Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

A new speed plane under developement

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Old 02-11-2014, 07:06 PM
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iron eagel
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Default A new speed plane under developement

Hopefully the third time is indeed a charm because I am working out a new speed plane design. Even though I haven't even gotten my "Screamin Demon" airborne yet I know it's not going to be all that fast, at least not extreme speed by any definition. Having an empty bench with no new project being built has to cease so I started on a new design. Based on my Stingray this will be the Stingray MKII and hopefully it will be fairly quick. It's just in the beginning phase and I am trying to learn CAD well enough to do the entire desing on the computer so it's going to take a bit to finalize the design hopefully by the end of the process I will have some idea of how to use CAD.
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Old 02-14-2014, 07:10 PM
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Figuring out the COG for this thing is a bit of a nightmare.
I built a 10.5 inch span glider and test showed the COG to be a lot further aft than anticipated. So I am going to build a flat foam test bed to get that issue resolved before I can go much further with the actual design work. Right now I am working out just how to stuff a motor into the nose of this thing.
Pictured below is the balsa glider on top of the foam test bed frame, as well as a jpg of the preliminary side view.

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Old 02-15-2014, 01:29 PM
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I think the larger foamy will give you a better idea if you load it with a proportional amount of weight to what the finished plane will come out at.
I think the larger mock up model will get more lift contributed from the center section during testing.
A SR-71 I built got way more lift from the forward area of the fuselage than I figured....so my first attempts at flying it weren't good. It was way too tail heavy.
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Old 02-16-2014, 10:50 AM
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It's pretty bad when you have to build a plane just to figure out how to design it...
I did notice some interesting effects regarding the center section with a few of the harder throws of the glider.
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Old 02-16-2014, 01:03 PM
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A reasonably quick to build facsimile [of full size model] can be made out of foam and skinned with tape for durability. Use coke can tabs taped to the control surfaces for "free flight" trim....then later add servo controlled surfaces with tape hinges and a basic [cheap] motor. Just do it down and dirty to get the hand launchand low powered flight ironed out before you commit to crafting the finished, labor intensive product.
I'd build a full size foam mock up with a flat bottom and airfoiled top...just to simplify it and to quickly ensure that it comes out.
with no warps.
Heavy grit belt sander rolls mounted on hunks of 2x4 lumber make great tools for hogging out the foam. Have a shop vac rigged to capture the mess as you cheese grate it off. I think within 2 hours you could whip out something like this from 1 inch thick high density foam. 3M77 makes quick glue joints, just spray a light coat on both surfaces. Once you sort out the crude prototype well enough to fly with limited power then you should be able to confidently tackle the high speed model.
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Old 02-16-2014, 02:27 PM
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I am in the process of building a foamy right now with the airfoil on the center section out to the swept wing part. It will be interesting to see what it does, I am a bit concerned about a few of the aspects of this one and have got to get an idea of how it will perform.
One interesting fact I discovered using a online CG calculator program, my glider was flying on about 35% of the MAC I suspect that may not be where the foam plane actually flies.
Now here is something interesting...
If you take that 35% MAC point on the glider it just so happens that it is right around the 25% point of the outboard swept wing.

