<HTML> <HEAD><TITLE>Richard Nakka's Experimental Rocketry Site</TITLE> </HEAD> <BODY bgcolor="99cccc"> <A NAME="top"></A> <HR SIZE=5><H2><CENTER>Richard Nakka's <EM>Experimental Rocketry</EM> Web Site</CENTER></H2> <HR WIDTH=50% ALIGN=center SIZE=2> <BODY bgcolor="99cccc"> <CENTER><H3><FONT COLOR="brown">Impulser Rocket Motors</FONT></H3></CENTER><BR> <CENTER> <IMG SRC="Impulser/Impulsers_sm.jpg" ALT="Impulser & Impulser-X"></CENTER><P> <CENTER><TABLE BORDER=1 > <TR><TD> <LI><A HREF="#Intro">Introduction</A></LI> <LI><A HREF="#Basic">Basic Dimensions and Configuration</A></LI> <LI><A HREF="#Propellant">Propellant Grain</A></LI> <LI><A HREF="#Nozzle">Nozzle</A></LI> <LI><A HREF="#Bulkhead">Bulkhead</A></LI> <LI><A HREF="#Casing">Motor Casing and Thermal Liner</A></LI> <LI><A HREF="#Igniter">Motor Ignition</A></LI> <LI><A HREF="#Drawings">Engineering drawings</A></LI> <LI><A HREF="#Performance">Performance</A></LI> <LI><A HREF="#Photos">Photos and Video Clips</A></LI> </TD></TR> </TABLE> </CENTER> <TABLE BORDER=0 WIDTH=93% CELLPADDING=50> <TR><TD> <A NAME="Intro"></A><H3><FONT COLOR="brown">Introduction</FONT></H3> The <EM>Impulser</EM> rocket motor was conceived in 2013 as the primary motor for my then-planned <EM>Zeta</EM> rocket. It was envisioned as an I-class motor powered by a choice of either KNSB or KNDX sugar propellant. The <EM>Impulser</EM> was subsequently static tested in October of 2013 and first flown exactly one year later. The <EM>Impulser-X</EM>, a stretched version of the <EM>Impulser</EM>, was developed soon after, having five grain segments versus four for the original <EM>Impulser</EM>. Since that time, the <EM>Impulser</EM> and <EM>Impulser-X</EM> motors have proven to be well suited to my experimental rocket flight activities, performing with a high degree of reliability and having a "just-right" impulse range for my <A href="DS.html"<EM>DS</EM></A> and <A href="zeta.html"<EM>Zeta</EM></A> rockets. With the advent of my <A href="Xi.html"<EM>Xi</EM></A> rocket in late 2017, being a somewhat larger rocket, I found that the <EM>Impulser-X</EM> was a bit underpowered. This led to a second stretch of the <EM>Impulser</EM>, from four grain segments to six. The latest version is deemed <EM>Impulser-XX</EM>. <P> <EM>Impulser</EM> is configured with a 4-segment BATES grain and has a nominal capacity of 300 grams of KNSB or KNDX. <EM>Impulser-X</EM> is configured with a 5-segment BATES grain with a nominal capacity of 375 grams of KNDX. <EM>Impulser-XX</EM> is configured with a 6-segment BATES grain with a nominal capacity of 450 grams of KNDX. Nominal impulse of <EM>Impulser</EM> is 400 Newton-seconds, 500 Newton-seconds for <EM>Impulser-X</EM> and 600 Newton-seconds for <EM>Impulser-XX</EM>.<P> <EM>Impulser</EM> is capable of launching a 2kg (4.4 lb), 2.5 inch (64mm) rocket to an altitude of 2800 ft. (850m.). <EM>Impulser-X</EM> can loft the same rocket to about 3500 ft. (1100m) and <EM>Impulser-XX</EM> can loft the same rocket to about 4200 ft. (1280m). <P> To date (July 2018), the <EM>Impulser</EM> family of motors have been fired 45 times:<BR> <LI><EM>Impulser</EM> fired 32 times (29 flights; 3 static)</LI> <LI><EM>Impulser-X</EM> fired 12 times (11 flights; 1 static)</LI> <LI><EM>Impulser-XX</EM> has been fired once (static).