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Old Apr 15, 2012, 10:29 PM
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Originally Posted by The Don View Post
Sorry it went down. Hopefully the electronics are still all OK. It almost sounded like one motor started to shut down like a LVC as it quit as you powered up. Each fan/motor wants to pull ~60 amps so ~120 total amps so it is possible on a 4S 4000 the voltage may have dipped a little to low and started to shut down one fan unit.
I think the electronics are okay thankfully. Don, I think you've nailed it.

I use Nanotech's which have been pretty iffy to be honest. I hate to think this one was lost due to a poor battery. However, that explanation leaves an opening for airframe #8.

Never say never!

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Old Apr 15, 2012, 10:33 PM
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Aros!! Go for airframe 8! Just fix the problem...
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Old Apr 15, 2012, 10:43 PM
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Well, if I was to go for #8, I still have the problem of hand tossing which is the primary problem. Once she's airborne (and the throws/CG/trim are correct) I don't usually have a problem flying her.

It's getting her in the air. What I would have to consider is retracts. That would limit me to flying only at the school on the track or parking lot which would limit my flying ability. Then again I guess it's better to have four successful flights a month versus 10 attempts that end in disaster.

This damn bird is like crack.
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Old Apr 15, 2012, 10:44 PM
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LOL! You are now addicted to 'Blackbird crack'...
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Old Apr 15, 2012, 10:51 PM
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IF IF IF I was to get another one, I might consider a PNP from BH. That way, if it crashes, no big deal. I can use Don's power setup and Joe's afterburnerz in a more stable and predictable air frame.

Does anyone have one they are flying all stock? If so, is it halfway decent? I mean, I know it would be a DOG compared to Don's setup but shoot, just to see it fly without ending in disaster - even if that means 20mph slower - it may be something to consider.
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Old Apr 16, 2012, 08:40 AM
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Sorry dude.....with all that power...maybe a long tarp to take off on?? Or a rail made of pcv ...put plastic skid plates on plane that would slide on pvc.. nice and slick....but I think the weight porblem is a real issue....and having to fly that fast really burns up the juice...but after 7 planes I might just move on for the sake of my mental health and nerves Just saying.....
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Old Apr 16, 2012, 12:42 PM
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Aros, I had similar problems trying to hand-launch a Skyray EDF (the plane I've been using as my EDF/SR71 trainer, it's a similar delta-wing jet but without the long nose of an SR71). I broke my Skyray airframe in-two no less than 3 times out of 7 hand-launch attempts... it just wasn't worth it. Turns out that with the landing gear plugged in even on grass runway with just a little head-breeze it WILL rotate and lift off, as long as the grass isn't too long (my club keeps it mowed close weekly though). I've had nothing but sucessful flights since abandoning the hand-launch idea! Though I haven't tried flying my SR71 yet I have fast-taxied it on my club's grass runway and it moved along very easily at less than 50% throttle.. 100% throttle and it would have lifted off I've no doubt of it. You really need to try with landing gear, you may not be able to get it up in the air 100% of the time but at least if it doesn't rotate and lift off you won't be tearing it up just shut'er down before you reach the end of the available runway area and taxi back.

Also anytime you have a loss of power (either intentionally or LVS!) put that nose DOWN below the horizon immediately and keep it there until you level out just before landing! You flatspinned just as soon as you pulled the nose up without power... I flatspinned my Skyray briefly just once when I lost too much airspeed at the top of a large loop, but I had enough altitude to power out of it in time it was scary though (it was coming down almost directly above my pilot station! Eeek!). You flatspin, you push the nose down and give full power and hope it starts flying again that's all you can do it worked for my Skyray it only fell maybe 30 feet before it started pulling out of it and that's with only a single 60mm edf fan unit. Also in most LVS situations if you kill throttle for just a second then you can "restart" and give it some power maybe 1/3 stick to help get you back to the runway for landing. When you kill the throttle completely the battery voltage will come back up above the LVS threshold and then as long as you don't pull it down below LVS voltage again you can keep some power on (as opposed to trying to deadstick land, some power is better than no power). Keep that nose below the horizon though, don't let it slow down no matter what!

