Foam Board SR-71 Twin 50mm EDF(?)

kilroy07

Legendary member
Yea, as mine grows, I'm concerned about weight as well...
I was hoping to see yours fly to prove it can be done... Hopefully the 69mm fans will provide enough umph to get her airborne!

Cheering you on for V3! ;)

Curious, do you have any incidence between the nacelles and the nose? She had (and I'm guessing here) something like 3-5 degrees "nose-up" (down thrust?) :unsure:
I wonder if that would help with lift somewhat? (I've been trying to figure out how to accomplish it with my model.)
 

Horseman3381

Well-known member
The 3rd nacell should be easy to mount, I just need to get a few fins drawn up to put on it.

When I did the testing with the props I also had an adjustable thrust cone I was using to test if adjusting that helped. I had originally designed the thrust tube to bring the exit area to 1:1 of the FSA. In the testing I found shrinking it slightly got me an extra 5g of thrust. I don't have the numbers handy, but I would guess it is probabaly 90-95%.

We will see how this one flys with the 50mm edf's. I may scale it up and fit some landing gear on it. This could also be good as the larger nacells may let me keep the nacell cones in during flight.

Yea, as mine grows, I'm concerned about weight as well...
I was hoping to see yours fly to prove it can be done... Hopefully the 69mm fans will provide enough umph to get her airborne!

Cheering you on for V3! ;)

Curious, do you have any incidence between the nacelles and the nose? She had (and I'm guessing here) something like 3-5 degrees "nose-up" (down thrust?) :unsure:
I wonder if that would help with lift somewhat? (I've been trying to figure out how to accomplish it with my model.)

I have a little in there, it is 1/8" of drop from back to front, I don't remember the specific degree off hand. Fortunately on this plane the nacells are just glued to the end of the wings, so was fairly easy to do.

I have learned on some of my other builds that the planes were built as they are for a reason. If you ignore details like that, even if they seem trivial, they can drastically change the planes performance.
 

Horseman3381

Well-known member
Any progress?

Sorry for the lack of updates, I have been traveling a lot for work the past 2 months and working on my FTFC19 entry along with another winter project of mine.

I have completed adding the 3rd nacell with the gremlin edf to version 2.

I also have version 3 built with the twin esf's, however I have been having some electrical issues with the esc's I have to sort out in regards to throttle range. The problem is that I cant calibrate the range because one of the esc's doesnt arm for 10 seconds after the first one, which at that point is beeping away for other programming settings. Unfortunately I should have done this when I was first soldering things together, because now everything is sealed in he plane. The throttle ranges are way off between the edf's to were one just starts to spin up at half throttle, and the other is at full speed.

I also have a version cut out but not assembled that I am going to install 2 f-pack motors in as pushers.

Once I sort out electrical issues and my schedule and the weather cooperate I will get them out to maiden. Will probably not be till mid March at the earliest.
 

DamoRC

Elite member
Mentor
Sorry for the lack of updates, I have been traveling a lot for work the past 2 months and working on my FTFC19 entry along with another winter project of mine.

I have completed adding the 3rd nacell with the gremlin edf to version 2.

I also have version 3 built with the twin esf's, however I have been having some electrical issues with the esc's I have to sort out in regards to throttle range. The problem is that I cant calibrate the range because one of the esc's doesnt arm for 10 seconds after the first one, which at that point is beeping away for other programming settings. Unfortunately I should have done this when I was first soldering things together, because now everything is sealed in he plane. The throttle ranges are way off between the edf's to were one just starts to spin up at half throttle, and the other is at full speed.

I also have a version cut out but not assembled that I am going to install 2 f-pack motors in as pushers.

Once I sort out electrical issues and my schedule and the weather cooperate I will get them out to maiden. Will probably not be till mid March at the earliest.

Ouch - sounds like she'll need surgery. Are they different ESCs?
 

Horseman3381

Well-known member
Ouch - sounds like she'll need surgery. Are they different ESCs?

No, they are the same. They are slim/low profile ones I bought that were labeled for use on race quads.

