Air Start

The Rocketry Forum

Help Support The Rocketry Forum:

Localx

Well-Known Member
Joined
Jan 19, 2009
Messages
101
Reaction score
0
What does "Air Start" motors mean, and how is it done?
 

Missileman

Well-Known Member
Joined
Apr 21, 2011
Messages
786
Reaction score
0
Air starting refers to starting extra motors, usually clustered while in flight.
Say a 5 motor cluster is launched, but only the center motor is lit at launch, 2 seconds later 2 opposing outboard motors are lit, then 2 seconds after that the other 2 are lit.
Usually done with timers.
 

Ryan S.

Well-Known Member
Joined
Mar 24, 2003
Messages
3,553
Reaction score
0
basically secondary motors are lit a certian amount of time into the flight. Altimeters can also be used
 

Rocketjunkie

Addicted to APCP
Joined
Jan 19, 2009
Messages
4,424
Reaction score
622
Here's a sequence pic showing the plume going from smoky to white. The central motor was a smoky M lighting 8 I white motors using Thermalite fuses.
 

Karl

Well-Known Member
TRF Supporter
Joined
Jun 30, 2010
Messages
2,460
Reaction score
26
Im just in the process of building a rocket that air-starts , ill post you some pictures when the electronics come!
-karl
 

eugenefl

Well-Known Member
TRF Supporter
Joined
Apr 22, 2009
Messages
4,375
Reaction score
10
Originally posted by Karl
Im just in the process of building a rocket that air-starts , ill post you some pictures when the electronics come!
-karl
Please do. I just received my Perfectflite MT3G timer and I'm looking for someone's build to see where the timer is mounted. I figure somewhere in an interstage coupler but I could be wrong. Also, where the heck is a timer mounted if you're doing airstarts from within a cluster mount?
 

loopy

Well-Known Member
Joined
Dec 13, 2009
Messages
4,586
Reaction score
2
Originally posted by eugenefl
where the heck is a timer mounted if you're doing airstarts from within a cluster mount?
I've seen a few rockets built with the electronics bay built into the motor mount between the centering rings and an access panel cut out of the body tube. Makes alot of sense to me - not too far to run the wires.

Loopy
 

n3tjm

Papa Elf
Joined
Jan 21, 2009
Messages
7,488
Reaction score
402
Location
Penns Creek, PA
My Magnum has the timer bay in the fin can... It is exposed till you join the fin can to the main airframe tube. :). I had two airstart flights with it. The first one plowed into the deck when the Central motor broke free and shot through the rocket. The most recent one was more sucessful... J500 airstarting two H128's :)
 

Micromeister

Micro Craftman/ClusterNut
TRF Lifetime Supporter
TRF Supporter
Joined
Jan 19, 2009
Messages
15,074
Reaction score
47
Location
Washington DC
Air starting is simply staging without the benifit of dropping the dead weight of motors casings.
 

eugenefl

Well-Known Member
TRF Supporter
Joined
Apr 22, 2009
Messages
4,375
Reaction score
10
Originally posted by Loopy
I've seen a few rockets built with the electronics bay built into the motor mount between the centering rings and an access panel cut out of the body tube. Makes alot of sense to me - not too far to run the wires.

Loopy
This makes sense, but I figured the heat from the motors would damage the electronics. I suppose the airframe would have to be a decent diameter to house even the smallest timer. Any chance of pictures?

Doug, if I understand your post correctly the fin can is removable? Any chance of pictures of your setup?
 

Elapid

Well-Known Member
Joined
May 2, 2009
Messages
1,734
Reaction score
0
they make ceramic ICs as well as the cheapo plastic ones...
ceramic ones can take a LOT of heat.
iirc
 

loopy

Well-Known Member
Joined
Dec 13, 2009
Messages
4,586
Reaction score
2
Originally posted by eugenefl
Any chance of pictures?
Sorry - wasn't my rocket, and I don't have any pictures. Although, if I'm not mistaken, there's a review of the Diablo on EMRR where the builder did this.

Loopy
 

loopy

Well-Known Member
Joined
Dec 13, 2009
Messages
4,586
Reaction score
2
Aha! Found it! It wasn't the BSD Diablo - it was the Binder Design Thug. Here's a link to the EMRR Review in question.
 

n3tjm

Papa Elf
Joined
Jan 21, 2009
Messages
7,488
Reaction score
402
Location
Penns Creek, PA
Originally posted by eugenefl
Doug, if I understand your post correctly the fin can is removable? Any chance of pictures of your setup?
Info about my timer bay:
https://www.rocketryforum.com/showthread.php?s=&threadid=3780

I since have built a platform running up the 54mm tube to mount my new PET2 timer on it, since it is to big for the centering ring idea. I will take a picture of that next time I have the Magnum apart.
 

