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REV 2.4 - Tue Aug 17 00:08:03 2010

Heavenly
Backdraft
 
 
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SPECS: 36.625" x 1.679 - 7.5 oz
ROCKSIM FILE: MISSING - please submit here
SpaceCAD FILE: MISSING - please submit here
REC'D MOTORS: D12-0/C11-3, E9-4/D12-0, E15-4/D12-3

EMRR Logo(05/19/08) I purchased the Heavenly Hobbies Backdraft because it sounded really different. The site says "The exciting Heavenly Hobbies’ BACKDRAFT (tm) is a dual-engine rocket...". Notice is said dual-engine, not cluster. It then went on to describe the rocket this way: "The BACKDRAFT(tm) looks like a 2-stage vehicle, with booster and sustainer sections. The propulsion module (booster) holds the primary 24mm engine. The sustainer holds a secondary 24mm engine. But the BACKDRAFT (tm) is not a 2-stage rocket. Cover/BagIn this model, the secondary engine has exchanged places with the recovery system. The secondary engine has been moved forward, behind the nosecone, while the parachute has moved back. This secondary engine has also been rotated 180°, so that the nozzle points to the sky while the rocket sits at the launch pad. This arrangement sets the stage for the TailWind (tm) delayed deployment system.

"The basic idea for Heavenly Hobbies' exclusive TailWind (tm) delayed deployment system is to reduce drift by skipping ejection at apogee and, after a suitable delay, use a "retro-firing" engine to slow down the rocket for deployment of its recovery system."

Okay, I get it and it surely sounds cool. So, as I said I bought one.

The rocket includes paper body tubes, laser-cut plywood fins and centering rings, 24mm tubes, estes-like motor retention, an 18" nylon parachute, balsa nose cone and piston, and various other standard parts. The parts quality and fit are excellent.

Backdraft Parts

CONSTRUCTION:

The instructions come on a CD and are printed out on 23 pages of 8½ x 11" paper. They contain color photo and illustrations to assist in the build. They also include flying instructions which require you to use the provided H.H. Simit computor software to determine the correct motors.

I would put this kit at a Skill Level 5 for several reasons:

  • Instructions can be a bit confusing
  • Fairly complex build techniques
  • Use of "green fuse" to enable the TailWind motor

When building this rocket, do not attempt to skip ahead and build some sections before others. Follow the instructions.

Many common techniques are used on the build, so I won't comment on those. On the other hand, I will comment and provide some warnings/tips for key areas of the build.

First warning/tip comes when the instructions say to tape (masking) the motor hook to the motor tube. The instructions then said to put glue on the motor tube and slide a plywood centering ring over the hook and up until it stops on the outward bent forward end of the hook. (picture from the instructions below)

Motor Mount

Well, the order of this prevented it from working, because I could not slide the centering ring over the masking tape. So I removed the masking tape, slid the centering ring over the hook and then taped the hook in place below the ring. I then applied glue and slid it into place.

This order of things is repeated for the secondary engine hook as well. However, in this case it caused a greater problem, because one of the last steps is to slide another centering ring down from the top of the rocket (where the nose cone fits) onto the secondary engine hook so that there is room for the nose cone shoulder. That tape was in the way and at this point in the build there was no way to remove it!

The next warning/tip was determined at the installation of the motor mount into the body tube. Here the instructions ask that you install the above pictured motor mount into the tube with only the one centering ring. The instructions warn you to "make sure that the engine mount assembly is aligned coaxially with the airframe tube." This was too much of a concern for me, so I made three tabs from scotch tape (PML style) on lower centering ring (the one not glued in place yet) and slide it in place to ensure the tube was centered. The tape tabs allow you to easily pull the unglued centering ring back out of the tube.

The fins are through-the-wall mounted fins and there were no concerns or issues.

The parachute compartment has a Heavenly Hobbies' EZJect™ balsa ejection piston. This is used to protect and push the parachute out of the compartment. What I found interesting here is that you are supposed to push a flimsy/soft piece of Kevlar through a 1" balsa piston with a little bitty hole!

Well, I did it, but here's the tip... wet the first 2" of Kevlar with epoxy, CA or white glue first and let it dry completely. This will make it stiff and then you can push it through without any issues.

Piston Piston

LassoHey, there cowboy! How's your lasso technique. This was an interesting step in the instructions. The purpose of this is to ensure that the nose cone shock tether is secure around the upper motor mount assembly. Since the shock tether is fed through the side of the upper body tube and the motor mount comes up from the bottom, this step is necessary. The instructions are clear and if done correctly it will look like mine (to the left).

I did run into a problem. I even posted a request on TRF for help (but it doesn't seem like anyone else is building this rocket!). Jose at Heavenly Hobbies responded to an e-mail requesting help.

Here's what I wrote: "I'm having some trouble here following the illustrations/instructions associated with steps 6 and 7 on part 12.

"This seems to indicate that we slide the 10.5" long 24mm tube with the cap and EZJect into the middle 10.5" BT50 (one with 3 upper fins). As you can see from my picture, if I follow the instructions, my 10.5" 24mm tube will not be long enough to reach the end of the 3" couple that is sticking out by 1.5".

"Am I reading this correctly or did I mess up somewhere?"

Backdraft Question

Jose answered back, "Section II.B, on page 10, instructs you to glue the front section (17.25") of the inner body tube to the middle section (10.5"). If you do that, the inner body tube will be long enough to protude past the coupler in the F end of the middle airframe."

