Chute Help on Crazy Design

Hello I am currently building a 3" diameter rocket that is going to be about 7 foot tall. It has three fins that are 1/8 G10 that come out roughly 5.5" then go into a 54mm tube, then that tube has 2 .092 G10 fins on it. The central rocket has a 54mm and the three outboard tubes will be air started and are 29mm. The whole rocket unloaded weighs roughly 7lbs (according to RockSim) and loaded it will weigh closer to 10-11 lbs. I am shooting for an altitude of 10,000 to 15,000 feet and am trying to determine what chutes to use. It will be a dual deploy set up with a drogue at apogee and a main at 500 feet. I currently purchased a TopFlight Ultra-X-Chute in 36" (Drogue) and 54"(Main) because this is what my local hobby shop carried. The big question is are these enough? This rocket will have a lot going on in the back end and I do not want it to come down hard so I need to make sure I have a soft landing, I was thinking in the 10-15 feet per second. I am open for any input and keeping the chutes I have or getting bigger/different ones if need be. Here are some of the 3D model pictures.

Here is a Build picture, I am currently putting on all the fins, The picture below the rocket is just put together with no glue.

First, very cool design!

See topflight's website: https://topflightrecoveryllc.homestead.com/descent_rates.html These are for 17-22 fps descent rates. You are definitely going to need bigger chutes!

DESCENT RATE GUIDE
X-TYPE 'CHUTES
10" 2-3 OZ.
18" 4-12 OZ.
24" .75-1 LB.
30" 1-1.75 LB.
36" 1.5-2.5 LB.
42" 2.5-3.5 LB.
48" 3.5-4.5 LB.
54" 4.5-5.5 LB.
60" 5.5-7.5 LB.
70" 7.5-9.5 LB.
80" 9.5-12.5 LB.
90" 12.5-17.5 LB.

Out of curiosity, how do you plan on air starting the outboard motors? Will you have flight computers in each external pod? Looks like a cool design!

A soft landing is a relative term. Where are you flying and what are the field conditions like? Are you out in the desert? Corn field? Sod farm? I find this page to be quite helpful:

https://topflightrecoveryllc.homestead.com/descent_rates.html

17 to 22 fps is a little aggressive IMHO so going with the next size up when considering the fragility if the rocket and the landing area.

In either case 50" main and 36" x-form will likely be enough unless the ground is rock hard. If it is, then maybe stepping up to a 60" may not be a bad idea.

Yeah I looked at a lot of different chutes and got my charts mixed up that is why I got the wrong sizes, I am just wondering if the x type chutes work good. I have heard good things about them but have never used them personally. So I guess my question was around what size would you recommend as well as are the x type good chutes.

As for the air starting I have some 1/8" tubing that is the same thickness as my fins that I am going to glue to the trailing edge. This will give me the ability to pass wires through to all three outboard rockets. From there One of the outboards will house my electronics to fire the motors. The electronics in this rocket are all custom (currently in the build phase as well) but for the sake of this thread the electronics in the side rockets will be separate. I use the XBEE PRO radios so I have a 1-2 mile encrypted connection from which I can program to fire or I can manually fire from a remote. My plan is to have a remote that fires these outboards that way if its to windy or the rocket goes a little crooked or what ever happens I am not locked in to lighting the outboards. I then only fire them when all is good. It has been a really fun build and I am hoping everything works as planned.

The first launch will be on a Cesoroni I360 for a test flight to 2,000 feet followed by a Cesaroni J355 for the second Higher altitude flight. If all that goes well the Plan is a J355 central (4sec burn) with 3 G33 (4.38sec burn) outboards, should give me just over 8 seconds of burn at an altitude of roughly 11,000 feet. Eventually if I still have the rocket and nothing goes bad the dream launch is a L730 with 3 I204 outboards and it should hit close to 15,000 feet.

DAllen said:

A soft landing is a relative term. Where are you flying and what are the field conditions like? Are you out in the desert? Corn field? Sod farm? I find this page to be quite helpful:

https://topflightrecoveryllc.homestead.com/descent_rates.html

17 to 22 fps is a little aggressive IMHO so going with the next size up when considering the fragility if the rocket and the landing area.

In either case 50" main and 36" x-form will likely be enough unless the ground is rock hard. If it is, then maybe stepping up to a 60" may not be a bad idea.

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I was reading the OP as a 54" x-form, which would be too small. If using an x-form, 80" or even 90" would be appropriate, assuming that your 10-11 lb weight is what would be coming back down. 58" or 70" on the main if going with a traditional chute.

With all of the time and effort you are going to put into this build (awesome design BTW) I would definitely go as big as possible if your main is set for 500'. Going by the Top Flight decent rate for the weight of your rocket I would go with at least the 80" chute for the main. 80" 9.5-12.5 LB. No sense banging up your nice rocket on it's first flight

PokerJones said:

With all of the time and effort you are going to put into this build (awesome design BTW) I would definitely go as big as possible if your main is set for 500'. Going by the Top Flight decent rate for the weight of your rocket I would go with at least the 80" chute for the main. 80" 9.5-12.5 LB. No sense banging up your nice rocket on it's first flight

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That is a very good point I guess I was trying to get the exact right one but why not go a little bigger just to be on the safe side.