Those afterburner lights of Joe's looked awesome in your SR71 Aros!! If I ever get mine maidened and a few good flights on it I may have to get me some of those! Soon maybe! :-)

ps. The Skyray F4D-1 is a good fun 60mm EDF delta-wing jet (similar in shape the the SR71 but without twin engines or that long nose)... only downer is that it doesn't come with retracts the included gear is fixed in place. You might try one, but don't hand-launch it and do bend the mains forward a bit so that they're closer to the CG so it will rotate better on take-off. Regards!

- Michael
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Old Apr 16, 2012, 12:51 PM
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Thanks Michael...Unfortunately I didn't realize LVC was hit when I was in a banking turn and the torque roll/tip stall was instant with not enough altitude to pull out of it and save her. As for the flat spin, I had applied full down elevator trying to get that nose down and build up speed but it was 100% unresponsive at that point. You can see in the video that she wasn't about to come out of that flat spin regardless of my inputs. I was trying everything to no avail. I was lucky that time that she landed flat-bellied. Yesterday, not so lucky.

If the SR-71 and I cross paths again, it will undoubtedly be with retracts. This bird is just not meant for hand tossing.

Thanks for the comments!
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Old Apr 16, 2012, 12:51 PM
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Quote:
Originally Posted by Aros View Post
IF IF IF I was to get another one, I might consider a PNP from BH. That way, if it crashes, no big deal. I can use Don's power setup and Joe's afterburnerz in a more stable and predictable air frame.

Does anyone have one they are flying all stock?
Aros that's the SR71 I have here but I have only taxied it not yet maidened... I cannot recommend BH however, they gave me heck over a defective elevon servo right outta the box took over 3 months before they finally sent me a replacement servo (I couldn't find 1 to match the size/shape needed to fit the pocket elsewhere and didn't want a non-matching set of elevon servos!). Since it was the gears inside the servo that were bad I simply took the gears from the replacement servo and put them in rather than cutting the wiring harness. I so do NOT recommend BH though their customer support is truely abysmal!

Anyways it taxies quite easily on grass runway (closely mowed) I don't forsee any issues with taking-off just haven't gotten the CG set on it yet I need to add something to the back-end to balance it thinking I'll do the whale-tail mod before maiden and then maybe add those cool afterburner lights later if I can fly it well enough. 3S 3000mah 35C max single battery pack in the battery bay, stock power system.

- Michael
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Old Apr 16, 2012, 01:01 PM
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Yes my BH tales of horror are well documented in the warbird forum I am primarily active in. I have been looking around and all the kits on the web are out of stock. I was thinking of putting my power system and afterburnerz in a different jet altogether but I can't find any twin 64MM EDFs out there I like anywhere near as much as the SR-71, and besides, this power setup of Don's is really meant for this bird.

So if I can find a kit, the hell with it. What's another airframe? More heartache potentially but what else do I do? The power system and afterburnerz don't do me any good sitting in a drawer in my garage. I may as well keep on keeping on. Maybe one day I will find Lady Luck with one of these air frames and have a Blackbird that actually lasts in my hangar longer than five flights.

The whale tail is a good mod, I agree with the pros in this thread, but it also adds weight as do the afterburnerz (I had to add an ounce of weight to the nose plus shove my 4s 4000 forward a few inches than I've had to in the past, cutting out a lot of foam to fit). So it's a toss up between having the whale tail mod and afterburnerz versus a lighter air frame. This is one jet you don't want to add weight to if you can help it.

However, I would build it the same as #7, except with retracts for pavement/track takeoffs and landings.
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Old Apr 16, 2012, 01:03 PM
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Thanks Michael...Unfortunately I didn't realize LVC was hit when I was in a banking turn and the torque roll/tip stall was instant with not enough altitude to pull out of it and save her. As for the flat spin, I had applied full down elevator trying to get that nose down and build up speed but it was 100% unresponsive at that point. You can see in the video that she wasn't about to come out of that flat spin regardless of my inputs. I was trying everything to no avail. I was lucky that time that she landed flat-bellied.
Sorry I watched your video with sound muted (the song though cute just wasn't doing anything for me)... without the sounds of motors it's pretty hard to tell what was going on throttle wise when things went south! Amazing that it can flatspin itself all the way to the ground without doing damage though...

