Will a aerotech d24-4t be able to life a 3fnc safely?

[ScrapDaddy]

Could someone run a rocksim simulation or a answer based on experience thanks

 

[ScrapDaddy]

Please

 

[The EGE]

Not unless you want to get eaten by a llama.

RASP says a 3FNC (20 oz, 3" Cd = 0.7) gets 144 feet with a max velocity of 84 fps and 2.3 second optimum delay.

With the delay 1.7 seconds after apogee, it's ejecting at just 100 feet. If the delay is even one second long, or if there's any delay getting the chute out and unfolded, your nice rocket is toast.

Not only that, at 24N average thrust you've got just a 4.3:1 thrust:weight ratio. That's not very safe, especially for a heavy rocket like the 3FNC.

Use the D24 on something that'll get a little higher, and save an E30 or F for the 3FNC. Even in calm conditions, with a perfect delay, and good deployment, it'd be a very risky flight, and most RSOs will not let you fly it.

 

[ScrapDaddy]

https://www.apogeerockets.com/pemtec_3FNC.asp scroll to bottem

 

[ScrapDaddy]

What If I drilled out 3 seconds of delay

 

[WillMarchant]

That web page has the recommended motors. You should use one of them for the first flight.

Or risk the wrath of the llama. Your choice. No pressure at all. Llamas have nasty bites, though... I mean, just look at this https://www.vivo.colostate.edu/hbooks/pathphys/digestion/pregastric/llamapage.html :shock: It says "fighting teeth" on that page!

 

[The EGE]

What If I drilled out 3 seconds of delay

That's a good way to get a CATO. Never drill a delay shorter than the shortest stock delay (for Aerotech motors) or the shortest certified delay (Cesaroni). Other wise you risk the motor pressure blowing through the delay and CATOing.

 

[Pem Tech]

Just to be clear, are you talking about a plain ole' 3FNC or the 3FNC kit we sell?
I can state, categorically, that the Pem-Tech 3FNC WILL NOT fly on a D-24, or an E-15, an E-28 or an F24. Well, not fly very far anyway...
The smallest motor that be used for a nominal/stable flight is a AT F-39. Anything smaller will not reach minimum stable velocity even on a 60" rod.
Here is the photo evidence.

This is the original prototype Pem-Tech 3FNC on an AT E18, off of a 60' rod, loop number one.

Loop number two......
:y:

The rocket was undamaged, thankfully, and it flew successfully a few days later on an AT F40.

Here are a couple of flight pictures of the 3FNC on an F39:

No, my old camera didn't have a fast shutter speed, that was how slow the liftoff was.


Then I tried it on an F24:

As it left the rod I could tell it was not going to be a good flight. She didn't have nearly the velocity required to stay vertical. You know how you get the cold sick feeling when you know it is going to prang but you can't do anything to stop it?
Well, that was what I experienced that day...
Then it got worse, or better, depending on how you look at it. If you look closely you will see that the igniter clips and wires are still attached to the rocket, even though it is in free-flight.
No good...
The resistance tilted her over just enough that she took off horizontally and skipped along the ground instead of arching over and pranging under full power.
:shock:
The airframe survived intact but all three surface mounted fins snapped off. Soon afterwards we went to TTW fins.

Hope this helps, and that I didn't just prattle on and put everyone to sleep.

 

[Pem Tech]

https://www.apogeerockets.com/pemtec_3FNC.asp scroll to bottem

Yes....
I have been meaning to speak to Tim about those motor recommendations.

Oh, and thanks ScrapDaddy for showing interest in our 3FNC.
It was our very first release, and I may occasionally wax poetically about her.

 

[Pem Tech]

That web page has the recommended motors. You should use one of them for the first flight.

Or risk the wrath of the llama. Your choice. No pressure at all. Llamas have nasty bites, though... I mean, just look at this https://www.vivo.colostate.edu/hbooks/pathphys/digestion/pregastric/llamapage.html :shock: It says "fighting teeth" on that page!

*in my worst scottish accent*
I warned you!
I warned you that they have big nasty pointy teeth.
https://www.rocketryforum.com/showthread.php?t=4609
I warned you the buggers bite but did anyone believe me?
Nooooooooooooooo
*end worst scottish accent*

 

[ScrapDaddy]

I was indeed talking about the pem tech on thanks alot you saved me alot of misery : )

 

[ScrapDaddy]

Yes I figured since tim recomened the e 25 I figured that all you needed to do was take half of the alltitude off

 

[stickershock23]

Nice LLama Death roll. bad llama bad llama.