Then it hit me and therefore I replied this way: "Okay, I see this. So the confusion comes in back at step 7 on page 8. I read use the coupler as a "plunger" which implied to me to take it back out. The instructions don't say to take it out, but I did. So now, once I put it back in and follow the instructions below, I'm moving again."

Nose ConeThe nose cone is next. It is already hollowed out and has two holes drilled in the sides for use with the "green fuse". The nose cone needs to be protected since it takes the thrust from the TailWind™ motor. To do this the inside of the nose cone is coated with high-temperature epoxy and the shoulder is protected with a piece of aluminum foil that is glued into place.

When the TailWind™ motor ignites it will blow off the nose cone. Here is another warning/tip. Be sure to test fit the nose cone with the aluminum foil wrapped, but not glued, around the shoulder. I had to sand mine to ensure a good fit. Once a good fit is established with the foil wrapped around it, then use a very thin layer of glue under the aluminum foil so that it doesn't add any significant diameter to the shoulder.

Nose Cone TetherAs mentioned, the nose cone will blow off, so there needs to be a tether to keep it attached to the rocket during recovery. This is done by attaching a small piece of piano wire into the outside surface of the nose cone. This spans the groove in the nose cone (see picture above right). I don't know about this, but it is done.

The tether is then run down the length of the body tube and loosely taped to the side of the rocket.

This essentially completes the build of the rocket.


Tether

Overall, for CONSTRUCTION I would rate this kit 3 ½ points. Following the build sequence is crucial. I personally got confused with some of the parts/instruction nomenclature so I believe some improvement could be made. The part fit and quality are excellent. There were no decals.

FLIGHT/RECOVERY:

Since the flight may be difficult to visualize, I asked Heavenly Hobbies to make a flight plan diagram. Jose did a nice job as you can see below.

Flight Plan

NERRF4 Flight Attempt:

First off, I'll say, I blew it!

I purchased fuse from Heavenly Hobbies and then asked them how fast it burned. They indicated to me that it burned 0.57 inches / second. Therefore, I could have used a 12 second fuse, of 6.8 inches, according to H.H. Simit software, while flying on an Estes E9-4 booster and an Estes D12-3 reverse motor.

If all went as outlined, the flight log would look like the below graph from H.H. Simit. You can see a flight to about 650 feet, then falling to about 300 feet, ignition of the reverse motor which would bring the rocket back to about 450 feet and then ejection and parachute recovery.

Graph

Instead, I "remembered" the e-mail saying 0.57 seconds / inch and used a 20" fuse. This created a 35 second fuse!

Now that I admitted my failure, I'll describe my overall experience:

I was successful installing the fuse into the reverse motor and having it held in place with the toothpicks and masking tape. I then taped an Estes ignitor onto the fuse tip with masking tape and stuck an ignitor into the booster's E9-4. Feeling ready (and confident) I went to the RSO table.

They gave me the side-ways look, delayed, asked for 3 opinions, and then finally got NERRF's launch director involved who okayed it.

Out at the pads everything set up nicely, but losing some confidence I angled the rocket away from the crowd just to ensure that there would be no incidents.

The launch time came and the rocket took off nicely. It was stable and went to a nice altitude arced over and started back down. The fuse was smoking so I new it had lit. It came all the way to the ground and PRANG. Interesting, the fuse was still smoking until...

... the D12 lit and the rocket flipped and flopped around on the ground (being substantially crushed) until the motor finished and 3 seconds later the ejection charge fired. So, according to H.H. Simit the rocket hit at a velocity of about 175 feet/second.

Graph

The rocket is not repairable and I regret my mistake!

Overall, for FLIGHT/RECOVERY I would rate this kit 3 points. It is clear that I made a mistake, however, I believe for flight and recovery the complex design and requirements make this rocket a challenge. Getting it past the RSO is the first step. Second, if the fuse does not light, then there is no recovery. Challenging.

SUMMARY:

I'm impressed with the kit and I would love to hear about other people's successes.

I think the instructions could use some clarification. I also think the flight and recovery are very challenging and may possibly be too difficult for many rocketeers.

That being said, I applaud the innovation and my experience with this kit has many ideas rolling around in my head for applications of the reverse motor and/or the fuse ignition. I thank Heavenly Hobbies for that.

Overall I would rate this kit 3 ½ points. Even if I had a perfect flight, my rating would be the same. It is a good kit and a unique flight profile, so if you are someone that is looking to try something new... go for it (then tell us about it!).


Rating
(Contributed - by Dick Stafford [Who's Who Page] - 08/02/08) Heavenly Hobbies Backdraft

Brief:
The Backdraft is a BT-60-based, 24mm-powered rocket that on face value looks like a standard 2-stager. If you've read the previous reviews (and I assume you will before you continue past this intro), you'll know that there is one major difference--the upper motor is used as a retro rocket. Heavenly Hobbies calls this the TailWind delayed deployment system. The upper stage is ignited with a slow-burning fuse ('green cannon fuse'), so the flight prep will be out of the experience base of most rocketeers. Heavenly Hobbies includes an electronic spreadsheet, H.H. Simit, to help with the motor/delay selection.

The glossy sheet provided with the kit says it is s/n number 17. This kit will be fun!

Construction:
The kit includes 40 parts, including lots of tubes, laser cut rings and fins, and a pre-hollowed balsa cone. The laser cut parts all fit well, however, the BT-60 couplers and nosecone shoulder required sanding.