DynaSoar

Well-Known Member
Joined
Mar 15, 2004
Messages
3,022
Reaction score
0
Originally posted by Micromister
Air starting is simply staging without the benifit of dropping the dead weight of motors casings.
So what IS the benefit of air starting then?
 

hokkyokusei

Well-Known Member
Joined
Apr 16, 2012
Messages
2,908
Reaction score
3
Originally posted by DynaSoar
So what IS the benefit of air starting then?

One advantage is when ignitng a large cluster. If you have a large central motor, you can use "airstart" electronics to ignite the other motors once it is confirmed that the rocket is moving.
Typically, it's done asap so it's an extreme case of airstarting.

There's no real 'advantage' of air starting, other than the cool factor. I guess you could argue that you can simulate a long burn motor with sequential short burn motors.
 

Rocketman248

Well-Known Member
Joined
Jan 30, 2009
Messages
2,395
Reaction score
12
The benefit of airstarting over clustering, besides the coolness factor, is increased altitude. With a cluster, you get a lot of liftoff velocity, but it slows down quicker. With airstarts, after the first motor burns out, you have more motors to continue the boost.

Here's a liftoff shot of a scratchbuilt 1/2 scale Doorknob on a K670GG. It then airstarted 2 I154J's.
 

solrules

Well-Known Member
Joined
Dec 30, 2003
Messages
366
Reaction score
0
Originally posted by Rocketman248
The benefit of airstarting over clustering, besides the coolness factor, is increased altitude. With a cluster, you get a lot of liftoff velocity, but it slows down quicker. With airstarts, after the first motor burns out, you have more motors to continue the boost.
Right, but how I see it is that the altitude fo a rocket increases as the square of the burnout velocity. So, am I right in thinking that the altitude is not *that* much greater (although it all depends on mass of rocket, aerodynamics, etc.) using airstarts? In fact, I would be willing to bet on some types of rockets (espically low thrust/weight ratio) would get a lower altitude airstarting than clustering.

Food for thought:
Quoted from https://my.execpc.com/~culp/rockets/rckt_eqn.html#Method
Notice: the rocket goes more than twice as far after the burn as during the burn!
 

loopy

Well-Known Member
Joined
Dec 13, 2009
Messages
4,586
Reaction score
2
Originally posted by solrules
Right, but how I see it is that the altitude fo a rocket increases as the square of the burnout velocity. So, am I right in thinking that the altitude is not *that* much greater (although it all depends on mass of rocket, aerodynamics, etc.) using airstarts? In fact, I would be willing to bet on some types of rockets (espically low thrust/weight ratio) would get a lower altitude airstarting than clustering.

Food for thought:
I think it depends on the characteristics of the rocket/conditions. smaller motors will still be able to accelerate a heavier rocket if it's already moving, correct?

Loopy
 

Elapid

Well-Known Member
Joined
May 2, 2009
Messages
1,734
Reaction score
0
ground start, velocity = 0
air start velocity >0

see signature.

I think it depends on the characteristics of the rocket/conditions. smaller motors will still be able to accelerate a heavier rocket if it's already moving, correct?
as long as the thrust is greater than air friction and other drag forces on the rocket, it will accelerate.
 

daveyfire

Piled Higher and Deeper
TRF Lifetime Supporter
Joined
Jan 26, 2009
Messages
3,218
Reaction score
55
Location
thank u, next
Originally posted by Micromister
Air starting is simply staging without the benifit of dropping the dead weight of motors casings.

...or the complexity of booster recovery in HPR models...

And it looks really cool too!
 

Karl

Well-Known Member
TRF Supporter
Joined
Jun 30, 2010
Messages
2,460
Reaction score
26
Yep , the change of smell , noise , flame , smoke is way cool ! I dont think I would call staging a HPR rocket that drops each stage away 'safe' without some sort of recovery device. Even if it was to be flown on the smallest/lightest motor available.
-Karl
 

FredA

Well-Known Member
Joined
Jan 19, 2009
Messages
2,203
Reaction score
370
Beyond being cool, the reason for airstarts is altitude!
Drag is proportional to velocity.
To minimze drag, minimize velocity.
In order to go as slow as possible, you need a constant push to overcome gravity.
Since motors don't burn constantly, you burn several in succession.
If you've got the guts....delay betweeen starts to slow down as much as possible....just gotta keep it going up straight!


If you can't stage, then airstart.
Don't light those motors on the ground!
Clustering on the gound just means you didn't buy a big enough motor IMHO.

FredA
 
Top