Tractor rockets

[dragon_rider10]

The NARAM 52 coverage in the current issue of SR got me interested in the competition aspect of our hobby.

The one thing I was curious about was the use of tractor rockets for 4a cluster altitude. I didn't see any illustrated. Does anyone have a photo of an example?

 

[JAL3]

This sounds interesting since I don't know the term.

I assume you're not taling about something in John Deere, Case or IH livery.

 

[MarkII]

A tractor rocket is one that has the motor placed in the front of the airframe, so that it "pulls" the rocket during thrust, rather than "pushing" it. Some well-known example are Dr. Robert H. Goddard's March 19, 1926 rocket (aka "Nell") and the launch escape rockets for the Mercury and Apollo space capsules. I imagine that tractor rockets must be rather difficult to stabilize because of the CG location. When I get back home I'll have to check my Nov./Dec. 2010 issue of SR again, because I don't recall seeing a reference to tractor rockets in it.

 

[JAL3]

That makes sense.

Thanks for the info.

 

[dragon_rider10]

When I get back home I'll have to check my Nov./Dec. 2010 issue of SR again, because I don't recall seeing a reference to tractor rockets in it.

Please refer to page 20, subsection 2.

 

[MarkII]

On the left is a photo that was taken during the pad abort test of the Apollo LES. The tractor rocket for the Launch Escape System pulls the aft-mounted Apollo capsule along behind it. The middle photo shows the launch escape rocket firing accidentally during the attempt to launch MR-1 on 11/20/1960. The last photo shows the launch escape rocket on the Russian Soyuz launch vehicle.

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[davel]

A tractor rocket is one that has the motor placed in the front of the airframe,... tractor rockets must be rather difficult to stabilize because of the CG location.

CG is the whole reason to consider a tractor design. With 4 motors at the back end, you either need to use excessively large fins or nose weight to get a stable design. Neither large fins nor extra weight are desired for a maximum altitude event.

 

[Micromeister]

CG is the whole reason to consider a tractor design. With 4 motors at the back end, you either need to use excessively large fins or nose weight to get a stable design. Neither large fins nor extra weight are desired for a maximum altitude event.

Not necessarily Davel:
Many of the 4, 5 and 6 motor cluster designes use longer core bodies to offset some of the mass of the motors allowing for some fairly small thin fins. Tractor and a number of "In-line" designs have been tired (mostly unsuccessfully) as far back as the early 70's. They proved to be exceedingly difficult to stabilize and align.
Not to say don't give a couple a try, They do offer same unique appearance and ignition wiring challanges, but do make for some interesting subjects of discussion over dinner later

 

[gdiscenza]

For some time now, I've been considering a Tres-style engine mount located far forward on a long-ish rocket. The reason I'm looking at this is to use the aft end space for a video camera of some type.
First thing I will need to do, is to buy the video gear and get an accurate weight so that the sim can be worked out correctly.

G.D.

 

[Bone Daddy]

Page 164-65 of the 7th edition of the Good Book has nice bit on parallel staging that may give you some ideas.

 

[davel]

Not necessarily Davel:
Many of the 4, 5 and 6 motor cluster designes use longer core bodies to offset some of the mass of the motors allowing for some fairly small thin fins. Tractor and a number of "In-line" designs have been tired (mostly unsuccessfully) as far back as the early 70's. They proved to be exceedingly difficult to stabilize and align.

Longer body tubes = more drag, more mass = lower altitude. Getting the CG ahead of the CP is, of course, imperative to a stable design - and moving the mass of some of those motors forward is a way to do that without increasing the mass of the model. I agree that a tractor design has its own challenges.

 

[Bone Daddy]

There is a commercially available kit that has a forward motor and an aft video camera. Can't remember what it's called. Saw it on The Rocketry Planet website at some point in time. Maybe someone will remember the name?