The 23 pages of photo-illustrated instructions are provided in Microsoft Word format and are quite detailed. I decided not to print them given the number of photos. However, the instructions have some minor errors and are a bit confusing in places. (Once again, make sure you read the other reviews, I will not repeat every "gotcha" they point out.)

Heavenly Hobbies Backdraft Aft airframe (booster) section - This section consists of a pre-slotted body tube, three fins, a 24mm motor tube, 2 rings, a motor hook and a coupler. The confusion factor started early. The instructions refer to a long 3.75" motor hook but the photos show what is clearly a shorter hook. In addition, some of the following dimensions (e.g., where to spread glue for the upper centering ring does not match the actual position of the ring.) Nevertheless, the booster fin can was straightforward and assembles like a typical rocket with TTW fins. If you build one, read the entire set of instructions before starting and dry fit things to make sure you see how they should go together. I found out about the coupler fit the hard way but, since you won't make this mistake, I won't go into the ugly details.

Heavenly Hobbies Backdraft Middle airframe section - The middle section consists of a body tube, three fins, 2 rings, a coupler, and a parachute tube subassembly. The body tube is pre-marked for locating the surface mount fins.

The parachute tube subassembly includes a BT-50 and a handful of other parts. The main features are a cap that protects the parachute from the booster motor's ejection charge and a balsa piston, which Heavenly Hobbies calls the EZject. The cap is attached to a centering ring with a Kevlar strap and is coated with high temperature epoxy. In my case I used JB Weld. The piston has a small hole pre-drilled in the middle and you merely center it between two knots in another Kevlar strap. This makes me wonder why more kits don't use this type of piston.

On this section, I dry fit and sanded the coupler so it fit properly, I also used epoxy vs wood glue so it wouldn't seize up. (Now you know where I had problems with the aft section.) Finally, I installed the top fins at the very end of the build rather than in sequence as directed in the instructions.

Upper body section - The upper body includes another BT-50, two more rings, a motor hook, Kevlar twine, and a short piece of a larger tube. Other than installing a motor at the wrong end, there is only one tricky part. That is lassoing the Kevlar twine around a centering ring. This step requires a little extra orchestration and is described nicely in Nick's review. The short ~3/8" piece of larger tubing is cut down an attached to reinforce the top of the body tube.

The instructions didn't say where to place the ¼" launch lug. I placed it on the upper tube near the loaded CG.

Heavenly Hobbies Backdraft Nose cone - The nose cone is hollowed and has two fuse ports pre-drilled. The surface is not as nicely finished as, say, a Semroc or FlisKits cone. Aside from the extra prep, there are several things you need to do. This includes coating the inside with high temp epoxy (J- Weld), cutting a channel for the shock tether, attaching a wire near the tip as an attachment point for the tether, and covering the shoulder with aluminum foil. The shoulder took a lot of sanding to get it to fit when covered with foil (I actually used metal duct tape). I had my doubts about the short wire as an attachment point for the shock cord, but decided to try building it stock. As it turned out, it wasn't in fact sufficient.

Due to the confusion factors in the instructions and the fit of the couplers, I rate this build a '3' since it's a non-standard configuration and even minor errors in the instructions threaten to affect the build. I also didn't ding the rating due to the problem I had due to the aft coupler fit. That's my problem--I should have dry fit this like all the other parts. However, the poor fit is worth a half point deduction.

Finishing:
Due to time constraints and the knowledge that a finished rocket is more likely to fail, the kit is still naked.

Construction Rating: 3 out of 5

Flight and Recovery:
Nick and I have flown this model twice at the time of writing on the last day of NARAM-50. The use of a retro motor and a fuse raised some eyebrows, but in the end the flights were approved.

The Simit spreadsheet allows the user to select motor and delay combinations and provides a graph of altitude, velocity, and acceleration. John Smolley's review describes the software, how to interpret the graphs, and includes several screen snaps. I fiddled around with various combinations but decided the default E9-4/C11-3 combo would be good for the inaugural flight and I have plenty of both those motors.

The fuse is cut to provided the desired delay and burns at ~0.57 sec per inch. I thought 12 seconds would be about right so on the field we cut a 6" section just to be conservative. The fuse is placed in the retro motor and is held in with pieces of a tooth pick. It routes to through the hole in side of the cone. An Estes igniter is placed in the end of the sheath of the fuse and secured with tape.

I cut a piece of scrap wire the length of the rocket to extend the fuse igniter down to the base. This and the booster's igniter were connected with a clip whip, although the leads could have been twisted.

The boost was nice and high. The booster separated and tumbled down safely. The rocket had barely arced over when the retro fired. This resulted in a long walk. The rocket was recovered less nose cone--the piano wire attachment had evidently failed.



Flight Video (although not great) Captures the Success!
(Video provided by Nick)

We wanted to try again so Nick acquired another cone and carefully bored it out by hand. We attached the shock cord to the tip with a woodscrew, washer, and a dab of 5-minute epoxy. He also coated the inside with the epoxy.

Flight 2 used the same E9-4/C11-3 motor combination and an 8" section of fuse. The boost was the same with the booster section recovering close by. I lost sight of the booster--until it went off at about 50' AGL. The rocket lifted about 25' and ejected on cue. A perfect flight!



Flight Video 2 - Missed it but listen to the excitement!
(Video provided by Nick)

As we were recovering it, we heard the PA announce that we were not to fly another rocket until we discussed the flight with El Presidente (a.k.a. Trip Barber). It was hard not to take note of the recovery and nobody warned the contest range. Anyway, Trip reviewed the rocket and the flight and merely told us not to fly it again. He was mostly worried about the retro motor igniting near or on the ground due to the possibility of a grass fire. This made sense.

