F motor on larger rocket

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lhedrick

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I plan to build a 4 foot tall 3 (76MM) inch diameter rocket with a long burn apogee f10 motor. I have been working with carbon for years and with my estimate of the weight the rocksim numbers are okay.

A question is that with a larger tube, will the F10 motor have enough charge to blow off the nose cone since it's volume will be much more then the 29MM motor in a 76MM body?
 
You can add black powder to the top of the motor. If I was the LCO of that flight I probably would not let you launch I dont see it getting off the rod fast enough or even at all.If it gets off the rod it would probably land shark
 
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Add a stuffer tube. I'd want to see or at least hear about a sim on that one too.
 
What is the weight of the rocket going to be? I'm tending to agree with g zilla that the F10 won't lift a rocket of that size.
 
If the F10 is like most 29mm F's in terms of design, it should have enough ejection power. What's the speed at the end of the launch guide according to rocksim? That should help with stability.
 
I've flown this motor a couple times, it's a very cool motor. But the rocket I used was a 29MM minimum diameter, about 30" long. It didn't weigh very much, but still didn't exactly leap off the pad. I would guesstimate I got about 3500-4000' out of that. You may want to check the thrust curve on this-if I remember correctly, the peak thrust is about 2 lbs, and falls to an average of about a 1/2 lb. of thrust. Your rocket won't be able to weigh more than about 6 ozs. or so, to have the safe thrust to weight ratio.
Cesaroni just released some really cool long burn 29MM motors. I haven't flown one yet, but those may be a better and safer option for you. As with the others above, I don't think your planned rocket would leave the pad.

Phil L.
 
From the sample tubes I have built my guess it that the weight will be about 12 ounces, the carbon is light. Rocksim shows the speed off a 48 inch rod to be 46 FPS. It's close. I could start with some faster burn F or G motors to see how is goes then move down toward the long burn F10.

I tried looking for models using the F10. The apogee aspire is not a good example in that is really just pure engine. I have not seen any kits which list the F!0 as a possibility other then the aspire. The specs say it's 1.8 Oz and that it can reach 5000 feet but, what's the point? I will be out sight. I am actually looking to build something just fast enough to be stable so we can watch the flight and the 7 second burn.

If it's not stable with a faster G burn motor then I guess I will know. I could build it and if the weight is too high, I can just go with more power.
 
12 oz is about 3.3N, so an F10 will barely make the minimum T/W ratio (3:1). If you cluster two of them it might work, and you'd get your nice long burn too. +1 on the long rod, though...
 
Liftoff weight is the TOTAL weight of the complete rocket, any paint and glues, recovery system and wadding and the motor. People often forget to consider the motor weight and that error can lead to disaster. A rocket that falls out of the sky and burns for that long can start a very big fire or multiple fires over a very large area as it thrashes around. Why, it can even go under your car and do serious damage or completely set it on fire!

Safety is #1.
 
Let me start off by saying "Welcome!"

It's hard for me to imagine a rocket of that size weighing less than 300 grams. Have you ever built a rocket of that size and kept the weight down? Believe me, it adds up fast. I'm assuming no paint. What weave of carbon are using and what is the mass/area? Is the nose cone going to be composite construction as well?

If the nose cone is pretty loose, then "Yep" it will pop off. The question is because the nose cone is so light it may not have the requisite inertia to pull out the laundry because of the large internal volume. If you cut the length in half than you will dramatically increase your likelihood of a successful recovery.

Also, this rocket would only be launched in no winds. In any kind of wind it will likely never be seen again after it weathercocks. So I would recommend a long rail (not a rod).

It's doable, but perhaps just barely. I think you are at the limits of what that motor can do.

Greg
 
When it actually works, a large rocket on an underpowered motor with a long burn is very enjoyable to watch. However, they mostly dont work, and when it does not go right, and it weathercocks, and takes off like a cruise missile, and you realize it still has another 5 seconds of thrust pushing it down range, those can be kind of terrifying. Often they crash into the ground under power with the motor still burning. Or the motor burns out with the rocket travelling parallel to the ground, but the delay is way too long, because the rocket is not going up, and they crash before ejection. Or the ejection happens before the crash, but the rocket is moving so fast, it rips the recovery gear to pieces and the rocket still crashes.
 
Everyone is stating valid points. I don't want to do this if it won't fly. As for the weight. I am building carbon fiber tubes which are .039 grams per cm2 so when I multiply the surface are of the cylinder, it will be light. I know I can keep the weight down but if it looks too close I won't even try it. I can use a smaller mandrel and scale it down with no trouble.

I appreciate everyone's comments about the possibility that is won't get off the rod with enough speed to be stable. I certainly don't want a long burn motor on the ground causing trouble.


