Tweeks’ L3 Project
5.5” “Black Friday Brant”
L3 Launch Location - LDRS 36
Higgs Farm, Price Maryland April 6th - 9th 2017
For TRA TAPs:
Bob Schoner <bob.schoner@gmail.com> � Pat Artis <pat.artis@gmail.com>� GDoc Link - www.tinyurl.com/tweeks-l3
�Thomas “Tweeks” Weeks tweeks@theweeks.org�TRA# 11056
L3 TAP Documentation Overview
The completed “Black Friday Brant”
L3 TAP Documentation Overview
Tweeks Drilling Fincan/BT Nut Mounts
L3 TAP Documentation: Rocket Overview
Rocket Specs:�Kit - MadCow Black Brant - II, 5.5”, all fiberglass + metal tip�Diameter - 5.5” Length - 108” Motor Mount - 75mm Dry mass - 401oz (25.1lbs) w/motor - 570oz (35.6lbs)�Altimeter 1 - GWiz LCX (accel based, two 9v) Altimeter 2 - PerfectFlight StratoLoggerCF (barro based, single 9v)�Chutes: Main - 144” Top Flight CF (Cd=1.4) Drogue - 60” Top Flight CF (Cd=1.4) �
Special “Tweeks” Modifications:� -Strengthened fin/MMT w/poured internal fin & ring fillets (by cutting out rear fin slots for external fin can assembly)� -Making fin-can a bolt-in for added convenience & maintenance� -Made double fincan u-bolts for 10ft kevlar “booster loop”. Connect booster-loop to Av-Bay via 2nd 20ft kevlar strap� -Bought new nosecone bulkplate & pushed forward 8” to front of nosecone coupler. Stronger U-bolt anchor + more stability� -Plan to reinforced weak aft-half-fin mount (no thru) w/external fillets+fin-tube-fin glassing � (verified problem w/MadCow BB designer)��
L3 TAP Documentation: Flight Simulation Data
Rocket Specs:�Kit - MadCow Black Brant - II, 5.5”, all fiberglass + metal tip�Diameter - 5.5” Length - 108” Motor Mount - 75mm �Dry mass - 401oz (25.1lbs) w/motor - 570oz (35.6lbs)�Cg = 72.52” (loaded, sim), Measured = (no motor yet) �Cp = 82.96” (per open rocket, not provided by MadCow)�Stability = 1.90 Cal (room for longer motors) �Motor - S.Use Aerotech M1350W (TI=5178 Ns)�Thrust : Weight = 8.5 : 1 ��NOTE: Last minute update. Actual scales put in the empty rocket at around 5lbs heavier than the sims (evenly between fore & aft). A quick re-sim knocks the speed from mach 0.8 to 0.7 and ~1,000ft off the apogee. Still looks fine/safe.
Expected Flight Data:�Rocket Flight Speed (w/ AT M1350W-P) � @ end of 6ft rod 59.8ft/sec � @8ft rod 69.1 ft/sec
Max Velocity 890 ft/sec (0.8mk)
Mag Acceleration 329 ft/sec2 (10.2g)
Apogee 8,973 ft� EVENT: Drogue eject @23sec, 10.8ft/sec�Drogue descent rate (60” Cf=1.4) 37 ft/sec� EVENT: Main ejection at 700 or 800ft �Main descent rate (144” Cf=1.4) 13.7 ft/sec� EVENT: Hit ground @195 sec
L3 TAP / TRA Pre-Flight Data Capture Form
L3 TAP Documentation: Parts List
General Construction�Black Brant - II 5.5 Kit
Aerotech M1350W-P (see right)
Aeropack 75mm (RA75P)
RF/Radio Bay (2” PVC in nosecone)�Av-bay 14” w/aluminum bulkplates
Aluminum ejection canisters�All 5/16” u-bolts and Av-bay all-thread�All 1/4" screws & nuts in Av-Bay and fin-can
Joints & Fins - Bob's Epoxy 15min
Fillets - West Systems Epoxy � (with HD 404 filler)
1515 Rail Buttons (pair)
������
Recovery Construction�Madcow 5.5” fiberglas+Al avionics (all 5/16” bolts/nuts)�60" Chute (Top Flight CF 60)
144" Main Chute (Top Flight CF 144)�Alt-1 - PerfectFlight StratoLogger-CF
Alt-2 - GWix LCX (accel based)
11" ABS Alt Sled (MadCow)
18" Chute protectors(x2)
20ft 5/16 Kevlar (w/swivel)�4-40 shear screws (x3)�Stainless 200lb 5/16" Quick Links (x8)
