Warlock Descent Rate?

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ThirstyBarbarian

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I have an LOC Warlock, and I want to get a new parachute that will provide a softer landing. This is my only rocket that seems to get landing damage from “normal” landings — in other words, it’s built stock (not heavy), it’s using the stock chute, the chute always deploys properly, but the rocket still gets some damage to the fins and has required some repairs. Recently I was standing very close to the rocket when it landed, and I saw that it hit hard and bounced, and I ended up having to redo a couple of fin fillets.

What descent rate should I be aiming for?

The stock chute is a flat 58” chute, similar to a Top Flight 58”. According to Top Flight, that 58” chute is the right size for a 9-12 lb rocket, and the 50” is recommended for an 8 lb rocket! That can’t be right for this rocket.

I haven’t flown an alitemter on this rocket, so I don’t have a measured descent rate. But according to several descent rate calculators, it’s probably coming down at about 22 ft/s on the stock 58” flat parachute. Because that chute isn’t working for me, I want a descent rate lower than 22 ft/s.

Spherachutes recommends their 66” chute for an 8 pound rocket, and a maximum of 72” (measured over the top, so the opening is actually about 45”). But I’m considering an 84”. The calculator I’m using predicts the descent rate as 20 ft/s on the 72” and 17 ft/s on the 84”.

And last, a 60” Fruity Chutes elliptical has a predicted descent rate of 15.4 ft/s.

In the past, most of my rockets have been small enough that if I wanted a softer landing, I could just buy the next size chute, and it didn’t cost much to give it a try. But this chute is likely to be expensive, so I want to get it right! I want it big enough for softer landings, but not so big it’s drifting away, and I don’t want to pay extra for a chute bigger than what I need.

Any ideas on the descent rate I should be aiming for?
 
What surfaces are you landing on?

Unless you have volume problems, a larger flat chute would be the most cost-effective, like a Top Flight PAR-70.

Thanks.

The surfaces are generally not bad. One club flies on a ranch with mostly pasture (although there are occasional rocks). The other club flies on a dairy farm that has huge fields of alfalfa, and it is generally a plowed field we land on. Occasionally you might land on a harder surface where the field has gotten muddy and then dried and.

I’m ok with spending a little bit of money as long as I get what I need and don’t have to buy a second chute to accomplish my goal.

The 72” Spherachute is $82.50 and the 84” is $120, so there’s a big jump between the two. I’d hate to pick the wrong one!

The Fruity Chutes elliptical is $143 plus $15 for custom colors, so $158.

The Top Flight 70” would definitely save money at $45.95, and the descent rate would be 18.3 ft/s.

I’ll have to take a look at my budget and decide what else I might want to buy for the upcoming LDRS launch, but first I need to figure out the descent rate to aim for. Any recommendations? I’m thinking it should be between 15 and 17, but not really sure.
 
May as well take it down to 17ft/s. No use just dropping 2 ft/s. You can reef it if you need to. And folks would be more willing to trade your larger for their smaller one if you decide you want to trade for a smaller one..maybe.

You posted as I was writing. Is it 8 lbs? In this particular case, I'd go with the Topflight 70". It's cheaper and does what you need. Unless you want something fancier. For less shroud lines maybe a 6 ft Rocketman for 50 bucks?
 
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I’ll have to take a look at my budget and decide what else I might want to buy for the upcoming LDRS launch, but first I need to figure out the descent rate to aim for. Any recommendations? I’m thinking it should be between 15 and 17, but not really sure.
If you don't know what rate you have now, it's a bit hard to say. You can always guesstimate the descent rate even if you aren't using an altimeter by simming the max altitude and then just timing how long it takes to come down. If the rocket lands on its fins then you probably want no more than 15 fps (I avoid rockets that land on their fins whenever possible.)