What ever I build, if the weight does not match my estimate by a larger amount I will move up on the power.

My original question was this. Let's assume that I actually can built it light enough, around 300 grams. Will the ejection charge on the motor have enough push to deploy the chute or will the volume of the tube be too larger?

As for why, I have watched hundreds and hundreds of rockets shoot of the rod so fast we almost don't get to see anything. I don't really have a thing for going as high as possible. This is just an idea to see something a bit different. I understand I can't get the same effect of a Saturn launch.

Again, I appreciate everyones comments regarding safety.
 
Here's an Idea. How about a Dual Motor Mount?
2 F10s' at the same time ought to be pretty cool.
 
lhedrick said:
Everyone is stating valid points. I don't want to do this if it won't fly. As for the weight. I am building carbon fiber tubes which are .039 grams per cm2 so when I multiply the surface are of the cylinder, it will be light. I know I can keep the weight down but if it looks too close I won't even try it. I can use a smaller mandrel and scale it down with no trouble.

I appreciate everyone's comments about the possibility that is won't get off the rod with enough speed to be stable. I certainly don't want a long burn motor on the ground causing trouble.


What ever I build, if the weight does not match my estimate by a larger amount I will move up on the power.

My original question was this. Let's assume that I actually can built it light enough, around 300 grams. Will the ejection charge on the motor have enough push to deploy the chute or will the volume of the tube be too larger?

As for why, I have watched hundreds and hundreds of rockets shoot of the rod so fast we almost don't get to see anything. I don't really have a thing for going as high as possible. This is just an idea to see something a bit different. I understand I can't get the same effect of a Saturn launch.

Again, I appreciate everyones comments regarding safety.
Click to expand...

How long is the stuffer tube and what is the volume of space you need to pressurize? I have an Estes Leviathan and it is a few inches shorter than 4 feet, with a 3" BT, and it ejects fine on Estes and Aerotech single-use motors, including a number of F motors. I'm not sure how an F10 compares to the single-use F's in terms of ejection charge --- someone else may be able to make that comparison, but they might need to know the amount of space being pressurized.
 
How about 2 Estes F15 motors? That will give you decent thrust levels and burn a reasonable amount of time, AND two F15 motor ejection charges are QUITE powerful.

AND they are easy to ignite in a cluster - especially if you use Quest Q2G2 igniters or classic Estes Solar Igniters with pyrogen tips.
 
The F10 actually peaks about 6 lbs. thrust, nice thrust curve for moving draggy and somewhat light objects. But converting your predicted weight to actual, 12 oz. * 4/3 = 1 lb. ;) ... so it's unlikely it will go straight enough to burn that long. Could try a F15 first, which also peaks out about 6 lbs.

The ejection should work but you really do want it to be reliable.
 
Well, I guess the answer it to just built it all out of carbon fiber parts which I will fabricate myself. Then I will be sure of the weight and have a better idea of what engines are suitable. I still have a target weight for the rocked to be 13-14 ounces complete.

It will still be a fun project and carbon always brings people around. Even if it comes in heavier then my target, people will still be amazed at the final weight and ask how it was built.

I just love building stuff people say I can't build.

Thanks everyone.

L
 
lhedrick said:
Well, I guess the answer it to just built it all out of carbon fiber parts which I will fabricate myself. Then I will be sure of the weight and have a better idea of what engines are suitable. I still have a target weight for the rocked to be 13-14 ounces complete.

It will still be a fun project and carbon always brings people around. Even if it comes in heavier then my target, people will still be amazed at the final weight and ask how it was built.

I just love building stuff people say I can't build.

Thanks everyone.

L
Click to expand...

You can't build that!

(Just trying to help with your enjoyment!)
 
Thanks for the encouragement. The worst that can happen is i am wrong. I can't remember if that has ever happened before? I'll give the build a try over the winter and post my results. I am lucky in that I can take things out to the Bonneville Salt Flats where there is nothing to hit or burn for miles and miles. After this project I hope to build a 6 foot carbon rocket for an I or J motor. I have worked with composites for years mostly glass and Kevlar. Carbon is not any different just more expensive.
 
lhedrick said:
Thanks for the encouragement. The worst that can happen is i am wrong. I can't remember if that has ever happened before? I'll give the build a try over the winter and post my results. I am lucky in that I can take things out to the Bonneville Salt Flats where there is nothing to hit or burn for miles and miles. After this project I hope to build a 6 foot carbon rocket for an I or J motor. I have worked with composites for years mostly glass and Kevlar. Carbon is not any different just more expensive.
Click to expand...

I was joking of course! And I wish you the best of luck. You definitely have the ideal environment for testing. I've driven through the area and there is NOTHING.
 

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