Improving the Estes Hi-Flier: Hot wash, lessons learned

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SolarYellow

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I turned into a BAR instead of just knocking out an Alpha per the instructions and getting on with life substantially because of the lameness of the Estes Hi-Flier. Last August, I went camping with my godson. We picked up an ARF launch set from Hobby Lobby and had a good time. After that trip, I thought it would be fun to build my own rocket. So before driving over to Hobby Lobby to buy an Alpha, I pulled up the web site just to make sure they actually had Alphas there. I saw this cheaper kit, so that was attractive. But a quick perusal of specs indicated it was heavier, even though it was smaller than the Alpha. I had to understand why, and down the rabbit hole I went. By the end of the day, I’d bought a Hi-Flier kit, measured and weighed all the components, and built it in Open Rocket. That started up my engineering OCD of figuring out how to improve it. I’ve chased down a bunch of other rabbit holes and done a lot of other stuff since then, but I finally got that one built, with improvements, last week and launched it at Lucerne Lake with ROC this weekend.

What sucks about the Hi-Flier and how to improve it:

The fins, although they look zoomy and aerodynamic to the aerodynamically ignorant, are too dang big. They move the center of pressure forward excessively due to their size and aspect ratio, and they add too much surface area and weight. Smaller fins improve the stability factor both by shifting the fins’ CP contribution rearward and reducing the weight hanging on the back of the rocket. Reducing the surface area reduces drag and increases performance.

The motor retaining hook, because the Hi-Flier is “minimum diameter,” has to go on the outside of the body tube. The hook adds unnecessary mass at the back of the rocket, reducing the stability factor, and putting the hook and its retaining sleeve on the outside of the body tube adds a bunch of drag for no reason. Much better to use some form of tape retention, such as the friction fit described in the Estes Wizard instructions, or just straight-up tape retention, from the outside of the body tube to the back of the motor.

Those two ideas formed the basic direction for this build. I picked the Little John prototype fin planform as one that looks particularly “rockety.” Since I was going to use the balsa provided in the Hi-Flier kit, I was only going to have three fins. I thus scaled them up to 4/3 size, or 133 percent, vs. what would be scale size on BT-20 tubing, and then added another 10 percent just to be generous. The result was still way smaller than the stock fin design. I left the body tube the length it comes in the Hi-Flier kit, rather than scaling it down. I used a green Estes motor block and tape retention. I used a nose cone I’d previously set up with an ebay to take an Altus Metrum microPeak altimeter and a few grams of BBs epoxied into the tip. Checked everything in OR and had a stability margin of about 15 percent of overall length. Generous and conservatively safe. And simmed to outperform the stock Hi-Flier apogee by about 300 feet on a C6-7.

Fins were rounded on the LE, wedged on the TE, and square on the tips. Glued on with Titebond III and eyeballs rather than a fin jig for alignment. TB III fillets. DAP wood filler thinned for the spirals and on the fins. Went back over the fillets a couple times trying to fill the bubbles and sanding lumps, using a diamond tapered round needle file to deal with the lumps as best I could. Still hate TB III for fillets due to the bubble problems.

Dumbass moment #1:
We glued the motor block in first, as the instructions show. At that point, I even thought, “Now, Stupid, don’t go and glue the fins on the wrong end.” Of course, after the fins were glued on, I realized that Stupid had stupidly glued them on the wrong end. In hindsight, or if I had been near my own supply of balsa and tubing, I would have added the tube to a box of random parts and started over. Would either wrap the front of the tube with some paper marked “fins other end” or glue the motor block in after the fins. But because I was in CA and trying to get it built with what’s here, I checked it and decided I could fit the streamer, wadding, and nose cone shoulder in the space between the motor block and now-forward end of the tube, and forged ahead.

