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Der Red Max comprimise
#1
I started looking around for a good sized Der Red Max that I could build and not be overly challenged...yet also not too simple (Level 1 E2X)....
and I came across this odd listing on eBay.   It wasn't a MEGA Der Red Max.... but it wasn't just a Der Red Max.

Instead, it was a MODIFIED Der Red Max, that has been altered to fit size D or E size motors into it.
The listing also indicated that it had been counter-weighted with a lump of clay in the nosecone or nose section, to move the CG forward of the CP....
(so it sounds like the guy knows what he's doing)....and also offered the original 18" plastic chute to go with it.

I was a little skeptical at first, but when he answered all my questions straight-forward, and agreed that it was no longer a kit, but an assembled rocket,
I trembled on the edge of bidding for it.  Finally, with just a few hours left in the auction, in a moment of weakness, I went ahead and bid the minimum,
thinking that I could burn off my excess D12-5 that I had purchased two months ago.

And to my amazement, nobody else bid.  I got it.  It's coming in the mail.
Did I do right?

The seller was very supportive and also shared that he had beefed up the fillets and had never gotten around to flying it.
What do you think?
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#2
I have upgraded the mounts on *many* Estes kits Smile

Pictures or link to the listing? The jury is out to the question and a good part of the answer is whether you are happy with the purchase. I personally don't buy built rockets but had a blast repairing a huge box of dead rockets received from an buddy.

I'd find a design file for the stock rocket, put your D12 in the new one and then make sure there is in fact enough clay. If not, it is an easy fix Wink Check the fins, motor mount, shock cord attachment and make sure they are sound. I would significantly lengthen the shock cord as the D12's ejection will be more energetic than stock and a beefed up nose cone will break a stock elastic/rubber one.
Member of MDRA, NAR and NARHAMS;
Level-2 certified but mostly fly G and under;
Volunteer compiler of manufacturer's news for ROCKETS Magazine.
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#3
(08-05-2015, 01:44 AM)Kirk G Wrote: And to my amazement, nobody else bid.  I got it.  It's coming in the mail.
Did I do right?

The seller was very supportive and also shared that he had beefed up the fillets and had never gotten around to flying it.
What do you think?

I think you did just fine. Be sure to post some pictures once it arrives.
You can always sim the rocket before flight if in doubt.
If you don't have open rocket/rocksim, you can at least figure out weight vs thrust...
Greg Young - L3
TRA 00234
NAR 42065
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#4
Yeah, if you don't have a sim program I'd ask someone on this forum, TRF or YORF to give you the CG of a stock model WITH a C6 loaded. That's just me. If the seller knew what a fillet was they most likely could also figure out how much nose weight to add.
Member of MDRA, NAR and NARHAMS;
Level-2 certified but mostly fly G and under;
Volunteer compiler of manufacturer's news for ROCKETS Magazine.
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#5
CG is easy to come up with; just balance the rocket in your hand, fully loaded with the motor you intend to fly.

CP, on the other hand, needs to be calculated.  Fortunately, the CP on a Red Max isn't affected by the MMT that's inside; only exterior shape changes affect CP.

The DRM is identical in proportions to the MDRM, which I just built.  CP on a DRM should be just a little below where the top of the fins meet the airframe.  See picture.

Your CG needs to be at least one body tube width forward (toward the NC) of the CP.  The CG is your balance point.  If not, add more nose weight.

   
John S.
NAR #96911
TRA #15253
MDRA
Level 1, 2014-Mar-15 -- Aerotech Sumo, H133BS
Level 2, 2014-Jun-21 -- Giant Leap Vertical Assault, J240RL
Level 3, 2016-03-12 -- MAC Performance Radial Flyer, M1101WH, 13,028 feet
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#6
Center of Pressure on the Der Red Max (1.6" version) is 13" from nose tip.


Later!

--Coop
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#7
Thank you for all the responses. The rocket arrived today, very well packaged. It is just as described, and frankly, looks GREAT! This guy is a real pro. I can't figure out why he sold it? Is it against NAR policy to modify a kit in this way? I hope to post photos tomorrow morning when I am at home with a camera and computer. Stay tuned...
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#8
(08-10-2015, 07:07 PM)Kirk G Wrote: Is it against NAR policy to modify a kit in this way?

