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I bought the 54 mm kit but am unsure if I should also get a 38 mm retainer. Would it be better to do this?
 
1Matthew said:
I bought the 54 mm kit but am unsure if I should also get a 38 mm retainer. Would it be better to do this?
Click to expand...
I would have thought you would want a 54mm retainer if you have the 54mm kit?

I would also be making or buying an adapter, 54mm downto 38mm, to give more flying options. That gives you choice of two motor sizes to fly.
 
Run a bunch of simulations on Open Rocket to see how well the rocket will perform with some of the 38mm motors that you might like to fly...38's are cheaper than 54's....and a lot of them will get you a good flight for your Lvl 1 flight - no need to go thousands of feet at mach chicken and have a failure when a low and slow flight can win the prize...
 
1Matthew said:
I bought the 54 mm kit but am unsure if I should also get a 38 mm retainer. Would it be better to do this?
Click to expand...
The word you’re thinking of is “adapter”, I think. The adapter allows you to use a narrower motor, the retainer prevents your motor from ejecting itself out the rear of the rocket.

There is some overlap in 38mm and 54mm impulse ranges. 38mm runs mostly G through J, 54mm runs mostly I through L. “Mostly” because Loki manufactures two 38mm K loads and a single 54mm M load.

If I were to make a recommendation on motor selection, I’d say your best bet is an H motor (available in 29mm and 38mm diameters) with strong but not excessive thrust. You don’t want to send the rocket too high or overstress it. There’s no need for the flight to be super impressive or break performance records, it just needs to be nominal, safe, and recovered without damage.
 
smstachwick said:
If I were to make a recommendation on motor selection, I’d say your best bet is an H motor (available in 29mm and 38mm diameters) with strong but not excessive thrust.
Click to expand...
Just fly what you want in the certification rocket. It is your cert and you can choose any motor in the H-I impulse range. If your rocket, as you have built it, should be capable and the flying field is appropriate then just choose a motor.

Many people recommend just using a small impulse H for L1. Personally I have certified on I, K and N. I chose to go one level above the minimum. Either way is right and within the rules. As the flyer you have the choice and need to evaluate the possible outcomes. Listen to other people but make your own decisions :) .
 
smstachwick said:
The word you’re thinking of is “adapter”, I think. The adapter allows you to use a narrower motor, the retainer prevents your motor from ejecting itself out the rear of the rocket.

There is some overlap in 38mm and 54mm impulse ranges. 38mm runs mostly G through J, 54mm runs mostly I through L. “Mostly” because Loki manufactures two 38mm K loads and a single 54mm M load.

If I were to make a recommendation on motor selection, I’d say your best bet is an H motor (available in 29mm and 38mm diameters) with strong but not excessive thrust. You don’t want to send the rocket too high or overstress it. There’s no need for the flight to be super impressive or break performance records, it just needs to be nominal, safe, and recovered without damage.
Click to expand...
I think SMS is correct. You are probably looking for a motor adapter. The retainer simply holds the stock size of motor in the tube while an adapter can hold a smaller motor in the stock sized tube. You can make your own adapter or purchase one from Aeropack or Giant Leap Rocketry. Look for a 54mm to 38 mm adapter.
 
OverTheTop said:
I would have thought you would want a 54mm retainer if you have the 54mm kit?

I would also be making or buying an adapter, 54mm downto 38mm, to give more flying options. That gives you choice of two motor sizes to fly.
Click to expand...
I meant adapter Woops!
 
Well, my rocket is finally done and ready to fly. I put it off for a long time and going out to fly it on Saturday. Ended up doing an Excel Kit and I really think it turned out great. Got a 54 mm kit, with a 38 mm adapter and planning to put an H100 in it. I think the paint turned out amazing and really excited to fly it. Here she is in my shop class, flying it with the rest of my class who are bringer there Level 1s. Only about 5 people so it should be nice.
 

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1Matthew said:
Well, my rocket is finally done and ready to fly. I put it off for a long time and going out to fly it on Saturday. Ended up doing an Excel Kit and I really think it turned out great. Got a 54 mm kit, with a 38 mm adapter and planning to put an H100 in it. I think the paint turned out amazing and really excited to fly it. Here she is in my shop class, flying it with the rest of my class who are bringer there Level 1s. Only about 5 people so it should be nice.
Click to expand...
The Excel is also a classic. Excellent (pun intended) choice.
 