Paint was a layer of Acryli-Quik white primer, blocked down until I was seeing about as many fuzzies as I was comfortable with. Followed that with Rusto Filler-Primer, wet sanded. Found that at a few points, some of the spirals where the glassine bridged over gaps in the tube beneath formed enough of a lump that I got through the primer while wet sanding and the glassine erupted a bit. I let it dry before putting on another layer of AQ white primer, and that at least locked down the fuzzies. They still needed filling, but I didn’t want to sand off a whole ‘nother layer of filler primer, so I decanted some Rusto FP into a red plastic cup and used an old hobby brush to paint it on just the spots where it was needed. That required a heck of a lot less sanding time to level the spots. I also drilled the altimeter vent holes at this time. I had brought the rocket back to Houston to finish it and the stickers were in CA, so I put two holes in line with the launch lug and a third on the other side, leaving areas for the stickers to fit. I sanded the raised burrs around the holes flat. Touched up the final layer of AQ white primer to cover the RFP grey. For some reason, I had waited until this point to glue in the actual rear motor block, and the combination of swelling due to water absorption and/or shrinking due to drying glue raised lumps at the spirals where they crossed the motor block. At that point, everything got dry sanded with 400 grit, and these spiral lumps fortunately were resolved.

My godson had chosen orange, so I went with that for the body tube. The Hi-Flier stickers are silver with a black outline. I had been wanting to try a can of Rusto Pro aluminum paint that’s been in my can collection in the garage for a few years, so I used that for the NC and one fin. All the other color was Acryli-Quik: the orange for the BT, black for a second fin, white for the third. With Little John-ish fins and a color scheme that sort of back-doored its way into being Aerobee-Hi NRL-41/42 inspired, I think it looks pretty good.

First color was white. By this time, I was trying to get the rocket ready for the ROC launch on June 10, which turned into a bout of go fever before I was done. I hit the first, white fin in the evening after work. I was in an automotive paint booth, drawing intake air from a conditioned zone, but the heavy thunderstorms we had that afternoon in Houston still made it too humid and the AQ blushed flat. Uniformly all over, zero gloss. I tried again the next day after a test spray of the AQ orange dried shiny. The fin got a little blush, but it polished out by rubbing with my cotton t-shirt, so I had one shiny fin. I had masked a perimeter around the fin on the BT to minimize added weight. I sanded it with 400 and the edge feathered nicely. For the orange BT color, I masked the remaining fins a little bit up from the roots, again thinking to avoid excess paint weight. Once the paint had dried for a few hours and the masking was removed, I tried to feather the masked edges, but on the flat surface of the fins (as opposed to the rounded surface of the BT), the primer was sanding faster than the color. I thought I had the blend nice and smooth, but it ended up with a step that is still clearly visible on the finished fin. The black and silver over the main body tube paint are much smoother than over the primer, though.

I used Tamiya 2mm masking tape on the fin roots. It was my first use of Tamiya tape, and it was awesome. Love the crisp edge. Will continue to use, and get more sizes.

I was kinda in a rush at this point and put masking on for the fins about three hours after spraying the orange. The orange felt solid and sanded more or less OK, but it still ended up taking texture marking from the tape where it was applied. Worse, the blue ink printing from the plastic grocery bag I used for masking, without thinking about the ink against the paint, was partly dissolved by the solvents still evaporating out of the paint and left blue marks all over the orange. I wet sanded the orange with 600 grit to get rid of the blue and it looked good enough from five feet away. The godson applied the stickers in the morning before the launch. The Rusto aluminum, despite being shaken for a full two minutes, spat blobs of paint onto the nose cone and fin. Spraying through the tip with brake cleaner seemed to resolve the spray issues, but too late for the rocket. The aluminum look paint also still has a grain too it, rather than looking like smooth aluminum.

I tried a new-to-me approach to shock cord retention. With the limited space in the body tube above the motor block mistake (I tried to unsuccessfully peel it out), I decided to go with about 30 inches of 100-lb Kevlar instead of Estes rubber. After several experiments done in parallel with the sanding/priming/painting schedule, I used a tri-fold made from woven polyester cloth tape and E6000 as the glue. Stuffed it down as close to the motor block mistake as I could and let it dry overnight before packing for CA. The E6000 stays slightly soft and rubbery, so it doesn’t concentrate the stress in the Kevlar at the edge of the glue. However, because of the rubberiness, there is definitely more friction, requiring more pressure to eject the wadding. Will come back to this…
 
About 1/3 of the way from the end of the shock cord, I used a square knot around a streamer I had sitting around from my Viking bulk pack. Used a Perfection Loop knot at the end. Put a fishing split loop connector on the nose cone cap loop, which enables me to connect the shock cord loop securely to the nose cone, change out nose cones, etc., without cutting off or trying to untie the shock cord loop each time.

