Off to build a SR-72 Dark Star using 64mmEDF's

[L Edge]

Not only trying 64 EDF's, but going to use Readi-board in the process. Took a lot of planning since it has to not only look something like a Dark Star, but can handle the G forces as well as being stable . The worst thing I'm hoping it will end up is with wrinkles, just like we do. Built a practice 3D plane, F-117 and a Sponz Wonder that holds up very nice to Readiboard. So onward.

Being old school, it's paper, tape for my gut feeling for what it will look like size and shape wise and the construction thoughts so it holds up especially with the long nose. It may not look like much now, but Rome wasn't built in a day. It is basically built the same way as my Sr-71 and has the same problems as when I solved the 64mm EDF problem.

For those who haven't seen my SR-71, here tis:

 

[L Edge]

Things I am looking out for are the landing gear position, joining Readi-board sheets with strength and increasing rigidity and trying to use only 3 sheets.

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Settled on a length of 48" by 33 and laid out general shape of a Dark Star (?). Went longer in the nose and changed width to get a little more area on wing. Trying to keep model light so will only use hot glue and some form to make it futuristic. Did a lot of laying out on paper(real early CAD system) and using my slide rule. Using elevons and differential thrust so it helps in the turns. Like the SR-71, the nose does not like to much of a high alpha which tends to flip the plane or to steep a turn which rolls it over and nose dives it.

Next step is to start carving out the parts and put it together to see what happens. No other choice since the plans are stealth.

Any comment or suggestion?

 

[FoamyDM]

I needed 1 wing spar (3/16 dowel or an arrow shaft) but longitudinally, the nacelle, and fuse shapes do a great job in keeping stiffness. are you planning tab in slot? I used grooves, with likely cause the wing flop that required the spar.

Good luck on this build

 

[L Edge]

Hey, thanks for the tip. Unsure at this point if I will need it, so build, adapt as you go. The Readi-Board is interesting stuff to work with. So far my 3 models of foam are good in strength after an average of 10-12 flights.

 

[L Edge]

Between 3 different builds, back to this one. Cut out wing and nose section. To add strength, tape the two pieces together, open up 45 degrees, filled with hot glue and laid flat until cooled.

Now for stiffness for wing , now laid over the long segments that cover over joint and go full length that also and hold tail.

Now added tail.

Nose stuff for looks, strength and stiffness will overlap into wing 3/4 of way and has to wait since nose gear stiffness also has to be built in.

So onto engine nacelles, EDF's and landing gear positioning.

 

[L Edge]

Here are the two 64mm 5 bladed EDF's, that I had to rip out of the top of the wing for the YC-14 flap blown used to explore a STOL transport.

Problems under the wing include the 2 EDF's, main gear in front of blades and proper location to balance everything. Using circular sheet of FFF for ducting that I had on the YC-14 wing.

Used white paper to design EDF ducting and put together 2 nacelles that will be glued to bottom of wing.

If you notice on the wing tips, I taped and glued the extensions on to the wing(board is only 30" long). That will improve the stiffness and as of now, I just used 2 full sheets of Read-Board. So project should only need 3 sheets.

Next is the designing of the landing gear so it doesn't collapse or tear off.

 

[L Edge]

Time has past where the project hasn't moved on(stuck on design of top shape). So ended up with this shape to get going to finish it. I am happy that cross seam has enough material above it to provide rigidity to the lengthwise fuselage.

Will add material below so nose gear doesn't rip out or Readi-Board doesn't crumple if I have tough landing. In order to finish up, I have to remove a 64 EDF from another flying plane for the second engine which is a tuff decision.(ain't coming from my F-117 or Warthog).

If you look above the plane, there is the ducting waiting for the EDF. May not be the best shape for a Dark Star, but if I did my calculations right, it flys. That's what is important.

 

[L Edge]

Ripped out a edf and glued it into the exhaust ducting. Positioned it on the under belly of the wing with the other and glued the ducting to the wing. Jammed in short segments of foam board with applied glue to prevent rolling of the ducting and edf's..

Next installed outer housing coving EDF and glued

Covered the second EDF and this is what it looks like.

Next need to put elevons and Esc's on. Then will fire it up. Don't know if I will put gear on this, if lite, just may chuck.

 

[Brian B]

Great build. I'm case you were not already planning to, I would seal off the EDF on the inlet, deep inside directly in front of the can, funneled if possible. I had a blunt-edged fan out in the wind, and besides lots of induction noise, it was very inefficient. I 3D printed a simple inlet funnel and the thrust improved dramatically.

That it gonna look so awesome!

 

[L Edge]

Great build. I'm case you were not already planning to, I would seal off the EDF on the inlet, deep inside directly in front of the can, funneled if possible. I had a blunt-edged fan out in the wind, and besides lots of induction noise, it was very inefficient. I 3D printed a simple inlet funnel and the thrust improved dramatically.
View attachment 239361
That it gonna look so awesome!

Thanks a lot for keeping an eye out on my project. Welcome any comments. Haven't addressed that issue yet since I glued the ducting to the wing. Hoping to string the elevon servo wire thru(?) the engine housing.

Don't have a 3D printer, that offers a good way to design the outer shape of upcoming 6th generation jets.

 

[Brian B]

3D printing was a cheat, so don't worry about not having that. That was just an example how I improved thrust.😉
You can just take a paper or plastic cup, circular trim for your EDF size, and project the box size upward and cut out the four resulting parabola curves. Then stuff into the opening ahead of the fan.

 

[L Edge]

Was able to glue in servos, decided to keep the ESC's on outer bottom fuse(cooling) and now stringing wires to an open hatch on top for battery position. Decided to use a 3S 3300 battery with 55C and did a weight and balance. It felt real light so I decided that perhaps I will not need any landing gear and will hand launch.