It appears a 7" section of fuse would be more prudent. Even though this flight worked perfectly, there wasn't much safety margin.

The post flight inspection revealed that the inside of the cone and the un-covered shoulder held up fine. There was some scorching in the fuse hole and below it on the outside. I will clean this up and cover the area with aluminum tape and/or JB Weld. Also, the Kevlar is the worst quality I've seen. It is coming unraveled and the individual strands are breaking. This may eventually need to be replaced. Due to the model's construction, this may prove difficult.

Despite my feeling that there is a high probability of failure, I have to give this kit a 4 for flight and recovery. After all, it performed well twice for me. The deductions were the nose cone loss and fraying Kevlar.

Flight Rating: 4 out of 5

I have sinced painted the Backdraft. It survived two flights naked. Now that it's painted, has the probability of failure increased? Luckily, the paint job ain't that good ;)

Painted

Summary:
This was an interesting kit to build and, with the benefit of two reviews, was not bad at all. Needless to say, the retro motor set-up is quite unique and the flights provide quite an adrenaline rush! You might check with your local RSO before buying one.

As I mentioned, I built off of the soft copy instructions. I personally hated this and won't do it again. I like having the instructions on the workbench and don't want my laptop anywhere near CA, epoxy, or sanding particles.

On another subject, H.H. Simit can be modified by the user to include additional motors and other rocket designs. You can even omit the retro motor to use it on 'ordinary' rockets. I don't need it for general designs but others might find this useful. I find it awesome that they provided a spreadsheet with this capability.

Thanks, Nick, for giving me the opportunity to build, fly and review this interesting kit!

Overall Rating: 3 ½ out of 5


Visit RocketryPlanet for the latest Rocketry News
Presented with written permission from RocketyPlanet:

Product Review by Dr. John Smolley, MD
Wednesday, June 18, 2008

Kit
Photo 1: The many, many parts in this kit are of very good to excellent quality

Bungee jumping for the fainthearted?

The new Backdraft, a BT-60 based three-foot rocket from Heavenly Hobbies, appears ordinary enough in its package, that is until you start looking for instructions. There are none. At least no written instructions. For those you need the enclosed computer CD.

Steve Shannon has commented on the issue of CD-ROM-based instructions in the Brutus review. It's one of those personal preference items like whether you want your meat near raw or well done. I liked them well enough, but like Mikey, I'll eat my steak either and any way. It is what else that is on the CD-ROM, which makes this most ordinary looking rocket, well, extraordinary.

Bundled with the usual kraft cardboard tubing, fins, chute, cone, and the like is software which helps the user to select two motors: one for the ascent and the second for the retrorocket firing. Thats right: A retrorocket firing that is timed and of sufficient impulse to stop a screaming, about to become rubbish, rocket dead in its tracks! Now if you're imagining the rocket to slow to a graceful stop, butt-end down, say like Apollo's Lunar Lander, guess again.

This is more like bungee jumping. The two motors are on either end of the rocket, nozzles pointing north and south. Rather than use electronics in a traditional dual deploy arrangement, the Backdraft goes one step further in its effort to reduce drift by allowing the rocket to arc over at apogee, come in ballistic, and then ignite the second motor at a low altitude, braking the descent sufficiently to get the laundry out safely.

Now when it comes to things like skydiving, bungee jumping, or out-of-bounds skiing, I must admit I'm a wimp. I love to watch others do it...but given a chance to let a rocket serve as proxy, sign me up. So it was with great anticipation I volunteered to do this review.

The Microsoft Excel-based software included with the kit allows one to compute the optimal time for the retrofire and a compatible pair of motors. Generally you need one impulse class down from the main motor-for example, recommended pairs are D12-0/C-11-0; E9-4/D12-0; E15-4/D12-3.

But the good news here is you are not limited to these motors, or even the Backdraft itself. With careful use of mass and Cd data, the simulation program works with any "nose motor" equipped rocket (or conventional rocket for that matter). With the Backdraft, the limitation on motors are twofold-the 24mm motor mounts themselves, and on the fact that the nose motor is lit by a fuse.

Parts
Photo 2: The semi-exploded view of the rocket, showing how the parts are laid out.

A fuse you say? For those of old-timers, this is not so shocking or outlandish. In the old days, if you wanted to airstart a motor with a delay or the stages were widely separate, this is how you did it. Of course there were failures, but I don't know that the rate was that much different than with today's advanced electronic timers/flight computers. The stock safety fuse is capable of igniting BP motors only. But with the size/motor mounts of the rocket, there really is no call for anything beyond an Estes E in the nose.

The Build:

The kit itself consists of forty parts, consisting in the main of high-quality kraft tubing, a balsa cone reminiscent of the original Big Bertha's, plywood fins, and a flat panel nylon chute. Part fit is very good to perfect, and so very little additional work was needed to assemble. Here the biggest exception was sanding the couplers.

Interestingly, for a rocket of this size, the maker recommends epoxy pretty much throughout, including the use of JB Weld or another high temp epoxy for lining the inside of the hollowed out nosecone. The cone is subject to the heat of the fuse used to delay/ignite the retro motor along with the initial blast of the motor itself. It's retained by Kevlar line and the chute is later deployed amidship using the ejection charge of the retro motor and a piston arrangement.

Fin Can
Photo 3: The lightly-glassed booster fin can, ready for primer.