</LI><P> <CENTER><IMG SRC="Impulser/Impulser-1.jpg" ALT="Impulser Rocket Motor"></CENTER><P> <CENTER><FONT COLOR="brown"><U>Figure 1</U> -- <EM>Impulser</EM> rocket motor</FONT></CENTER><P> <CENTER><IMG SRC="Impulser/Impulser-X.jpg" ALT="Impulser-X Rocket Motor"></CENTER><P> <CENTER><FONT COLOR="brown"><U>Figure 2</U> -- <EM>Impulser-X</EM> rocket motor</FONT></CENTER><P> <HR WIDTH=50% SIZE=1> <A NAME="Basic"></A><H3><FONT COLOR="brown">Basic Dimensions and Configuration</FONT></H3> The <EM>Impulser</EM> motors have an outside diameter of 1.50 inches (38mm). <EM>Impulser</EM> has an overall length of 13.6 inches (345mm), <EM>Impulser-X</EM> has an overall length of 16.2 inches (410mm), and <EM>Impulser-XX</EM> has an overall length of 20.4 inches (520mm). All utilize steel nozzles and aluminum alloy casings and bulkhead. A pair of standard o-rings seal the nozzle and a single o-ring seals the bulkhead. The nozzle and bulkhead are both retained with snap-rings. To protect the aluminum casing from combustion heat, a thermal liner is employed. The motors are designed for unlimited re-use. Minor nozzle throat erosion does occur with each firing, resulting in a small deviation in performance over time.</CENTER><P> <CENTER><IMG SRC="Impulser/impulser-cross-section.gif" ALT="Impulser cross-section"></CENTER><P> <CENTER><FONT COLOR="brown"><U>Figure 3</U> - Cross-sectional view of the <EM>Impulser</EM> motor assembly</FONT></CENTER><P> <HR WIDTH=50% SIZE=1> <A NAME="Propellant"></A><H3><FONT COLOR="brown">Propellant Grain</FONT></H3> The <EM>Impulser</EM> motor can utilize either sorbitol-based KNSB or dextrose-based KNDX propellant. Four BATES segments make up the propellant grain, with combustion initially occuring along the core and at both ends of each segment. A bonded inhibitor prevents combustion from occuring on the outside surface of the grain segments. <P> The <EM>Impulser-X</EM> and <EM>Impulser-XX</EM> were designed solely for use with KNDX propellant. Five and size BATES segments, respectively, which are identical to those of <EM>Impulser</EM>, make up the propellant grain for these two motors.<P> Propellant segments are separated within the motor by <EM>spacer rings</EM>. The spacer rings serve an essential purpose, ensuring that all the segment ends start burning immediately upon motor start-up. To maximize performance and reliability, the grain segments are cast using a dedicated mould system which allows for propellant curing under spring pressure. This is done to ensure a good bond between the casting tube and propellant. A secondary reason for curing under pressure is to eliminate all trapped air, maximizing density and providing consistent burn characteristics. After casting and trimming, the propellant surfaces are coated with <A href="ignexp.html"><EM>Combustion Primer</EM></A></CENTER> to ensure rapid ignition of all grain surfaces and to provide for swift motor start-up.<P> <CENTER><IMG SRC="Impulser/Impulser-grains.jpg" ALT="Grain segments"></CENTER><P> <CENTER><FONT COLOR="brown"><U>Figure 4</U> - BATES grain segments (prior to priming)</FONT></CENTER><P> To produce the grains, molten propellant slurry is poured/scooped into casting tubes, which serve the additional role as <EM>inhibitor</EM> to control which surfaces are exposed to burning. The casting tubes are fabricated from <A href="https://www.thespruce.com/tagboard-1254081">poster board</A> (or tagboard), which is first treated with one or two coats of oil-based polyurethane varnish (to improve its resistance to charring) and allowed to thoroughly dry. Cut out as strips, the poster board is rolled around a mandrel to form a two-ply tube. The plies are bonded together with <A href="http://www.elmers.com/product/detail/E584">glue-stick</A> adhesive. <P> The Spacer Rings are made in an identical manner to the casting tubes, using the same mandrel.