Wimpy Q Jet Ejection Charge

[rcktnut]

I tried my first first Q Jet motor out yesterday, C12, ejection charge popped nose cone, chute, dog barf, shock cord all left inside body tube. I used a Quest Thunder Bird, Hawk what ever its called (OOP), 1.36 dia 18 inch tube. Had a 12 inch chute, 2-2/12 in. dog barf, loose nose cone. Everything was packed loosely. I know the first Q Jets had too much of an ejection charge, just wondering if any one else has experienced the opposite like I did. I just wanted to see what the motors are like and only brought the one LPR rocket. Could not try the second motor in the pack due to crunched BT. Like the motor otherwise.

 

[AeroTech]

What delay time did you use?

 

[rcktnut]

What delay time did you use?

Thanks for the reply, it was a 6 second delay. Estes C6-5's always worked good in this rocket. I figure maybe just happened to be a motor a little light on the ejection charge. Wish I could have tried another flight, but only brought this LPR rocket just to see the characteristics of the motors. Like very much, want to use these for flights with the grandsons in the High School field I live adjacent to, just don't want to have this type of recovery!! I will try again with some other LPR rockets, and report results in this thread.

BTW: the red ejection charge cap was tipped up on one side still in the well, looked like it did not move up the well at all, just one side opened up.

 

[KennB]

BTW: the red ejection charge cap was tipped up on one side still in the well, looked like it did not move up the well at all, just one side opened up.

It's unlikely, but did anything interfere with the red cap? Did the motor hook happen to trap it?

 

[BEC]

It's unlikely, but did anything interfere with the red cap? Did the motor hook happen to trap it?

The motor hook can't trap the red cap (well, at least not a normal 2.75 inch motor hook anyway) as the hexagonal shaped portion of the motor that contains the ejection charge (and that red cap) project past the hook when the motor is installed.

I have had some Q-Jet flights where the nose cone/chute got out but the wadding didn't on Big Bertha-sized models. I don't use dog barf much so can't say if that matters (but in thinking about it, perhaps the gases would go through dog barf rather than having the wadding acting more like a piston pushing out the 'chute, so it may matter). I have had one where there was no ejection charge (red cap retained) out of the ~100 of them I've flown since they were introduced.

The only other lawn-dart I've had with a Q-jet was when the motor mount blew out instead of the 'chute/nose cone....

 

[KennB]

The motor hook can't trap the red cap (well, at least not a normal 2.75 inch motor hook anyway) as the hexagonal shaped portion of the motor that contains the ejection charge (and that red cap) project past the hook when the motor is installed.

I have had some Q-Jet flights where the nose cone/chute got out but the wadding didn't on Big Bertha-sized models. I don't use dog barf much so can't say if that matters (but in thinking about it, perhaps the gases would go through dog barf rather than having the wadding acting more like a piston pushing out the 'chute, so it may matter).

That's why I said it was unlikely; it the cap got caught on the hook, the aft end of the motor wouldn't catch the other end of the standard hook. Just eliminating the outlandish. With some hooks you have to rotate the Q-Jet to line up a flat of the hex to get past it.

On larger diameter body tubes I like to wrap a bunch of dog barf in a piece of wadding open end up and then pile in more dog barf. This prevents the blow-by you can get with just loosely packed dog barf.

 

[BEC]

I figured if the OP got the motor all the way in, hanging up the red cap couldn't happen. I have several models in which it takes a little fussing and finesse to get that hex by the upper end of the motor hook.

When I use dog barf I tend to do the same thing. Some wadding first forming a sort of cap or cup, then cellulose.

 

[jrap330]

Since I never had a Q-JET and it would be hard to see down the airframe w/ motor installed....is their an issue the red cap and an Estes/Quest motor hook? Has Aerotech design the engine so hook is in no way capable of locking on to cap?

 

[BEC]

Since I never had a Q-JET and it would be hard to see down the airframe w/ motor installed....is their an issue the red cap and an Estes/Quest motor hook? Has Aerotech design the engine so hook is in no way capable of locking on to cap?

Maybe this will help those who haven't seen one. This is a (spent) C12-6 in a clear-bodied Alpha (body PST-50, motor tube PST-20) I built for educational purposes. As you can see the ejection charge well projects past the upper end of the motor hook. If the red cap were still present in this motor, it would be visible inside the hole in the top of the ejection charge well in the second image.

You can also tell, if you look closely, that in this particular case the upper end of the motor hook had to be pushed back a bit by the ejection charge well to get it in. This is what KennB was talking about in his post just above when he said "With some hooks you have to rotate the Q-Jet to line up a flat of the hex to get past it."

