PDA

View Full Version : L2 on an ACME Spitfire



Wiley
25th October 2010, 01:23 AM
Hey folks! Today I have a motor question. Since I have almost two years to design, build, and possibly sucker someone into test-flying a project for my L2 (the L1 rocket is already built and tested, courtesy of Dad’s L1:D).

I’m thinking of constructing a ~4X upscale ACME Spitfire (8” diameter, about 5.5’ tall), but with many lightening modifications, out of home made fiberglass. Some of the features I intend to build into it are: a modular fin can (tired of repairing busted fin cans with a hacksaw and a sledgehammer :gavel:), a removable 3’ diameter central tube, and timer based recovery.

To loft this beast, I have settled on an AMW/Pro-X 54-2550 load, hopefully a Skidmark, but probably not because of fire issues. I actually have two questions. Supposing the weight of such a large, draggy rocket is ~30 pounds with the motor, do you think a K or L1000ish load will take it to under 2000’?

My other question is if any of you have seen the K1075 skid perform. Is it a “true skid” the way AMW used to make ‘em? Pictures and videos are more than welcome! Thanks for your time!

Wiley
27th October 2010, 02:12 AM
Hey folks! Today I have a motor question. Since I have almost two years to design, build, and possibly sucker someone into test-flying a project for my L2 (the L1 rocket is already built and tested, courtesy of Dad’s L1:D).

I’m thinking of constructing a ~4X upscale ACME Spitfire (8” diameter, about 5.5’ tall), but with many lightening modifications, out of home made fiberglass. Some of the features I intend to build into it are: a modular fin can (tired of repairing busted fin cans with a hacksaw and a sledgehammer :gavel:), a removable 3’ diameter central tube, and timer based recovery.

To loft this beast, I have settled on an AMW/Pro-X 54-2550 load, hopefully a Skidmark, but probably not because of fire issues. I actually have two questions. Supposing the weight of such a large, draggy rocket is ~30 pounds with the motor, do you think a K or L1000ish load will take it to under 2000’?

My other question is if any of you have seen the K1075 skid perform. Is it a “true skid” the way AMW used to make ‘em? Pictures and videos are more than welcome! Thanks for your time!

Since I'm new here, I'm not sure how soon people reply to a post, but if any of you are able to answer the above info, I would be much obliged! Thanks!:D

BsSmith
27th October 2010, 04:18 AM
It sounds like a cool idea. I can't answer most of your questions, but it is a cool idea.

I also have two more years until I can get my L2 and 3, but I'm also finding out that it is probably a good idea to wait to get it. It almost seems that I am rushing to meet a goal that I won't be able to follow up on until after college. I have several L1 and L2 capable rockets already built, and I will probably get my L2 with one sometime in college, but it won't be a huge thing.

P.S.- Look up the ACME Spitfire launched at NSL 07. I believe that it was a 12" that flew on an M skid.

bandman444
27th October 2010, 04:28 AM
Bs that was a sweet rocket...

heres the link

http://www.rocketryplanet.com/content/view/1928/38/

BsSmith
27th October 2010, 05:27 AM
NSL 07 was the first big rocket launch that I went to, and that ACME was just awesome, because I had just finished a fliskits one.

I have a picture of me standing next to it somewhere, I just have to find it.

jflis
27th October 2010, 11:22 AM
That was an incredible launch, to say the least :) I've seen several sizes of the ACME Spitfire and they've all flown flawlessly. I have even seen them used for certification flights (L1).

I am looking forward to this project and hope someone can answer your questions soonest! :)

jim

Handeman
28th October 2010, 01:19 AM
Hey folks! Today I have a motor question. Since I have almost two years to design, build, and possibly sucker someone into test-flying a project for my L2 (the L1 rocket is already built and tested, courtesy of Dad’s L1:D).

I’m thinking of constructing a ~4X upscale ACME Spitfire (8” diameter, about 5.5’ tall), but with many lightening modifications, out of home made fiberglass. Some of the features I intend to build into it are: a modular fin can (tired of repairing busted fin cans with a hacksaw and a sledgehammer :gavel:), a removable 3’ diameter central tube, and timer based recovery.

To loft this beast, I have settled on an AMW/Pro-X 54-2550 load, hopefully a Skidmark, but probably not because of fire issues. I actually have two questions. Supposing the weight of such a large, draggy rocket is ~30 pounds with the motor, do you think a K or L1000ish load will take it to under 2000’?

My other question is if any of you have seen the K1075 skid perform. Is it a “true skid” the way AMW used to make ‘em? Pictures and videos are more than welcome! Thanks for your time!

Sounds like a fun build, but it might be just a bit much for L2, especially if you are just getting an L2 cert. Figuring 10" dia due to nose hat and shape of body tube, .8 Cd and 480 oz. (30lbs) it will get 1,350-1,400 on a K675-SK and only about ,1950 - 2,000 ft on an L1030-RL. That is definately do-able, but is definately on the top end of L2.