Here it is, complete with dings. The lower fin in the first photo is the silver one, it just looks white with the lighting.

IMG_3092 - web.JPG

IMG_3094 - web.JPG

Out in CA, a quick swing test with a C6-7 in the back before loading up to drive out to the lake was successful. Sent it up on an A8-5. It came down faster than I would have liked, so I added the Hi-Flier kit streamer a few inches away from the Viking streamer. With the Kevlar, I was still able to easily fit both streamers and the shock cord in the BT-20. The second flight was better. Still, on both flights, the airframe landed on the tip of the black fin, denting it severely. Second flight was a B6-6, and I kept it in sight against the uniform overcast sky all the way back to the ground. Third flight was a C6-7. This was finally highish performance, and it disappeared after boost. The tracking smoke was indistinguishable from the sky. After watching the sky for long enough that I knew it had to be down, I started walking in the direction I thought it went and eventually saw the two streamers waving in the breeze. The streamers showed up well on the dirt. The orange of the body tube was surprisingly less visible.

I was surprised to find that on the third flight, I had dual ejection. The ejection charge managed to get the streamers and wadding out, but the blue masking tape I used to hold the motor in also let go of the motor. The C6-7 is somewhere out there on the lake. With no motor, the airframe was stable and fell nose-first, so there is a little ding on the end of the tube. I’m not sure how much of this might have been due to higher pressure developed due to a slightly tighter packing of the wadding against the E6000-coated tri-fold patch and how much was weakening of the masking tape adhesive due to the additional heat of the C6 vs. the A8 and B6. I did have four wraps of 1/4-inch wide masking tape on the back of the motor (double thrust surfaces and no inward step) that the blue tape was sticking to, so it wasn’t against the case itself.

The blue masking tape also left texture on the orange body tube paint. Don’t know how much of this was just the combination of adhesive, paint, and temperature, or if it wouldn’t be an issue if the paint had been on the rocket for more than two days. Will obviously find out in the future.

After just the first flight, I noticed that the spirals were starting to show back through the paint, but as raised ridges. They were blocked perfectly smooth in primer, so this was clearly the 0.013-inch thick cardboard not doing a good job containing the ejection pressure/heat. More on this in later…

My litany of screw-ups:
  • fins glued to the opposite end of the tube from where the motor block was already glued
  • trying to paint with multiple colors on too tight a schedule (go fever), which led to
    • painting in too high humidity, causing issues with gloss
    • masking over paint that wasn’t dry enough
    • masking tape texture on the paint
    • transfer from the grocery bag ink to the paint
  • thinking I could feather the edge of a masked paint line on a flat surface, leaving obvious difference in finish on the fins
  • flying a rocket with paint that had only been on it for two days
    • masking tape texture on the paint?
Other knowledge gained:
The shock cord attachment I did on a previous BT-20 build was a lot better. Will go with that in the future; will document and post about it on the next build I use it on.

Balsa is easy to cut and sand, but hard to make look good. There’s a strong tendency for the wood filler to chunk out of large grain flaws or end grain porosity, leaving voids that are difficult to see until they’re primered and then take extra rounds of filling.

Balsa fins make a rocket that’s launched on the dry lake even more of a consumable than it normally would be. The balsa is guaranteed to get dinged up excessively, especially if you’re bringing it back down quickly on a streamer or small chute. Get ready to accept a dinged-up rocket or a lot of touch-up/repair work if you want it to stay looking good and maintain aerodynamic performance.

The best looking finish if I was to do this one over would probably be achieved by painting the silver and black fins all over orange with the body tube paint before laying down the silver and black. It would be a little more paint weight, but much smoother and glossier.

For the lightest paint, either go with the same color on fins and body tube to do the whole thing at once with one layer of paint, or get bold and try to mask the first colors much closer to the final transition line. This will need some skill/process development before I expect it to come out well.

I’ll follow HCMBanjo’s painting protocol in the future. It should lead to fewer total layers of paint and thus less paint weight. For a C6-7, my sims were coming out over optimum weight. For a D, more weight and smoother paint would probably both be good things.

