Three stage w/ estes F-15s...Max liftoff weight?

I am building an upscale Centuri Arrow 300, with the estes F-15 for a power plant. The air frame is a BT-55 tube.
My question is this. What should I use for the stage one booster? The F-15 only hits @ 5.5#so I am a little worried about liftoff weight.
Its nice and light (don't have a weight yet ) so I think it will be fine .
Does anyone know the Actual Max Liftoff Weight of a F-15?

Thanks
-Barry

Per the Estes catalog (as found on their website), it's 19 ounces for the F15-0.

iam5150 said:

I am building an upscale Centuri Arrow 300, with the estes F-15 for a power plant. The air frame is a BT-55 tube.
My question is this. What should I use for the stage one booster? The F-15 only hits @ 5.5#so I am a little worried about liftoff weight.
Its nice and light (don't have a weight yet ) so I think it will be fine .
Does anyone know the Actual Max Liftoff Weight of a F-15?

Thanks
-Barry

Click to expand...

BRILANT!......thanks !
That's going to be cutting close. Its going to have some serious GRUNT off the pad...(For a black powder motor)

I built a two stage rocket using Estes 29mm motors in both stages.

For its first flight I used an Estes F15-0 in the booster and got a “Slow Realistic” liftoff as a result.

Not sure how well that motor would perform if it was attempting to lift two additional BP “F” motors as opposed to only one.

How about some strap on boosters?
Got a picture or a sim file?

Alternative would be smaller engines for the upper stages. This would drop your lift off weight and improve your chances of recovery.

STRAP ONS????:y: BRILANT!!!!
That's why I posted this !!!!

some pics to follow!

A smaller 29mm aerotech motor like the F42-4R in the booster. That motor might kick it hard enough that it will still be flying vertical after 4 seconds of delay. The ejection should fire off the F15 in the second stage==F42-4 to an F15-0 to the F15-8..... sounds awesome. But will it work?

This is a 4 stage rack rocket with F15's in each stage. The rocket without motors only weighs 3 oz.
[YOUTUBE]6WZrA9sLHpI[/YOUTUBE]

iam5150 said:

STRAP ONS????:y: BRILANT!!!!
That's why I posted this !!!!

some pics to follow!

Click to expand...

As I am sure you already know, the strap-ons will alter your CG, so you will need to adjust your design (more/bigger fins, longer rocket, and/or nose weight) accordingly.

Also:
If you are already L1 certified and flying under a waiver, disregard the following:
Keep track of your total propellant mass. You are going to be very close to the high power range on this bird.

Straight Trails!

Tom

I think you need a harder kick off the pad, or you risk the rocket heading off at an angle with 6 seconds of burn time to go! Yikes! Cruise missile power prang!

The F15 thrust curve looks like it takes awhile (.5 seconds) to get up to max thrust, and the max thrust is not actually very high. Look at an E12 or a D12, and the motors get up to max thrust in half the time (.25 seconds) and the max thrust is higher (33N instead of 25). It's intuitive to want the "bigger" motor in the booster, but would it make more sense to have a harder-kicking, faster-burning E12 or even D12 in the booster for a quick start off the pad, and the longer burning F15 in the sustainer? Plus, you get to see it stage right in front of you at low altitude!

Or, if you are considering clusters or strap on boosters, maybe consider some of these faster burning motors for that.

Nice video, RocketJunkie!

Someone please correct my math: you want about a 5:1 or better ratio of thrust to weight. One Newton equates to 0.224808943 pounds of force. So 15 Newtons = 3.372134145 pounds. Divide this by 5 to get your 5:1 ratio, and you get 0.674426829. Since you are measuring your rocket in ounces, multiply this by 16 and you get roughly 10.8 ounces.

Where is Estes getting 19 ounces for this motor? Even if you go by the NAR minimum of 3:1, you get just under 18 ounces. So is my math wrong, or is Estes wrong?

Bat-mite said:

Someone please correct my math: you want about a 5:1 or better ratio of thrust to weight. One Newton equates to 0.224808943 pounds of force. So 15 Newtons = 3.372134145 pounds. Divide this by 5 to get your 5:1 ratio, and you get 0.674426829. Since you are measuring your rocket in ounces, multiply this by 16 and you get roughly 10.8 ounces.

Where is Estes getting 19 ounces for this motor? Even if you go by the NAR minimum of 3:1, you get just under 18 ounces. So is my math wrong, or is Estes wrong?

Click to expand...

I think it is because the 15 N is the average thrust for the duration of he burn. If you look at the thrust curve, there is going to be an initial thrust spike that is higher than the average thrust.

ThirstyBarbarian said:

I think it is because the 15 N is the average thrust for the duration of he burn. If you look at the thrust curve, there is going to be an initial thrust spike that is higher than the average thrust.

Click to expand...

Right on the nose- Maximum Thrust: 25.3N
So using the 5:1 number you get 18 and change ounces.

kj

Thanks. Makes sense.

well crap! that didn't work!

hope this works

OK! now that I have this figured out I can get the show on the road!
This is MY version of the Centuri Arrow 300.
It used C6-0s and a C6-7 OR!! for all us old schoolers out there B14-0 core burners and a B14-7 ! (I've done this!)
I used the BT-55 tubes from Balsa Machining as well as 29mm tubes and couplers for the boosters.

last pic for now till I paint it
Just wanted to say that Balsa Machining was AWESOME! they have very light tubes and couplers, but they are strong!
I put the order in on Jan 2nd (fri of a long weekend) And I got the stuff on MONDAY!!!


-Barry

have you got a weight yet?