Added: third image of another C12-6 with the red cap barely visible. Looks like the camera focused on the fins....

 

[jrap330]

Maybe this will help those who haven't seen one. This is a (spent) C12-6 in a clear-bodied Alpha (body PST-50, motor tube PST-20) I built for educational purposes. As you can see the ejection charge well projects past the upper end of the motor hook. If the red cap were still present in this motor, it would be visible inside the hole in the top of the ejection charge well in the second image.

You can also tell, if you look closely, that in this particular case the upper end of the motor hook had to be pushed back a bit by the ejection charge well to get it in. This is what KennB was talking about in his post just above when he said "With some hooks you have to rotate the Q-Jet to line up a flat of the hex to get past it."

View attachment 426880View attachment 426881

Thanks, in this case , The educator clear body, clearly help educate the members.

 

[AeroTech]

The -6 and -8 second delays have a smaller ejection charge to avoid damaging body tubes in the smaller rockets they are usually used in. The -4 second delays have a larger ejection charge because they are normally used in larger, heavier rockets.

On your next flight try using the wadding supplied in the motor pack instead of the dog barf. I have had good results with it personally.

 

[neil_w]

The -6 and -8 second delays have a smaller ejection charge to avoid damaging body tubes in the smaller rockets they are usually used in. The -4 second delays have a larger ejection charge because they are normally used in larger, heavier rockets.

Well that is interesting info, good to know. This applies to the Cs and Ds? Is there a particular interior volume range that the different versions are designed for?

 

[AeroTech]

Yes, it applies to the Black Max Cs and Ds and also the new upcoming WL versions.

No particular volume range, just relied on a lot of customer feedback and field experience.

Well that is interesting info, good to know. This applies to the Cs and Ds? Is there a particular interior volume range that the different versions are designed for?

 

[Joshua F Thomas]

Maybe this will help those who haven't seen one. This is a (spent) C12-6 in a clear-bodied Alpha (body PST-50, motor tube PST-20) I built for educational purposes.

BEC, this is really neat. I’m a science teacher-in-training, specifically physics. This model would be helpful in classes and rocket clubs. Do you have instructions / parts for how to build one?

 

[BEC]

BEC, this is really neat. I’m a science teacher-in-training, specifically physics. This model would be helpful in classes and rocket clubs. Do you have instructions / parts for how to build one?

It's simply a bulk Alpha kit with the body tube replaced by 7.75 inches of PST-50 and the motor tube replaced with 2.75 inches of PST-20. Glue used for all joints was Pacer Formula 560. I got my clear tubing from Semroc. It appears eRockets (which now owns Semroc) does not have any of these sizes right now, but ASP Rocketry has both in 24 inch lengths at the bottom of this page: https://www.asp-rocketry.com/ecommerce/Model-Rocket-Body-Tubes.cfm?cat_id=13

That said, there is of course the recently re-released Estes Phantom: https://estesrockets.com/product/001207-phantom/ I actually intended to take those pictures this morning with mine, but since I've stuck the lovely cutaway motor that comes in the Phantom kit in mine with some double-sticky tape, I didn't want to pry it out so I could put a Q-Jet into it for the pictures...so I grabbed the clear Alpha I'd built before.

 

[Joshua F Thomas]

Thanks!

 

[Bill S]

We stopped trying to "decontaminate" our groceries, but we're still washing our hands a lot and using hand sanitizer before we touch anything in the car.

The -6 and -8 second delays have a smaller ejection charge to avoid damaging body tubes in the smaller rockets they are usually used in. The -4 second delays have a larger ejection charge because they are normally used in larger, heavier rockets.

On your next flight try using the wadding supplied in the motor pack instead of the dog barf. I have had good results with it personally.

I have some of the reddish wadding Quest gives you with the motors. But the wadding sheets are bigger than the usual Estes type - how many do we need to use, or is it a case of trial and error?

 

[Zeus-cat]

BEC, this is really neat. I’m a science teacher-in-training, specifically physics. This model would be helpful in classes and rocket clubs. Do you have instructions / parts for how to build one?

Just to be clear, you can't fly these clear rockets. The ejection charge would cloud the clear plastic.

 

[AeroTech]

Usually 2 or 3 sheets are sufficient. Others here might have additional advice.

I have some of the reddish wadding Quest gives you with the motors. But the wadding sheets are bigger than the usual Estes type - how many do we need to use, or is it a case of trial and error?

