Question About Super Sonic FG Little John (from Mad Cow)

[rbezenek]

Hello everyone,

I have put together a very well built fiberglass Little John from Mad Cow rockets. I used epoxy on every joint except for the motor retainer where I used JB Weld.

Last weekend I took it out and flew it on an I-364 FJ with no issues.

I've been poking around for other motors that I might want fly in this bad boy and was wondering if anyone has flown one of these with a J-800?

It appears (from the RockSim simulations) that the J-800 might take this rocket super sonic or thereabouts and I was hoping someone could give me some feedback on whether or not they've successfully flown a Little John at mach speeds.

Thanks in advance and regards,
Ryan Bezenek

[New Ocean]

Should have no problem past mach 1... but don't assume that it will break mach. A 4 inch rocket breaking mach on a J is not so easy...

How did you reinforce the fins on the inside?

[bobkrech]

You should have no problem launching on a J800 provided you assembled the rocket according to the instructions, but I doubt it will hit Mach 1.

Depending on the Cd you'll likely apogee between 4000'-4500'.

Bob

[rbezenek]

Thanks guys.

The fins are through the wall construction with epoxy fillets both on the motor tube attachment points and on the inside/outside where they connect with the body tube. I also beveled the edges of the fins (what a pain in the rear that was doing it manually). I roughed up the fiberglass really well so hopefully the bond is strong...

Maybe I'm being optimistic about mach speeds - just going off the RockSim data with the motor. It's showing 7160 altitude and 762.55 ft/sec. on a J800. It was pretty accurate for my maiden flight of the rocket: 3200 altitude and 562 ft/sec. respectively. Altimeter logged 3175 and 375 MPH.

[New Ocean]

You should know that "supersonic" is mach 1.2

I bet a fiberglass rocket with fiberglass fins(?) and fillets on the inside could probably do mach 2 no problem. This rocket has a really nice profile for that kind of work, but it will take a 75mm motor to get it done!

[3stoogesrocketry]

rbezenek , unless you meant to type 762.55 MPH , 762.55 Ft / Sec . is only around 520 MPH . You will be fine on the J800 . I am willing to bet that you could stuff a K1100 in there no problem , as long as your fins are straight and not bent . Ive had 4 inch cardboard go mach with no reinforcment with no issues .

Eric

[bobkrech]

By definition, Supersonic speed is a rate of travel of an object that exceeds the speed of sound (Mach 1). For objects traveling in dry air of a temperature of 20 °C (68 °F) this speed is approximately 343 m/s, 1,125 ft/s, 768 mph or 1,235 km/h.

[3stoogesrocketry]

" By definition, Supersonic speed is a rate of travel of an object that exceeds the speed of sound (Mach 1). For objects traveling in dry air of a temperature of 20 °C (68 °F) this speed is approximately 343 m/s, 1,125 ft/s, 768 mph or 1,235 km/h. "


This is also at sea level , and not at altitude.

Eric

[bobkrech]

Actually it only depends on temperature, not pressure...

[kenstarr]

I did my L2 with that model last summer. First flight, parachute did not deploy but NC came off so it fell about 5000' and banged up a fin.... 2 hours later, and some 5min epoxy, a successful L2 flight. Can't remember what motor, J-3xx CTI. I wouldn't hesitate to put a CTI K2045 in it! (first I would remove my minor 5min epoxy job and fix it up nice with the Aeropoxy)

[rbezenek]

Yes - 3stoogesrocketry you are correct. What I posed was a mistake...I meant MPH. I just ran another RockSim simulation and it came out to 7719.98 ft. in altitude and 1145.41 ft/sec. which if I'm not mistaken is ~781 MPH.

In any case it sounds like the model and my construction of it should survive those forces.

I really do appreciate and thank you all for your responses. I'm pretty new to the HPR thing and am eager to learn as much as I can from all of you.

Cheers,
Ryan

[New Ocean]

Mach .8 to 1.2 is, colloquially, transonic. This is a "there is no such thing as a parasheet" comment, but it is worth noting when people get to mach 1.00001 and claim supersonic.

[gldknght]

Thanks guys.

The fins are through the wall construction with epoxy fillets both on the motor tube attachment points and on the inside/outside where they connect with the body tube. I also beveled the edges of the fins (what a pain in the rear that was doing it manually). I roughed up the fiberglass really well so hopefully the bond is strong...

Maybe I'm being optimistic about mach speeds - just going off the RockSim data with the motor. It's showing 7160 altitude and 762.55 ft/sec. on a J800. It was pretty accurate for my maiden flight of the rocket: 3200 altitude and 562 ft/sec. respectively. Altimeter logged 3175 and 375 MPH.

Mach 1 is roughly 1,126 ft/s at sea level at 68 degrees F. Sorry, but your sims aren't even close to that speed.

[gldknght]

oops just saw the updated info on your sims. Disregard the previous post, work computer is excessively slow/

[UPscaler]

I've got a 4" little john(in my avatar picture), it's not the all fiberglass version, and I didn't build it, but it has been flown on K motors with no issues (it is fiberglassed, however)

I believe that it will break mach, and possibly get to 1.2, because it's a small rocket for a J800!


Giving me ideas here....

[rbezenek]

I've got a 4" little john(in my avatar picture), it's not the all fiberglass version, and I didn't build it, but it has been flown on K motors with no issues (it is fiberglassed, however)

I believe that it will break mach, and possibly get to 1.2, because it's a small rocket for a J800!


Giving me ideas here....

Okay - now you've got me all excited.

Can't wait to get out to the launch site next month!