Why do you want to do timer based recovery? Is it because you think the BT shape will mess up baro altimeters? It might make data recordings slightly off, but a baro should still work for apogee deploy and be quite accurate for dual deploy.

Wiley
28th October 2010, 01:49 AM
Actually, that's exactly what I was thinking. Could you tell me more about this? After reading an article on barometric altimeters on Vern Knowles' site, which said that they shouldn't be placed near any high or low pressure zones on the rocket. Since nowhere on the ACME is turbulence free:blush:, I decided to go with timers. Otherwise my first choice would be the Perfectflite HiAlt45K altimeter.

BsSmith
28th October 2010, 03:18 AM
Actually, that's exactly what I was thinking. Could you tell me more about this? After reading an article on barometric altimeters on Vern Knowles' site, which said that they shouldn't be placed near any high or low pressure zones on the rocket. Since nowhere on the ACME is turbulence free:blush:, I decided to go with timers. Otherwise my first choice would be the Perfectflite HiAlt45K altimeter.

The deviance in the pressure only happens as the rocket is going fast. Because of that, the baro data will be slightly off, but when the rocket slows down to deployment speed it will be fine. Another thing that you could do is use an accelerometer based deployment, which I personally think is more accurate (both will deploy the parachute at a reasonable speed, though). For not too much more than the Perfectflite, you could get a Raven, which uses both Accelerometer and Baro with 4 output channels.

Wiley
28th October 2010, 03:48 AM
Thanks for the info! :D Whatever electronics I use, it will be to deploy the chute at apogee. The electronics will be located in the second "kink" in the airframe down from the nose cone. Just to be sure, if a barometric altimeter is used, will the deployment be near or at apogee every time, no matter what conditions? Also, about how large should the static ports be, seeing that they will be engulfed in a lot of turbulence from the nose cone and the kinks in the tube? Just another one (don't let anyone tell you I'm long-winded). Will the timer based scheme work, if I use two timers, with one backing up the other a second later? Thanks!:)

Pantherjon
28th October 2010, 04:55 AM
Sounds like an interesting endeavor!..Here is my view as far as altimeters: baro v accelerameter..I would go with the barometric one..Why? As I am familiar with them..Also, take a close look at the design of the ACME Spitfire, sure it has 'kinks' but they are on 2 axis' the other 2 are straight, use that to your advantage and place your vent holes there..:2: ;)

Handeman
28th October 2010, 11:14 PM
The vent hole for the altimeter are sized to allow the altimeter to read correctly, but not so big that wind and turbulence will cause spikes and valleys in the pressure readings. This is accomplished by using multiple smaller holes rather then one large hole.
Since this rocket is going to stay well below Mach, I would use four or more small holes to vent the av-bay.

cjl
29th October 2010, 12:46 AM
Personally, due to the massive turbulence and odd pressure zones around the rocket, I'd use an accel-based altimeter for deployment. The Featherweight Raven would be an excellent choice.

Wiley
29th October 2010, 02:15 AM
The Raven looks like a really good deal. Do you know if its attached to a regular 9V if it will fire a 24" long Rocketflite ematch reliably (these take at least 1.6 amps of current for at least 1 second to fire reliably)? Also, are you aware of a place that sells the Raven for "less?" Wildman sells 'em for $155:y:. Would a combonation of an accelerometer and a timer be a good idea?

BsSmith
29th October 2010, 04:23 AM
They would light the e-match with no problem at all. I'm pretty sure that you could even light a Big Un' ignitor with a fresh 9v.

The combination of accelerometer and timer may not be a very good idea. I've never been a big fan of timers, there's just too much room for error. Honestly, the Raven is worth the $155, and it will most likely pay for itself at some point. Also, if you certify on al L motor, the motor itself will cost more than the altimeter.

cjl
29th October 2010, 05:08 AM
Agreed. The raven is quite a deal for $155 (I personally own 2), and it has 4 outputs, so you can attach more than one charge if you feel the need to (you could even set one of the channels to simulate a timer, if you really wanted).

Lamp
29th October 2010, 06:51 AM
I own a few Ravens and I think they are great value for the money.

It does not matter if you get them from Wildman, Aerocon, any other retail supplier or the Featherweight shop they will still cost $155. ;)

bobkrech
29th October 2010, 03:47 PM
I’m thinking of constructing a ~4X upscale ACME Spitfire (8” diameter, about 5.5’ tall), but with many lightening modifications, out of home made fiberglass. Some of the features I intend to build into it are: a modular fin can (tired of repairing busted fin cans with a hacksaw and a sledgehammer :gavel:), a removable 3’ diameter central tube, and timer based recovery.
A 4x scaleup of the ACME Spitfire should come in about 12 pounds, so I think you are overbuilting if the rocket weights 30 pounds. I would consider using 8" sonotube which does not need to be glassed, and use 12 ply 1/4" Finnish birch for the fins and the rings. It's virtually as stong as fiberglass and 1/2 the weight.

