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

[GliderGuy]

Heads up…Flipped the bird over for some cleaning and found the outer elevon control horns and ball clevis had developed some thinning from occasional ground scrapes.

It is suggested that a periodic check for this wear is advisable. Would hate to see something as preventable as this cause a loss of control.

One solution would be to insert and glue a small carbon tube surrounding the exposed push rod with some overhang cut into the tube to protect the horn/ball clevis from ground scrapes.

-GG

[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

[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]

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]

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]

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.

[Aros]

Nice recovery!

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

[GliderGuy]

Reference my post 302 above….

If you elect to upgrade from the 4 stock 17g wing control servos, the MKS HV69 is almost a perfect fit replacement. Some very minor Dremel adjustments to the white plastic wing servo sockets and the servos’ mounting tabs is all that is needed.

I used these in the past and on the MiG-29 full flying stabs with good results.

Note: They talk to you a lot more while sitting idle on the ground…especially if a gust blows on the control surface. They fight the gust’s attempt to move the control surface with an auditable sound.

-GG

[f4u ausie]

Good job gg. U cannot. Ever. Ever. Beat experience no matter what

[GliderGuy]

OoooEEEE!!!!! I am here to report more EXCITEMENT than a flea has when seeing an elephant!

YOU CAN survive an elevon servo failure!

Took off and she didn’t feel quite right after about 15 seconds. Made a left cross wind turn at about 200 ft up and she went into a steepening left bank with the nose dropping. Not responding!!!!

A fleeting vision of a pile of foam snapped my years of experience into action..RUDDER!!!! SWITCH ROLL CONTROL TO RUDDER!!! Maybe it will work?!

Sure enough, with a few seconds to impact, she rolled level and pitch became sorta active. I got her level and made a hasty yet gentle pattern to land. On final, she was rapidly oscillating in roll 45 degrees bank right to 45 degrees bank left.

Luckily, she touched with 0 degrees bank…lucky timing.

So why did she go bonkers when the outer right elevon servo fail? That was the failed control. My guess is that the gyro was having a tough time figuring out what inputs to feed the servos with one failed. I surmise this from the rapid bank oscillation on final approach.

Now….where’s that spare servo?

-GG

PS My RC Experience gained since 1965 paid off handsomely this evening.

[Evan D]

For me a gentle but firm push, you are compressing each cell back flat.

I have been trying, i must be doing something wrong. I have the spoon in the freezer for about an 30 minutes, then rub aggressively, but I’m not having a ton of luck

[Alphonso]

Sanding alone will simply damage the surface of the individual foam cells and leave you with a fluffy surface. Fine grit is worse on epo, it removes nothing until it it goes too far. I have sanded EPO successfully with course grit as it cuts and removes material. You then need to fill the damage done with a spackle and sand smooth but you have half a huge model to do and the panel lines make it an unenviable task. I would rather buy a new one than do all that for it to still look less than perfect.
If you really want to do it, I would fill every panel line and do a full repaint. Would likely be quicker than trying to match the factory finish.

[ggillila]

I’ve had good luck rubbing a cold spoon across to reduce it.

I have been trying, i must be doing something wrong. I have the spoon in the freezer for about an 30 minutes, then rub aggressively, but I’m not having a ton of luck

[Evan D]

I’ve had good luck rubbing a cold spoon across to reduce it.

[ggillila]

Oh i just wanted to add
At the end of the day, enjoy it. Nothing is perfect. So while I am saying be more careful, I’m also saying enjoy it and don’t just have it collecting dust because you’re focused on keeping it perfect. Get a good balance🤙🏻

[ggillila]

I am the guy who reported it to GG, so i figured I should say my exact conditions so the rest of you can avoid it.

It was mostly cloudy, and the sun was behind a cloud for 2/3 of the time mine was outside. The plane was only outside for about 5 minutes including the flight. It was 75°

When I landed, I went to grab it and the entire right side looked like a snake, the side that faced the sun for maybe a minute when I was doing final checks. This was only my second flight :(

So this time of year, as GG said, unless it’s COMPLETELY cloudy, do not bother unless it’s early morning or late afternoon. I was very careful with mine because I’ve had something dark like this before, but can’t be too careful as read here.

As for the future of mine….its totally just aesthetic so obviously it’s not out of service and ready to fly whenever, no internal issues or anything. Nothing was hot internally (aside from the battery of course). As mentioned it’s only on one side…..a whole new meaning for “get my good side.”
Now I’m back and forth over if I should sand it down to give it the “wear” look with super fine sand paper because it’d give me a reason to get rid of the snake skin, or if i just leave it because you can’t see 5 feet away anyway (or on the good side)

Aros thoughts?

[Aros]

Yep there's a reason we added a section on the product page about gatoring. Extreme caution is needed to avoid the dreaded basketball texture.

[GliderGuy]

A report about bad foam gatoring has reached me. So, be cognizant that care must be taken to not expose the SR-71 to mid-day sunlight.

To maintain the factory new finish this time of year, I’m going to fly early mornings and late afternoons only, unless it is overcast.

A cloth covering while in the transport vehicle isn’t a bad idea.

-GG

[GliderGuy]

Made 10 late afternoon SR-71 flights today. This puts me about 75 or 80 flights. Here are some general observations based on being more familiar with the bird.
- She flies very similar to most EDF jets this size.
- No bad habits…loops, rolls, inverted are all good. I have avoided stalling her.
- Seems to feel better with a little touch of added throttle when the gear are put down.
- 3:30 at 60% cruise leaves plenty in the tank for a go-around even after a couple of high speed passes with a 6000 mAh battery.
- With factory CG, she’s a ground lover on take-off. But apply lots of up elevator and as soon as the nose rotates, quickly ease off the “up” and “wheelie” her on the mains to liftoff. Looks sooo cool.
- If a tad slow on final down low, she responds well to a burst of power if she begins to drop. A few times, I have stopped the drop with up elevator. She will stop the drop, but this will drag the bottom of the jet nozzles. That makes one heck of a noise.
- I am comfortable with the sight picture as she flies around. Not that hard to tell what she’s doing, “IF” you pay attention.
- After beefing up the anti-torsion bars on the landing gear, I have had no more issues.
- You really CAN make good landings with her at the factory CG.
- I am not uncovering any airframe structural design issues. I’m not seeing any stress creases in the foam anywhere.

So bottom line…nothing unusual about the SR-71 if you are an experienced large EDF jet pilot. She’s a solid flier. One day I may tweak the gyro sensitivity up on the ailerons to reduce the wing rock on final that sometimes happens. For now, I just ignore the slight wing rocking and don’t try to fight it when/if it happens.

-GG

[Aros]

I get why people ask, because the majority of us do fly off of grass fields. Sadly, some models - like this one - are not made for grass, period. It's not impossible, but again, the grass better be like a putting green or you are asking for problems.