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

[GliderGuy]

Sure….but no need for any lightening voids. The SR-71 obviously puts a lot of stress on this arm, so the stronger the better. It’s on bottom, so scale for me is a don’t care. Not flying a $700 bird for lack of a $5.00 part is a downer.

Of course, they’ll need to be designed with the triple tang design of the SR’s design.

Thanks! This is good feedback.

-GG

[GliderGuy]

Hi Aros and all…

Ahhh the discoveries to be made when shaking down newly released models.

Disregard anything I have posted before about the anti-torsion arm being plastic. They are most definitely BRITTLE metal.

After 30 total flights (4 more made at sunrise today), one of them broke on a main gear. She stops pretty short when a main rotates 90 degrees….and it was a smooth landing!?!?!?

I did come up with another solution for a “keep it flying” fix, but a well designed 3DP plastic piece that is less brittle is needed.

Evan’s suggestion to try the ones off the FW 70 mm Panther experiment is delayed in shipping. Hopefully, that anti-torsion arm design will fit and is stronger.

Some of y’all with 3DP expertise might take a stab at a totally new and stronger and less brittle design for this part.

Now…off to fix arm #2 so I can fly it tomorrow.

The asphalt surface I fly off is not the silky smooth, fine aggregate type. I would classify the surface as small pebbles. No doubt the small pebble bumps are stressing the arms, but a ton of flights with other models are flown without gear issues being caused.

Until a more robust fix is available, operating the SR-71 off rough surfaces (grass if possible) will likely cause these arms to snap within a few flights.

-GG

[GliderGuy]

The repair lasted 4 flights and all were good main-first landings. Back to the drawing board to repair the anti-torsion arm.

25 total flights….getting the hang of it and loving it!

-GG

Update: The outer end of the part that the bolt goes through is metal. Hmmm…may be an all metal part after all, but I didn’t investigate by scraping paint off.
This time, I wrapped the whole thing in steel aircraft safety wire…minus the hinge areas, of course.

More landings will test it. The 70 mm Panther Jet main with the aluminum anti-torsion arm did not arrive today. So, that experiment is delayed another day.

[Kitchnpassmastr]

Ref the post about avoiding paint peeling when masking your model. I’ve had great luck with applying two coats of water-based polyurethane with a brush first before doing anything with the model like decals or painting. Not only do the decals go on better and blend well, but low tack tape is not prone to peel off the paint.

[Evan D]

From an old show... Verrry interesting.

[GliderGuy]

As my dad used to say, “If that’s not a strong repair, then I am a monkey’s uncle.” I went for strength and not beauty - LOL.

I lost the “C” clip, so ended up using a bolt/nut and added a dollop of Foam Tac on the nut to secure it.

If you don’t have a 3DP, and you decide to strengthen the anti-torsion arm on the nose gear before it breaks, carbon sheeting and Foam Tac seems to do the trick. Time will tell.

Carbon was also added to the strut side of the anti-torsion arm. 2 days of curing and the glue is solid.

Regardless of your approach, strengthen the anti-torsion arm BEFORE it breaks.

I also generously coated the bottom portion of the arm in JB Weld epoxy which you see if you zoom in. You could use carbon and FT glue on that part of the arm as well. Epoxy wouldn’t hold the broken top part of the arm.

The MRC 70mm Panther jet main that Evan suggested arrives tomorrow. It has an aluminum anti-torsion arm. I’ll report back as to how it fits into the SR-71 nose gear assembly.

-GG

[Evan D]

People have reported that they have tried and failed.

[ElCid]

I wouldn't hope for that, because in my opinion it's clearly not a grass runway aircraft... that wouldn't be appropriate for the species and it's certainly not fun to fly on grass on a regular basis. You'd be better off looking for something that can fly on grass, like an A-10, MIG-29, MIG-25/31 or something like that, that will definitely make you happier. sorry for my direct answer to you. You can also hang this beautiful thing from the ceiling, this machine looks very good there too. Of course, only if you buy it and then don't want to fly it on grass.

Someone will try it they always do. Hell, the b2 flies off grass just fine and I have all of the planes listed and then some.

[Aros]

I’ll reach out to our Freewing liason so he can look into this issue. Thanks for letting us know!

[GliderGuy]

Looks like a fairly easy 3DP fix, with the weak points beefed up.

Go for it…if you have a 3DP which I don’t. That’d be great if someone would design the improved version and share the 3DP files here.