5g Alum. Ejection Canisters (4)
Nylon 9v Batt Holders (x3)
MOD - 5.5" Bulkplate for nose cone
MOD - Glass the fin/boat-tail joint
Motor - Aerotech M1350P�(single use for cost & KISS)
For complete cost breakdown w/parts links - �https://docs.google.com/spreadsheets/d/1Z2Hb1rr7qX7GkYaj232avu-TNH1g3OvGYhYoAiGUBlg
L3 TAP Documentation: Overall Design (1 of 3)
Main chute:�144” Top Flight
Main shock cord:�20ft ½” kevlar
Four 4gram�Ejection canisters
Drogue chute:�60” Top Flight
Drogue shock cord:�20ft ½” kevlar
Fincan cord U-loop:�20ft ½” kevlar
Two fin-can �U-bolts (for u-loop)
14” Avionics Bay w/Al bulkplates
6in boat tail
75mm Aeropack�Motor retainer
Stainless u-bolts
2k lb stainless quicklinks
Radio/GPS/Noseweight Bay
quicklinks
L3 TAP Documentation: Airframe Design (2 of 3)
¼” t-nut & bolts
¼” brass insert & bolts
4-40 Nylon �Shear Screws
½” Kevlar strap (20ft)
½” Kevlar strap (20ft)
½” Kevlar booster loop (20ft, 10ft effective)`
5/16” S.steel quicklinks (2000lb)
Removable fin-can
GPS/RF/Radio Bay
Main - 144” �Top Flight CF
Drogue - 60” �Top Flight CF
L3 TAP Documentation: Safety Design (3 of 3)
Ejection & Recovery Safety:
For a 35lb rocket traveling at near mach-1, safety is a huge concern. The following safety measures have been taken:��1) Different Altimeters:�As per the L3 required, I not only have two altimeters, but I used two different brands. This is so that if some condition causes one to fail (such as mock lock), the other will still fire as expected. This is further reinforced as Atl-1 is accelerometer based and Alt-2 is barometer based.��2) Triple Power:�Each altimeter not only has separate power sources, and alt-1 actually has both a digital logic power source as well as dedicated pyro power source. Three 9v batteries in all. �
3) Cross wired ejection canisters:�The igniters are cross wired (four igniters going into two canisters) per chute. So whichever altimeter fires first, both ejection canisters blow. This does two things.. 3a) if either altimeter fires, the full load of BP goes. 3b) since ½ charge is used per canister, there is zero chance of a simultaneous overpressure event. The only disadvantage I’m aware of is if one altimeter fires prematurely, all BP goes at once. But even still, this is a fail safe mode (for the crowd) instead of an error state that causes a ballistic descent.�
4) Shock cord & hardware ratings:�The “weakest link” in the recovery harness is not less than 2,000 lbs test (stainless quick links).
Construction Photos
Full Photos - https://goo.gl/photos/qvQDGVjyEt3FSYKK8
Design - Shear Pins, Three #4-40 Screws
I’ve been using polystyrene rod for shear pins for years, but never in a project this large. TAP-1 (Bob) didn’t like the idea of ⅙” polystyrene rods (just from his flying experience). After looking at the numbers and the weight of the heavy nose cone, and hand simulating a ejection/cord “jerk”, I agreed that the event and forces are in the same order of magnitude as the small shear load levels.
After looking at a few shear-pin experimental data sets[1], we �estimated that three #4-40 nylon screws should suffice in my �nose config (38.3 lbs/pin * 3 = 115 lbs shear force), even though �most calculators list almost twice as many. ��I taped the nosecone on, drilled the holes and <zzzzip>, pushed�them in. I did trim them down a little to prevent ejection cord hangs.