Even with all its flaws, the rocket looked darn good at five feet, or even three, especially before it got dinged up on the playa.

Where to go from here?
I like the way this came out. I like the small, cheap rocket going fast and high on cheap motors. I like the look. I am eager to do better on the next one.

I didn’t like having it disappear. I’d like to fly even higher and faster, exploring the 18mm APCP D motors. That means I need tracking. I have an Eggfinder Mini, so that’s the plan. It doesn’t fit in BT-20. I have some BT-20+ from eRockets on hand and some 20mm (Quest size) inbound from BMS. Either of those will take the EF Mini cleanly. The BT-20+ is the same wall thickness as BT-20, whereas the 20mm is 0.020 thick and should hold up to ejection pressure better, as well as overall hard-life knocks of being a rocket on the playa. So I think I’ll be going that direction next. One could just buy the Quest Novia kit (or a bulk pack), but I’ll be 3D printing nose cones with resin.

Trying to decide whether the next build will have bass or G10 fins. Bass is cheaper and easier to fabricate, but G10 is even more durable. G10 can also be had in colors at 1mm thick, and inexpensively, so you can skip the paint altogether. G10 drives toward the use of epoxy for fillets, so no Titebond bubbles to waste time dealing with. Just need to work out a bulletproof means of dealing with the fiberglass dust. Will haunt Craigslist for quality used tile saws.

Will use Tamiya paint next time I want aluminum look, and see how that goes. Might not be able to do that on the nose cone if I’m trying to transmit EF Mini data from inside the nose cone if there is actual metal in the paint. Ground testing is required, or maybe just compromise and make it a non-metallic grey.

This rocket is limited to Estes survey-tape streamers due to the motor block mistake. Not screwing that up will allow the use of a range of streamers (wider) and possibly small parachutes to get the descent speed down.

I don’t like launch lugs. They add drag, which sucks, but they are also a fiddly PITA that slows down the build process. They get in the way when sanding, to the extent that it was actually fairly challenging to do good sanding around the lug and fins where they got close to each other on this small rocket. I’m working on a small, readily portable tower. I’ve run sims on rockets from BT-5 to BT-55 and confirmed that rockets I’m going to want to launch from it will be going plenty fast enough when they clear it.
 
I'm not sure all that is better than a built-stock Hi Flier. But you have earned years of experience in one go! Congrats .
 
I’d like to fly even higher and faster, exploring the 18mm APCP D motors. That means I need tracking. I have an Eggfinder Mini, so that’s the plan. It doesn’t fit in BT-20. I have some BT-20+ from eRockets on hand and some 20mm (Quest size) inbound from BMS. Either of those will take the EF Mini cleanly. The BT-20+ is the same wall thickness as BT-20, whereas the 20mm is 0.020 thick and should hold up to ejection pressure better, as well as overall hard-life knocks of being a rocket on the playa. So I think I’ll be going that direction next. One could just buy the Quest Novia kit (or a bulk pack), but I’ll be 3D printing nose cones with resin.
Interested in how that works out. I've been eyeing one of my older Minis and thinking about shaving it down, but I keep coming back to BT-20's OD being smaller the thrust ring diameter of the Aerotech 18/20 case (and - though I've not yet measured them - likely the thrust rings of Quest motors and the Green Monkey research cases too), and I wonder why I'd bother instead of going to a larger tube. Trouble with the larger tubes is of course nose cones, so I'll probably put any project in that area on hold until I have the recently-arrived printer online.
I’m working on a small, readily portable tower. I’ve run sims on rockets from BT-5 to BT-55 and confirmed that rockets I’m going to want to launch from it will be going plenty fast enough when they clear it.
A short, handy tower that trades launch velocity (hence perhaps needing punchier motors) for being easier to transport, setup, and teardown has crossed my mind at times. I've not pondered it in depth though. One of my other requirements would be easy adjustability for various diameters and fin counts (though I suppose for portability sticking to three fins would make some sense), and I won't have the time for that level of design anytime soon, plus adjustability would inevitably work against the handy and portable goals.
 