Buildiing lighter will allow you to get the same altitude with 1+ impulse class lower motor, cutting your motor cost in half, and allowing you to launch on fields suitable for J and K motors vs L motors. A quick sim shows that a minimum delay Pro38 6 grain or Pro 54 2 grain will apogee about 1000' in a draggy 8" 12 pound rocket. A minimum delay 3 grain Pro54 will apogee ~1500'. A lightweight surplus 10' military chute (tie dyed?) or (3) surplus 5' parachutes (dyed red, white and blue) would give a reasonable descent rate.

Just some thoughts.

Bob

Wiley
30th October 2010, 03:35 AM
Thanks for the sugesstion, but I intend to build the rocket entirely with composites. The outer 8" tube, since it doesn't bear a great deal of structural load, will be about .05" thick and the central tube will be a 3" diameter about .08" thick. The rocket will only have two 8" centering rings, one at the extreme rear, and one at the joint between the top two tubes. The other tubes will be butt glued and the joints fiberglassed together on the inside. The entire top section of tube will be left open (and it'll be about .1" thick or so to prevent zippers). The base of the NC will be left open so that I can use the combined volumes of the top tube and the NC to pack my chute and shock cords. The fins will be made from 1" foam board, shaped and glassed, and they'll be removable. The central tube will be removable, retained by small aluminum bolts at the back and with a fillet of silicone at the top. You can see in the attached photo how the bolts work. This is the motor retainer on my dad's Patriot. If this central tube is ever damaged (flameout), all that's needed to remove it is to undo the bolts and scrape off the silicone with a sharp putty knife.

Wiley
30th October 2010, 03:38 AM
Oops! Forgot to metion this in my last post :blush:. When you say "10 foot chute" do you mean a 10 foot diameter parasheet or a hemispherical chute? I will be sewing a hemi chute for it.

Wiley
20th November 2010, 07:18 PM
If I sim this design on Rocksim, it can simulate everything except the asymmetrical NC and the kinks in the airframe. Will the CP be altered by these factors on the real rocket, or will they have no negative effect on stability?

DAllen
20th November 2010, 11:51 PM
Does Fliskits have the CP figured out for the original?

Assuming that the CP in the Rocksim file over here (http://www.rocketreviews.com/cgi-bin/search/searchall.cgi?acme+spitfire) is correct then it is safe to say that the CP will be the same distance from the N/C proportionally on the upscale.

Example...if the original is 24" long and the CP is 18" from the N/C and the upscale is 48" long then the CP on the upscale will be 36" from the N/C.

-Dave

Wiley
21st November 2010, 01:50 AM
Thanks for the info! I emailed Jim Flis, but he said that he doesn't really know where the CP is. Won't keeping the CG in the proportionately same place on the upscale as on the kit also yeild a satisfactory result?

Just to throw this in, I found a rather similar rocket to the one I intend to build on the web which also proves that this thing will "go" on a 54-2550 K or L;). The site is www.mercuryjoe.com. Of particular interest is the flight on a K1075GG, since this motor has detestable progressive burn. The only reason it flew crooked on this flight is because of the issue with the binding/twisting on the rail.

DAllen
21st November 2010, 06:11 AM
Thanks for the info! I emailed Jim Flis, but he said that he doesn't really know where the CP is. Won't keeping the CG in the proportionately same place on the upscale as on the kit also yeild a satisfactory result?


Yes, that is a perfectly logical conclusion as far as I am concerned. If it's stable in the little version it should mimic the same in the larger version.

BTW...This is a build where I would strongly recommend against over building. There are a lot of short pieces of BT and if they are adequately glued together I suspect it will be quite rigid. Glue is going to make up a big chunk of the weight. This isn't exactly a super sonic speed demon design so copious amounts of fiberglass and epoxy really aren't going to help. You may need to add nose-weight to adjust the CG.

-Dave

Wiley
21st November 2010, 05:04 PM
This is a build where I would strongly recommend against over building. There are a lot of short pieces of BT and if they are adequately glued together I suspect it will be quite rigid. Glue is going to make up a big chunk of the weight. This isn't exactly a super sonic speed demon design so copious amounts of fiberglass and epoxy really aren't going to help. You may need to add nose-weight to adjust the CG.

-Dave

That's exactly what I had in mind. Because its made entirely (or very nearly so) of home made composites, the idea is to make it as light as possible. For example, it will only have 2 CRs in the 8" airframe, one near the tail end and the other at the joint between tubes 3 and 4 (the top two tubes). Tube 4 will be left open and used for the parachute compartment. All the other joints will be fiberglassed together.

jflis
22nd November 2010, 12:15 PM
Thanks for the info! I emailed Jim Flis, but he said that he doesn't really know where the CP is. Won't keeping the CG in the proportionately same place on the upscale as on the kit also yeild a satisfactory result?



Assuming that your final design is a true upscale of the original you should be fine. I have seen several upscales that were true upscales and this has held true and they've all flown just fine. That M2100 sparky flight was a sight to behold :D