<P> To maximize reliability and for most consistent performance, KNSB and KNDX grain segments are <A href="sorb.html#Casting">cured under pressure</A>. <HR WIDTH=50% SIZE=1> <A NAME="Nozzle"></A><H3><FONT COLOR="brown">Nozzle</FONT></H3> Nozzles are conical profiled, deLaval supersonic type machined from low-carbon steel, with 30<SUP>o</SUP> convergent and 10<SUP>o</SUP> divergent half-angles. The nozzle is "free-floating" within the motor casing, retained within the casing by a <A href="Impulser/snap-ring-137.gif">N1300-137</A > snap-ring.<P> The nozzle is pressure sealed with a pair of -123 o-rings (Buna-N nitrile), well-lubricated with silicone grease.<P> The <EM>Impulser</EM> throat diameter is dependant on whether KNSB or KNDX propellant is utilized. Due to its faster burn rate, KNDX requires a slightly larger throat to achieve the same max chamber pressure. Otherwise the nozzles are very similar in design.<P> The inlet to the throat is radiused in order to accelerate the combustion products more gradually. This reduces two-phase flow performance loss (see <A href="th_intro.html">SRM Theory</A> section for details). It has been found that a small amount of nozzle throat erosion occurs during each firing. For the <EM>Impulser</EM>, the erosion per firing amounts to about 1 thousandth of an inch, or 33 microns (<EM><A href="Impulser/Impulser-nozzle-erosion.gif">Click</A> for chart</EM>). For the <EM>Impulser-X</EM>, the erosion is greater, about 3 thousandth of an inch, or 80 microns (<EM><A href="Impulser/Impulser-X-nozzle-erosion.gif">Click</A> for chart</EM>). <CENTER><IMG SRC="Impulser/impulser-nozzle-2.jpg" ALT="Impulser Nozzle"></CENTER><P> <CENTER><FONT COLOR="brown"><U>Figure 5</U> -- <EM>Impulser</EM> nozzle</FONT></CENTER><P> <HR WIDTH=50% SIZE=1> <A NAME="Bulkhead"></A><H3><FONT COLOR="brown">Bulkhead</FONT></H3> The bulkhead forms the forward closure of the motor. The bulkhead is machined from 6061-T651 aluminum alloy. For sealing, a -123 o-ring (Buna-N nitrile) is used in conjunction with silicone grease. The bulkhead is retained with a <A href="Impulser/snap-ring-137.gif">N1300-137</A > snap-ring.<P> <CENTER><IMG SRC="Impulser/I-bulkhead.jpg" ALT="Impulser Bulkhead"></CENTER><P> <CENTER><FONT COLOR="brown"><U>Figure 6</U> -- <EM>Impulser</EM> bulkhead, with o-ring and snap-ring</FONT></CENTER><P> <HR WIDTH=50% SIZE=1> <A NAME="Casing"></A><H3><FONT COLOR="brown">Casing</FONT></H3> The motor casing is made from 1.50 inch (38.1mm) 6061-T6 aluminum alloy drawn tubing with a wall thickness of 0.065 inch (1.65mm). Grooves are internally machined near each end to seat the snap-rings which retain the nozzle and bulkhead. To protect the casing from the hot combustion gases, a <EM>thermal liner</EM> is fitted inside the casing. The thermal liner is fabricated from a sheet of posterboard, rolled around a mandrel. The liner is two-ply, with the overlapping portion bonded together with <A href="http://www.elmers.com/product/detail/E584">glue-stick</A> adhesive. To provide added resistance against charring, a one or two coats of oil-based polyurethane varnish is applied to the interior surface of the liner, and allowed to fully dry, prior to rolling. Further thermal protection is achieved by covering the outer surface of the liner with a single layer of aluminum foil, bonded (prior to rolling) with glue-stick.