Interested in how that works out. I've been eyeing one of my older Minis and thinking about shaving it down, but I keep coming back to BT-20's OD being smaller the thrust ring diameter of the Aerotech 18/20 case (and - though I've not yet measured them - likely the thrust rings of Quest motors and the Green Monkey research cases too), and I wonder why I'd bother instead of going to a larger tube. Trouble with the larger tubes is of course nose cones, so I'll probably put any project in that area on hold until I have the recently-arrived printer online.

A short, handy tower that trades launch velocity (hence perhaps needing punchier motors) for being easier to transport, setup, and teardown has crossed my mind at times. I've not pondered it in depth though. One of my other requirements would be easy adjustability for various diameters and fin counts (though I suppose for portability sticking to three fins would make some sense), and I won't have the time for that level of design anytime soon, plus adjustability would inevitably work against the handy and portable goals.

The rear closure of the 18/40 case is only 0.740, so that's 0.004 larger than BT-20 OD. You'll probably be bigger than that after paint. Masking tape is about 0.0035 thick, if you use that for retention. But 0.740 will fit inside BT-20+ or Quest T20 for a super-clean tail end.
 
The rear closure of the 18/40 case is only 0.740, so that's 0.004 larger than BT-20 OD. You'll probably be bigger than that after paint. Masking tape is about 0.0035 thick, if you use that for retention. But 0.740 will fit inside BT-20+ or Quest T20 for a super-clean tail end.
You're right. I was misremembering the ring as being more like those on the 24mm cases. Just checked my spreadsheets and confirmed your numbers. Hmm. Maybe I will shave the board on a Mini after all.
 
About 1/3 of the way from the end of the shock cord, I used a square knot around a streamer I had sitting around from my Viking bulk pack. Used a Perfection Loop knot at the end. Put a fishing split loop connector on the nose cone cap loop, which enables me to connect the shock cord loop securely to the nose cone, change out nose cones, etc., without cutting off or trying to untie the shock cord loop each time.

Here it is, complete with dings. The lower fin in the first photo is the silver one, it just looks white with the lighting.

View attachment 586130

View attachment 586131

Out in CA, a quick swing test with a C6-7 in the back before loading up to drive out to the lake was successful. Sent it up on an A8-5. It came down faster than I would have liked, so I added the Hi-Flier kit streamer a few inches away from the Viking streamer. With the Kevlar, I was still able to easily fit both streamers and the shock cord in the BT-20. The second flight was better. Still, on both flights, the airframe landed on the tip of the black fin, denting it severely. Second flight was a B6-6, and I kept it in sight against the uniform overcast sky all the way back to the ground. Third flight was a C6-7. This was finally highish performance, and it disappeared after boost. The tracking smoke was indistinguishable from the sky. After watching the sky for long enough that I knew it had to be down, I started walking in the direction I thought it went and eventually saw the two streamers waving in the breeze. The streamers showed up well on the dirt. The orange of the body tube was surprisingly less visible.

I was surprised to find that on the third flight, I had dual ejection. The ejection charge managed to get the streamers and wadding out, but the blue masking tape I used to hold the motor in also let go of the motor. The C6-7 is somewhere out there on the lake. With no motor, the airframe was stable and fell nose-first, so there is a little ding on the end of the tube. I’m not sure how much of this might have been due to higher pressure developed due to a slightly tighter packing of the wadding against the E6000-coated tri-fold patch and how much was weakening of the masking tape adhesive due to the additional heat of the C6 vs. the A8 and B6. I did have four wraps of 1/4-inch wide masking tape on the back of the motor (double thrust surfaces and no inward step) that the blue tape was sticking to, so it wasn’t against the case itself.

The blue masking tape also left texture on the orange body tube paint. Don’t know how much of this was just the combination of adhesive, paint, and temperature, or if it wouldn’t be an issue if the paint had been on the rocket for more than two days. Will obviously find out in the future.