-GG

I didn’t think about a 3DP solution, since I don’t have one. Thanks for being on top of it!

[Evan D]

Good luck GG, you'll figure it out for sure.

[GliderGuy]

Thanks Evan!!! Ordered and will see if it fits. Appreciate your help!

I gave my attempted fix a gentle test this morning. The Foam-Tac isn’t quite cured hard, yet. But, it seems like it is going to work. There is good adhesion to the plastic and carbon sheeting.

Landing stresses will tell all.

-GG

[Evan D]

Look at the one on the 70mm Panther main struts.

Update…JB Weld wouldn’t hold. Cleaned it all up and am trying Foam-Tac. It will withstand fracturing better than epoxy. Basically, a sheet of carbon is being glued to the top and bottom flat faces of the anti-torsion arm which “cover” the area of the fractured plastic expansion fork/anti-torsion arm.

Whatever you might engineer, a suggestion is make your anti-torsion arm stronger BEFORE it breaks. It is a spare part on MRC, but this part isn’t shipping, yet.

-GG

[EDF-Jetpilot]

Anyone know if the EG01 can be used for steering as well? Just Y into the RUD maybe? I usually install the Assan AG61 in all my EDFs but I don't have an extra for this one and could not find anything in the manual.

I'm not a fan of steering gyros on the nose wheel, but the B2 is almost impossible to control on the ground in crosswinds without one. But since the SR-71 is much longer than an F-16, I don't think it's needed here. My EDF jets don't usually fly completely straight on the ground, but you can easily correct that during takeoff. I love gyros in the air, but I don't need them on the ground, except for the B2. The longer the wheelbase, the less a nose wheel gyro is needed and vice versa. That's simple physics in my eyes. But to each his own, as far as I'm concerned you can mount a nose wheel gyro on the SR-71 too, I think that's a bit excessive.

[GliderGuy]

Update…JB Weld wouldn’t hold. Cleaned it all up and am trying Foam-Tac. It will withstand fracturing better than epoxy. Basically, a sheet of carbon is being glued to the top and bottom flat faces of the anti-torsion arm which “cover” the area of the fractured plastic expansion fork/anti-torsion arm.

Whatever you might engineer, a suggestion is make your anti-torsion arm stronger BEFORE it breaks. It is a spare part on MRC, but this part isn’t shipping, yet.

-GG

[GliderGuy]

Temporary fix. I will sand it smooth once the Foam-Tac cures.

Basically, I built a carbon fiber box around the weak nose gear expansion fork/anti-torsion arm.

Suggest you reinforce yours before it breaks. Easier now than after it breaks.

-GG

[GliderGuy]

Hi Aros, Time to put the FW re-design team to work.
After 21 flights, GG has uncovered the first design weakness.

The plastic expansion fork/anti-torsion arm on the nose gear is too weak. It MUST be made stronger! The arm snapped. Of course, no steering after that, and when I lifted the bird, the wheels+shaft fell out.

This is going to require some thought as to how to fix it and get the bird going again before spare parts become available.

I’ll start to engineer a solution this evening. Stay tuned. I’m gonna look at a carbon fiber solution.

I have faith your team will come up with a more robust solution. If it must be plastic, then make it a solid piece without any mold cut-outs. The thin molded cut-out area is where it snapped.

So far, other than this, the bird is a solid, robust design. Reinforce yours BEFORE it breaks!
The black line shows where it broke.

-GG

[Aros]

At least on calm days…maybe this is the way to land her short. Impressive! Need to experiment up high first.
No claim to the video’s authenticity is made. Attempt only if you decide it’s safe.

https://m.youtube.com/watch?v=s9pQ6LIorV8

-GG

I believe that video shows Jon (Two Brothers RC) at his well aft of recommended CG flights, not totally sure, plus of course it's slow motion obviously. For me personally I am sticking to recommended CG, at least for my initial flights.

[Aros]

There is a spare parts listing for it, so I hope so.. Just need to wait for stock now.

Yeah I forgot I added that spare part, lol! Total brain fart. The latest estimates are early March but they are verifying exact ETA.

[GliderGuy]

At least on calm days…maybe this is the way to land her short. Impressive! Need to experiment up high first.
No claim to the video’s authenticity is made. Attempt only if you decide it’s safe. So far, I haven’t come close to doing this. I’ve been landing like the AL-37…about 4 clicks of throttle on final until round-out.

https://m.youtube.com/watch?v=s9pQ6LIorV8

-GG