Nope. You're even allowed to (gasp) build rockets from scratch!

Modifying motors, that's against the NAR safety code. But modifying kits is fine.

... I haven't changed the motor mount size in very many kits I've done, but arguably I should have done it more! A lot of Estes kits really are underpowered. Example, the Xarconian Cruiser. Estes gives an estimated weight of 3.7 oz (without motor) and recommends flying on B6-2 or C6-3. The C6-3 weighs 0.85 oz for a total weight of 4.55 oz. But in the catalog Estes says the maximum total liftoff weight for a C6-3 is 4.0 oz! Granted, the maximum weights they cite are conservative and depend on many factors. 4.55 oz with this particular rocket is probably not unsafe, but it's certainly pushing the motor's limits. BUT that assumes the rocket really is 3.7 oz. The one I'm building is so far 4.4 oz, excluding added nose weight, and that's before painting! Chris Michielssen's blog talks about building one and his came out significantly heavier than the Estes estimate too. He upgraded the motor mount from 18 mm to 24 mm, and so did I.

Another one I modified was the Squirrel Works Callisto: I replaced the single 18 mm mount with a 3x13 mm cluster mount. That had a fun flight earlier this summer.
Rich Holmes
Camillus, NY
Secretary / newsletter editor
Syracuse Rocket Club

http://richsrockets.wordpress.com
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#9
(08-10-2015, 07:07 PM)Kirk G Wrote: Thank you for all the responses. The rocket arrived today, very well packaged. It is just as described, and frankly, looks GREAT! This guy is a real pro. I can't figure out why he sold it? Is it against NAR policy to modify a kit in this way? I hope to post photos tomorrow morning when I am at home with a camera and computer. Stay tuned...

You're not allowed to modify your motors under NAR rules. In Tripoli, you can do it if you are Level 2 or above. But there is absolutely nothing prohibiting you from experimenting with your rockets.
John S.
NAR #96911
TRA #15253
MDRA
Level 1, 2014-Mar-15 -- Aerotech Sumo, H133BS
Level 2, 2014-Jun-21 -- Giant Leap Vertical Assault, J240RL
Level 3, 2016-03-12 -- MAC Performance Radial Flyer, M1101WH, 13,028 feet
Reply
#10
(08-10-2015, 07:20 PM)Rich Holmes Wrote:
(08-10-2015, 07:07 PM)Kirk G Wrote: Is it against NAR policy to modify a kit in this way?

Nope. You're even allowed to (gasp) build rockets from scratch!

Modifying motors, that's against the NAR safety code. But modifying kits is fine.

... I haven't changed the motor mount size in very many kits I've done, but arguably I should have done it more! A lot of Estes kits really are underpowered. Example, the Xarconian Cruiser. Estes gives an estimated weight of 3.7 oz (without motor) and recommends flying on B6-2 or C6-3. The C6-3 weighs 0.85 oz for a total weight of 4.55 oz. But in the catalog Estes says the maximum total liftoff weight for a C6-3 is 4.0 oz! Granted, the maximum weights they cite are conservative and depend on many factors. 4.55 oz with this particular rocket is probably not unsafe, but it's certainly pushing the motor's limits. BUT that assumes the rocket really is 3.7 oz. The one I'm building is so far 4.4 oz, excluding added nose weight, and that's before painting! Chris Michielssen's blog talks about building one and his came out significantly heavier than the Estes estimate too. He upgraded the motor mount from 18 mm to 24 mm, and so did I.

Another one I modified was the Squirrel Works Callisto: I replaced the single 18 mm mount with a 3x13 mm cluster mount. That had a fun flight earlier this summer.
Yeah, I like to upgrade the mounts on a lot of kits, whether required or not Big Grin  Underpowered kits are another good reason for 18mm reloads to exist, however you generally have to plan for them in advance. 

Just a few of the Estes mods:

Fatboys: 29mm, 3 x 18mm, 7 x 18mm
Big Daddy: long mount for E motors, 29mm
Cluster Bomb: 24mm
Mega Mosquito: 29mm, 3 x 24mm canted mount
Baby Bertha: 29mm
Member of MDRA, NAR and NARHAMS;
Level-2 certified but mostly fly G and under;
Volunteer compiler of manufacturer's news for ROCKETS Magazine.
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