After just the first flight, I noticed that the spirals were starting to show back through the paint, but as raised ridges. They were blocked perfectly smooth in primer, so this was clearly the 0.013-inch thick cardboard not doing a good job containing the ejection pressure/heat. More on this in later…

My litany of screw-ups:
  • fins glued to the opposite end of the tube from where the motor block was already glued
  • trying to paint with multiple colors on too tight a schedule (go fever), which led to
    • painting in too high humidity, causing issues with gloss
    • masking over paint that wasn’t dry enough
    • masking tape texture on the paint
    • transfer from the grocery bag ink to the paint
  • thinking I could feather the edge of a masked paint line on a flat surface, leaving obvious difference in finish on the fins
  • flying a rocket with paint that had only been on it for two days
    • masking tape texture on the paint?
Other knowledge gained:
The shock cord attachment I did on a previous BT-20 build was a lot better. Will go with that in the future; will document and post about it on the next build I use it on.

Balsa is easy to cut and sand, but hard to make look good. There’s a strong tendency for the wood filler to chunk out of large grain flaws or end grain porosity, leaving voids that are difficult to see until they’re primered and then take extra rounds of filling.

Balsa fins make a rocket that’s launched on the dry lake even more of a consumable than it normally would be. The balsa is guaranteed to get dinged up excessively, especially if you’re bringing it back down quickly on a streamer or small chute. Get ready to accept a dinged-up rocket or a lot of touch-up/repair work if you want it to stay looking good and maintain aerodynamic performance.

The best looking finish if I was to do this one over would probably be achieved by painting the silver and black fins all over orange with the body tube paint before laying down the silver and black. It would be a little more paint weight, but much smoother and glossier.

For the lightest paint, either go with the same color on fins and body tube to do the whole thing at once with one layer of paint, or get bold and try to mask the first colors much closer to the final transition line. This will need some skill/process development before I expect it to come out well.

I’ll follow HCMBanjo’s painting protocol in the future. It should lead to fewer total layers of paint and thus less paint weight. For a C6-7, my sims were coming out over optimum weight. For a D, more weight and smoother paint would probably both be good things.

Even with all its flaws, the rocket looked darn good at five feet, or even three, especially before it got dinged up on the playa.

Where to go from here?
I like the way this came out. I like the small, cheap rocket going fast and high on cheap motors. I like the look. I am eager to do better on the next one.

I didn’t like having it disappear. I’d like to fly even higher and faster, exploring the 18mm APCP D motors. That means I need tracking. I have an Eggfinder Mini, so that’s the plan. It doesn’t fit in BT-20. I have some BT-20+ from eRockets on hand and some 20mm (Quest size) inbound from BMS. Either of those will take the EF Mini cleanly. The BT-20+ is the same wall thickness as BT-20, whereas the 20mm is 0.020 thick and should hold up to ejection pressure better, as well as overall hard-life knocks of being a rocket on the playa. So I think I’ll be going that direction next. One could just buy the Quest Novia kit (or a bulk pack), but I’ll be 3D printing nose cones with resin.

Trying to decide whether the next build will have bass or G10 fins. Bass is cheaper and easier to fabricate, but G10 is even more durable. G10 can also be had in colors at 1mm thick, and inexpensively, so you can skip the paint altogether. G10 drives toward the use of epoxy for fillets, so no Titebond bubbles to waste time dealing with. Just need to work out a bulletproof means of dealing with the fiberglass dust. Will haunt Craigslist for quality used tile saws.

Will use Tamiya paint next time I want aluminum look, and see how that goes. Might not be able to do that on the nose cone if I’m trying to transmit EF Mini data from inside the nose cone if there is actual metal in the paint. Ground testing is required, or maybe just compromise and make it a non-metallic grey.

This rocket is limited to Estes survey-tape streamers due to the motor block mistake. Not screwing that up will allow the use of a range of streamers (wider) and possibly small parachutes to get the descent speed down.

I don’t like launch lugs. They add drag, which sucks, but they are also a fiddly PITA that slows down the build process. They get in the way when sanding, to the extent that it was actually fairly challenging to do good sanding around the lug and fins where they got close to each other on this small rocket. I’m working on a small, readily portable tower. I’ve run sims on rockets from BT-5 to BT-55 and confirmed that rockets I’m going to want to launch from it will be going plenty fast enough when they clear it.
A lot of good info for this build, nice job!!
 
Was looking through old photos on my phone and found this pic I took when trimming the fins. Printout of a screen cap of the OR fin design. The paper cutout is from the OR printout packet. I used it for sizing, but used the big printout to improve accuracy of the straightedge angle when making the cuts.