Thanks by the way to everyone for liking the design, I have way way way to many hours into modeling and redesigning the rocket and the fins. I bet in the fins alone I redesigned them 20 times. Its nice to finally see it coming together.

The other problem with a design like this is getting your chutes tangled in the fins on deployment. Any ideas on how you will avoid that?
Steve

Random thoughts/questions:

That looks like a really cool project! If it were me, I'd be more concerned with the up part than the down part. I assume you are going to reinforce the @#$% out of it to stand an L flight. Also, those outboards better all come on. Does the loaded 10-11lbs include the stuff you're going to burn on the way up? I'd go on the conservative side when sizing the 'chute as a single pod will take the initial landing jolt.

Did I say it's a cool project?

SDramstad said:

The other problem with a design like this is getting your chutes tangled in the fins on deployment. Any ideas on how you will avoid that?
Steve

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Great point I did not even consider this. The drogue will come out of the booster section and the main out the nose cone side (have not decided if I am going to use shear pins at middle joint or eject nose cone) of the rocket. I am thinking one way to avoid this getting tangled is to make the booster side shock cord really long so that when drogue is out it keeps the top half 15 to 20 feet away from the booster. That way when the main is deployed there is no way for it to get below the booster section, does that seem like a good solution or what am I missing?

rstaff3 said:

Random thoughts/questions:

That looks like a really cool project! If it were me, I'd be more concerned with the up part than the down part. I assume you are going to reinforce the @#$% out of it to stand an L flight. Also, those outboards better all come on. Does the loaded 10-11lbs include the stuff you're going to burn on the way up? I'd go on the conservative side when sizing the 'chute as a single pod will take the initial landing jolt.

Did I say it's a cool project?

Click to expand...

Yes I plan to reinforce the piss out of it, The whole rocket is made from PML Phenolic tubing. The Motor mounts are all phenolic and are the main is the kwik switch XL, and all motor mounts are glued in with 3 centering rings. I also plan to fill motor bays with expanding dense foam. All fins pass through the main body and glue directly to the motor mounts and will have 6 fillets, 2 on the motor mount, 2 on the inside outer tube, and 2 on the outside tube. I initially thought about putting a layer of glass on the outside but was not sure I needed to go that far as I am not sure I will ever get up to an L in this rocket but hey a guy can dream. I plan on building my Level 3 Cert rocket this winter so that one will be a bit beefier.

As for the outboards I do agree that the hope is the all come on at the same time but the rocket is a little on the over stable side with no motors so I am hoping that the fins will help keep it on a somewhat straight line if 1 of the outboards does not light.

The loaded weight is with motors so I am guessing on the way down after burn out the rocket will be close to 8 or 9 pounds. However I need to account for abandoning firing the outboards as these will be remotely fired and if I do not like how the rocket is going I will not fire them. With that said I need a chute that can handle the weight of the rocket a 54mm 6grain Cesaroni tube and possible 3 unburned 6grain 29mm Cesaroni motors.

Sounds like you have this well thought out. Can't wait to see more as the build progresses...and of course the flight video.

Houdeani01 said:

Great point I did not even consider this. The drogue will come out of the booster section and the main out the nose cone side (have not decided if I am going to use shear pins at middle joint or eject nose cone) of the rocket. I am thinking one way to avoid this getting tangled is to make the booster side shock cord really long so that when drogue is out it keeps the top half 15 to 20 feet away from the booster. That way when the main is deployed there is no way for it to get below the booster section, does that seem like a good solution or what am I missing?

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I would go with the long shock cords. Only way to find out for sure is push the button! Good luck! It is a nice looking rocket.
Steve

As one approach to avoiding possible fouling of the chutes; have you considered having the rocket separate and come down in multiple sections?

Perhaps the deployment of the drogue blows the “Fin Section” free which then deploys its own separate chute/s from one or more of the “Pods”.

The only other recommendation I have is to stand way back and take video.

boomtube-mk2 said:

As one approach to avoiding possible fouling of the chutes; have you considered having the rocket separate and come down in multiple sections?

Perhaps the deployment of the drogue blows the “Fin Section” free which then deploys its own separate chute/s from one or more of the “Pods”.

The only other recommendation I have is to stand way back and take video.

Click to expand...

Interesting thought but the amount of electronics required for tracking both sections and for timing ejections goes way up with that approach. I also already have the side pods pretty much complete so it would be hard to add the required hardware to get chutes in there. I do have to say though it would be cool to have a chute in each of the side pods and have it come down on 3 smaller chutes and a small drogue in the main section.

Given the leverage of the outboard motors and the lack of alignment of the thrust axis with the region between the CP range and CM, even slight thrust asymmetry is going to potentially cause some radical maneuvers. IMHO, this is a cool looking but dangerous design.