[2] Shear Pin Simulator - http://speedmotionrockets.com/Black%20Powder%20-%20Shear%20Pin%20Calculator%20Rev4.xlsx � Measurement Data - http://www.telerover.com/rockets/L3/HPR_ShearPinTests.pdf
Calculations - Ejection Canisters for Main (payload)
To calculate the powder load needed for this, we work from the volume of our payload cavity (Vp ).�
Vp = Areanc Lcavity Anc = π r² = π(5.35”/2)² = 22.48 in2 �Vp = (22.48 in2 ) (20” - 6”) = 314.7 in³
Divide by the area to convert Ft to P (in psi) :
P = Ft / Anc = 235 lbs / 22.48 in2 = 10.45 psi
To calculate the amount of black powder for this pressure:�
W = (P V / R T) 454 gm/lb = W grams of BP
R is the combustion gas constant, 22.16 (in- lbf/lbm R) for FFF black powder.
T is the combustion gas temperature, 3307 degrees R for black powder.
W = ( (10.45 psi * 314.72 in³) / ( 265.92 in- lbf /lbm * 3307 degrees R) ) * 454 gm/lb �
WBP-Main = 1.70 g → round up ~2.0 g��
This figure “feels right”, but I found an online calculator that validated my numbers [3]
The approximate force to reliably pop off a nose cone (Fnc) is between ~100-150lbs. �So we let:�Fnc = 120 lbs
Additionally, the experimentally measured shear force for one #4-40 nylon shear screw:�Fp ~ 38.32 lbs [1]
�Bob (TAP1) suggests three shear pins, so:
F3p = 115 lbs
So the total force required for reliably shearing fill the main payload volume and shear ll three pins + the nose cone is:
Ft = F3p + Fnc = 235 lbs
Calculations - Ejection Canisters for Drogue (booster)
A larger space, but less pressure (due to no shear pins).
To calculate the amount of black powder for this pressure, again we just plug in the values:�
W = (P V / R T) 454 gm/lb = W grams of BP
R is the combustion gas constant, 22.16 (in- lbf/lbm R) for FFFF black powder.
T is the combustion gas temperature, 3307 degrees R for black powder.
W = ( (5.34 psi * 674.4 in³) / ( 265.92 in- lbf /lbm * 3307 degrees R) ) * 454 gm/lb =�
WBP-Drogue = 1.86 g → round up to ~ 2.0 g
�Cool. Bigger space, less pressure, same load. �Makes it simple!
Working on ground testing these figures now.
Since the drogue does not need to shear pins, and from what we covered in the previous main calculations, the approximate force to reliably separate the payload from the booster section, we’re saying that the force for this is simply:�Fav = 120 lbs
However, given that, the volume of our booster section is a bit larger (~30 inches), to volume we’re dealing with is:
Aav = π r² = π(5.35”/2)² = 22.48 in2 � and so..
Vp = (22.48 in2 ) (30 in) = 674.4 in³
Divide by the area to convert Fav to P:�
P = Fav / Aav = 120 lbs / 22.48 in2 = 5.34 psi
L3 TAP Documentation: Recovery System Schematic
M1
M2
D1
D2
GWiz Alt(1)
PFlite Alt(2)
B1alt1
Redundant Drogue�Chute Canisters
Redundant Main Chute Canisters
B1pyro1
Arm1alt1
Arm1pyro1
Arm2alt2
B2alt2
Main charges
Main charges
1/2 the M-charge sealed with Alt1+2 igniters
1/2 the M-charge sealed with Alt1+2 igniters
Drogue charges
Drogue charges
1/2 the D-charge sealed with Alt1+2 igniters
1/2 the D-charge sealed with Alt1+2 igniters
This is a simplified wiring diagram of my redundant altimeter configuration. The GWiz altimeter(1) is accelerometer based with dedicated digital + pyro batteries, while the PerfectFlite Stratologger-CF(2) is a barometric unit also with its own single battery. At the suggestion of Pat (TAP2), I will be wiring the each pryo output in parallel to each ejection canister (four e-matches per chute). The advantage is two fold. By cutting each charge by 50% and putting Alt1 & Alt2 igniters in each canister, both canisters will be ignited at the soonest event ( E(1) || E(2) ). The second advantage is that there is no risk of a double-full-charge, over-pressure event (with 2x the powder). The one added risk though is that a premature event (very rare) will cause a full, premature ejection. Possibly bad for the rocket, but good for crowd safety.