The argument of epoxy vs. yellow glue is a horse that's been beaten to death on various forums so let's leave the flayed nag at the glue factory. Use either, but build strong and be particularly careful about selecting an adhesive that won't freeze during coupler insertions. I came very close myself to oopsing it here, even though the dry fit seemed fine. I chose to reserve epoxy for the fins, the fiberglassing, and lining the nosecone. (In retrospect, it may have been a better choice for those steps dealing with the cardboard couplers.)

As to the instructions themselves, I was confused on a couple of occasions, but overall they are quite readable and the accompanying pictures were very helpful. In total there are 24 pages, with 1 or 2 steps per page. Omitted was any mention of the launch lug, I mounted mine near the flight-ready balance point.

What would have been a nice addition (at least for the mechanically challenged like myself) would be the inclusion of an "exploded" diagram so that one has a good sense from the beginning of where all 40 parts go, and how they fit together.. But definitely, and not my habit, these are best read from top to bottom before starting the build.

What wasn't clear to me until I got my hands on the kit and software is that the booster fin can is designed to separate before the retro ever fires. If you plan on using tumble recovery, build it strong. (I used 2 layers of light FG to beef up the tube, and epoxy fillets throughout the through-the-wall construction to enhance durability.) Which comes to my next point: there is plenty of cargo room within the fin can for its own recovery.

EndCap
Photo 4: On the left, the cap that protects the chute from the primary ejection charge. On the right, my mod to add a streamer to the booster fin can.
EndCap
Photo 5: The prepped rocket with streamer in place in the fincan.

So I decided to attach a high strength shock line to the fin can for two reasons. The first is that there is no reason (given you're careful in protecting the chute or streamer from the ejection gases), that the booster can't have its own recovery, and secondly by connecting it to the shock line of the top half of the rocket, one can fly this rocket in a conventional mode, leaving out the retro motor entirely. (For single motor use I would simply connect a short length of booster shock line to the cap covering the "sustainer" chute tube and untie the cap's tether. At ejection there should be enough force/momentum to pull the chute free as the booster separates. I haven't tested this, however.)

Photo 1 shows the many, many parts in this kit are of very good to excellent quality. A few differ slightly from the pics on the CD assembly, but with care, will all fit together as intended.

Photo 2 is a semi-exploded view of the rocket. The retro motor ejection charge is vented back toward the fins and uses a piston to eliminate the need for wadding. The chute deploys just rear of the second set of fins. A sleeved cap protects this end from the ejection charge of the primary motor.

The lightly-fiberglassed fin can ready for prime coats is shown in Photo 3. This section separates from the rest of the rocket at the primary motor's ejection charge. The 95mm motor length ends at the leading edge of the fins, giving you an idea of the amount of room for a chute or streamer, versus the default tumble recovery.

In photo 4, the left side, taken from the instructions, is of the aft end of the vent/chute compartment, showing the clever cap and tether arrangement that protects the chute from the primary ejection charge. On the right in the same photo it shows the mod I did: by drilling a small hole in the front centering ring of the fin can, I attached some of the surplus Kevlar in the same way to use as a shock cord for the booster recovery/single stage option mentioned above. Photo 5 shows the prepped rocket with streamer in place in the fincan.

The hollow nose cone, shown in photo 6, has a groove in which the Kevlar tether is stowed during ascent. The attachment point is near the tip of the cone so it dangles along side the rocket during the retro burn. This will be lined with hi-temp epoxy to protect the fragile balsa cone from the blast of the retro motor.

Nose Cone
Photo 6: The hollow nose cone, showing the groove in which the Kevlar tether is stowed during ascent.
Motor Mounts
Photo 7: Both ends mean business in this rocket.

About the Software:

I was concerned regarding the assumption that every hobbyist wanting to build this bird has access to Microsoft's Excel and Word (or even wants to). So I made sure that both the simulator and instructions were compatible with shareware that is available on the Internet. I used the Sun Microsystems Openoffice suite and was relieved to find all went well-almost that is-like Steve I had some glitches, but in the end man prevailed over machine!

First, I suspect this kit might raise a collective eyebrow in the rocket community-if not for the ingenuity of the product, from the standpoint of safety concerns. After all, what separates a ballistic core-sample recovery and a gentle, happy landing is a few inches of cannon fuse, a successful retro motor ignition, and math. Fortunately, the math is done for you in the spreadsheet: it comes with data entry for several Estes and AeroTech C-F impulse motors. By manually entering a small RASP-style data set, any motor not pre-entered can also be simulated.

Prepping the rocket begins by selecting the motors using the included simulation program:

The accompanying instructions are quite clear. The first thing is to select a couple of motors and deliberately pick too long a delay. That is shown in the accompanying chart. Impact occurs at about T+17 seconds. (Yellow curve is altitude, the violet velocity, and black, acceleration).

This is the lawndart come true scenario: obviously 17 seconds is beyond the upper limit of the fuse induced delay of retro ignition.

The motors used in this simulation were the Estes E9/D12 combo. The second chart reveals a situation we are also trying to avoid, that of completely overcoming the downward (negative) velocity and overshooting a near standstill to the point of a significant upward velocity.

Ready to Fly
Photo 8: Backdraft poised on one of C.R.A.S.H. pads. Awaiting it's maiden voyage as Todd Edmands assists with the pad.

As cool as the bungee bouncing/pogo-stick flight might seem, there is one small problem with this: the fins are on the wrong side of the rocket! Stability will be maintained only while there is sufficient downward velocity. An overshoot beyond this velocity would most likely lead to some harmless skywriting, but it is at least potentially unsafe and one will lose style points.

