Nose Cone Assembly

Design Review

Design Overview

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COTS: Madcow Rocketry 6” ID :5:1 Von Karman NC with metal tip

Cut off bottom to 6” OD

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Dominic

Nose Cone Tip Design

• Tip Design is driven by aero-thermal balance
• Decide:
• Material
• Metal or Ablative
• Length of Tip
• Longer tip - less heating
• Shorter tip - lighter
• Tip Radius
• Smaller radius - hotter, less drag
• Larger radius - cooler, more drag

Dev

Analysis Approach

Theoretical

• 1D transient thermal model using predicted flight path

Size the Nose cone tip radius�Estimate ascent temperature profile near tip

• 3D transient thermal model fixed temperature on boundary

Determine required length of tip to ensure connected parts survive

Experimental

• Blowtorch test�(Samples of nose cone mounted), and blowtorched. Temperature monitored)

Validates thermal model and thermal constants used

Allows us to experimentally determine ablative behaviour - potentially determine thermal constants needed to use ablatives.

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Metal vs Ablative

Metal

• If material stiffness decreases due to aero-thermal heating to a point where it deforms/melts off the tip
• If the metal connected to the rest of the nose cone reaches the max service temperature of connected material

Ablative:

• If the critical ablation temperature is reached and the ablative is eaten through
• If chunks of the ablative break off and either thermal protection is lost or hits another part of the rocket

Preferred to use metal, as we can model it, and design it to survive

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Ascent Heat Flux

• Nose cone tip heating is dominated by convective heat transfer
• NASA Ames in 1987 suggested that ascent heat loads can be modelled using:

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• Double nose cone radius => heat flux (and temp) decreases by ~30%

[1] Tauber, M. E., Menees, G. P., & Adelman, H. G. (1987). Aerothermodynamics of transatmospheric vehicles. Journal of Aircraft, 24(9), 594-602.

Heat Flux

5 mm Tip

10 mm Tip

Using 10mm radius instead of 5 reduces the heat flux by ~30%

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Total convective heat in:

5mm: 5.2e7 J/m^2

10mm: 3.6e7 J/m^2

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(Change in flight profile due to tip radius is not considered)

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1D Model

Convection Model:

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Conduction

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Radiation:

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No Heat Flow

Convection

Radiation

Conduction

Simulation Results

10 mm Nose Cone Tip

10mm

Melting Point

5mm vs 10mm Cone Tip

Thermal Sim Results (10mm)

SS 316

Melting Point: 1370 C

Service Temp: 700-900 C

700C: <10.5s, <0.1 in

900C: <5s, <0.03 in

Nose Cone Tip Summary

• Metallic Nose Cone Tip Suggested:
• Stainless Steel 316 should not melt
• For about 10 seconds 0.1 in of the tip could be beyond service temperature
• Nose cone tip radius of 10 mm is minimum, but larger radius is preferred if drag impact is less significant.

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• We will experimentally determine if the service temperature will be a problem using thermal rig (discussed later)

Thermal Analysis

Thermal Desktop is being used to model heat flow through the nose cone.

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Model Assumptions:

• The top of the nose cone tip is set as a boundary node to 950 degrees fahrenheit (based on stagnation temperature temperature for 3.5 Mach)
• There is only heat applied to the top of the nose cone
• The nose cone tip shape can be approximated by a regular cone (dimension: 4 inches long, diameter of 1.7 inches)
• There is no heat loss due to radiation or convection

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Dominic

Thermal Analysis

Stainless Steel

Titanium

Dominic

Thermal Analysis

Inconel

Dominic

DAQ

Supports temperature sensors, accelerometers, and load cell(s)

PCB Dimensions: 2 “ x 3” x ~0.5”

Mounted on M3-0.5” standoffs on NC stack

Strain relief

Power controlled by switchband

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CAD - Nose Cone Tip

Diameter: 2.305 inches

Length: 6.1526 inches

10mm Bluntness

• 4” length is probably a better option. There seems to be very little difference between 4” vs 6”. However, we should consider its effects on the center of mass.

Material for Nose Cone Tip

Stagnation Temperature: 510°C (Mach 3.5)

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Mass 6”: Steel: 1.36 kg, Titanium: 0.79 kg, Inconel: 1.43 kg

For 4” Tip: Steel: 0.51 kg, Titanium: 0.3 kg, Inconel: 0.54 kg

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NC Planing Jig

• Purpose: To secure the nose cone, so that it can be cut to 6” OD.
• Currently 6” ID, 6.18” OD.
• Estimated length of cutting: 3.3”
• Assuming there are no flat parts after the von Karman shape.

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Procedure for cutting nose cone to 6” OD:

• Mark the distance.
• Cut.

NC Planing Jig

NC Tip Attachment

Four holes for the cables coming out from the Thermocouples attached to the tip.

CAD: Payload Bulkhead

Bolts Connecting NC to Bulkhead

• Must withstand force from deployment of the piston
• Calculate the maximum force from the piston:
• Recent sims -> the maximum force on the whole system = 2250lbs

F_nc_section = F * M_nc_section/M_whole_rocket

• Currently, the mass budget of the rocket has a dry mass of 79 lbs. Assuming

M_nc_section = M_nc + M_nc_tip + M_nc_extension = 5.6 lbs

F_nc_section = (2250lbs)*(5.6lbs)/(79lbs) =160 lbs

• Applying the safety factor of two and adding a couple of pounds to the nose cone in case it goes over its mass budget,

F_nc_section = (2250lbs)*(10lbs)/(79lbs)*2 = 570lbs.