I'd take most of the descent rate calculator numbers with a grain of salt. There are a lot of flawed assumptions about what Cd means referenced to what area, etc. In my experience a Spherachute of diameter D they way they measure it is not much more effective than a parasheet of diameter D (but the Spherachute packs smaller, is better made, and looks cool). The Fruity Chutes descent rate numbers are likely more reliable but you pay the price for that.
 
I have an LOC Warlock, and I want to get a new parachute that will provide a softer landing. This is my only rocket that seems to get landing damage from “normal” landings — in other words, it’s built stock (not heavy), it’s using the stock chute, the chute always deploys properly, but the rocket still gets some damage to the fins and has required some repairs. Recently I was standing very close to the rocket when it landed, and I saw that it hit hard and bounced, and I ended up having to redo a couple of fin fillets.

What descent rate should I be aiming for?

The stock chute is a flat 58” chute, similar to a Top Flight 58”. According to Top Flight, that 58” chute is the right size for a 9-12 lb rocket, and the 50” is recommended for an 8 lb rocket! That can’t be right for this rocket.

I haven’t flown an alitemter on this rocket, so I don’t have a measured descent rate. But according to several descent rate calculators, it’s probably coming down at about 22 ft/s on the stock 58” flat parachute. Because that chute isn’t working for me, I want a descent rate lower than 22 ft/s.

Spherachutes recommends their 66” chute for an 8 pound rocket, and a maximum of 72” (measured over the top, so the opening is actually about 45”). But I’m considering an 84”. The calculator I’m using predicts the descent rate as 20 ft/s on the 72” and 17 ft/s on the 84”.

And last, a 60” Fruity Chutes elliptical has a predicted descent rate of 15.4 ft/s.

In the past, most of my rockets have been small enough that if I wanted a softer landing, I could just buy the next size chute, and it didn’t cost much to give it a try. But this chute is likely to be expensive, so I want to get it right! I want it big enough for softer landings, but not so big it’s drifting away, and I don’t want to pay extra for a chute bigger than what I need.

Any ideas on the descent rate I should be aiming for?

Go with the TFR50. That's what I use in my Warlock. I would go with no bigger than the TFR Par58. A Par70 would be in the safe range for a 20# rocket.
 
We just added in our 70" and larger standard Top Flight chutes that you can have the chute made in two colors instead of one for the same price. Our 60" Crossfire parachute would be a good option as well for you and you can order it in whatever colors you want that we have available (we can make them with 6 different colors per chute order).....When I get home from my day job, I'll check our descent rate charts for your Warlock.....is your weight 8lbs.?

Preston

Thanks.

The surfaces are generally not bad. One club flies on a ranch with mostly pasture (although there are occasional rocks). The other club flies on a dairy farm that has huge fields of alfalfa, and it is generally a plowed field we land on. Occasionally you might land on a harder surface where the field has gotten muddy and then dried and.

I’m ok with spending a little bit of money as long as I get what I need and don’t have to buy a second chute to accomplish my goal.

The 72” Spherachute is $82.50 and the 84” is $120, so there’s a big jump between the two. I’d hate to pick the wrong one!

The Fruity Chutes elliptical is $143 plus $15 for custom colors, so $158.

The Top Flight 70” would definitely save money at $45.95, and the descent rate would be 18.3 ft/s.

I’ll have to take a look at my budget and decide what else I might want to buy for the upcoming LDRS launch, but first I need to figure out the descent rate to aim for. Any recommendations? I’m thinking it should be between 15 and 17, but not really sure.
 
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Go with the TFR50. That's what I use in my Warlock. I would go with no bigger than the TFR Par58. A Par70 would be in the safe range for a 20# rocket.

Thanks for the reply. The stock chute is already 58" and the rocket has hit too hard on that.
 
We just added in our 70" and larger standard Top Flight chutes that you can have the chute made in two colors instead of one for the same price. Our 60" Crossfire parachute would be a good option as well for you and you can order it in whatever colors you want that we have available (we can make them with 6 different colors per chute order).....When I get home from my day job, I'll check our descent rate charts for your Warlock.....is your weight 8lbs.?