Ok, so what if we were to let it drop longer and therefore have a greater ballistic velocity to overcome. The results are shown in the next chart: while better in the sense that the peak positive velocity is not as great, this situation is also to be avoided.

Going back to the bungee metaphor, if you want your bungee long enough to plunge within three inches of the ground, first ask yourself are you really that confident, the cord won't stretch just a bit more than predicted? Same here; the software assumes perfectly vertical flights under specific conditions with exactly so much impulse. Motors vary, conditions vary, Mr. Murphy (of Murphy's Law) has been known to attend launches. So please do yourself, your friends and any spectators a favor-take heed of the designer's advice by giving yourself a significant margin of error, especially in early flights or with unflown motor combinations. Remember the line about "there are old pilots and there are bold pilots, but there aren't any old and bold pilots".

By now, it is hopefully clear that the D12 retro motor is just too big. So next step is to try a smaller impulse motor. The C11 was handy, as well as a recommended pairing, so lets give that a shot. In the next chart the improvement is readily apparent. The rocket brakes perfectly, only briefly showing any positive velocity. Lets see what can be done by shortening the delay.

Voilà! In this chart, you can see we still have the near-perfect braking and at a considerably higher altitude. Consider it cheap flight insurance.

The final screen in the series shows the H.H. Simit input screen. With the Backdraft kit, all data comes preloaded along with the advice to weigh your own rocket. Mine actually came in significantly lighter for the sustainer, and a bit lighter for the booster where I fiberglassed and added a lightweight streamer.

nose motor
Photo 9: A closeup of the nosemotor with fuse in place and exiting via side of cone.

What is not shown in these plots (and by no means necessary to the concept itself) is the separation of the booster. Given the relatively small number of choices in delay lengths, there is not a lot of flexibility here-one has three choices, use a short delay for a boosted dart effect, try to separate at apogee, or carry the booster well over the top and eject during the ballistic descent. I chose to keep it simple, and chose near apogee separation. (Also, I doubt that the Simit software would model any additional kick in velocity of the "sustainer" section, if the separate-while-screaming groundward option was chosen).

Prepping and Flight:

Much of that is covered above as the most important ingredient of success here is done before you ever get to the range. Select a pair of motors that will work, and a delay that is appropriate.

The next step which I did on the range was to measure the burn rate of the fuse. Here a stopwatch is needed and a few inches of fuse. Divide the time taken to burn into the length to get the rate. Should be something like 0.5 inches per second (about what the BATFE defines as deflagration these days ;-D) So a 14 second delay needs 7 inches of fuse. In the end I weenied out by figuring for about 12-13 seconds delay as I have enough gray hairs as is. Apart from that, sticking said fuse in a motor on the wrong end of the rocket, and stowing the Kevlar line in the nosecone groove, it's a conventional prep that went without a hitch.

The other different aspect of prepping this rocket is the need to use two igniters, one for the booster motor and the second to simultaneously light the fuse. I didn't have my big range box where I keep sundry igniters, pyrogens, and BP. So unsure of how reliably an Estes igniter would work with Visco fuse, I opted to manually light the fuse. That way I figured there would be zero chance of worst case scenario: successful primary ignition but no joy on fuse. Plus, if for whatever reason the booster motor didn't light, I'd be close and have time to yank the fuse out of the nose motor. Otherwise one ends up with a humiliating static test.

Launch
Photo 10: The author flees the scene after lighting the secondary fuse, but the Backdraft is already gone.

The result is shown to the left. As I'm backpedalling back from the pad after ascertaining that the fuse had burnt to the 13 second mark, the Estes E wastes no time into coming to life. The rocket wobbled some on the way up-maybe because of a high polar moment of inertia/smallish fins (dumbbell effect owing to motors on both ends)-but skyward she went with some anticipated weathercocking (another reason I weenied a bit on the delay). The booster/fincan separated just beyond apogee, and the heart stopping plunge towards Terra Firma began in earnest.

At about 300-400 feet up, my heart resumes beating when the nose motor kicks in and saves the Backdraft from certain death. That it "overshoots" a bit and does a brief mid-air thrash is easily forgiven. Few seconds later, we have the welcome sight shown in Photo 11!

Only one small fly in the ointment-the yellow nose which should be dangling along side the rocket is nowhere to be seen. The clue as to why is here in this review, winners receive a years free subscription to Rocketry Planet.

Discussion:

I suspect that this rocket might generate some controversy. I know it raised differences of opinion among the Rocketry Planet moderators who act as RSO's.

Recovery
Photo 11: Success, we have recovery!

Is this rocket sufficiently safe to fly? In trying to answer this, I looked at all the relevant safety codes and could find no reason to disqualify the rocket. Maybe on account of the fact I'm an old-timer, who has used real honest to God mercury switch/capacitor fired/flashbulb cannon fuse for airstarting BP motors, and seen it work, I wasn't as skeptical as some. No I have never flown a retro rocket before, but in the end, the relevant question is: does this rocket present that much greater a hazard than others we fly?

Bottom line, I say, no. Sure it would be great and likely safer to electronically perform the same task. No different than deploying the main at 500', one should at least be able to ignite the retro at x altitude, or ideally x feet per second. But this is about adding a new twist to mid-power fliers who cannot or choose not to splurge for electronics. I would treat this rocket just as C.R.A.S.H. did-a heads-up flight, with an additional element of fire risk.

