Official Freewing Twin 70mm SR-71 Blackbird with Gyro EDF Jet Thread

[Aros]

Yep, it can be done but it's definitely a high wire act.

[EDF-Jetpilot]

Oh my, yes, the Blackbird is notorious for a vertical nose high attitude if slowed/flared too much on approach. I flew the LX version hundreds of times and I can't count how many times it happened to me on approach. Luckily it rarely caused damage but looks hilarious on video. I just had it happen to my E-flite version a couple weeks back. We got a good laugh at the field. Wobble, wobble, wobble and then nose to the sky, slam the elevator stick full down and she plops down, lol.

With the Blackbird she needs to come in with speed and the nose AoA just barely over horizon. She wants to be flown to the ground, and not like an F-16 in High Alpha either.

He can land the SR-71 with high alpha... but I doubt it always works that well.

https://www.youtube.com/watch?v=t5gIJomxkAE

[Aros]

Oh my, yes, the Blackbird is notorious for a vertical nose high attitude if slowed/flared too much on approach. I flew the LX version hundreds of times and I can't count how many times it happened to me on approach. Luckily it rarely caused damage but looks hilarious on video. I just had it happen to my E-flite version a couple weeks back. We got a good laugh at the field. Wobble, wobble, wobble and then nose to the sky, slam the elevator stick full down and she plops down, lol.

With the Blackbird she needs to come in with speed and the nose AoA just barely over horizon. She wants to be flown to the ground, and not like an F-16 in High Alpha either.

[GliderGuy]

One YouTube video comment is, “Don’t stall it! The nose won’t come down…it over rotates, and it won’t recover.”

Basically a high alpha lock situation.

Has anyone witnessed this happening (crash)? Or….is this the pilot’s “assumption”?

As in full scale birds during FAA certification flights, they use spin chutes to get the nose down when experimenting with aft CG stall conditions to get out of the high alpha lock.

Worth a try if you get into an unrecoverable high alpha lock situation…pop the chute out. It might just save your bird.

-GG

[Glideman]

Anybody have the factory gyro settings for SR71 Blackbird Freewing gyro ?

[EDF-Jetpilot]

Thanks! But I’m not going down without a fight! This has been an interesting journey. Appreciate all the guidance and comments. Now we know more than we did a few weeks ago.

All three are beefed up…starting with a good wash/scrub with isopropyl alcohol:

1) Voids are filled with JB Weld epoxy
2) The entire length of each 1/2 is wrapped in 0.6 mm steel aircraft grade safety wire embedded into a layer of JB Weld before the epoxy cured
3) An outer covering layer of JB Weld is painted over the entirety of each 1/2.

I’m also going to fly ONLY on smooth concrete or smooth asphalt…,no gravel. No more 40F flights…warmer air temperature flights to enhance the metal’s flexibility.

I hope all this will make them last. Spares will be kept on hand once they can be ordered because 100s of flights is gonna stress my attempts to beef them up. Dremel removal of the black paint down to bare aluminum before 1, 2, 3 above will be a first step, if they are painted black.

-GG

OK... good! You seem to be a real model building genius.

[GliderGuy]

Thanks! But I’m not going down without a fight! This has been an interesting journey. Appreciate all the guidance and comments. Now we know more than we did a few weeks ago.

All three are beefed up…starting with a good wash/scrub with isopropyl alcohol:

1) Voids are filled with JB Weld epoxy
2) The entire length of each 1/2 is wrapped in 0.6 mm steel aircraft grade safety wire embedded into a layer of JB Weld before the epoxy cured
3) An outer covering layer of JB Weld is painted over the entirety of each 1/2.

I’m also going to fly ONLY on smooth concrete or smooth asphalt…,no gravel. No more 40F flights…warmer air temperature flights to enhance the metal’s flexibility.

I hope all this will make them last. Spares will be kept on hand once they can be ordered because 100s of flights is gonna stress my attempts to beef them up. Dremel removal of the black paint down to bare aluminum before 1, 2, 3 above will be a first step, if they are painted black.

-GG

[EDF-Jetpilot]

The 70 mm FW F9F Panther Jet mains have the same anti-torsion arm. Thanks Evan! I will be removing the arms and installing them on the SR-71 ASAP.

SKU FJ22111084

Available option until the SR-71 spares open for ordering if you are in a “gotta have” situation like I
am.

Update: Installed the Panther Jet’s anti-torsion arms on the SR-71. Perfect fit! I am in business again.

-GG

Photo of the Panther Jet’s main gear.