You will have thrust asymmetry and mass asymmetry during the burns. That is a guarantee. The motors will not exactly match ignition times, burn durations, and therefore mass flux. So the CG will be moving laterally during the burn, as will the thrust vector and center. It is going to take excursions. If things are sufficiently out of match, the excursions could get large. This would be a relatively expected condition for such a rocket so I consider it too risky for a high power flight.

I apologize for throwing the rain.

Gerald

I am open for criticism and I do understand the principals at play. The first 2-3 flights will not have any outboard motors and will fly on a baby I to the full I range. If those flights prove to be successful and stable like rocksim says than and only then will I move to the outboards. Now I will do everything in my power via electronics to ensure all match have continuity and fire simultaneously. With that said you are correct and there is no way to guarantee all motors start at the same time and even if they do they most likely will burn slightly different. The saving grace here is they will never light from the ground that will always be the central motor only. If flight is stable then I will air start outboards. By then the rocket should be doing 300-400 mph and be at an altitude grater than 2000 feet so if it does go wonky then no one is at risk. I am building lots of fails ages into this so I am optimistic it will be stable.

I ended up getting a 7' main and 2' drogue and am planning the maiden voyage this Saturday.

Most importantly, ,
You have the correct approach. ..
Seriously cool design, , really radical, , take it slow,, let it prove flight worthy on low and slow flights before you begin pushing the envelope with it..
On these low and slow flights you should be able to see deployment,,
both apogee and main.. After a few of these flights you'll have a better feel for how it's behaving in all the different parts of a flight.. I am doing the same thing with an air starting rocket.. Just starting to push now after four flights... Because of the distance of the outboards from the centerline don't use them first flight.. Then when you do,, make them small enough to be almost insignificant, ,, see how the rocket behaves when they light..
You are most certainly on the right track...
Super cool rocket..
Take it slow at first is very safe...

For sure..
drogue is way to big..
The drogue is just to stabilize everything on the way down from apogee..
Especially if you have hopes of high flights,, you want a very fast decent rate on drogue. .
I try for 90 fps but don't get it.. I get kinda close though.. Maybe 80 I think..
I shouldn't quote #'s right now, I don't have to figures, I think I'm at about 25 lbs hangin on a 14" Cato ..
I know that rocket is flying really great.. And about 14 lbs or so on the air starting tocket and that's hangs on a 12" Cato... That's flying really nice too.. I like really tough chutes for drogue because they get beat up dragged through the air that quickly. . X form ultra or Cato..

Oh,, and your main is definitely too small..
Get a bigger one and deploy it low, , maybe 700 or so..

All the best of luck..
A super cool, really ambitious project....

Teddy

For the chutes, consider something like the Tender Descender. With both chutes out the front and the drogue then pulling the bag off the main, there is almost no way to get the chutes tangled with the fins.
Those fins will have a lot of drag on the way down, so the drogue does have to be big enough to be sure the rocket is not horizontal, floating under the drogue. But even if it was the bagged main should come out cleanly.

Also, while it's a really cool design, regarding the up part, I would have to agree with G_T above

Thanks guys for all the input, I am planning to take it slow with this one to prove it is flight worthy before ever adding out boards. The first outboards will be either big F's or a small G so it should not alter the rocket to much being that the assembled loaded weight will be around 12-15lbs. I have already purchased chutes so at this point I am locked into my decision, I ended up going with RocketMan chutes just because my local vender had them on had and I like to support the local guys. I bought the strong drogue chute version for the 2ft and the other one is the standard 7ft which seems pretty durable. I thought about going to the 8ft but to be honest its already hard enough to wrap the 7ft nicely and get it into a 3" airframe. I had the whole assembly laid out in the grass so I could make sure that the shock cord lengths and chute positions should have no way to hit the fins. I will try and take some pictures of this once I finish up the clear coats tonight. If you want to see more details on the build please take a look at my build thread.
https://www.rocketryforum.com/showthread.php?127308-Cluster-F/page2

Again thanks for all the input it has helped me to make this a much better rocket in my mind.

On one other note the 2ft drogue I bought was because RockSim said I would have around a 83ft/sec descent rate.

If you run into concerns about tight packing and performance, you might consider Fruity Chutes Iris Ultra designs. With a Cd of about 2.2 (which is amazing) you can get a lot of performance out of a smaller sized chute.

https://fruitychutes.com/parachute_recovery_products/iris_ultra_parachutes.htm

Greg

GregGleason said:

If you run into concerns about tight packing and performance, you might consider Fruity Chutes Iris Ultra designs. With a Cd of about 2.2 (which is amazing) you can get a lot of performance out of a smaller sized chute.

https://fruitychutes.com/parachute_recovery_products/iris_ultra_parachutes.htm

Greg

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I did consider them and that was my number 1 choice but the price was the limiting factor for me. I would love one of their chutes though as I think they look amazing.