Preston

Thanks. Yes, the rocket is just under 8 pounds without a motor, and probably slightly over with a spent motor. If you could check your descent rates on a flat chute and a crossfire, that would be cool.

How is the 2-color standard chute laid out with the 2 colors? Are they laid out as panels (gores)? Or is it larger sheets?
 
They're made using two separate pieces of fabric, basically sewn together with 2 different stitch patterns down the middle of the chute. Our fabric comes in widths between 60"-64", dending on the "Run" we get from the mill. All of our 70" and bigger are made this way in the standard chute line.

Crossfire chutes are made using a panel/gore method.

Preston

Thanks. Yes, the rocket is just under 8 pounds without a motor, and probably slightly over with a spent motor. If you could check your descent rates on a flat chute and a crossfire, that would be cool.

How is the 2-color standard chute laid out with the 2 colors? Are they laid out as panels (gores)? Or is it larger sheets?
 
58" standard Top Flight chute at 8lbs. would be 16-17fps. 70" standard Top Flight chute at 8lbs. would be 12-13fps. 60" Top Flight Crossfire chute at 8lbs. would be 16-17fps. In all cases with descent rates, this will depend on what the flier wants for their own/personal descent rate(s). We recommend a descent rate of 17-22fps.

Hope this helps.

Preston

Thanks. Yes, the rocket is just under 8 pounds without a motor, and probably slightly over with a spent motor. If you could check your descent rates on a flat chute and a crossfire, that would be cool.

How is the 2-color standard chute laid out with the 2 colors? Are they laid out as panels (gores)? Or is it larger sheets?
 
58" standard Top Flight chute at 8lbs. would be 16-17fps.
Is this a calculation or an actual measurement?

For example, my Darkstar 3 with a mass of 9.4 lbs descends at about 21.7 fps on a PAR-58.
 
58" standard Top Flight chute at 8lbs. would be 16-17fps. 70" standard Top Flight chute at 8lbs. would be 12-13fps. 60" Top Flight Crossfire chute at 8lbs. would be 16-17fps. In all cases with descent rates, this will depend on what the flier wants for their own/personal descent rate(s). We recommend a descent rate of 17-22fps.

Hope this helps.

Preston

Thanks. The rocket currently has a 58” flat chute that is very much like Top Flight Chutes I’ve bought in the past. In fact, I wondered if LOC got the chute from TFR, it was so similar. I haven’t flown an altimeter on this rocket to actually measure the descent rate, but I feel like the rocket is landing faster than that.

Is this a calculation or an actual measurement?

For example, my Darkstar 3 with a mass of 9.4 lbs descends at about 21.7 fps on a PAR-58.

That’s what I’m wondering too. I’ve plugged the PAR-58 stats into a couple of descent calculators, and they are estimating closer to 21 fps, but those are just sims. Is this figure also a sim, or is it measured?
 
My number, 21.7 fps on a PAR-58 and 9.4 lbs, is an actual measurement from altimeter data.
 
It's a calculation based upon pretty much perfect weather conditions....which can vary at any altitude and change rapidly. The altimeter data is a great tool for descent rates after a flight.

You're also adding almost 1.5 lbs. to the OP's original weight of 8lbs, this would increase your descent rate as it weighs more.

Preston

Is this a calculation or an actual measurement?

For example, my Darkstar 3 with a mass of 9.4 lbs descends at about 21.7 fps on a PAR-58.
 
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It's a calculation based upon pretty much perfect weather conditions....which can vary at any altitude and change rapidly. The altimeter data is a great tool for descent rates after a flight.

You're also adding almost 1.5 lbs. to the OP's original weight of 8lbs, this would increase your descent rate as it weighs more.

Preston

Thanks, Preston.
 
You're also adding almost 1.5 lbs. to the OP's original weight of 8lbs, this would increase your descent rate as it weighs more.
Sure, but it would be interesting to compare the actual descent rate against what your calculation predicts.

