CTI F240

[awseiger]

Hello All...

I just realized that the motor vendor that attends most of the launches I go to carries the CTI F240 24mm motor.

Of course, I just built a 24mm Minimum diameter rocket, and forgot to put in a motor block. Alas, I am extremely temped to throw this monster in my rocket... OpenRocket says it should hit Mach 1.56. Even with large sim errors, I've got the sound barrier on a rocket around the size of an Estes Yankee...

So I ask, Will this motor just rip the fins off my rocket? Will it just crush the Estes BT-50 tube? I'm kind of at a loss as to whether this is a good or a bad idea. I know that at 2,500 feet, it's gonna be hard to track, but I am confident that I will be able to do so.

FYI, the fins on this rocket are 1/8in basswood. I have not painted it yet, so I could add some small epoxy clay fillets to strengthen my fins. Right now they are just tacked on with wood glue. (I can post a picture, if this would help in determining the safety of this venture)

Also, I plan on using a combo of friction-fit and "tape around the bottom" to hold the motor in. Will this be OK at these high speeds?

I just don't want to have my first attempt at breaking the sound barrier to end up with an out-of-control F240. Something tells me RSO's don't like it when that happens...

[fyrwrxz]

Just my 2 cents- yup- reinforce your fillets fer sure, BUT not knowing the design of your fins, these could shred about .8 mach from flutter. If they survive you'd prolly only be above mach for a bit and then transonic back down into the buffet zone and below very quickly. Sand thru any paint you mite have and I'd use a real epoxy w/filler rather than clay. Make sure you're not screwing up your CG/Cp with the added mass in the back. Tower launch? A lug or rail buttons dirty up your Cd. Try a sim with about .75 to be conservative if you have these. Other than that- hold your breath and don't blink!

[maxvelocity]

Use small fins and you should be ok. My big daddy flies on the f240 all the time the big balsa fins stay put. I know it doesn't go as fast but it still books it. I think with the right fins you'll be ok the motor only burns a third of a second. The hardest part will likely be finding it.

[Eric1]

Think of the F240 as a rifle cartridge!
Seriously it's 3-2-1- BANG! It's gone!!

[KennB]

Alex,

As sometimes LCO and sometimes RSO at many of the launches you attend, I can tell you, I'm not thrilled by any rocket that flies out of sight or can't be tracked. I'm not so worried about an Estes Quark-type rocket; if it gets recovered and has a second flight, it's more by happenstance. I also like the OMG factor of the V-Max and similar motors and have pushed the button on many with varying results.

Let me suggest you sim out the other 24 mm CTI motors to see what may give the same altitude. Fly your bird on that so you have a chance to track it during a "normal" flight and you can see what you'll be able to "see" at about a half-mile away. As big and bright a streamer you can fit would help. If you're going to have electronics on board to confirm the Mach travel, you'll want to be sure you're going to get them back along with the motor casing.

I want everyone to enjoy our launches and this type of motor is always popular as long as the rocket flies straight and true. The main thing is we don't want to do anything that will put us in a bad light with the field owners be it a city park or a private farm. Flying beyond the field or leaving untracked rockets behind can cause us all problems.

Kenn
Unofficial Buzz killer

[New Ocean]

How long is the airframe? If longer than a few inches, I would worry about it folding up under thrust. Ive shredded an estes kit on "only" an F72 of comparable size. The fins were a fincan so they lasted. It was the airframe that shredded.

[cwbullet]

Think of the F240 as a rifle cartridge!
Seriously it's 3-2-1- BANG! It's gone!!

Or Mortar round. Reserve it for a strong rocket.

[awseiger]

I want everyone to enjoy our launches and this type of motor is always popular as long as the rocket flies straight and true. The main thing is we don't want to do anything that will put us in a bad light with the field owners be it a city park or a private farm. Flying beyond the field or leaving untracked rockets behind can cause us all problems.

Kenn
Unofficial Buzz killer

I was hoping one of you would pick up on this... Yea, that's what I figured. I already lost an Altimeter one on your watch... Learned my lesson about clouds and just how low they really can be (or just how high 2000 feet really looks with a small rocket) last time. My parents and I walked over almost every inch of the field looking for that, and still found nothing. I'm almost sure the steamer didn't deploy, we would have seen all 8ft of caution tape on the way down if it had...

So no it is then. It'll fly plenty high and fast with one of those new Estes E12's. I'll save Mach for a slightly larger rocket.

Mind you, I am very sure it would come back down on the field in Berwick. I kinda figured I'd put a giant streamer on it and watch for it to fall (See above, this has failed me once before). There'd also be some ground-up sidewalk chalk in there so we can see it at apogee, but alas, I agree with your buzzkill.

Anyone actually ever flown a rocket on this motor and gotten it back in one piece? I can't image most rockets can even remotely take that kind of punishment. Even the 1G F72 is kind of crazy.

[Aksrockets]

Do you have a Rocksim or Openrocket file?