Great, I wish you luck! From the looks of it, it's exactly the same cast aluminum as the SR-71, just not painted black, not promising... but I don't want to dash your hopes and wish you good luck and a long life.

[Evan D]

You’re very welcome

[GliderGuy]

The 70 mm FW F9F Panther Jet mains have the same anti-torsion arm. Thanks Evan! I will be removing the arms and installing them on the SR-71 ASAP.

SKU FJ22111084

Available option until the SR-71 spares open for ordering if you are in a “gotta have” situation like I
am.

Update: Installed the Panther Jet’s anti-torsion arms on the SR-71. Perfect fit! I am in business again.

-GG

Photo of the Panther Jet’s main gear.

[GliderGuy]

Possibly, but FW/MRC quality shows that for the birds I have purchased and have flown way beyond any reasonable design limits..all do a great job of holding up to tons of flights.

If a milled upgrade isn’t offered as a fix, then this may be the only weak point in this beautiful SR-71. I’m not seeing anything else (30 flights only).

-GG

[f4u ausie]

Next weakest.. that is

[f4u ausie]

There (Always) is......

[GliderGuy]

Good info…thanks. Luckily I have less-convenient access to a concrete surface and also a smooth-surface asphalt surface. Just need to get the spare parts opened for order. Will nix the gravel surfaces….heads up to all.

FedEx confirms delivery of the Panther Jet mains today. I’ll be evaluating the anti-torsion arms on them.

-GG

[Evan D]

And once fixed is there a next weakest link?

[EDF-Jetpilot]

Which supports my prior “pot metal” comment. Broken cast iron pot surfaces look just like the broken surfaces of the anti-torsion arm. A 3DP version of this arm in a strong plastic and not brittle material may be a better solution than the cast metal part.

One thing I neglected to mention. When these broke, it was about 40F. These parts may be less suceptible to being brittle when the air is warmer. If you have only flown your bird in 60F temps, that may be why yours haven’t snapped.

-GG

PS Flying cold-soaked LiPos below 50F has been stated to be harmful to the battery. Mindful of this precaution, I was keeping my batteries in a very warm truck.

Exactly... I think the SR-71 is really made for smooth runways, not grass and gravel. Your gravel runway probably puts too much strain on the pivot points on the wheels, which jolts and tears the undercarriage too much over time. I don't think it's a material defect, because no one else has reported this problem. Things like this would pile up quickly if it were a real problem, like the elevator on the first MIG-29 delivered back then. However, if you can find a suitable milled part made of solid aluminum, it will hold, a printed plastic part is far too weak in my opinion, unless there is at least a printed CFK. Although realistically I think that the problem cannot be solved on your runway.

[GliderGuy]

Update on the paint match….
The foam block I inverted her on compressed the area just ahead of the parachute doors. Note to self….use more foam blocks and support in more areas.

This area required filling and sanding to restore. The Tamiya satin black proved to be much too shiny. A better match is the following:

RUST-OLEUM FLAT BLACK
2X ULTRA COVER PAINT+ PRIMER

Once well dry, buff the newly painted area with a dry Mr. Clean Magic Eraser sponge. This sponge has a very fine abrasive which is perfect for getting the newly painted flat black area to a matching look.

It takes several thin coats to “hide” the filler texture.


-GG

[GliderGuy]

A rough surface on metal parts usually occurs for one reason only: it is a cast part, i.e. cast and not milled. Cast parts are much more susceptible to breakage than milled parts.

Which supports my prior “pot metal” comment. Broken cast iron pot surfaces look just like the broken surfaces of the anti-torsion arm. A 3DP version of this arm in a strong plastic and not brittle material may be a better solution than the cast metal part.

One thing I neglected to mention. When these broke, it was about 40F. These parts may be less suceptible to being brittle when the air is warmer. If you have only flown your bird in 60F temps, that may be why yours haven’t snapped.

-GG

PS Flying cold-soaked LiPos below 50F has been stated to be harmful to the battery. Mindful of this precaution, I was keeping my batteries in a very warm truck.

[EDF-Jetpilot]

Any chance of a photo of the fracture surface. Preferably magnified. "Grainy" appearance is a classic sign of embrittlement.

https://gearsolutions.com/department...re-mechanisms/

A rough surface on metal parts usually occurs for one reason only: it is a cast part, i.e. cast and not milled. Cast parts are much more susceptible to breakage than milled parts.

[DCORSAIR]

I can never apply decals properly it seems, I got most of the top side ones on with no issues but messed up the stars and bars, I was doing good at first but don't ask, I hate applying decals so I could use a set if anyone has the stock decal sheet you didn't use.???