• Analyze the shear strength of the bolts to calculate the arrangement, number, and size of bolts

Stress = Force/Area

Shear Area = (Number_bolts)*(Diameter_bolt)*(Thickness)

(Number_bolts)*(Diameter_bolt) = (570lbf)/(15000 lbf/(in^2) * .09 in) = .4222 in

Diameter_bolt = .4222/8 = .0528 in

• So, essentially any standard bolt in an 8 hole radial pattern will suffice.
• To test shear strength of G12 fiberglass, we’ll apply the same force to a similar setup on an Instron

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Bolts Connecting MP tube to Bulkhead

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• Must withstand force due to the acceleration of the rocket, especially everything it’s attached to (AV tower, piston, recovery, NC assembly)
• Calculate maximum force on the bolts
• Recent sims -> most aggressive predict maximum acceleration of about 25G
• F = (50lbs)(50G) = (22.68kg)*(490 m/(s^2)) = 11113.2 N = 2498.35 lbs.
• Calculate number and diameter of bolts

Stress = Force/Area

Shear Area = (Number_bolts)*(Diameter_bolt)*(Thickness)

(Number_bolts)*(Diameter_bolt) = (2498.35lbf)/(15000 lbf/(in^2) * .09 in) = 1.851 in

Diameter_bolt = 1.851/8 = .231 in

• We also need to analyze the shear strength of the fiberglass tubing in this case, so we're planning on running a similar test in this case to ensure it won't break/deform.

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Sketches of Overall Electronic Assembly

Temperature Measurement

Structures + Payload

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• Measure and record interior NC temperatures at selected points starting from launch until landing
• Objectives:
• Determine heat distribution along NC surface, compare against thermal model
• Infer vehicle attitude and thermodynamic heat coefficient across NC from temperature distribution
• Method: Strategic placement of Thermocouples and RTDs (Resistance Temperature Detector)

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PRTD vs. Thermocouples

Joseph

In order to ground our model for the S1 flight (to better inform the nose cone design for S2), we plan to use temperature sensors to measure the temp of the inside wall along three or more points. There are two main options for sensor choice. We plan to use both.

Temp Measurements: PRTD sensor

(Platinum Resistance Temperature Sensor) M-Series 32208zzz

Good for up to 500℃ continuous use

Cons: More expensive (not prohibitively), lower temperature range, lower measurement speed

Pros: More accurate and repeatable measurements

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Joseph

Temp Measurements: Thermocouples

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5TC Series from OMEGA, Glass Braid Insulation 900 F

Cons: less accurate measurements

Pros: cheaper, faster measurement speed, vast temperature range

Joseph

Sensor Arrangement

Create heat map

Measuring internal temperatures

4 levels to get most data from sensors

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Eric

Sensor Integration

Attach sensors to interior of nose cone with epoxy

Epoxy on leads for strain relief

Wire harness and connector easily attaches to DAQ

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Eric

Thermocouple Attachment Option

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Copper thermal bridge to measure exterior temperatures

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Heat

Epoxy/Attachment Options

ProLine: Good up to 500F

Cotronics 4700: 600F, Needs Heat Cure 1.9 W/mk heat conductivity

Thermal Paste: 8-13 W/mk 662F Filling Properties Flashpoint shouldn’t be till well over 1000F, but more research is needed

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Sensor Integration (Tip)

Need thermocouple because of lower profile and higher temperature range.

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Redundancy

Use both thermocouples and PRTDs

Thermocouples for high temperature and speed

PRTD are more accurate

We can use PRTDs to calibrate the thermocouples

We only get one launch, and it is very expensive, we might as well get as much data as possible.

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Accelerometers - 2 Axes

• Measure and record axial and lateral vibrations in the nose cone starting from launch until landing
• Objective: Characterize vibrational environment to set criteria for future payloads

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Accelerometers - circuit

Recovery Load

• Measure and record recovery system deployment loads
• Objective: Infer what occurs during recovery deployment
• Data routed through payload bulkhead to DAQ

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NC Tip Manufacturing Plan

NC Tip

• Get stock material: 316 Stainless Steel, Titanium Rod
• Misumi US is sponsor. Should be free.
• Tap the hole.
• Turn it on lathe.
• Oxidize if necessary.

3D Printing from Markforged - Unlikely

Ceylan

NC Tip Manufacturing Plan

Washer

• Aluminium (or not?)
• Waterjet and then tap a hole.
• Use epoxy to attach washer to nose cone.
• Cotronics 4700 (315 C), phenolic/cork microballoons + West Systems epoxy
• Bolts, if epoxy is not heat resistant enough or not strong enough.

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Ceylan

NC Tip Assembly

• Attach washer to the nose cone using glue (or bolts).
• Attach thermocouples to the tip.
• Make sure thermocouples are okay.
• Attach tip and washer together with threaded rod and nut.
• Make sure everything is well aligned.

Potential Ablatives

• Phenolic microballoons + West Systems epoxy
• Cotronics 4700
• Cork microballoons + West Systems epoxy

Oliver

Testing: Thermal (Blowtorch test)

Dev and Oliver using blowtorch to test different ablatives

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Dev/Oliver

Open Issues

• Feasibility of embedding thermal sensors in inner wall of nose cone (what kind of adhesive to use?)
• Connecting thermal sensors to the DAQ to ease integration
• Feasibility of embedding copper bridges into nose cone for external measurements

Yay rockets!