4 inch Canadian Arrow

[DynaSoar]

I bought a partially built scratch 4" V2, and have been working on fixing it up. In the process, I stretched it and turned it into a Canadian Arrow. Here it is finally competely put together except for a couple details, and of course finishing.

Pre-built: fin can/boat tail with 38mm motor tube; 5/16" nylon strap shock cord anchor attached between motor tube and top centering ring; nose cone.

Added: 11" of quantum tube with 8" long coupler; attached end of anchor through hole in top centering ring making a loop; 8 foot 5/16" nylon tube shock cord (tied with bowline to anchor loop, able to slide on anchor for more vertical landing) with 1.5 foot of kevlar wrapped 1/8" elastic bungee shock absorber; 36" military flare chute with 8 + 1 center shrouds; threaded quick-connect links on recovery system components; 38mm Slimline retainer with 38/29mm Slimline adapter; double layer 6" square fiberglass mat chute protector.

Still to determine: where to glue in the 38mm thrust ring to fit the most likely 38mm motors (choice limited by 10" long motor tube) and then finish the 29mm adapter to fit this; if there's more than a couple inches of motor tube forward of the choice of thrust ring placement, possibly add a copper/steel mesh ejection baffle; choice of 1/4" round launch lug or Acme rail lugs (have both, can't decide, bird is 2.5 pounds fully loaded except motor but only 40" long) or maybe buttons. Heck, simple wood screws should make adequate buttons.

 

[hokkyokusei]

Why use a thrust ring at all? It just limits the choice of motor. I quite often fly motors that are longer than my motor mount.

 

[DynaSoar]

Originally posted by hokkyokusei
Why use a thrust ring at all? It just limits the choice of motor. I quite often fly motors that are longer than my motor mount.

The number of people who have never had a taped motor slide out of place either way are outvoted in my mind by us few who have. I'll always use positive retention in both directions. I don't need to be able to fly every motor as long as I can fly enough.

 

[powderburner]

I think I understand your desire (paranoia?) to retain the motor casing. Another thought: go ahead and put the thrust ring into the most forward position possible, and follow it with an *unglued* length of MMT tube (slotted down the side to remove circumf, rolled to smaller diam to slip into main MMT) to space most of your motors back to the correct position. You still have the choice of pulling out the spacer later for longer motors.

 

[hokkyokusei]

Originally posted by DynaSoar
The number of people who have never had a taped motor slide out of place either way are outvoted in my mind by us few who have. I'll always use positive retention in both directions. I don't need to be able to fly every motor as long as I can fly enough.

You've seen a motor with a tape thrust ring fly through the motor mount? Wow, I didn't think I knew anyone that had seen that. Do you know what sort of tape was used, and how was it applied?

I've seen lots of motors "retained" with tape come out the back end though.

 

[lalligood]

Originally posted by hokkyokusei
You've seen a motor with a tape thrust ring fly through the motor mount? Wow, I didn't think I knew anyone that had seen that. Do you know what sort of tape was used, and how was it applied?

I've seen lots of motors "retained" with tape come out the back end though.

In either case above, post-flight analysis couldn't be any easier: you didn't use enough tape.

Have I had a casing kicked out because of too little tape? Yup. Once. And it won't happen again. But I'll continue to use masking tape. Masking tape is cheap. Use enough of it & it will keep a motor securely inside a motor tube everytime. I have also used masking tape as a thrust ring on single use motors with a 100% success rate to retain them in my Phobos which has an Aero Pack retainer (which is completely comparable to the Slimline).

Permanent thrust rings inside the MMT tube would be entirely too limiting for me. I've also seen other folks have problems with PML's Quik-Switch system limit their motor choices because of the threaded ring inside the MMT tube.

Here's to keepin' it simple...

 

[hokkyokusei]

Originally posted by lalligood
In either case above, post-flight analysis couldn't be any easier: you didn't use enough tape.

Note that I didn't actually say it had happened to me!

I'm quite happy to use a tape thrust ring. I'm not talking about wrapping tape around the motor to retain it. I usually fit aft motor retention for that. It makes the motor easier to remove when you're done.

 

[Chilly]

Biggest problem I've ever had with tape retention is getting the @$&! empty casing out afterwards. It works too well, IMO.

