DER RED MAX (cluster)

[BrianS]

Since I like stuff a little different has anyone done a cluster 3 x 18mm in a der red max.
thoughts on performance? etc etc could it survive?

 

[Andrew_ASC]

That sounds cool.

 

[rharshberger]

Should be fine structuraly, performance will best be determined by using a program such as Rocksim or Openrocket to simulate the build. May need nose weight due to additional weight at aft end of rocket.

 

[BrianS]

So 3 motors should just give it more power to take off. the altitude would still be the same for the given motor ex. a83 b64 etc. am i thinking correct ?

 

[dhbarr]

Nope, your altitude is going to go up appreciably, since you'll need to add nose weight to offset the increased motor mass.

 

[dpower]

I flew a DRM on 3 motors a bunch. It flies great. Just check your CG with 3 motors loaded, and add nose weight (only) if needed. With 3xB6-4, you essentially make a D18-4 (not a full D, but still a D). 3xC6-5 makes an E18-5. Definitely get more altitude, and a lot more flame and smoke! Clusters are always more fun.

 

[BrianS]

oh yeah. getting excited starting to build tomorrow.

 

[new2hpr]

With the huge fins on the DRM, extra noseweight is likely not necessary. Check with Rocksim or Openrocket, though.

 

[BABAR]

Okay I got a safety question.
I have never been an RSO but seems like with a three engine cluster simmed stable with three motors possibilities as follows:

3 engines light and flies safe as simmed

0 engines light and never leaves the pad but nobody endangered

How about if only 2 engines light or only one lights?

Is this a far pad heads up flight?

 

[snrkl]

Okay I got a safety question.
I have never been an RSO but seems like with a three engine cluster simmed stable with three motors possibilities as follows:

3 engines light and flies safe as simmed

0 engines light and never leaves the pad but nobody endangered

How about if only 2 engines light or only one lights?

Is this a far pad heads up flight?

Having just sat the RSO course - a few thoughts if I was RSOing it:

1) clusters and stages need to fly from the pad appropriate to the total impulse of the flight. We had a 12xC6 saucer that had a total impulse of 72N, so an F equivalent. You would fly on the pad appropriate for F motors.

2) Complex birds (clusters and staging) fly from the pad one up from the allocated.

So if I was RSOing it I’d likely ask that it fly from the mid power rails / rods as a minimum.

We have a pretty good launch system for clusters, we can fire up to eight birds at a time, so for small clusters it’s not unusual for a flyer to use multiple leads and simultaneously fire multiple “slots” - it’s been very reliable to date.

As for heads up, any complex flight (cluster, stage) or maiden flight of a new bird is a heads up flight.

 

[Marc_G]

I've done DRM (regular length and extra length versions) with replaceable motor mounts accommodating either single 18 mm, triple 18 mm, or single 24 mm motors. Flies great either way.

If only one of three lights, it won't get that far, so I agree with the suggestion of flying it from a farther pad than just a single C. So, I believe C and below the distance is 15 feet; D makes it 30 feet. Folks correct me if my distances are off. But 30 feet is a reasonable distance, as it won't go fast or far on one 18mm while weighted by two duds. I have had this failure mode before. Went about 20 feet laterally, max 15 feet high.

 

[dpower]

So, I believe C and below the distance is 15 feet; D makes it 30 feet. Folks correct me if my distances are off.

The NAR Model Rocket Safety Code states 30 feet for engines larger than D, so a cluster of 3 C6 motors would warrant 30'. I launch low power clusters quite often, and use a 40' cord, which gives me a comfortable 30'. At our large club launches, which can have many spectators, we put the LPR pads at 50', giving us additional safety margin.