<P> <HR WIDTH=50% SIZE=1> <A NAME="Igniter"></A><H3><FONT COLOR="brown">Igniter</FONT></H3> To achieve rapid ignition and optimum performance of the motor, an electrically initiated <EM>pyrogen</EM> type igniter is employed. Inserted through the nozzle up to the head end of the motor, the pyrogen igniter fires a jet of flame along the motor core toward the nozzle, rapidly igniting the exposed surfaces of the propellant grain. The igniter consists of a 6cm length of plastic tube ("drinking straw") filled with <EM>MDP</EM> or <EM>Black Powder</EM> pyrolant, sealed at both ends with hot glue. A short length of nichrome bridgewire initiates the charge. Two slits in the tube wall near the aft end of the igniter control the burn rate and allow for escape of the hot gases in the form of flame jets. (<EM><A href="igniter.html#MDP-pyrogen">Click</A> for full details</EM>).<P> <HR WIDTH=50% SIZE=1> <A NAME="Drawings"></A><H3><FONT COLOR="brown">Engineering Drawings</FONT></H3> <OL> <LI><A HREF="Impulser/Impulser_motor_assembly_dwg.pdf">Impulser Motor Assembly</A></LI> <LI><A HREF="Impulser/Impulser-X_motor_assembly_dwg.pdf">Impulser-X Motor Assembly</A></LI> <LI><A HREF="Impulser/coming.gif">Impulser-XX Motor Assembly</A></LI> <LI><A HREF="Impulser/Impulser_nozzle_KNSB_dwg.pdf">Impulser Nozzle (KNSB)</A></LI> <LI><A HREF="Impulser/Impulser_nozzle_KNDX_dwg.pdf">Impulser Nozzle (KNDX)</A></LI> <LI><A HREF="Impulser/Impulser-X_nozzle_dwg.pdf">Impulser-X Nozzle</A></LI> <LI><A HREF="Impulser/coming.gif">Impulser-XX Nozzle</A></LI> <LI><A HREF="Impulser/Impulser_bulkhead_dwg.pdf">Bulkhead</A></LI> <LI><A HREF="Impulser/Impulser_casing_dwg.pdf">Impulser Motor Casing</A></LI> <LI><A HREF="Impulser/Impulser-X_casing_dwg.pdf">Impulser-X Motor Casing</A></LI> <LI><A HREF="Impulser/Impulser_thermal_liner_dwg.pdf">Impulser Thermal Liner</A></LI> <LI><A HREF="Impulser/Impulser-X_thermal_liner_dwg.pdf">Impulser-X Thermal Liner</A></LI> <LI><A HREF="Impulser/Impulser_thermal_liner_mandrel_dwg.pdf">Thermal Liner Mandrel</A></LI> <LI><A HREF="Impulser/Impulser_grain_dwg.pdf">Propellant Grain</A></LI> <LI><A HREF="Impulser/Impulser_grain_spacer_ring_dwg.pdf">Grain Spacer Ring</A></LI> <LI><A HREF="Impulser/Impulser_propellant-mandrel_dwg.pdf">Propellant Grain Mandrel</A></LI> </OL><P> <HR WIDTH=50% SIZE=1> <A NAME="Performance"></A><H3><FONT COLOR="brown">Motor Performance</FONT></H3> The <EM>Impulser</EM> and <EM>Impulser-X</EM> motors were designed with the aid of <A href="softw.html#SRM">SRM_2104.xls</A> "Solid Rocket Motor Performance" software. The design parameters are presented in Figure 7. Note that actual performance may vary depending upon specifics of propellant preparation (e.g. particle size, moisture content, etc.). <P><CENTER><IMG SRC="Impulser/parameter-chart-rev.gif" WIDTH=696 HEIGHT=183 ALT="Impulser parameters"></CENTER><P> <CENTER><FONT COLOR="brown"><U>Figure 7</U> - Design Parameters for <EM>Impulser</EM> and <EM>Impulser-X</EM> motors </FONT></CENTER><P> <UL> <U><EM>Impulser</EM></U> Design Performance graphs, with KNSB propellant: <LI><A HREF="Impulser/I-KNSB-kn.jpg">Kn graph</A></LI> <LI><A HREF="Impulser/I-KNSB-press.jpg">Chamber Pressure graph</A></LI> <LI><A HREF="Impulser/I-KNSB-thrust.jpg">Thrust graph</A></LI> </UL> <UL> <U><EM>Impulser</EM></U> Design