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        Discussion 69MM SR-71 Blackbird

#1 Aros Mar 26, 2011 09:56 PM

69MM SR-71 Blackbird
3 Attachment(s)
Grabbed the ubiquitous 64mm airframe from Hobby King, didn't bother installing the retracts since my club's field is grass, put two 69mm E-flite Delta V 15 fans with the 15 motors in her (after some carving out of the motor mount area) with two E-flite 60amp ESCs for over 1,300 watts. Running a 4s 4000 45C battery.

Today was the maiden and holy CRAP what a rocket! :eek: :D

I didn't have a gun but I would guess she was WOT early in the fresh battery phase at 105-110 mph...This is my fourth SR-71 but the first one where it was an airframe and given a worthy power plant. Now that I have the CG, throws and trim where I want them I can't wait for the next flight. Anyone else putting larger fans and motors in their 64mm SR-71?

#2 Corelli Mar 26, 2011 10:03 PM

Sweet. Im wondering how much could be gained from removing those cones on the intake .

You got any way to take video?

#3 j3tman Mar 26, 2011 10:08 PM

Wow nice job, I would also like to see some video if you have it :)


#4 Aros Mar 26, 2011 10:27 PM

No video but it's high time I get a video camera to log some of these flights. I'll see what I can do. Corelli, I'm not sure on the cones but due to their shape and minimal weight I don't see them as being much of an issue in regards to drag. Plus I'm a scale geek. :)

Check out these afterburners I'm getting from Joe1320...He's building a test kit for the SR-71 and was kind enough to make one for me. I can't wait!!


#5 Corelli Mar 27, 2011 12:11 AM

Kelly Johnson took Dr. Alfred J Eggers research on lifting body technology and designed the SR-71. It was designed to fly at 152,000 ft of elevation . The problem with turning that model into a scale flyer is that @ our elevation the plane has too much lift . Something that started out as incredibly fast becomes a fight to undo the inherit lift created as you gain speed.

To make a SR-71 scale model be as fast or faster as its originator it has to break from its scale appearance.

The SR-71 has an equator. The structure above this line makes up 75% of the planes mass. This was needed in the low atmosphere of space. If we want this plane to be the guided missile it can be we need to change the mass . We need to change that 75% down to approx. 56% above the centerline . Change the shape of the SR-71 . To all the scale connesours it will be an obvious violation. But the overall outcome could be amazing.

#6 Aros Mar 27, 2011 12:30 AM

Very fascinating if not way beyond my knowledge point, lol. My goal with this bird was to get over 100mph and I've done that. Cones and all! :)

#7 AIR SALLY Mar 27, 2011 01:23 AM

might go faster with a bigger cone and smaller tailpipes;)

#8 Paul5910 Mar 27, 2011 02:23 AM

Good looking bird Aros! I would give anything to see that bird streaking by at my flying field. Do you think retracts would be hard to install? Is there plenty of room, etc.? Did she come in fast for landing?


#9 Aros Mar 27, 2011 03:41 AM


Originally Posted by Paul5910 (Post 17798608)
Good looking bird Aros! I would give anything to see that bird streaking by at my flying field. Do you think retracts would be hard to install? Is there plenty of room, etc.? Did she come in fast for landing?


Retracts are easy to install...The ones that come stock with the airframe are fairly self explanatory. In the past, I found the retracts to be fine. I never had a problem with them. Cheap as they are, they always seemed stout to me.

They have made plenty of room for the retracts. In fact, it's one of the areas of this plane that I thought they did a decent job, even early on. Flight dynamics is another matter. Understanding how fundamentally different this bird is to fly versus anything else you will ever fly due to it's delta wing and elongated fuse is paramount to have many successful sorties with her but retracts is definitely not one of the issues.

As for landing, she slows nice and easy, but you have to be mindful of the flare phase as the nose likes to point to the heavens in a hurry if you aren't careful. I forget the author who said the following (in the Don's Wicked SR-71 thread) but I find this a helpful bit of information in regards to landing the SR-71, regardless of size:

...I believe that it's the tail (or rear half of the plane) stalling, and being heavier than the nose (or front half of the plane) the back of the plane sinks rapidly... I believe this is a characteristic of all delta wing aircraft, when they no longer have enough flying speed to create lift they'll try to do a backflip as the back half of the plane starts to free-fall and the front half of the plane get's pushed up and over by the oncoming airflow. That Concorde that crashed in France did the same thing when the pilots stalled it (trying to keep the nose up with the engines failing, the plane reportedly did a complete backflip and fell onto the hotel below).

In fact, it happened on my maiden today. I gave the controls to a trusty RC pilot and buddy who is a better flyer than me. Although he showed impressive skills during the flight, coming in for the landing I warned him of the nasty tendency for the Blackbird to pitch up drastically with flare right before touchdown and sure enough, it happened. Luckily the plane plopped on the ground hard before hitting a fence (it was actually his flying skill that saved my Habu's front fuse from looking like tiny pieces of black popcorn) and just needed to be re-glued from the original hinge point. A clean break and a lucky one to boot.

#10 Paul5910 Mar 27, 2011 04:07 AM

Aros, I think I see what you are talking about with the delta style planes pitching up while trying to flare. I even think that I may have read in one of the threads about the squall doing something similar. Thank you for taking the time to explain that to me.. Rest assured if I ever find myself behind the sticks of a delta type, I will remember that very good explanation. I will need considerably more stick time before you will catch my transmitter bound to an SR71 though.:)


#11 Aros Mar 27, 2011 05:26 AM

I hear ya...Just know it's worth it. :)

#12 Aros Mar 27, 2011 04:17 PM

I grew tired of waiting for the rain to stop and said to hell with it, time for another recon mission!

My first hand toss (my friend tossed it for me on the maiden) was a bit hairy...I launched it with less AOA than I thought and just about smashed it into the ground...Yikes! Once I established climb we were off to the races. I fly on a hill surrounded by evergreen trees and the echo she makes is almost as cool as the speed!

For landing I really had to fight the urge to flare as any up stick at low throttle and she wants to go vertical. I had to go around and try again and finally just flew her down to the ground.

I need more batteries. :)

#13 Aros Apr 02, 2011 08:56 PM

My friend has a gun so we are going to clock her probably tomorrow, weather permitting. We both estimate she's WOT on a fresh charge around 110mph. It will be interesting to see how close - or how far off - we are.

#14 ApexAero Apr 02, 2011 09:21 PM

Here's the cone program.

#15 Aros Apr 02, 2011 10:24 PM

Thanks Apex...What would this do exactly?

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