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

[Aros]

Nice recovery!

Man, that will put some more hair on your chest! GREY hairs at that!

[GliderGuy]

Does your SR-71 “feel” differently of late? What’s up with that?!

I’ve been going out late afternoon to avoid strong sunlight and the potential for foam gatoring. The air temperature and humidity are still quite high for north Texas (30 inches of rain so far this spring).

She feels different…more sluggish and more up trim is needed,

Ah Ha! Density Altitude effects. Hot air and high humidity combine to make a high density altitude even at our low field elevation. Note: Thin, less dense air is defined as high density altitude.

The impacts are: Less lift, Less thrust for a given throttle position setting.

So, 15% to 20% more throttle is needed to make her feel solid again, in these conditions. You may need to land 30 seconds sooner than you did when the weather was cooler due to the higher throttle setting.

It’s not the SR-71…it’s the impact of density altitude on the SR-71!

Most birds are overpowered, so one doesn’t notice. The SR-71 is not classified as being overpowered for its weight.

-GG

PS The A-10 V2 just laughs at density altitude. It has soooo much power.

[GliderGuy]

It has been awhile since the SR-71 has seen any posting. I’m continuing to add to the number of flights on mine and finding she can handle 7-8 knots of wind just fine….10 knots in a pinch.

I prefer to fly her on more calm days because light wind means less wing waggle. Sooo neat looking in smooth air!

She is more challenging to fly than my other birds and demands you pay attention. But I would not classify her as hard to fly.

Landings can be buttered on. The more I fly the SR-71, the more likely the landings will be good. I still manage to drag the plastic bottoms of the exhaust outlets at times. There is just the right time to reduce power while in ground effect to avoid a float or avoid an exhaust strike.

Limiting myself to rolls and loops and inverted flying. Pretty tame scale flying. But definitely enjoyable!

A bird for the novice, she’s not. I’ve seen a video where 80 mm fans were added along with 2 batteries. She handled that fine. Seeing that weight didn’t seem to be a bad thing…On my “to try” list is 2 6000 mAh batteries on board to extend the flight time. I have a LONG runway to fly from, so should be OK.

Some day….

(Maybe someone already has?)

-GG

[GliderGuy]

Heads up…you SR-71 drivers may want to buy some main gear door parts. Even though I strengthened the torsion arms (they have lasted many,many landings), one finally broke today. The one main strut and 3 wheels departed the plane, and she tilted on a wing tip to a stop. The outer main door snapped off one of its hinge pins.

Since I have proven the torsion arms may break over time (even after strengthening them), you may also want to order a main gear replacement for L and R sides. Couldn’t hurt.

I’ve got her repaired and ready to go.

-GG

PS ATTENTION MRC…Need the torsion arms to become orderable instead of showing OUT OF STOCK. Sure would be helpful.

[GliderGuy]

......:

-GG

PS ATTENTION MRC…Need the torsion arms to become orderable instead of showing OUT OF STOCK. Sure would be helpful.

Man, That's service. I got notification that the anti-torsion arms are open for order entry. Got some on order!! Yet another reason why MRC is my "go-to" company...customer service is hard to beat!

Thanks MRC for listening.

-GG

PS In case you are interested in how to strengthen the anti-torsion arms, here is the method I use that works well....may eventually break, but proven to last many, many landings;
- Materials: 0.020 or 0.032 steel safety wire
- JB Weld epoxy (JB KWIK 5-min epoxy will work, but it is not as strong)
- isopropyl alcohol

You can do the work without having to remove the anti-torsion arms, but it requires more of the 'thread the needle' action with the safety wire. For the best bond, Dremel off the black paint.

Steps:
- Clean the anti-torsion arm and safety wire with alcohol
- Fill each arm's voids flush with epoxy and thinly coat all sides of the arm with epoxy. Take care not to get epoxy into the hinge areas
- Once the epoxy hardens, cut about 6 inches of safety wire. Begin at the widest part of the anti-torsion and spiral wrap with safety wire starting at the widest part of the anti-torsion arm
- Spiral wrap each half of the arm individually with the steel wire to the smallest taper just short of the hinge area
- Squeeze with pliers to a tidy wrap. Don't leave the ends of the wire sticking out
- Finally coat the entire spiral wrapped half (each half) of the anti-torsion arm with epoxy. BE CAREFUL not to get epoxy into the hinge.
- Once the epoxy sets, test for freedom of movement. If an area of epoxy is too thick, Dremel it thinner.

[GliderGuy]

Merry Christmas, everyone....

Figured it might be of interest to others / reflections on the FW/MRC SR-71 after almost a year of flying the Blackbird and after making several hundred flights with her.

Modifications made:
- Beefed up the anti-torsion arms on every landing gear strut (see post 305 above) and...
- Replaced all the wing control surface servos with MKS HV69 servos....left the rudder servos stock FW.
Note: The servo replacement was prompted by a stock FW outer "aileron" servo failure which resulted in having to use rudder for roll control in order to bring her back down safely.
- I wanted to reduce the chances of another servo failure...that failed servo was not easy to overcome and continue to fly.

GENERAL COMMENTS:
- The SR-71 is a well built airframe. I'm not seeing any indications of foam wrinkling or stress cracks anywhere. Granted, the most stressful maneuver I do with her is loops.
- She handles wind fairly well. Anything above 5 mph is apt to cause some wing-roll oscillations. A 10 mph to 12 mph wind is well tolerated (she's stock set-up on the stock gyro).
- Approach on final with a bit of power (20%) and nose up attitude, use throttle to adjust the rate of descent. She lands easily with little, if any, tendency to crow hop after touchdown.
- With an Admiral 6000 6S 50C LiPo, expect a flight time of 3:30 at 60% cruise throttle and a bit of hot-rodding. Longer flights are possible, but you'd be eating into your emergency go-around option.
- Initially, the mains tended to tighten up and not roll well after several landings. This takes some wheel trimming and lower fork tweaking to reduce the rolling friction caused by the design "settling in". It didn't take long to solve this issue.
- I have not stalled the Blackbird....seen some do it on YouTube. I have no desire to stall this bird.
- My CG is a tiny bit ahead of the factory mark, but other than a longer take-off run and slightly higher landing speed...I am fine with her CG location.
- Because of the way the controls move to roll into a tight-ish bank, the nose tends to drop. This takes a bit of getting used to...requiring one to add more up elevator than most RC planes. This might also be CG related.
- - It somewhat feels like she wants to go out of control. However, this is not the case at all. it is just a result of the way the elevons move to roll the bird. You get used to it quickly.
- The sight picture takes some getting used to. So, keep her in close for several flights until you get used to it.
- Set the expo on the ailerons to about 50%. You'll be glad you did.
- I do not use dual (high) rate, although i set it up.
- Aileron rolls, loops, inverted flight, Cuban 8 are all easily accomplished.
- Moving the CG back a bit will (per YouTube reports) improve the aerobatics and reduce the length of the take-off roll. I have not moved the CG back.
- No attempt to operate her on grass.

She's not a bird for the novice! However, once mastered, it's difficult to imagine another bird that commands as much presence in the air. She's a real crowd pleaser.
For such a unique shape, FW/MRC did a commendable job with this design. I fly her as often as possible.

-GG