Found it: https://www.rocketryplanet.com/content/view/2897/38/

 

[Micromeister]

Longer body tubes = more drag, more mass = lower altitude. Getting the CG ahead of the CP is, of course, imperative to a stable design - and moving the mass of some of those motors forward is a way to do that without increasing the mass of the model. I agree that a tractor design has its own challenges.

Humm! did you not notice two of the examples shown set national altitude records in their motor class? Longer bodies only = more drag if not finished well. Further in most cases (4A thur 6C) the extra mass for these compeition models as proven negligible. 4xA was pass out in the thin air of mile high Denver, while 6xC cluster/alt current Nat'l records have yet to come close thanks.

The point I was trying to make is Tractor model Setups have YET to produce any Positive results in all these years of trying. In theory they seem like something that should have merit, in practice they have proven to be all but a waste of time while providing some Great best mid-western flight dinner conversation.
Another thing your totally overlooking is Throw Weight or coasting mass (Optimum Mass) is far more important in cluster altitiude compeititon then the lightest model of equal finish and frontal area.

 

[dragon_rider10]

Not necessarily Davel:
Many of the 4, 5 and 6 motor cluster designes use longer core bodies to offset some of the mass of the motors allowing for some fairly small thin fins. Tractor and a number of "In-line" designs have been tired (mostly unsuccessfully) as far back as the early 70's. They proved to be exceedingly difficult to stabilize and align.
Not to say don't give a couple a try, They do offer same unique appearance and ignition wiring challanges, but do make for some interesting subjects of discussion over dinner later

Micro,

Tell me more about that orange 6C cluster. The heat exhaust on those ports above the fins is from ejection charge?

 

[Micromeister]

Hi John:
All 5 outboard motors are C6-0's the small ports are covered at liftoff with a tiny piece of de-tacked cellophane tape. These pieces are just slightly larger then the opening and burnised down as smoothly as possible. At burn thru boosters produce a small amount of after burn and enough pressure to pop the tape keeping the friction fit casing in place. The Core motor is a C6-7.
If you think the Altitude is a fluke, check out the Current 6C Cluster/Alt A-division record by Mike Filler flown the day before with a model of my design @ 657m. I've never quite understood why my 666m C division record was retired but it was.

Been using this basic design since Naram-39 with 3x1/2A cluster altitude. I have some pics of 5xB model that didn't use balsa bulkheads and suffered pod cover blowouts. Was a great flight but did not close track at 224m Second flight with taped on field fitted covers was good enough for second place at a 463m.
I'd love to have been able to track my 10.5mm 5B cluster alt attempt. but it was out of sight so quickly neither of the tracking stations even saw the smoke trail. only heard a very faint pops WAY Way up there, never saw the streamer, or the model again.

 

[Lentamental]

Pardon my ignorance, but I don't see how any of Micromeister's rockets are tractors. All of his motors are located around the base of the rocket, not part way up.

 

[Micromeister]

Pardon my ignorance, but I don't see how any of Micromeister's rockets are tractors. All of his motors are located around the base of the rocket, not part way up.

Look a little closer in post #8 photos 3 and 5, both are Stacked cluster Tractors.

 

[UPscaler]

I believe it was Erik Gates who designed the tractor tower for the playhouse on that episode of master blasters.




Braden

 

[MClark]

Our club has sponsored some contests at LDRS, a black powder altitude contest, no impulse limit as long as they were BP, and of course the (in) famous Bowling Ball Loft.
We were tossing around ideas for other high power contests and one suggestion was “Tractor Motor Altitude”. The gist of it was we would have an impulse limitation in the HPR range and it had to be a tractor design, our definition at the time was all parts of the motor must be ahead of the CP and CG. Any number of motors could be used. We brought up the idea with “Others” and universally got a massive sucking noise follow by trembling. In their defense I must say we were proposing L or M range.
Anyway it has not happened as we got burned out doing the Bowling Ball Loft for ten years and have been on a “sabbatical” from contests for a while.


Mark