As packaged, I'd say it makes the short list of all the under-F powered kits that truly were in one sense or another, revolutionary. If I had to prune that list to say six, they would include the Estes Astron Spaceplane (boostglider), the Estes Gyroc (helicopter recovery), the Centuri Hustler/Lil Hustler (designed for BP F engines), the first multiengined rocket/s (not certain these are right - Estes Apogee (staged) and Ranger(cluster)), the AeroTech Phoenix R/C rocket glider, and the Backdraft. Thats pretty select company.

I picked those because each of these rockets opened up a new vista in sport rocketry, and yet none were particularly aesthetically appealing rockets. The Backdraft fits this bill entirely. It's certainly not about to turn heads sitting near your field box, in fact it's a tad homely. But as the rocket barrels in destined for certain destruction, just then, the nose motor kicks in, gracefully braking the banshee-like descent, and a few seconds later, gently floating under chute, she will most definitely turn heads when flown. One can immediately think of all kinds of interesting competitions based on the concept, and roaming into the domain of high power and extreme rocketry, maybe some applications there as well.

I strongly recommend the kit based on high KEWL factor, innovation, and overall quality. And a definite strong thumbs up goes to Jose Andrade-Cora, the designer and proprietor of Heavenly Hobbies.

Retro Rocket/Backdraft Background:

Jose provided me with a memo he had written previously about the inspiration and development of the Backdraft:

Back in 2002, as our family vacation loomed near, I placed an order for some NARTS publications to provide some relief from the "packaged" distractions found in the big Florida theme parks. Among the assorted reports and technical papers, there was one that seriously caught my attention. It was a NARAM-34 report by Bruce Markielewski about construction of what he termed "retro-rockets". These models were rockets that bypassed ejection at apogee for a delayed deployment of their recovery system. To counteract the gravity force during re-entry, a second engine was fired. This second engine would slow down the rocket sufficiently for the recovery system to take over. I thought that "retro-rockets" were a great idea, as they added complexity and interest to the usual rocket flight patterns that, frankly, were getting old.

Markielewski's stated objective was to "...design and build a reliable, functioning model rocket using a 'retro-rocket' technique to slow the descent of the model rocket before deploying a parachute or other recovery device." This objective, however interesting, failed to focus on the possibility of using the "retro-rocket" concept to reduce the drift of the model from the launching pad. Common Dual Deployment™ techniques use electronic actuators to force the ejection of a streamer or small "drogue" parachute to cause a fast, but controlled, descent. A larger parachute is subsequently deployed by similar means. The idea is to reduce the time the rocket is subject to crosswind drag, therefore reducing the drift.

However, a rocket using the "retro" techniques does not "break up" to deploy a recovery device in its coasting phase after apogee. It, therefore, presents a smaller frontal area to crosswinds. Less frontal area means less drag and less drift. Also, crosswinds acting on parachutes create lift forces, so not having a parachute in this phase of the descent also helps. Moreover, a compact rocket presents a much more aerodynamic profile in the vertical direction, allowing higher (more negative) terminal velocity limits. This leads to much reduced periods during which the model rocket is subject to crosswinds, and again, less drift. In simple words, the "retro-rocket" technique is superior to the common Dual Deployment technique in reducing crosswind drift.

To put Markielewski's work in perspective, one must realize that to achieve his objectives, a fair amount of mathematical calculations were required, perhaps too many or too intensive for the average modeler. However, I realized right then and there that the limitations that were real in 1992 were no longer there in 2004. The personal computer had removed them from the picture! In other words, I had found an alternative for Dual Deployment which, provided the rocketeer had a computer at home, didn't require expensive electronics or demanding mathematical calculations, rendering it attainable to many more rocketeers. This was the birth of the TailWind delayed-deployment system.

Soon after my vacation was over, I started working on the first prototype for my version of the "retro-rocket". It was a single-stage, large diameter rocket with ducted ejection gases for rear ejection. That design never took to the skies. To my knowledge, the available software was not able to model the unusual shapes and flight paths that I was conceiving. I had realized that the controlling software was even more essential than the rocket itself. My top priority then became to develop the software that would take the place of the deployment electronics. The software was essentially a simulation program, optimized for the Backdraft model. It obviously had to take into consideration gravity, thrust and drag, but it also had to give due weight to the unusual changes in physical characteristics that would occur during flight. This work eventually became the H.H. Simit simulation software.

H.H. Simit (v1) is included in all new Backdraft kits. It provides simulated altitude, velocity and acceleration information for the model's flight. It also allows the flyer to easily choose primary and secondary engines (and their respective delays) using the provided data. These choices are critical for the safe flying of the model. Future rocket or engine modifications will not be a problem as the information database is user-editable. You don't need to buy a new version of H.H. Simit to fly a new version of Backdraft or to accommodate the thrust characteristics of a new engine! As development continues, H.H. Simit will be made available as a separate product.

Subsequent prototypes abandoned the large-diameter airframe for a more energy-efficient BT-60 based design. The final design offers a booster-style detachable propulsion module, straight-through ejection gas ducting and EZject piston-actuated system for rear ejection. With the EZject system, flameproof wadding and / or parachute protectors are completely unnecessary, making field preparation a breeze! EZject is different from other piston-based ejection systems in that its simplicity and low manufacturing cost makes it available to all rocket designs, even the most simple and basic (see the Heavenly Hobbies' Stratos-13 ELM and Stratos-18 ELM models).