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I will admit the problem could be with my soldering skills and I may have a bad connection somewhere.
 

LitterBug

Techno Nut
Moderator
REALLY Love this bird and the fact that you are making a great stab at it! KEEP UP THE GREAT WORK!

Cheers!
LitterBug
 

kilroy07

Legendary member
Idea...
You could use a 'profile' nacell cone for flight, a triangle cross so that it has the look but with very little disturbance of airflow. If you make then a press fit you can swap them for full cones when displaying the model. Something like this...
View attachment 124636
I was looking at something very similar myself today.

After the full mock-up I realized I needed to design tail-cones (which I will probably do on the 3D printer, I thought I could do cones at the same time...)
 

Horseman3381

Well-known member
Apologies for the lack of updated on this plane. Weather and a number of electrical issues (builder error) on the few days I was able to get out to fly this.

Any who, I was finally able to get a version of the plane out and get a few decent flights out of it.


I am not a big fan of putting props on a jet, but I really wanted to get a version of this plane flying. I decided that to get proof of flight for the fuselage I would put on some proven motors with enough thrust to give better than a 2 to 1 power ratio.

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It was fast, but I'm not sure why I would have expected anything different with two F-pack motors. Even with 10% throws on the ailerons they were still very sensitive. I was able to get it trimmed out for level flight at anywhere from full to 5/8 throttle, however when it slowed down the plane would go into a high alpha and then tail stall(?). From what I have seen, even when a jet is in high alpha stall it is still a nose stall, where as this is standing on it's tail vertically and falling to the ground. Though I shouldn't complain because it makes for a gentler "crash" landing.

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I am going to paint up this version and continue to fly it because I grin from ear to ear every time I get it in the air.

I tweaked the plans after this latest build and am going to build one more version of it with the EDF's and one more version with props to vet the plans, then I will publish them. I am planing to donate the second prop version to the Veterans airshow at FFE.
 

kilroy07

Legendary member
Well done man! Happy to see it in the air! (y)(y)
I think that's the first model SR that actually looks like it's flying scale speeds! :ROFLMAO:

Her big sister will maiden soon (Alpha build) a tail cone is on the 3D printer now! ;)
 

PoorManRC

Master member
I know I haven't been around for a while...
I just saw this come up on my email, and HAD to check it out!
That is such an unreal - GOOD representation of the Bird dearest to my Heart.
...... I just wish my Dad was still alive to see the stunning work that you and Tim have been doing.

Yeah..... Props. :eek: But hey, totally understand that need to get her in the Air, quick, dirty or otherwise!! (y)(y):cool:

A Foam Core Board SR-71 is definitely beyond the thinking of most Engineers. If I may throw in my 2 ¢ just based on conversations I've had with people closely connected with the real flying Masterpiece....

This was literally the first successful non prototype of a "Lifting Body" Design. The front Chines create a surprising amount of Lift!
Possibly - the CoG is farther forward than the Aircraft Designer's Mind would concieve.

The Real thing had the "Gliding capabilities of a ROCK" below 220 knots - as my Dad, Noel Widdifield, Terry Pappas and several other Pilots used to tell me!!

High Alpha Landings and very special Main Tires were the norm, to cope with the MINIMUM 180 knot Landings...
At least until the early fly-by-wire Systems were integrated into the Bird in the early/mid 80s.

High Alpha Refuelings were also the norm.

Even with your Props in the back, at least you've put the Thrust where it should be by design...
Putting a Prop in the Nose would certainly help flight characteristics - BUT IMHO - would be sacrilege!!! :oops:

I know that was LONG WINDED. Sorry-not-sorry? I just have always loved talking about the HABU!!

If you're up for a small risk... Try moving the CoG forward, PAST where common sense might dictate.
I don't know if that will work - but my pedestrian knowledge of Aerodynamics and understanding of the Blackbird, says it's worth trying.

Or, I wouldn't be offended if you ignored this whole post. ;)
 

Horseman3381

Well-known member
The Real thing had the "Gliding capabilities of a ROCK" below 220 knots - as my Dad, Noel Widdifield, Terry Pappas and several other Pilots used to tell me!!