L3 TAP Documentation: Pre-Flight Checklist (on site)
Body, Chutes and Av-Bay:�-Chute: Attach chute protectors (2)�-Cords: Check & secure ejection cord mounts (lay it out) (4)�-Chute: Attach chutes (layout open) Mooster=Droge, Payload-Main (2)�-U-Bolts: Wiggle-test fincan u-bolts for tight & secure (2)�-Bolt Fincan: Screw together fincan & booster BT (5/16”) (6)�-Av-Bay Safe: Turn off arming circuits (3)�-Av-Bay Batts: Insert fresh batteries (3)�-Av-Bay Connectors: Connect Altimeter power connectors (3)��Av-Bay - Prep DROGUE Powder Charges:�-Ematch Cont. Check: Check continuity on four e-matches (4)�-Drogue Eject-1: Wire up Alt-1-Dr (GWiz) to canister D1 and D2 (2)�-Drogue Eject-1: Insert powder loads for Alt-1-Dr (GWiz) into D1 & D2 (2)�-Drogue Eject-2: Wire up Alt-2-Dr (PFlight) to canister D1 and D2 (2) �-Drogue Eject-2: Insert powder loads for Alt-2-Dr (PFlight) into D1 & D2 (2)�-Drogue Eject Seal: Cap & tape canisters D1 & D2 (2)��Av-Bay - Prep MAIN Powder Charges:�-Ematch Cont. Check: Check continuity on four ematches (4)�-Main Eject-1: Wire up Alt-1-Main (GWiz) to canister M1 and M2 (2)�-Main Eject-1: Insert powder loads for Alt-1-Main (GWiz) into M1 & M2 (2)�-Main Eject-2: Wire up Alt-2-Main (PFlight) to canister M1 and M2 (2) �-Main Eject-2: Insert powder loads for Alt-2-Main (PFlight) into M1 & M2 (2)�-Main Eject Seal: Cap & tape canisters M1 & M2 (2)�
Assemble Av-Bay:�-E-Check: Visual check of e-match wiring(8), power(3), canisters(4)�-Mechanical Check: Sled, all-thread/bolts, fit�-Orient Av-Bay: Fore-UP, Aft-DOWN�-Bolt Av-Bay: Bolt Av-Bay to payload section (6)��Load Main Chute: (upper / payload / nosecone)�-Fold Main: Lay out and fold up cute, shroud lines�-Wrap Main: Wrap chute in protector�-Load Main: Load chute & protector into payload/nosecone & close (1)�-Shear Pins: Close nosecone/payload & Install shear pins (3)��Load Drogue Chute: (lower / booster / Av-bay)�-Fold Drogue: Lay out and fold up cute, shroud lines�-Wrap Drogue: Wrap chute in protector�-Load Drogue: Load chute & protector into booster/Av-Bay & close (1)�-Booster Check: Check tightness/looseness of booster/Av-Bay coupler��Load Motor:�-?Motor Eject? Remove Motor ejection, reassemble, and Install forward plug�-?75mm? - Insert motor + Screw on Aeropack retainer (2)�-?54mm? - Bolt on 75/54mm motor adapter�-?54mm? - Insert motor + screw on Aeropack retainer (2)�-Igniter: Verify correct igniter (fits in motor, goes all up)�-Igniter: Tape igniter to fin (1) + secure a backup igniter (1)��Nose Cone & Final Mechanics�-Check Upper: Check for secure Nosecone, Av-bay/payload (2)�-Check Lower: Check secure Fincan/Booster + Smooth Booster/AvBay separation (2): �-Check Buttons: Visual + mechanical rail-button check (2)