The table on the Top Flight website says the PAR-58 recommended weight is 9-12 lbs, presumably for a descent rate of 17-22 fps, but since I'm at almost 22 fps with a weight of only 9.4 lbs, that table doesn't seem quite right.

Not intended as a criticism of Top Flight, I use your chutes almost exclusively and I think they're great and very cost-effective.
 
The TFR descent rate charts have been used by flyers for 28 years. The descent rate testing was done in the Space Shuttle assembly building by one of NASAs engineers. So I have complete faith in the results. I myslef do not agree with some of the descent rate programs.
 
Eric,

I've flown my DoorKnob with the stock 58" chute a handful of times. The Lock-n-Tab construction has held up fine. I have gotten more landing rash at Snow Ranch (from rocks) than at TCC. Personally, I'd either leave it alone or maybe go up one size (TFR 70"). It isn't a rocket that I'd spend a lot of money on the recovery system for. It has tons of room so a large parasheet should suffice. I use more expensive chutes (Fruity Chutes) is when recovery room is at a premium.


Chris
 
The TFR descent rate charts have been used by flyers for 28 years. The descent rate testing was done in the Space Shuttle assembly building by one of NASAs engineers. So I have complete faith in the results. I myslef do not agree with some of the descent rate programs.

I have probably a dozen TFR chutes. They’re well made and affordable, and I’m sure I’ll get more in the future. But I’ve found that in general, I have to scale the chutes up from the recommended size in the sizing charts. So for example, I might buy an 18” for a rocket, based on the charts, but I find the rocket lands too hard, so I order a 24”, and it works great. I went from the recommended 30” to a 36” on another rocket. I haven’t been flying altimeters on these rockets to verify descent rates, so it could be the charts are accurate, but the recommended descent rate of 17-22 fps has been too fast for my given field conditions.

Anywhooooo... that takes me back to my original question, which was what descent rate should I be aiming for with this particular rocket, not what chute should I buy based on various vendors’ sizing charts.
 
Anywhooooo... that takes me back to my original question, which was what descent rate should I be aiming for with this particular rocket...
Slower than what you have now and are not happy with? I'm not sure how to answer the question. I'd just go up a size and see if you like that better.

A lot of the time damage is more about exactly how and what the rocket happens to hit, not so much about the descent rate.
 
Eric,

I've flown my DoorKnob with the stock 58" chute a handful of times. The Lock-n-Tab construction has held up fine. I have gotten more landing rash at Snow Ranch (from rocks) than at TCC. Personally, I'd either leave it alone or maybe go up one size (TFR 70"). It isn't a rocket that I'd spend a lot of money on the recovery system for. It has tons of room so a large parasheet should suffice. I use more expensive chutes (Fruity Chutes) is when recovery room is at a premium.


Chris

No doubt that would solve it in a pretty common sense way, Chris. That’s what I’ve always done with TFR chutes — go up one size from what I had if what I had was landing too hard.

(But I might still splurge on a sphereachute if I decide I want something that looks more snazzy!)
 
Honestly Gary, I think it was the perfect way to test them. I’m pointing out that at least out here we rarely have wind free days. As I understand it wind can increase the descent rate. That will vary with different parachute designs too.

Another thing to remember is that the ground tents to be pretty dry and hard out here.


You are so right ideal conditions. But how else would you get a test done? The outside weather is different all the time. Plus just flying knowledge helps a lot. The decent rates are all just a guide conditions are always different.
 
Slower than what you have now and are not happy with? I'm not sure how to answer the question. I'd just go up a size and see if you like that better.

A lot of the time damage is more about exactly how and what the rocket happens to hit, not so much about the descent rate.

I think the Warlock is a kind of unique rocket in that it is a large size, but relatively light. Part of what makes it light is the relatively thin fin material and the fact that the fins do not go through to the MMT. That light material also makes it subject to fin damage at the fin tips, which I have experienced, and the Loc-n-tab design makes it vulnerable to flexing at the fin roots, which can damage the fillets without actually dislodging the fins.

