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

kilroy07

Well-known member
#61
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.)
 
#62
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.
 
#64
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

Well-known member
Mentor
#65
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?
 

kilroy07

Well-known member
#70
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...)
 
#71
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.

20190428_132405.jpg

20190428_132411.jpg
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.

20190428_132416.jpg

20190428_132428.jpg

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

Well-known member
#72
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

Well-known member
#73
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. ;)
 
#74
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.