 

[lalligood]

Originally posted by Chilly
Biggest problem I've ever had with tape retention is getting the @$&! empty casing out afterwards. It works too well, IMO.

THAT is precisely the proper amount of masking tape you should use

 

[DynaSoar]

Originally posted by powderburner
I think I understand your desire (paranoia?) to retain the motor casing. Another thought: go ahead and put the thrust ring into the most forward position possible, and follow it with an *unglued* length of MMT tube (slotted down the side to remove circumf, rolled to smaller diam to slip into main MMT) to space most of your motors back to the correct position. You still have the choice of pulling out the spacer later for longer motors.

Zackly. Except I use coupler tube stock. I buy a full 34" length at a time, and cut it as needed the night before a launch (unless I have one already cut to length from before). I've done this with my ex-Mirage too.

I did extend the MMT in this one with 7" of coupler glued into the motor tube, so I could use steel and copper scrubber pad baffling. It needed to be longer because the 29mm Slimline adapter tube is 12" long, to handle an Ellis H S/U motor (11").

And I went with a 5/16" styrene tube launch lug (1/4" ID) so I could launch it off my Mantis. Now to find a place I can go launch any time. Texas seems to have plenty of space, so it shouldn't be tough.

 

[DynaSoar]

Originally posted by lalligood
In either case above, post-flight analysis couldn't be any easier: you didn't use enough tape.

On the other hand, in trying to use "enough" tape, you can end up having to push it in so hard that it crimps the edge of the motor tube, or the body itself, or you bend the body trying to pull it out. I'm not going to ruin another rocket by trying to be cheap.

Have I had a casing kicked out because of too little tape? Yup. Once. And it won't happen again.

Me either.

Permanent thrust rings inside the MMT tube would be entirely too limiting for me.

It can handle any 38mm motor up to 7" and any 29mm up to 11". There's plenty of G and H motors to choose from. 2000 feet on an H48 is plenty for a scale model. It's not supposed to be a cloud buster.

 

[DynaSoar]

I flew it for my L1 attempt at Herne on an Ellis H50-6. Launch area was on the crossover between the taxiway and runway at the south end of the air strip.

It arced over to horizontal during the first 100 feet and kept going that way. It flew nearly arrow straight right up between taxi and runways. If it had supposed to have been a V2, the launch site could have been Peenemunde and the antenna and windsock midfield London; it would have made a great re-creation.

The grass was 2 feet tall and very thick. It was probably travelling 200 to 300 MPH went it coasted into the grass, and probably tunnelled quite a way under it. I searched for 1.5 hours, but no joy. I quit when the lightning started. An airfield is no place to be hiking in the lightning.

Had I been able to find it, I'd have been able to determine what appeared to those watching: it coasted for a lot longer than 6 seconds after launch. I would have disqualified myself for such a marginal flight, but if the ejection had gone off before it hit I'd should have been able to easily see the 36" white flare chute. I'd at least like to have gone down on the record with an engine malf as well as a probable problem with the CP on the C.A. Rocksim file from their site.

As for most of the rocket, hey, things happen. I can't very well take up the offer to trade the nose for a pointed one because the blunt on is lost, but so's the rocket, so it doesn't matter. But it really eats my lunch to lose $45 worth of Slimline retainer and adapter.

 

[sandman]

Sounds to me like you just didn't have enough thrust in an H50 motor.

Just to low a thrust.

It sounds like it was stable it just could'nt climb and just started to tip over.

Have you gone back to look for it?

I wouldn't give up.

 

[DynaSoar]

Originally posted by sandman
Sounds to me like you just didn't have enough thrust in an H50 motor.

Just to low a thrust.

It sounds like it was stable it just could'nt climb and just started to tip over.

Have you gone back to look for it?

I wouldn't give up.

The H50 has 20+ pounds of kick in the first half second and 15 pounds sustain for another 5 seconds. The bird was less than 3 pounds loaded. It got off well, but acted marginal. I think the Rocksim I found on the Canadian Arrow site wasn't accurate as far as the CP. It simmed out fine in flight profile, but I'd just accepted this calculated CP result. Considering how well it flew horizontally, it must have gone from marginal to stable after arcing. If it hand't been my L1 attempt, I'd have thought "cool!"