Only negative would be on landing, could destroy the blades. Going to shoot for launch day next Saturday.

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[L Edge]

Finished off Dark Star with 3s 3300mah battery aboard weighing in at exactly 2 lbs. With the 5 bladed fan and held vertical, it hovers in the house with 1/2 throttle. Using a V Tail mixer, now have differential throttle to help turns and synchronize the fan speed for even thrust.

Cut out hatch to insert battery and electronic parts. Really unsure of CG. So test steps will be used to see if it can fly.

Look, it's flying. Be interesting to see how it holds up using the Adams Readi-Board.

View showing a lot of air between the EDF blades. Lots of tradeoffs when you use EDF's. You don't have top speeds, I prefer 3s weight compared to 6S.

Will do video of flight.

 

[L Edge]

Things I forgot. Using Readi-board and the 3300 battery way forward, needed to strengthen nose from bending. So ended up using balsa wood and used epoxy to bond. If there is a nose plant, will reduce crumpling with balsa and of course used black package tape to cover it up.

Notice that I located battery vertical so it would be movable(no velcro) and not move for balance in flight. Space is tight

To better protect Readi-board from bending due to G loads, epoxy hardwood 2 strips along hatch area and hope it holds.

All that is left to see is to button it up and see if it does fly?

 

[Brian B]

Good luck! Should look like a dart up there.

 

[L Edge]

Today was check the CG segment. Net result after three low launches is I am really unsure of where the CG is. Minor dings, but Readi-Board isn't the strongest material.

With the EDF's below the wing, it tends to collect the grass and dirt which can trash them. So best choice is to go back and add landing gear and use the parking lot to launch and land in the soccer field. Good way to find out how well the material holds up to gear.

 

[L Edge]

Finally finished with the landing gear for Dark Star.

Being an experimental plane and using Readi-Board, came up with using my pylon racing landing gear and wheel and felt it should hold up pretty good where it is hot glued to the side EDF frame and also to the wing.

For the nose gear:

It is under the battery(non steerable) and wheel bent back 45 degrees so it takes shock of clumpy grass and the 45 degree bar helps in reducing gear being torn off. Black blob is balsa wood with hollow brass tube where wire is inserted and bent on top and glued so it doesn't rotate wheel. At least is doesn't add much weight to the overall weight.

Going to industrial park tomorrow and see what happens to determine where CG is. Object is to gather speed, apply blip of elevator and see what happens. Did the same with the SR-71, F-117 and A-10 Warthog.

 

[L Edge]

Day 1:
No video, took Dark Star on a run to see if it would lift off and no luck. After high speed run, it took a sharp left turn and hit the curb and stopped where I couldn't see. Result, the nose wheel and mount ripped off. Moved battery back.
So glued it together and went for second try. Got up to high speed and sound of EDF changed and no hits this time. Had to spend 15 min looking for fan blades, it slipped off the shaft.

Day 2:
Moved battery back, ready to go, full throttle and in about 24 ft (3 stripes) lifted off and then dropped and bounced later and then back to day one and not only crashed into the curb, it bounced up on it and did some more damage. So end result, my plane is now showing battle scars of the war on CG (still need to go back further), but is still winning.

I give the Readi-board a 9 for the G loads it took and keeps me trying. Other annoying noise in video beside noisy wheel (just figured out is camera is loose in the hat frame) will be solved.

Here is the video. Run it in slow motion to see it lift off with that short distance. Hoping that I will be able to fly it off the parking lot of the soccer and not hit the guard rails like the F-117.

 

[L Edge]

Finally, Dark Star is in the air. It was a short run (maybe 2 secs) and it 's flight required no control movement while there until I nosed it over and cut the throttle. Guessing it went into the air at about 30+ ft from start and leveled off about 8-10 inches high. I would suggest if you have gear, try to incorporate a steerable nose gear. If I would have chucked it, not doing it this way, would have nose planted it and I would have a crinkled mess and gave up.

I am impressed that building light and only have 2 5 bladed 3S EDF system allows that kind of acceleration. Won't have top speed, if successful, I'm happy I resolved the issues(more than CG) what it took to get it going. Besides, I want to design and fly the bird, not using a FC or gyro. For best results, slow the video speed to .25 rate and watch from 4-6 sec to see actually liftoff and a noisy landing. I probable covered +300ft for entire flight where it took quite the roll to stop. Differential thrust helped keeping my direction straight.

Next, facing me is the guard rail and the thick clumpy grass soccer field for the big one. Go look at my F-117 takeoff to see what I mean. So will my front LG take the stress(3300 battery above it) on a power on landing? I plan to fly it in with power on.

 

[Mr NCT]

Finally, Dark Star is in the air. It was a short run (maybe 2 secs) and it 's flight required no control movement while there until I nosed it over and cut the throttle. Guessing it went into the air at about 30+ ft from start and leveled off about 8-10 inches high. I would suggest if you have gear, try to incorporate a steerable nose gear. If I would have chucked it, not doing it this way, would have nose planted it and I would have a crinkled mess and gave up.

I am impressed that building light and only have 2 5 bladed 3S EDF system allows that kind of acceleration. Won't have top speed, if successful, I'm happy I resolved the issues(more than CG) what it took to get it going. Besides, I want to design and fly the bird, not using a FC or gyro. For best results, slow the video speed to .25 rate and watch from 4-6 sec to see actually liftoff and a noisy landing. I probable covered +300ft for entire flight where it took quite the roll to stop. Differential thrust helped keeping my direction straight.

Next, facing me is the guard rail and the thick clumpy grass soccer field for the big one. Go look at my F-117 takeoff to see what I mean. So will my front LG take the stress(3300 battery above it) on a power on landing? I plan to fly it in with power on.

47 thumbs up - good job!