Just to be clear, are you talking about a plain ole' 3FNC or the 3FNC kit we sell?
I can state, categorically, that the Pem-Tech 3FNC WILL NOT fly on a D-24, or an E-15, an E-28 or an F24. Well, not fly very far anyway...
The smallest motor that be used for a nominal/stable flight is a AT F-39. Anything smaller will not reach minimum stable velocity even on a 60" rod.
Here is the photo evidence.

This is the original prototype Pem-Tech 3FNC on an AT E18, off of a 60' rod, loop number one.

Loop number two......
:y:

The rocket was undamaged, thankfully, and it flew successfully a few days later on an AT F40.

 

[The EGE]

Yes I figured since tim recomened the e 25 I figured that all you needed to do was take half of the alltitude off

Normally, yes, doubling the total impulse doubles altitude. However, the smallest possible motor that still gets the rocket in the air will often lift it well less than half of the next-size-up motor.

This happens with rockets around 2 ounces, where they'll get just 100-150 feet on an A8 but 400-500 on a B6.

It's why you also have to check the delay, and average thrust. On a longer rod on a very calm day, the E28 probably has enough thrust to get the 3FNC marginally stable. The D24, though, has lower thrust and a shorter initial spike, so it will not render it stable. In addition, even if it did get in the air, the D24 still doesn't have a short enough delay.

If you don't want to spend the money on Rocksim or SpaceCAD - either of which would be a good investment - then download OpenRocket. It's very similar to SpaceCAD and free.

 

[ScrapDaddy]

Isn't it funny how tim mentions the built in baffle system in the 3fnc 3 times on his page? ( is he trying to sell the baffle or the kit?) I have a story about the 3fnc it was a gloomy day in the skies of America Germany was winning ww2 and all hope was lost The the mad scientists at pem-tech created a 3fnc rocket, supplys were very scarce so the rocket had to be as minnimal as possible (except the interier baffle system and the 18 inch nylon ripstop parachute, and Kevlar shock cord, and the nomex chute protector) it was a technological wonder as nazi Germany's V2 was a 4fnc (when the guy did the barrowmans stability equation he forgot to subtract one)the rocket was launched at nazi Germany the D-24 engine instaled by a nit wit (that me) burned out as the rocket returned to earth it landed in the Pemberton familys backyard and and 60 years later while umm oh gee I forgot the name umm well umm..... Oh yeah Layne Pemberton And a friend were burying a goldfish they found the 3fnc and founded pemtech and so the 3fnc design was claim a success in the U.S.A.( And porto Rico!!) and so pemberton technologies was on it's way to sucess hope you enjoyed the story!!! Oh and contary to popular belief the desruction acctually DO self destruct after reading! Pem tech was also founded on oppiste day because more than three fins and a nose cone doesn't apply here!

 

[DAllen]

Why in the world would anyone want to put a baffle in that rocket? If you did, you'd never be able to fit an I200 in there.

I guarantee many happy llama's with that rocket and motor combo...

-Dave

 

[ScrapDaddy]

And I will garontee a void in the warrenty E:roll:

 

[Pem Tech]

Why in the world would anyone want to put a baffle in that rocket? If you did, you'd never be able to fit an I200 in there.

I guarantee many happy llama's with that rocket and motor combo...

-Dave

Actually, an I200 will fit in a 3FNC. Getting it back from 6000 feet will be a trick.

:shock:

 

[ScrapDaddy]

isnt that what elevators are for?:roll:

 

[ScrapDaddy]

Just to be clear, are you talking about a plain ole' 3FNC or the 3FNC kit we sell?
I can state, categorically, that the Pem-Tech 3FNC WILL NOT fly on a D-24, or an E-15, an E-28 or an F24. Well, not fly very far anyway...
The smallest motor that be used for a nominal/stable flight is a AT F-39. Anything smaller will not reach minimum stable velocity even on a 60" rod.
Here is the photo evidence.

This is the original prototype Pem-Tech 3FNC on an AT E18, off of a 60' rod, loop number one.

Loop number two......
:y:

The rocket was undamaged, thankfully, and it flew successfully a few days later on an AT F40.

Here are a couple of flight pictures of the 3FNC on an F39:

No, my old camera didn't have a fast shutter speed, that was how slow the liftoff was.