I looked for an hour and a half at the time, until lightning forced me to quit. It's 164 miles away so I can't easily get back to look more. If I'd known that flying at an airfield meant contending with thick, high grass, I'd have brought the sonic locator. I looked at it, though my only problem would be hard tarmac landings, and left it.

What I have figured out is that Ellis counts their delay from burn-out, not startup. Having a 6 second ejection on a 5.5 second burn would be a bad idea. Having a 3 second ejection on a 5.5 second burn just doesn't make sense, but they make a G20-3 with a 5.5 second burn. They must use burn-out time. That makes the H50-6 an 11 second flight time, and that makes sense for this failed flight. It was in the grass by 10 seconds. If the charge went off, it was already buried.

Ah well, I've still got another H50 to try again with, but it's a 10 second. My rebuilt Mirage may be too much for it, so I'll get the Rock-A-Chute Mk IV ready like I'd originally planned.

 

[xenon]

All motors count their delay from burnout, composite motor delays do burn from the start of the burn, but it is counted from the end of the burn. I've seen a lot of problems with Ellis motors, especially, that they don't have the initial thrust that they advertise.

 

[lalligood]

EM motors are best suited for use in either extremely light, aerodynamic rockets or high drag models (like any of Art Applewhite's kits). With the high drag models, which is what I have used the EM motors for, I have removed the ejection charges, so delay time(s) didn't matter to me because of aerobrake recovery.

BTW, if you find your rocket days/weeks later with everything intact & it's in flyable condition, you'd still get your cert!

 

[DynaSoar]

Originally posted by lalligood
EM motors are best suited for use in either extremely light, aerodynamic rockets or high drag models (like any of Art Applewhite's kits). With the high drag models, which is what I have used the EM motors for, I have removed the ejection charges, so delay time(s) didn't matter to me because of aerobrake recovery.

BTW, if you find your rocket days/weeks later with everything intact & it's in flyable condition, you'd still get your cert!

No I wouldn't. I withdrew it before they said anything and before I went looking. That flight wasn't acceptable to me, even if it was to them. I might figure out the problem, fix it, and try again with it though. More likely with something else. Engineering can be Just Good Enough, but I'm more about doing well than just doing. I get more out of it that way.

 

[Stymye]

I'm with Dyna on the thrust ring, I like to retain the longest motor I plan to fly. it looks better , it works better(no guessing if I'm using the right amount of tape) and dropping in a spacer is quicker and foolproof.

I like to put a little more effort into a motor mount than just winding tape around everything.

I guess to me it's like seeing a trim carpenter relying on a caulking gun... mabey I'm too anal..I have used tape in the past,I just want to advance beyond on(masking,duct) tape.

I'm not knocking the tapers out there, just my preference

 

[GL-P]

I use tape for small stuff (MPR) but I hate it when I have too much tape but I can't get it out even though it's sticking out half way.

 

[11bravo]

Originally posted by DynaSoar
snip
It arced over to horizontal during the first 100 feet and kept going that way. It flew nearly arrow straight right up between taxi and runways.

One of the "From the ground up Survivor" rockets at this year's AirFest did something like that.
It got maybe 30 feet up, flopped over and flew right down the line of spectators; if it had been planned, it would have been perfect execution.
IIRC, the body was made of that foam wrap you put around pipes to help keep them from freezing, and the nose cone was made of a 0.5 liter water bottle crammed in and held in place with "The Handyman's Secret Weapon".

my best (as if I cared) french accent-
Tre kewl!

Greg

 

[DynaSoar]

Rick from the Texas High Power group explained the strange behavior as "low polar moment". Short stubby rockets have their mass nearer the center of gravity in all directions, not just aft/CP. It takes less pressure to make one turn in an unexpected direction. Figure: you stick your arms out to keep your balance. If you didn't (your mass was closer to your CG) you'd tip over more easily with less push.

Even though it was "stable" it was more sensitive than a longer rocket to unexpected pressures. That's why it tipped in a direction not parallel to the wind, and kept tipping until it had a lot of speed. The H50 was plenty enough to lift it, but not to get it going fast enough for stability to overcome this tendency.

This explains why V2s often act like this, despite being "stable" and built from a supposedly well designed kits.

The fault, Dear Brutus, lies not within our motors, but within our mass distributions.