as long as it is capable of performing the geometry of the maneuver. The maneuver is what is scored, not the airplane.

Sheldon

big_G

I won a few Sportsman and Intermediate contests with a Hobbyking Airoso..about62 inch wingspan. Smaller planes can win, but 2 meter birds fly better. Just a fact. Perhaps we as a group might consider giving a handicap to smaller planes, like maybe 5 points per round to encourage new blood. Just a thought.

MHester

My Feedback: (1)

Wow....all these years later.....heh!

You don't need it, but you have my blessings anyway!

-Mike, the long lost VF3 guy

kenh3497

Thanks! The build will start shortly, well in the next month or so. I'm on a budget so the decision for the smaller version. In any case it will fly better than what I currently have which is nothing! Well at least not pattern wise.

Stick around and give us poor guys some advice on how things should be done

Ken