Just to reiterate, the Hi-Flier sims as more stable, not less, with these reduced-size fins.

IMG_3027 - web.jpg
 
You have to accept a few compromises in looks on rockets that you launch. They tend to get wear from launches and recoveries, also just from carrying them to the launch and back. I paper my fins which adds a lot of work but makes them look a little more finished and makes them stronger, but the edges can still get dinged depending on where you fly. Fortunately most of my rockets land on soft grass or weeds. I have one that landed in the street and still wears those scars on a couple of fin tips.

A C motor is more than I want for any rocket smaller than BT-55 (1.3" diameter). I like to keep mine in sight so I have more chance of recovery.

It is great to take a kit and modify it to your liking, most of my builds these days are either like that or they are complete scratch builds.

In the old days all motors were friction fit. I know how to do it but I'm lazy and I much prefer metal engine hooks. Friction fit requires walking the narrow line between a motor that will eject itself and a motor that you might damage the rocket trying to get it out.
 
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Just to reiterate, the Hi-Flier sims as more stable, not less, with these reduced-size fins.
It seems that as rockets go up in size the CG moves forward and fins can be relatively smaller. The HF being relatively small the CG is far enough back to be within the fin shape so part of the fin area is working against you, that's why cutting off the front part of the fin improves stability. I think the HF has its fin shape for design more than function. I have the HF XL which has the same fin shape just scaled up, much more fin than it needs. I have a second one that I built with much reduced fin area basically scaled to recreate an AerobeeHi and it flies great. I actually cut the new fins out of the material of the original fins. I also have an Estes Vapor which is similar to the HF XL maybe a bit longer, with a lot less fin area.
 
It seems that as rockets go up in size the CG moves forward and fins can be relatively smaller. The HF being relatively small the CG is far enough back to be within the fin shape so part of the fin area is working against you, that's why cutting off the front part of the fin improves stability. I think the HF has its fin shape for design more than function. I have the HF XL which has the same fin shape just scaled up, much more fin than it needs. I have a second one that I built with much reduced fin area basically scaled to recreate an AerobeeHi and it flies great. I actually cut the new fins out of the material of the original fins. I also have an Estes Vapor which is similar to the HF XL maybe a bit longer, with a lot less fin area.
I'm upgrading my HF XL to 29mm motors and 2 stage. The original fins are for the booster with smaller fins for the 2nd-stage. All of my rockets fly with a flight computer. That additional weight forward greatly reduces the required fin size.
 
Friction fit requires walking the narrow line between a motor that will eject itself and a motor that you might damage the rocket trying to get it out.
Something I inadvertently learned from recent cluster ignition tests in which I've friction-fitted motors into the test "stand" (the carcass of a 4x24 which lost its original rear retention to a CATO) is that regular old duct tape crosses that line. One little patch of it is incredibly effective at motor retention, yet also incredibly resistant to motor removal.

I'm actually thinking I might use it on 18mm motors with some carbon tubes I have, but it would be a real rocket destroyer with cardboard.

Edit to add: I've had good luck with far less bulky and aggressive tapes, including the 3M blue painters' tape I always have to hand.
 
I've had good luck with far less bulky and aggressive tapes, including the 3M blue painters' tape I always have to hand.
I used to use standard masking tape but these days almost always use the blue tape because I always have it around. My trick was always to wrap the tape around the motor in somewhat of a spiral so when it overlapped the front part of the overlap was off the front edge of the tape below. That way there was a smooth ledge where the tape go thicker and the body tube couldn't catch the edge of the tape and try to roll it over on itself so the adhesive was on the outside. If I test fit and needed more tape the next dab of tape would be offset a bit in front of the tape below to achieve the same smooth ramp up and over the thicker tape below. I learned that when you were nearing the right fit a little bit of tape added or removed made a big difference. Another thing to remember is to remove the engines as quickly as you can after the launch. Several times I've gotten lazy and put the rockets back in the car and then try to remove the engines a week later and they don't want to come out, even with rockets with motor hooks and no tape. I had to really mangle a D12 this morning to get it out and this was a rocket with a motor hook and no tape was used.
 
I've had mixed results when it comes to when to remove a friction fit engine. Whether I do it right after it lands or later, it's made no noticeable difference for me.
 
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