I made my own 24mm minimum diameter out of fiberglass for a few bucks. I would get some fiberglass cloth and laminating resin if you dont have any. Glue a bunch of spend 24mm engines to use for a mandrel. Wrap with parchment paper. Wrap the fiberglass around the mandrel and wet out with epoxy. Leave to cure. Slap some fin on that thing and an estes NC and voila' a super sturdy 24mm minimum diameter rocket.

I'll be flying mine with an F32T.

[awseiger]

Using spent engine casings as a mandrel is a great idea... Hmm. My biggest fear for this rocket wasn't stability or the fins tearing off, but more the body tube simply imploding under the stress. Fiberglass would fix that..

I'll follow Kenn's sound advice and fly with smaller motors for now.

BTW Here's a picture of the bird. The epoxy fillets need some work, but here it is:



The upper white tube is a payload bay. My plan was to put a tootsie roll in there and enjoy some supersonic candy

And yes, I do have an OpenRocket File. The Name E-Shak is kind of an inside joke with my friends (who gave me this terrible but tempting idea). Here that is:

EShak_2.ork

The .ork file is missing the bulkhead in the upper tube. I did the sim more for finding the CP, so internal parts were not really taken into account.

[maxvelocity]

Also, vmax has very good tracking smoke so they are easily visually tracked. All my high g v max flights have been tracked without needing to turn on my reciever. Even my 3 inch J drag race rocket thst went 3000 ft in just over 3 seconds (and won the race) on a J1520. So tracking may not be such a huge deal. I'd use a large streamer so its visible after the smoke trail is gone.

[billspad]

Anyone actually ever flown a rocket on this motor and gotten it back in one piece? I can't image most rockets can even remotely take that kind of punishment.

Yes, on that very field. It was a very windy day and the rocket was a Ptiny Pterodactyl which is all plastic and fiberglass. Even with the wind it went straight up. There's no way I could get a picture of it on the way up but this is it on the ground.

[awseiger]

Yes, on that very field. It was a very windy day and the rocket was a Ptiny Pterodactyl which is all plastic and fiberglass. Even with the wind it went straight up. There's no way I could get a picture of it on the way up but this is it on the ground.

That wasn't the day it was really cold too, was it? The CMASS Maine Exile Launch? I remember one rocket going off that sounded like a gunshot. It actually made me jump, it's possible this is the rocket I heard.

I think I'm beginning to understand that motors like this are intended to go in motor adapters on larger rockets... Guess I should build up my 24-29mm motor adapter.

[cwbullet]

I have one picture of a F240 bird. It was a blur and all luck catching on film.

[maxvelocity]

I have an excellent shot (that I didn't take) of my big daddy just leaving the pad on an f240. Mach diamonds!!! I will post it sometime Monday.

[cwbullet]

I certainly does deliver a fast flight. I am not sure of the flight speed. I suspect mach is possible.

[New Ocean]

http://www.youtube.com/watch?v=W42tkqEjSTM

The crazy part is that thrust ended maybe 25 feet in the air or so.

[awseiger]

I'll have to do some sims, but I feel like this would go well into the Aerotech Initiator I just started epoxying together... Mach Diamonds... Loud Noises.... Right up my alley. Paired with a rocket I'll get back this seems like an awesome idea.

[McKailas Dad]

Ah-chooo! My first thought after watching that video was to say "gazuntite!"

[kenstarr]

I flew it last year in my Blackhawk 24 on the Salt Flats. 3-2-1, Bang, Gone. I didn't watch the launch, just looked in the sky for the burst of orange chalk dust. Even with the chute reefed up to the size of a baseball, it seemed to take FOREVER to come down. Lost the casing on the second flight but new one is ready to go!

[Aksrockets]

I flew it last year in my Blackhawk 24 on the Salt Flats. 3-2-1, Bang, Gone. I didn't watch the launch, just looked in the sky for the burst of orange chalk dust. Even with the chute reefed up to the size of a baseball, it seemed to take FOREVER to come down. Lost the casing on the second flight but new one is ready to go!

The video is on the Hellfire 16 montage. THIS flight gives the word teleport new meaning. Do you have any idea of the speed?

http://www.youtube.com/watch?v=8jAV7-Kks1Y
skip till 1:06
or just watch all of it. I dont mind

Alex

[billspad]

That wasn't the day it was really cold too, was it? The CMASS Maine Exile Launch? I remember one rocket going off that sounded like a gunshot. It actually made me jump, it's possible this is the rocket I heard.

That was the day.

[n3tjm]

My PML MR-1 with a F240

[Initiator001]

I apologize for interrupting this thread..

I'll have to do some sims, but I feel like this would go well into the Aerotech Initiator I just started epoxying together... Mach Diamonds... Loud Noises.... Right up my alley. Paired with a rocket I'll get back this seems like an awesome idea.

You do not and should not use epoxy to assemble AeroTech kits.

AeroTech kits are designed to be assembled differently than other 'traditional' MPR kits. All epoxy will do is add weight and make the model less durable.

This was tested when I worked for AeroTech. Kits were built with epoxy and CA. The epoxy assembled kits did not last as long as the CA assembled models.

It's all in the engineering.

I now return you to the original content of this thread...