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Old 02-18-2014, 06:42 PM
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Using a online COG program I got this as a result. It looks like it is fairly close and seems to take in account the long nose.
Already one small change the outboard swept wings got clipped a bit, and depending upon the results of flight test they may be clipped even more.
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Old 02-19-2014, 09:58 AM
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The more I look at this design the more I think it would work very well for composite construction. I always thought a speed delta design in fiberglass would be really cool.
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Old 02-19-2014, 10:44 AM
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Like a Whiplash?
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Old 02-19-2014, 10:47 AM
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This thing may require composites, the wing at the root is .44 inches thick, tip is .24 inches thick.
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Old 02-19-2014, 11:51 AM
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Iron, from what I can see that would be an easy layup using 1/16" balsa as a core material. A single hatch at top and you would be good to go. One would even be able to mold in engine rails.
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Old 02-19-2014, 12:13 PM
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Easy for you perhaps.
I have never done a layup in my life, and here I am working on a plane that I'll have to get CNC molds made up to build it, or from a a plug to make molds something else I have never done.
Then there always Combatpiggs idea of wire cut foam and glassing it, yet another thing I have never done.
I build tissue and balsa, woodies or silk covered airplanes (with a bit of carbon fiber or fiberglass incorporated) I am comfortable with that.
This little project is going so far beyond anything I have attempted it's a bit daunting.
By the way it's going to be electric I am not good enough with high performance glow, to get the type of power I need for this planes envelope, to fit into it or even run right.
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Old 02-19-2014, 03:07 PM
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AN update to show you how the elevators may be set up.
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Old 02-21-2014, 04:32 PM
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Just to give you an idea here is a shot of the root of the swept wing portion of the plane.
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Old 02-23-2014, 11:14 AM
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Well after much deliberation I decided to go even a bit closer to the edge.
Now we are talking about a 32 inch wingspan airframe.
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Old 02-23-2014, 01:36 PM
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Just taking a break and doing some reading, looks like the German boys have changed the rules to prohibit the use of a launcher.
I think they have an idea of where I was headed with this one.
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Old 02-23-2014, 02:17 PM
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Would someone please translate the measurements regarding area and alike into English measurements. It looks like these guys are building a box to protect their style of aircraft.
  • weight:
    minimum take-off weight 28 oz
    maximum take-off weight 176 oz
  • total area (wing + stab):
    minimum 10.67 dm^2
    maximum 150.00 dm^2
  • wing load (wing + stab) calculated without fuel, but with battery:
    minimum 12.0 gr/dm^2
    maximum 75.0 gr/dm^2
  • propeller driven propulsion only (no ducted fan!)
  • rigid and/or folding props allowed (single blade, 2-blade, 3-blade etc)
  • single/twin/triple etc engine configuration allowed up to a maximum combined capacity of 10 cc
  • tractor and/or pusher config allowed
  • F3S-F maximum motor battery voltage is 72V (measured without any load). Above 60V an electric shock protection for all involved metal contacts and connectors according to DIN EN 61140 or VDE 0140-1 is mandatory.
  • any kind of fuel is allowed, e.g. from regular FAI pylon 80:20 blend up to super high percentage nitro or other exotic (but non-toxic) mixtures
  • turbocharging, supercharging, nitrous injection or other kinds of charging is allowed as long as the engine capacity does not exceed 10 cc .
  • the engine/motor must feature a R/C controlled shut-off device for safety reasons that stops the engine within 5 seconds (i.e. for glow engines a fuel shut-off or a throttle that closes fully)
    each scoring flight does last 240 seconds. Within this period of time (not before!) the engine has to be started and at least two corridor (100 m + 200 m) fly-bys in both directions have to be performed. After 240 seconds at the latest the pilot has to stop the motor(s) and must land immediately.
  • for speed planes without any (fixed or retractable) landing gear only hand-launches are allowed. A dolly or launch pad like this is illegal
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Old 02-28-2014, 08:35 AM
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Now that I have generated a pile of foam chunks time to start assembly, the piles of foam hint at the finished shape of the body. All of those ribs are just for the body the wings on this test be will just be flat foam with a bit of tow to keep them from flapping about. I still have to build the motor mount to integrate into the body. The motor I selected is about the same weight as the one I would like to use, but a larger diameter so the duct/mount will seem a bit large on this plane, keep in mind this test model is just to test the control surfaces so if the shape isn't perfect that doesn't matter that much. Pretty much this test modle is just to see if this thing can fly and is controllable.
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Old 02-28-2014, 11:52 AM
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From the looks of the shape, the next test will be an autonomous touch and go on a carrier deck..
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Old 02-28-2014, 12:26 PM
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More like Groom Lake for this one...
The shape is still in a state of flux.
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Old 03-05-2014, 08:33 AM
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Got a bit of work done, the shape slowly starts to emerge.
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Old 03-05-2014, 09:45 AM
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It's looking nice.
Seeing the 3D shape makes it look much less radical than the 2D overhead view does.
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Old 03-05-2014, 11:55 AM
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Pretty bad when the only way you can generate a 3D view of something is to build it.
At least it looks close to the shape I had pictured. Now to see if I can actually make it fly. It's still pretty radical when you look at it from the side it's still a lot different than most airframes. Getting this thing to balance is going to be a real exercise in parts placement, that and still allowing access to the motor for mounting in particular.
As you can see my workbench is a shambles at the moment not even photoshop can hide that fact.

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Old 03-05-2014, 12:26 PM
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You can always stretch the aft end if it comes out nose heavy, or with too much area forward of the CG. A big fin that sweeps back would help with that.
If all this plane wants to do is flat spin upon release, then that is the symptom of the side area inbalance.
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Old 03-05-2014, 04:39 PM
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You're wondering about dm 2. It is square decimeters. A decimeter is 10 cm, or 3.94 inches. About the size of a cigarette pack. The wing loading is Grams per square decimeter. Like oz. per square foot, except in the dreaded metric.
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