1Matthew said:
Well, my rocket is finally done and ready to fly. I put it off for a long time and going out to fly it on Saturday. Ended up doing an Excel Kit and I really think it turned out great. Got a 54 mm kit, with a 38 mm adapter and planning to put an H100 in it. I think the paint turned out amazing and really excited to fly it. Here she is in my shop class, flying it with the rest of my class who are bringer there Level 1s. Only about 5 people so it should be nice.
Click to expand...
She's a beauty, @1Matthew !

What's her name ?

Where are you going to fly her ?

Good Luck !

-- kjh

p.s. Your picture reminded me that I may have a 25-year old 4-inch Excel up in the attic !

Thanks for that !

Now I've got to look !!
 
Going out to Lucerne Dry Lake Bed. Waking up at 4:30, driving to school. Going to be a long day but super excited!!!! Don’t have a name for her yet. I’m planning to fly on an H100, low and slow. After this I’m hoping to build something bigger with a group of my classmates and would like to build something for some altitude within the level 1 range but that’s getting ahead of myself.
 
1Matthew said:
Going out to Lucerne Dry Lake Bed. Waking up at 4:30, driving to school. Going to be a long day but super excited!!!! Don’t have a name for her yet. I’m planning to fly on an H100, low and slow. After this I’m hoping to build something bigger with a group of my classmates and would like to build something for some altitude within the level 1 range but that’s getting ahead of myself.
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That's great !

Lucerne is one of my favorite sites and the people at ROC are a great group.

Good luck again !

-- kjh
 
I've simmed the Excel with the H100 and Im getting around 1490 ft with a speed off the rail at 34.7 ft/s. Weighed my rocket today in the shop with the motor at 4.06 pounds, a bit heavy. Without the motor Open Rocket says it 3.43 lbs. My concern right now is parachute sizing, I think there is a 36" chute in my rocket, which should be large enough but with that Im getting a ground hit velocity at 23.6 ft/sec which seems fast. Do I need a bigger chute?
 
1Matthew said:
I've simmed the Excel with the H100 and Im getting around 1490 ft with a speed off the rail at 34.7 ft/s. Weighed my rocket today in the shop with the motor at 4.06 pounds, a bit heavy. Without the motor Open Rocket says it 3.43 lbs. My concern right now is parachute sizing, I think there is a 36" chute in my rocket, which should be large enough but with that Im getting a ground hit velocity at 23.6 ft/sec which seems fast. Do I need a bigger chute?
Click to expand...
Check the rail length in your sim, but 35fps is too slow, and if your sim is .6 lbs underweight then your real speed will be even slower.

Your descent speed is at the high end of where you want to be. Whether that's acceptable depends on how soft your recovery area is. It's also likely to be higher because of your incorrect sim weight as well.
 
1701926675584.png

This was my sim, I have a piston ejection I added on the kit, I can't seem to get the velocity higher, I know some of my parts weights are off, I tried to find some of the info online and a lot of the stuff I just did not weigh. my ground hit speed is also high. This is on a 36 inch chute. My dry weigh is still slightly off. Not sure what to do. I followed the Excel's instructions, so it should fly fine, but sim says otherwise?
 
1Matthew said:
View attachment 618622

This was my sim, I have a piston ejection I added on the kit, I can't seem to get the velocity higher, I know some of my parts weights are off, I tried to find some of the info online and a lot of the stuff I just did not weigh. my ground hit speed is also high. This is on a 36 inch chute. My dry weigh is still slightly off. Not sure what to do. I followed the Excel's instructions, so it should fly fine, but sim says otherwise?
Click to expand...
Time to pick out a different motor? I know my shop teacher just bought a bunch of H100s but they seem too slow. Ive talked with my peers who are also flying with me and they are getting slow off rod velocity as well.
 
I feel bad raining on your parade at the last minute, @1Matthew

The end of the semester is approaching and the ROC launch is Saturday.

Is there a deadline for your flight ?

