My rockets does not go straight

[dagabu]

smaller fins = less losing performance

[THEONE]

Question: when you use a payload (stick rockets) the CG moves forward so you will need a smaller stick, it is like you are adding weight to the nosecone to move the CG forward correct ?... Edited September 8, 2011 by THEONE

[THEONE]

fins will probably weigh as much as a suitable stick i would not worry about the performance loss if you use a light weight material. if the fins weigh the same as a stick they will out perform it, more aerodynamic and less drag.

if you decide to make a recovery system or any headers the weight of the fins is not important since you add more they just have to be big enough and light enough.

 

dan.

 

I say that if a rocket will not fly well it means that the CP is forward than CG

So you can add more-bigger fins to move the CP upward OR add more weight to move the CG forward...

That i want to say is that when you add more weigh to your rocket to move the CG forward it will loose drastically efficience , so i believe that it is better to make bigger or more fins... ok you have more drag with more fins but i dont think so it will be the same when you add weight... 20% more weigh is 20% lower eficcience...

[dan999ification]

I say that if a rocket will not fly well it means that the CP is forward than CG

So you can add more-bigger fins to move the CP upward OR add more weight to move the CG forward...

That i want to say is that when you add more weigh to your rocket to move the CG forward it will loose drastically efficience , so i believe that it is better to make bigger or more fins... ok you have more drag with more fins but i dont think so it will be the same when you add weight... 20% more weigh is 20% lower eficcience...

 

 

i add 50% or more weight to them and they still fly to a safe height, with no load they just go higher faster.

how much do your finished motors weigh? a few grams of balsa will not hurt.

i think of finned rockets stability like projectiles, an air rifle pellet and a shotgun slug work on the same principles : the front is heavy and the rear is normally hollow and lighter this alone makes them fly straight it is a carefull balance, if the fins are too small and you dont have enough weight at the nose it will tumble like a baton round, if they are too big they will experience cross wind, and if there is too much weight it will just be slower or not go up at all.

i also think that you may need different fins for weighted flights or a more powerfull motor in the same setup

test test test

 

dan.

[dan999ification]

Question: when you use a payload (stick rockets) the CG moves forward so you will need a smaller stick, it is like you are adding weight to the nosecone to move the CG forward correct ?...

 

making bp rockets i have never had to look at the relationship between the two

 

 

nose weight and drag have to be balanced, my rockets would not fly straight with smaller sticks unless it was windy

 

dan.

[Mumbles]

I really think you're thinking into this too much Theone. I'd guess 90-95% of the people who make pyrotechnic display rockets have never given 1 second of consideration to center of gravity, center of pressure, size of fins, getting the optimal preformance from the motor, etc. All they care is that is goes up to a safe height and displays appropriately. What you're discussing is really more in the realm of amateur rocketry. If that is what you're interested, you'd probably be better suited finding a different forum more suited to that. We do not have a whole lot of people here who really understand all that stuff as well as you may need to answer your questions.

[dagabu]

Like these:

 

http://www.youtube.com/watch?v=036YqxmkXIA

 

 

 

 

 

[allrocketspsl]

I really think you're thinking into this too much Theone. I'd guess 90-95% of the people who make pyrotechnic display rockets have never given 1 second of consideration to center of gravity, center of pressure, size of fins, getting the optimal preformance from the motor, etc. All they care is that is goes up to a safe height and displays appropriately. What you're discussing is really more in the realm of amateur rocketry. If that is what you're interested, you'd probably be better suited finding a different forum more suited to that. We do not have a whole lot of people here who really understand all that stuff as well as you may need to answer your questions.

 

yep!I ram a motor top it with a header fused to go off at 4 secs normally(my rockets are just at apogee with 4 secs)then add a 4 foot stick 5/16 square top fuse it and watch the night sky get painted with lots of color or thunder,not once is there a need for any balance of any kind,my only concern is weight !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! All

ps: nuff said go fly one!!

[allrocketspsl]

Like these:

 

http://www.youtube.com/watch?v=036YqxmkXIA

 

 

 

 

 

that first one sounded like a lear 18 going over head mate

[dagabu]

The finned rockets are easy and fun. My son and I are working on a batch for PGI next year and are developing the fuels we want to use.

 

-dag

[dagabu]

This is just a silly little end burner from way back, I am getting back into serious design for PGI's 50th in Gillette. I will do all the non-pyro building this winter and load motors into the bodies this summer for testing. My 'dream' is to make a successful and repeatable 2 stage rocket with either a shell with parachuted red flares or smoke.

 

I want to use a primary lifter consisting of BP in a core burning motor, perhaps an extended spindle platform and a sustainer end burner consisting of whistle fuel with MgAl for sparkies.

 

The intent is to light the end burner at the same time the primary lifter is lit, I can get 20 seconds from my 7.5" end burners with slow BP, gives about 1.5 lb of thrust. I can get 3 lb of thrust from the whistle but it limits me to about 4-5 seconds of flight time.

 

The reason I am lighting them at the same time is due to the "second stage tip" effect that happens nearly every time I see a 2 stage rocket. This will not in fact be a 2 stage but rather a tandem burn rocket with my ultimate goal being able to have three end-burners surrounding one core burner. With time fuse and a good nosing, i could delay each of them 3-4 seconds for sustainers.

 

[WillowPineAndBoom]

Longer stick ,the nozzle at the center and very tight taping the stick to the motor, plus the stick must be taped straight on the motor! Simple staff nice to help you guys!

[dagabu]

Longer stick = windvaning...

 

Use two shorter sticks and glue them on with tape over that.