Performance graphs, with KNDX propellant: <LI><A HREF="Impulser/I-KNDX-kn.jpg">Kn graph</A></LI> <LI><A HREF="Impulser/I-KNDX-press.jpg">Chamber Pressure graph</A></LI> <LI><A HREF="Impulser/I-KNDX-thrust.jpg">Thrust graph</A></LI> </UL> <UL> <U><EM>Impulser-X</EM></U> Design Performance graphs, with KNDX propellant: <LI><A HREF="Impulser/IX-KNDX-kn.jpg">Kn graph</A></LI> <LI><A HREF="Impulser/IX-KNDX-press.jpg">Chamber Pressure graph</A></LI> <LI><A HREF="Impulser/IX-KNDX-thrust.jpg">Thrust graph</A></LI> </UL> <UL> <U><EM>Impulser-XX</EM></U> Design Performance graphs, with KNDX propellant: <LI><A HREF="Impulser/IXX-KNDX-kn.gif">Kn graph</A></LI> <LI><A HREF="Impulser/IXX-KNDX-press.gif">Chamber Pressure graph</A></LI> <LI><A HREF="Impulser/IXX-KNDX-thrust.gif">Thrust graph</A></LI> </UL> <HR WIDTH=50% SIZE=1> <A NAME="Photos"></A><H3><FONT COLOR="brown">Photos and Video Clips</FONT></H3> <OL> <U>Photos</U>: <LI><A HREF="Impulser/Impulser-org-1.jpg">Machined nozzle o-ring grooves</A></LI> <LI><A HREF="Impulser/Impulser-nozzle-turning.jpg">Turning external profile of nozzle</A></LI> <LI><A HREF="Impulser/Impulser-srg-1.jpg">Machining snap-ring grooves</A></LI> <LI><A HREF="Impulser/Impulser-srg-2.jpg">Tool bit for cutting snap-ring grooves</A></LI> <LI><A HREF="Impulser/Impulser-grains-feb-2017.jpg">Stash of Impulser grain segments</A></LI> <LI><A HREF="Impulser/IX-grains-primed.jpg">Primed KNDX grain segments for Impulser-X</A></LI> <LI><A HREF="Impulser/Impulser_thermal_liner.jpg">Thermal Liner</A></LI> <LI><A href="sp/IST-2-author.JPG">Author with <EM>Impulser</EM> rocket motor</A></LI> <LI><A href="sp/IXXST-1-author.JPG">Author with <EM>Impulser-XX</EM> rocket motor</A></LI> <LI><A HREF="Z-31/2017-06-15_12-09-42.jpg"><EM>Flight Z-31</EM> powered by Impulser-X</A></LI><P> <U>Video Clips</U>: <LI><A HREF="Impulser/I-350MotorTest.wmv">Impulser (prototype) static test firing (3.3 Mbyte)</A></LI> <LI><A HREF="Impulser/IX-1_static.MP4">Impulser-X static test firing (2 Mbyte)</A><BR> <LI><A HREF="DS-1/DS-1_tripod_camera.MP4">Launch of DS-1 rocket powered by Impulser with KNDX (7.1 Mbyte)</A></LI> <LI><A HREF="DS-4/DS-4_Nikon.MP4">Launch of DS-4 rocket powered by Impulser with KNSB (6.3 Mbyte)</A></LI> <LI><A HREF="Z-16/Z-16_Pad_Camera.mp4">Launch of Z-16 rocket powered by Impulser-X (1.8 Mbyte)</A></LI> <LI><A HREF="Z-21/Flight_Z-21_tripod_camera.MP4">Launch of Z-21 rocket powered by Impulser with KNDX (6.9 Mbyte)</A></LI> <LI><A HREF="Z-25/Z-25%20NIkon.MP4">Launch of Z-25 rocket powered by Impulser-X (4.3 Mbyte)</A></LI> <LI><A href="videos/IXXST-1-camera-1.MP4">Impulser-XX static test firing</A> (<EM>camera 1</EM>) &nbsp;&nbsp;6.6 MBytes</LI> <LI><A href="videos/IXXST-1-camera-2.MP4">Impulser-XX static test firing</A> (<EM>camera 2</EM>) &nbsp;&nbsp;8.6 MBytes</LI> <LI><A HREF="Impulser/IXXST-1-graph1.gif">Impulser-XX static test results</A></LI> <LI><A HREF="Impulser/IXXST-1-graph1-SI.gif">Impulser-XX static test results (SI units)</A></LI> </OL><P> </TD></TR> </TABLE> <HR WIDTH=50% ALIGN=center SIZE=2> <CENTER><IMG SRC="pix/sched2.gif" ALT="Last updated"></CENTER> <CENTER><H4>Original posting&nbsp;July 28, 2017</H4></CENTER> <CENTER><H4>Last updated&nbsp;July 11, 2018</H4></CENTER> <CENTER><A HREF="#top"><FONT SIZE=+1>Return to Top of Page</FONT></A></CENTER> <CENTER><A NAME="Back to home page"></A><A HREF="index.html"><FONT SIZE=+1>Return to Index Page</FONT></A></CENTER> <HR SIZE=5 NOSHADE> </BODY> </HTML>