I don't recall ever seeing an H100W back in the days when I was flying a lot in SoCal but the thrust profile of the H100W looks very similar to a G74W -- slightly progressive where peak thrust is about half-way thru the burn.

This is a GREAT profile for a light rocket but not so great when a heavier rocket leaves the rail at a low speed and is then subject to weathercocking and gravity turning -- and all this is happening while the motor is still coming up to full thrust !

The H550ST will definitely work but there is also a Blue Thunder DMS H219T motor with the same total impulse ( and price ) as the H100W.

The H219T is a typical Blue Thunder motor with a slightly regressive thrust curve ( full thrust at ignition and then it tails off toward burn-out ).

How does the H219T Sim ?

HTH.

-- kjh

EDIT: p.s. I used to land at 25 ft/sec on Lucerne Dry Lake bed -- it depended on how windy it was that day.

OTOH, if I was going for a certification, I might try to land a just little softer than I normally would ...

Windy says the Saturday should be a nice calm day and you're young: Windy: Lucerne Dry Lake Bed - 34.51735349402785, -116.96703787455668 :)
 
Last edited:
1Matthew said:
View attachment 618622

This was my sim, I have a piston ejection I added on the kit, I can't seem to get the velocity higher, I know some of my parts weights are off, I tried to find some of the info online and a lot of the stuff I just did not weigh. my ground hit speed is also high. This is on a 36 inch chute. My dry weigh is still slightly off. Not sure what to do. I followed the Excel's instructions, so it should fly fine, but sim says otherwise?
Click to expand...

Now that you've finished the build, override the dry weight and CG with your actual measurements (at the stage level in the parts tree). This will give you the most accurate sim.

You also need to correctly set the rail length (edit simulation button). If the club has 8' rails, you generally get 6' of guidance or so between the blast plate/standoff/etc. plus your rail button placement.

Another consideration for your descent rate: how thick are your fins? I wouldn't want to come down that fast, that heavy, with 1/8" fins, but 1/4" would be better off.
 
Last edited:
kjhambrick said:
I feel bad raining on your parade at the last minute, @1Matthew

The end of the semester is approaching and the ROC launch is Saturday.

Is there a deadline for your flight ?

I don't recall ever seeing an H100W back in the days when I was flying a lot in SoCal but the thrust profile of the H100W looks very similar to a G74W -- slightly progressive where peak thrust is about half-way thru the burn.

This is a GREAT profile for a light rocket but not so great when a heavier rocket leaves the rail at a low speed and is then subject to weathercocking and gravity turning -- and all this is happening while the motor is still coming up to full thrust !

The H550ST will definitely work but there is also a Blue Thunder DMS H219T motor with the same total impulse ( and price ) as the H100W.

The H219T is a typical Blue Thunder motor with a slightly regressive thrust curve ( full thrust at ignition and then it tails off toward burn-out ).

How does the H219T Sim ?

HTH.

-- kjh

EDIT: p.s. I used to land at 25 ft/sec on Lucerne Dry Lake bed -- it depended on how windy it was that day.

OTOH, if I was going for a certification, I might try to land a just little softer than I normally would ...

Windy says the Saturday should be a nice calm day and you're young: Windy: Lucerne Dry Lake Bed - 34.51735349402785, -116.96703787455668 :)
Click to expand...

If I was a little concerned about an H-100 (ish), I'm including H135's, H115's....., I would Recommend what you suggested, but will throw an H-283 (38mm) into the mix. It has slightly less total impulse than the 219, but a very similar motor. The 283 also has less impulse than an H-100 from recollection, but has more than double the thrust at the go.
 
Last edited:
Donnager said:
If I was a little concerned about an H-100 (ish), I'm including H135's, H115's....., I would Recommend what you suggested, but will throw an H-283 (38mm) into the mix. It has slightly less total impulse than the 219, but a very similar motor. The 283 also has less impulse than an H-100 from recollection, but has more than double the thrust at the go.
Click to expand...
Thrust off the pad is more important to a successful flight than impulse. Does ROC have an on-site vendor that you can buy a motor and/or chute from?
 
I really hope so, otherwise I'm not sure what we will do. What would happen if I flew the H100? Would the rocket leave the rail and get angled by the wind?
 

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