Then I tried it on an F24:

As it left the rod I could tell it was not going to be a good flight. She didn't have nearly the velocity required to stay vertical. You know how you get the cold sick feeling when you know it is going to prang but you can't do anything to stop it?
Well, that was what I experienced that day...
Then it got worse, or better, depending on how you look at it. If you look closely you will see that the igniter clips and wires are still attached to the rocket, even though it is in free-flight.
No good...
The resistance tilted her over just enough that she took off horizontally and skipped along the ground instead of arching over and pranging under full power.
:shock:
The airframe survived intact but all three surface mounted fins snapped off. Soon afterwards we went to TTW fins.

Hope this helps, and that I didn't just prattle on and put everyone to sleep.

Iv seen the Picture of the 3FNC on a F24 on your website and i LOVE how you took the picture BEFORE it hit the ground

 

[MattieShoes]

The airframe survived intact but all three surface mounted fins snapped off. Soon afterwards we went to TTW fins.

Hope this helps, and that I didn't just prattle on and put everyone to sleep.

I've been wondering... Snow skis have bindings on them designed to let loose when there's too much torque -- better to have a ski come off than break your leg. Does this not apply to fins? I just wonder if TTW fins could potentially cause more damage to the body tube/nose cone because they don't come off in an impact. I have no idea, just curious.

 

[MysticalRockets]

Actually, an I200 will fit in a 3FNC. Getting it back from 6000 feet will be a trick.

:shock:

This is why we bring kids to launches. So they can chase them down for us. That way, we can sit back in our chair and relax, drinking beer and discussing how high it went.

 

[rocket999]

Why in the world would anyone want to put a baffle in that rocket? If you did, you'd never be able to fit an I200 in there.

I guarantee many happy llama's with that rocket and motor combo...

-Dave

I agree with him....

 

[ScrapDaddy]

I've been wondering... Snow skis have bindings on them designed to let loose when there's too much torque -- better to have a ski come off than break your leg. Does this not apply to fins? I just wonder if TTW fins could potentially cause more damage to the body tube/nose cone because they don't come off in an impact. I have no idea, just curious.

Well The Actual Purpose of TTW fins is The INTIAL strength.

 

[ScrapDaddy]

I agree with him....

Well Actually an I200 will fit in the 3FNC getting it back from 6000 feet will b e the problem

 

[cjl]

Well Actually an I200 will fit in the 3FNC getting it back from 6000 feet will b e the problem

I doubt very much if an I200 will fit if you install a baffle though.

 

[cjl]

Then I tried it on an F24:

As it left the rod I could tell it was not going to be a good flight. She didn't have nearly the velocity required to stay vertical. You know how you get the cold sick feeling when you know it is going to prang but you can't do anything to stop it?
Well, that was what I experienced that day...
Then it got worse, or better, depending on how you look at it. If you look closely you will see that the igniter clips and wires are still attached to the rocket, even though it is in free-flight.
No good...
The resistance tilted her over just enough that she took off horizontally and skipped along the ground instead of arching over and pranging under full power.
:shock:
The airframe survived intact but all three surface mounted fins snapped off. Soon afterwards we went to TTW fins.

Hope this helps, and that I didn't just prattle on and put everyone to sleep.

Really? That's an F24? It looks more like an F12 to me...

 

[5x7]

Really? That's an F24? It looks more like an F12 to me...

My thought exactly...

 

[ScrapDaddy]

To me it kinda looks like the oOP D3 or maybe a suped up MMX engine

 

[MarkII]

I've been wondering... Snow skis have bindings on them designed to let loose when there's too much torque -- better to have a ski come off than break your leg. Does this not apply to fins? I just wonder if TTW fins could potentially cause more damage to the body tube/nose cone because they don't come off in an impact. I have no idea, just curious.

Some rockets actually are designed with break-away fins. Water rockets (the hobby type, not the toys) frequently use foam board fins that are designed to snap off when the rocket contacts the ground. That is especially true of lower-end models that have somewhat crude recovery systems. (Water rocketry also has produced some sophisticated designs with electronics, phased recovery system deployment, aerial photography, etc.)

In our branch of rocketry, break-away fins have been used on occasion, too. I can't recall the specifics right now, but I do remember viewing a website a couple of years ago that documented a large Level 3-type rocket project. One of the things that the author (and his partners) did was to design the fins so that they fit into brackets and were attached via a pivot at the upper end of the fin root. The rest of the root length was held in the bracket by bolts that were designed to shear off if the fin struck the ground with a certain amount of force. The fin could then pivot up on the hinge at the top so that it would not get jammed into the ground and act as a lever to produce damage to the rest of the rocket. The bolt-shearing also absorbed a bit of the impact when the rocket contacted the ground. I don't recall too much else from the site, including whether the fin attachment method worked as intended when the rocket was flown.

Mark K.