I would have thought with your power system that 100% throttle and down elevon's it would have been able to get out of a flatspin with enough altitude...

Perhaps all-up weight/wing-loading was the underlying problem?

Never give up! Never surrender!

- Michael
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Old Apr 16, 2012, 01:26 PM
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Aros I just watched the final flight video... assuming you weren't goosing the throttle, it sounds like your ESC's were programmed to turn-off (hard-shutoff) on LVS. You were barely 3 minutes into the flight... how long were your previous flights on that battery pack? I'm thinking if your ESC's were programmed to hard-shutoff on Low Voltage and your pack was giving up earlier than previous flights then 1 or both motors were shutting down... BUT, hard-shutoff should have shut the motor(s) off completely and kept them shut-off until you went down to 0% throttle (to reset LVS) and then back up again. So I have to question whether LVS was occurring or not. I think soft shutoff would be preferrable on a twin EDF plane so as to prevent sudden power loss on 1 side or the other... soft shutoff simply slows the motor(s) down instead of turning them off completely. I use soft shutoff LVS on my Skyray and it's happened a few times when I tried to push my 6 minute flight time I reset throttle and came in for landing immediately at 1/3 power nose down all the way.

Have you gutted the remains yet? It looks like most of the back of the plane was still intact there's no reason you couldn't recharge the pack (or use a different pack) to check for operation for 3-4 minutes of runtime simulating your last flight... just to see what it does and if everything is actually working right, or not. Run it to LVS and see what it does. I'd be curious myself, might answer some questions about that last flight!

ps. The onboard camera while really cool probably doesn't help the flight characteristics any and must have added yet more weight. This is 1 plane I wouldn't dare do that with!

pps. Really interesting seeing the deflection of the cockpit during flight your plane was flexing quite a bit.

- Michael
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Old Apr 16, 2012, 01:51 PM
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The Nanotech's I use for the SR-71 are not very good. I've had numerous issues when charging them at times...Sometimes "low voltage, check battery" sometimes "over voltage, check battery"...They are the only batteries I've run into that issue. I've read reports that others have had a lot of issues with the Nanotechs, so in the future I will not be using them any more.

What the battery had to do with the crash is speculation but I agree with Don's theory "...Each fan/motor wants to pull ~60 amps so ~120 total amps so it is possible on a 4S 4000 the voltage may have dipped a little too low and started to shut down one fan unit..." especially with the above-mentioned issues I've had trying to charge those particular batteries at times.

Soft shutoff sounds like a very good idea with this jet. As I think we saw, losing one ESC to LVC even for a fraction of a second creates an instant lateral stability issue as the other motor is still going at full power.

I did gut the remains...Although I could have patched the back end together, I don't like that Frankenfoam look to my planes after too many crashes not to mention the integrity of the airframe at that stage. It's too bad the kit seems to be out of stock everywhere because it's cheap and easy to replace. In my case I should order in bulk!

My flight times are usually 3 to 4 minutes which surprises me because I don't fly WOT the entire flight and I would think a 4000 mAh battery would give me an extra minute or two of flight times.

As for the camera, you're right, as light as they are, they do add a little bit of weight. I've always wanted an onboard cam for the SR-71 and I'm so glad I have that video of the successful maiden. So next time (still debating if there will be a next time) I would go sans cam and add retracts and use a different sized and type of battery, or dual 4s in parallel.

That cockpit deflection had me curious! There was a lot of flexing going on. Is that normal?
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Old Apr 16, 2012, 02:13 PM
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Aros,

My condolences...

You may want to look at the Dynam A-10 kit that NP sells... I think it goes for about $40 when they have it in stock. I picked one up a while back, and it's a pretty nice plane. If I had to build another one, the only mods that I would make would be to add some carbon fiber to the wing to stiffen it up, and replace the nosegear. I just put a new nosegear on mine that I made out of 3mm music wire... much stiffer and will hopefully hold up a bit better. I run parallel 3S 2200's in it, and it's got plenty of power with 4800kV motors. The A-10 never had afterburners, but it would be a cool mod...
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Old Apr 16, 2012, 02:22 PM
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Thanks Cobra...Are you talking about the A-10 or SR-71 i.e. nosegear and CF mod to the wing?
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