What I was hoping for was an answer like, “Given the materials and design of the Warlock, the descent rate should not exceed XX fps.” Or, “I have a Warlock, and it hits the ground at xx fps with no damage to fins or fillets.”

Obviously, the descent rate should be slower than before, and I could accomplish that by picking a chute of the same design but bigger, but I’m considering chutes of different design as well, so “go bigger” doesn’t really apply in this case, and a descent rate number would be more helpful.

That said, I think I have worked backwards from what I think my current descent rate probably is, reduced it a bit and picked a design and a size that I think will work and will also look pretty cool.

Thank you for your help, and thank you to everyone who took the time to reply! I’ve got what
I need. Thanks!
 
Here’s an update. I bought an 84” Spherachute. It’s a great looking Chute, and I knew it might be oversized, but I could reef it if necessary, or use a chute release.

I took the Warlock and the new Spherachute and the old standard 58” flat chute to LDRS. I did my L2 cert attempt with the Warlock while I was there. Unfortunately, it was a bit windy and there was a nearby wheat field where people were losing rockets, so I wanted to bring the rocket down nearby. That meant either using the new chute and reefing it, which I didn’t want to do, because I had never used the chute before, and wasn’t sure how much to reef it. Or using the new chute with a chute release, which it didn’t want to do in case of chute release failure. Or using the stock chute, which is what I decided to do.

The rocket did what it has it has always done on that chute. Descended too quickly and swung back and forth and around in a spiraling circle the whole way down. It hit the ground swinging quickly, and tore one of the Loc-n-tab fins right out through the cardboard! Cert fail!

I took the rocket back back to my table and did emergency field surgery on the rocket with some 30-minute epoxy, and put some fat epoxy fillets on that fin.

The next day was the I motor Monkey Loft. Sims showed my rocket going only 1,000 feet or so, so I wasn’t worried about drift, and I used the new 84” Spherachute. That chute is really beautiful! The hemispherical chute is also much more stable than the flat chutes, and the rocket hung still below the chute with no swinging. But it’s also definitely oversized. At times, it seemed like the rocket just hung there in the air, not descending at all. I should have got a 72”.

The next day, I used the 84” chute on my Comet rocket’s maiden flight. This rocket is 8oz lighter than the Warlock, so it’s pretty close. I decided to reef the lines a bit by tying then off by maybe 15” above the swivel. The chute seemed to take forever to unfurl after the ejection charge, and I did have a minor heart attack. But it opened eventually, and brought the rocket down very gently. This rocket has long, pointy fins that extend below the rocket, so a gentle landing is important. Worked great! But I think this rocket would do better with a 72” hemispherical.

Later that day, I did another monkey loft using the 84”. The chute did well, but I still got a small crack in one of the wood glue fillets. It was mostly just a paint crack, but I wanted to do another L2 attempt the next day, so I dug out the fillet, and made another fat epoxy fillet. I’m probably going to do that with all the wood glue fillets.

The next day was my second L2 attempt. It was very gusty, and I didn’t want to drift into the wheat on an ultra-slow descent from apogee. But I also didn’t want to land hard on the stock chute. And I didn’t want to reef the lines on the Spherachute, in case that’s what caused the delay in the chute unfurling on the flight of the Comet. So I tried the final option — 84” Spherachute, with Chute Release at 700’. Success! The chute release opened, the big, beautiful Spherachute opened, and the Warlock settled gently to the plowed field several hundred yards short of the wheat.

So, lessons learned. The stock Warlock chute tends to oscillate and gyrate and descend too,quickly. An 84” Spherachute is much more stable, but descends a bit too slow, and probably a 72” would be better. The Chute Release mitigates the 84” chute’s drift. The Warlock Loc-n-tab design allows a lot of flex, and a hard landing can apply a lot of torque with no lever arm on the inside to resist it, so epoxy fillets are probably a good idea.
 
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