GR L695BL

Um, I was looking at the thrust curve for the Gorilla L695 Black Lightning, and discovered that is is massively progressive. Has anyone ever flown it? Would the 5:1 ratio even work with this motor and a larger rocket (say 5" wide by 10' tall and about 20-25 lb. empty)?

Yikes. That's a tricky one. I'd say that a 20-25lb rocket would be a touch too heavy for that. The initial thrust is only about 75lbs, so you'd want a rocket that weighs no more than about 15lbs on the pad.

Once it starts to ramp up, it would give it one heck of a ride!

Rudy Haselbauer and his son flew this motor at NEFAR last year-
https://www.nefar.net/gallery/2010-06/index.html
(about 1/2 way down the page)

And yes, it was a wild ride!

The liftoff thrust is only about 400 N =~ 90 lbs. That's the figure I would use to determine your max liftoff weight. Given that, I would limit your rocket weight to about 17lbs (including the motor) to use this. Black lightening motors are not designed for performance, but effect. As a friend is fond of saying "All show and no go" - at least initially. There is a large amount of wasted energy in these motors. Personally, I would not use this motor on the rocket you want to use it on. While the effect won't be as great, go with the L1150 white cloud version for this case; it has ample thrust for your project. If you want the sparky, step up to the 75/6000 BL (L1065); that motor has enough liftoff thrust for your 20lb+ rocket.

Wiley said:

Um, I was looking at the thrust curve for the Gorilla L695 Black Lightning, and discovered that is is massively progressive. Has anyone ever flown it? Would the 5:1 ratio even work with this motor and a larger rocket (say 5" wide by 10' tall and about 20-25 lb. empty)?

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So, would a Loki L780 Spitfire be adequate for this size/weight rocket (basically a PR Indimidator 5)?

That would probably work. It would give it a nice gentle liftoff, followed by a good acceleration.

I've heard that the Loki L930 uses only 3 O-rings. How does that work?

Wiley said:

So, would a Loki L780 Spitfire be adequate for this size/weight rocket (basically a PR Indimidator 5)?

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It might work, but depends on final weight of the rocket. Under 22lbs (including motor, casing and recovery) and with little wind you should be fine (I stress SHOULD). I'd be more skeptical on a windy day. And heavier than 22lbs PLUS a windy day - no way! That 5:1 ratio is typically a bare minimum suggestion under calm conditions. That ratio must be increased according to wind conditions. To me, you are really close to bare minimum levels here which I do not suggest flying under...there's potentially too much risk especially with a rocket in the 20lb+ class.

For comparison, here is my intimidator 5 - 24lb empty - 29 lb on the pad - on a K1085. Gives about 250 lbs of initial thrust. It was only a full K so it didn't get too high (3000 ft) but it had decent acceleration off the pad. I'm not sure i would fly mine on a motor with half the initial thrust.


https://www.youtube.com/watch?v=FtDicoYffFM

Wow, nice video COrocket! Looks like a nice motor too!

So, since the Loki L930 has a similar thrust curve to the K1085, would it give a nice straight boost in your rocket to about 5K (the loaded weight of the rocket should be about 31 lb.)? Thanks!

Wiley said:

Wow, nice video COrocket! Looks like a nice motor too!

So, since the Loki L930 has a similar thrust curve to the K1085, would it give a nice straight boost in your rocket to about 5K (the loaded weight of the rocket should be about 31 lb.)? Thanks!

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Yeah, that looks like a great motor. My sim says around 32 lbs loaded, and an altitude of about 5400 ft.

Does anyone have pictures of an L930LW in action ?

Don't have a picture, but judging from this YouTube video, the motor looks pretty awesome

https://www.youtube.com/watch?v=DsMKibQfr88

GaryT, doesn't your I5 weigh about 25 pounds ready for flight, but with the motor subtracted? Would you fly your rocket on a Loki L780, without any (or too many) worries about underpoweredness?

You have a 10' rocket which will have alot of polar moment of inertia (meaning its not gonna want to turn around its CG alot). That motor is up to 500# thrust after 0.5sec where your rocket may only be 1/3' up the rail.

Given light winds and a long rail you may be ok with that motor and that long rocket. A simulation is your friend.

Oh, I definately simmed it. On the L780, with a pad weight of 33.88 pounds, a rail 8 feet long, 10 mph winds, and 2000 feet above sea level, it went 4019.225 feet. Max Velocity was 357.76 mph, max acceleration was 52.5 m/s, and the time to apogee was 16.8 sec.

However, when I simmed it on an AT K560 in the same conditions, here are the numbers I got: altitude of 3090.702 feet, max velocity of 275.028 mph, max acceleration of 45.5 m/s, and 15.2 seconds to apogee.

On both of these flights there are no warnings, therefore the simulator thinks that these would be safe flights in these conditions.

What do you guys think of these numbers? The first part of the thrustcurves for the L780 and the K560 look about the same. However, the the thrust progresses on the L and regresses severely on the K.

Hello,

Personally I like at least a 5 to 1 ratio just so I know I shouldn't have a problem on lift off. So for me the motor you show has a 125lb initial thrust so for me a 25lb launch ready rocket would be max. For a 34lb rocket I would be looking for about 170lbs of initial thrust for a minimum. And that's my 2 cents worth!

Wiley said:

Oh, I definately simmed it. On the L780, with a pad weight of 33.88 pounds, a rail 8 feet long, 10 mph winds, and 2000 feet above sea level, it went 4019.225 feet. Max Velocity was 357.76 mph, max acceleration was 52.5 m/s, and the time to apogee was 16.8 sec.

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You want to examine the rocket speed when it leaves the rail. You need to figure top rail button placement when you program the 'length' of the rail.

I'd like to see at least 40 ft/s or 4 times the wind speed, whichever is greater.

Is this a picture of a Polecat 10" Goblin? I know the motor is an L780 Spitfire. About how much does the average 10" Goblin weigh?

If you go to this link https://www.mdra-archive.org/photos/RedGlare5/PeterAbresch/ and click on the top right video entitled "...The Bad and The Ugly," you will find the flight of this same orange-and-black Goblin about 1/3 of the way through video.

Judging from how slowly the rocket lifted off and flew, I estimate that it probably weighs ~25 lb. empty. What do you think?

Wiley said:

Is this a picture of a Polecat 10" Goblin? I know the motor is an L780 Spitfire. About how much does the average 10" Goblin weigh?

If you go to this link https://www.mdra-archive.org/photos/RedGlare5/PeterAbresch/ and click on the top right video entitled "...The Bad and The Ugly," you will find the flight of this same orange-and-black Goblin about 1/3 of the way through video.

Judging from how slowly the rocket lifted off and flew, I estimate that it probably weighs ~25 lb. empty. What do you think?

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I have this flight announcment on video, and it was 35 lb. on the pad.

Aha! thank you for that interesting piece of information, Syclone! That means the "minus motor" weight was about 28 pounds!

Also, because the Goblin is a far less aerodynamic rocket than an Intimidator 5ish rocket, the I5 lookalike (weighing about 23 pounds) should perform a nice, slowish liftoff (even in some considerable winds, since there wasn't a lot of wind when the Goblin flew), followed by a nice straight trajectory (maybe a slight angle into the wind), and ejection at well over 4K. Thanks again !