The essential physical difference between the Backdraft and a common 2-stage rocket is that the second-stage engine has exchanged places with the recovery system. The secondary engine been moved forward, behind the nosecone, while the parachute has moved back. This secondary engine has also been rotated 180°, so that the nozzle points to the sky while the rocket sits at the launch pad. As I said before, when lit, this engine will provide thrust to counteract the force of gravity and slow down the rocket sufficiently, so that the parachute can open without tearing to shreds. Since the parachute can open as close to the ground as desired, drift is reduced considerably. The reduction in drift allows the hobbyist to fly higher and/or in windier conditions. This is the magic of the TailWind delayed deployment system.

Since the secondary engine is far removed from the primary engine, the primary engine cannot be used to directly ignite the secondary one. This problem would normally be remedied with an electronic timer or other similar artifact. However, it was a design objective for the Backdraft to "kick it old school" and avoid any electronic control artifacts inside the rocket. As a result, a good old visco fuse ("cannon fuse") is used to delay the firing of the secondary engine. This fuse is lighted at the same time as the igniter for the secondary engine, so a good 12-volt launch system is needed. You also need to time your fuse accurately, so a stopwatch will come in handy also.

It is critical to follow the instructions in building and flying this model. I have gone through several prototypes in perfecting a safe and reliable flying procedure, so you don't have to! Use H.H. Simit to your advantage, and remember to allow yourself a margin of error in your calculations.

Happy flying!

Jose M. Andrade-Cora
Heavenly Hobbies LLC

Now in fairness, this idea goes back at least as far as the 1970's when it was discussed in a rocketry magazine article. The first large public launch was at NARAM 1992, where Bruce M. staged a test flight in conjunction with his R/D report. Many have tried more or less the same approach with varying degrees of success both before and since, but never to my knowledge with quite this level of sophistication, and certainly not in a kit with integrated software.

It was something of an honor for me to fly this at a C.R.A.S.H. launch. After all, this was Bruce M.'s old club and launch site. Sadly, Bruce passes a few years back. His legacy certainly lives on, and the Backdraft a fitting piece of such. I am sure Bruce smiled from beyond the Saturday my Backdraft flight took place.

[Submit your Opinion]

GUEST's OPINION:
06/08 - "Excellent review, exactly what I look to this site for--a unique rocket I would never have heard of or seen browsing typical retail outlets. I've been interested in building a retro-rocket for a few years, and will have to pick this one up. Pricey at $60, but probably because it also includes simulation software." (C.S.)

GUEST's OPINION:
06/08 - "My experience was different. (I did respond BTW at TRF or at least to some build thread over there--denverdoc is the avatar). I agree that this is a challenging kit, and for those of us not used to following instructions or making up our own, even more so. ;-D Part of those instructions IIRC instruct one do their own fuse burn rate determination. (Even environmental factors could influence this some what). I believe had you done that, and gotten a feel for the Visco fuse versus just some number, the outcome might have been different. Here I think being an old man may have helped me as I have used green fuse in various projects in the past. Plus I was using a donation that had no specs and so HAD to measure the burn rate. But this is not a cub scout build to say the least. I found parts of the instructions confusing as well, and would love to see an "exploded" diagram one could refer to as its just too unorthodox a build to rely on instinct and the computer instructions are excellent with the details but may even obscure the big picture somewhat. Other than that, I think your review fairly summarizes the build. I would advise anyone else building the kit,tho, against the E9/D12 combo. The D12 is a bigger than needed and a C11 is perfect." (J.S.)

[Enter Rocket Specific Tip]

SPECIFIC ROCKET TIP:
"" (x.x.)

[Enter Flight Log]
Date Name Motor Ejection/
Altitude
Wind Notes
06-20-2008 EMRR Est SU E9-4 / Est SU D12-3 None - Staging Failure 5-10 mph winds RIPEvent: NERRF
- Rocket flew great up on the E9, but I used too much fuse and the rocket came in ballistic. While it layed on the ground the fuse burned, then lit the D12, flopped around and ejected. Concept-wise I can see how the fuse would work, but... Status: Not Repairable
08-01-2008 Dick Stafford Est SU E9-4 / Est SU C11-3 Just Past (1-2sec) 0-5 mph winds Event: NARAM-50
- The first flight was with a 6 fuse that should give around a 12 second delay. The boost was high and the booster ejected on cue. The retro motor went off while the rocket was still high and the parachute ejected 3 seconds later. The high ejection made for a long walk. The rocket was recovered sans nose cone.
08-01-2008 Dick Stafford Est SU E9-4 / Est SU C11-3 Very Late 0-5 mph winds Event: NARAM-50
- This time Nick cut an 8 piece of fuse (~16 second delay). The up direction was the same. I lost the sustainer until the retro motor fired at about 50'. The rocket rose about 25 (WAG) and recovered nicely. This was awesome, but had a pucker- factor of 10.
08-17-2008 Dick Stafford Est SU E9-4 / Est SU C11-3 Very Late 0-5 mph winds Event: ESL-122
- The retro motor was ignited with a 7.25 fuse. I lost sight near apogee until the retro motor went off at about 400'. Everyone though it was cool. Some damage and missing parts. Needs rework.
08-14-2010 Dick Stafford EST SU E9-4/EST SU C11-3 Very Late 5-10 mph winds Event: ESL-147
- 4th flight on this motor combination and again used 7.25 of fuse. This model guarantee's high pucker-factor flights and it didn't disappoint. Great flight but, as usual, parts came off.
   

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