The same guy who flew my 747 during the testing flight did a flight with this and when landing he basically flew it to the ground to get it to land on the bell It skidded for a ways. I will probably just need to learn to do that.

If you're up for a small risk... Try moving the CoG forward, PAST where common sense might dictate.
I don't know if that will work - but my pedestrian knowledge of Aerodynamics and understanding of the Blackbird, says it's worth trying

I have the battery all the way forward right now. I can maybe try a bigger battery. Currently the CG is at the front of the nacelles, so it is pretty close to the front of the wings as it is and I have it trimmed with up elevator to get level flight. Fortunately I have plenty of up elevator left if i want to try.
 

FAI-F1D

Free Flight Indoorist
So, I have finally found this thread!

Craftydan ended up with the painted up prototype. Pretty airplane, although the fuse showed wear and tear from flight attempts, as one would expect. We got it in the air here at the farm and it showed the same high alpha "Sabre Dance". I added a bigger battery (3s 2200 I believe), and it became a completely different airplane. I have about 5 minutes of flight time on it...it was an awesome experience, although orientation was a pain in the neck due to the profile of the plane. She's a gorgeous bird, though, and wonderfully fast even at low power settings. With the more forward CG, landings are very "normal" and can be made power-off, so long as you closely monitor airspeed on the way down so you still have enough energy to flare and arrest the sink rate.

I really want one now. And now I can have one since I've found the plans!
 

Mr Man

Elite member
I have loved the SR-71 Blackbird for as long as I can remember, and have wanted an RC version ever since I started flying. I drew up plans for an twin 80mm version a year ago, but never built is as I was a little to unsure it would fly to invest the time and money into it.

View attachment 118876

However, recently Ben Harber designed and built a B-52 powered by eight homemade EDF units using a gremlin motor, 1.9" props and 3D printed motor mounts. Check out his forum post HERE for more details. After seeing this it got me thinking, would 2 of these be able to power a foam board SR-71?

I took a 3 view of the SR-71 and scaled it to fit Ben's Gremlin EDF's which left a plane roughly 3'-0" long with a wingspan of 1'-7 1/2". At this scale I though that if I built it "geometrically" it would not need any internal structure, and if fit on 2 sheets of foam board it may be possible. After a few hours of drafting I came up with a set of plans.

View attachment 118868


Then a few hours of cutting and gluing later...

View attachment 118869 View attachment 118870 View attachment 118871

The plane is surprisingly rigid at this scale. I was torn on weather or not to add rudders, but ultimately opted to make this a bank and yank flyer for now. If during test flights it appears rudders are needed I will add them. The nacelle nose cones are currently removable because I am waiting on motors and ESC's which should arrive tomorrow. I plan to do the initial test flights without them and see how the motors perform. If the cones end up being a permanent fixture during flight I will likely need to cut "cheater holes" in the nacelles to let in extra air (approximately 1 square inch in size). I still need to cut a battery hatch in the plane, but am going to wait till the motors are installed so I know where the battery needs to go and get it cut it in the correct spot.

I was able to do some glide testing with this version to find where the CG should be. It looks to be about 1/4" behind the front of the engine nacelles. An interesting thing I discovered during flight testing is that with this design it has a lifting body effect that causing the plane to stall like it has canards. With the proper CG set I was able to get this glide 30'-40' throwing it horizontally from the ground which has my hopes up that the motors will have enough thrust for it to fly.

All said and done the plane should weight 630 grams. In Ben's testing he said he got 130 grams of thrust per motor. I bought a higher kV version of the motor than he was using (mine are 6,000kV), and I am going to put 5 blade props on it instead of 4 blade. So assuming the motors don't melt I am hoping to get closer to 180 grams of thrust per motor. With that the plane won't have vertical clime capabilities, but will hopefully fly. I am planning to get everything installed and test fly the plane this Friday or Saturday (weather permitting).

View attachment 118885
Do you have build video or instructions?