 

[rcktnut]

I will use wadding next time. I've been using dog barf with no problems with the E brand motors. I use it because I have almost a full bail yet and it is much cheaper than the paper wadding. Evidently there is not much of a problem with this happening very often. Like I said first time I used a Q-Jet, and wanted to see if this was a common problem.

 

[rcktnut]

The motor hook can't trap the red cap (well, at least not a normal 2.75 inch motor hook anyway) as the hexagonal shaped portion of the motor that contains the ejection charge (and that red cap) project past the hook when the motor is installed.

I have had some Q-Jet flights where the nose cone/chute got out but the wadding didn't on Big Bertha-sized models. I don't use dog barf much so can't say if that matters (but in thinking about it, perhaps the gases would go through dog barf rather than having the wadding acting more like a piston pushing out the 'chute, so it may matter). I have had one where there was no ejection charge (red cap retained) out of the ~100 of them I've flown since they were introduced.

The only other lawn-dart I've had with a Q-jet was when the motor mount blew out instead of the 'chute/nose cone....

The Big Bertha and bigger LPR are the size models I like to put a C or 18mm. D in. Most my LPR are that size, and that is why I bought the C&D Q-Jets. Sounds like the C's & D's could use a little more umph as far as the ejection charge goes. I don't believe in putting these motors (C D) in something that is real small and turns into a one shot deal. That is what A's & B's are for.
I'll see how the wadding works.

 

[BEC]

Just to be clear, you can't fly these clear rockets. The ejection charge would cloud the clear plastic.

When kids ask me if they can fly, I tell them "yes, but after the flight they won't be clear anymore." There was someone last week on YORF who actually flew a Phantom and took some steps to keep it from being completely ruined by this with reasonable results.https://www.oldrocketforum.com/showthread.php?t=18719

On how much Quest wadding to use....since the object is to get ~2 diameters of the tube filled in a 1.3 inch model I'd probably use three sheets. Or - fold one in quarters and try to put it into the tube so that it forms a sort of "cup" and then put the dog barf in above that about as much as you would have used anyway. Same approach to BT-60/1.6 inch models like a Big Bertha. I actually normally put a baffle (most often the Semroc cup style—https://www.erockets.biz/semroc-ejection-baffle-kit-conical-fiber-bt-60-sem-eb-60/— in models that size and usually only use the one folded "cup" sheet of wadding above the baffle if I use any at all.

 

[5x7]

In a 1.3” tube, you can use two wadding squares together, turned 45 degrees so it looks like an eight pointed star, cup it, and put the dog barf inside, saves wadding and having the square under the wadding should act like a piston and push it all out. Other than the flight you posted here, have you had dog barf left in the tube after a deployment before?

 

[rcktnut]

In a 1.3” tube, you can use two wadding squares together, turned 45 degrees so it looks like an eight pointed star, cup it, and put the dog barf inside, saves wadding and having the square under the wadding should act like a piston and push it all out. Other than the flight you posted here, have you had dog barf left in the tube after a deployment before?

Yes there has been dog barf left in the BT, but the chute deployed. The gas produced by the charge should be enough to deploy the chute regardless of what chute protection you use, as long as nothing is jammed packed into the tube.

 

[5x7]

In my opinion, the hot gas is bypassing the dog barf left in the tube so you don’t get all the protection you want anyway without a square or two of wadding underneath.

 

[neil_w]

I'd had that happen before (barf stays in tube, everything else ejects) with no ill effects on the parachute or shock cord.

 

[dpower]

In my opinion, the hot gas is bypassing the dog barf left in the tube so you don’t get all the protection you want anyway without a square or two of wadding underneath.

Agreed - this is the problem with dog barf, and why I stopped using it. With just dog barf, and a loose chute, the expanding gas can get around those, reducing the effectiveness. Wadding makes for a better seal allowing the expanding gas to push the bundle up and out.

 

[rcktnut]

Follow up here, launched the same rocket ( post #1) today using the wadding instead of dog barf on Q-Jets, deployment was fine on both flights.

 

[rharshberger]

Usually 2 or 3 sheets are sufficient. Others here might have additional advice.

I tend to use a single sheet of wadding (its relatively expensive per sheet) and use it as a cup for dog barf, only about one tube diameter amount of dog barf, zero issues in many launches with chutes getting scorched or difficulties ejecting.

 

[BEC]

I tend to use a single sheet of wadding (its relatively expensive per sheet) ...

The way to economize on wadding is to pick it up off the ground at club launches. Many people use way too much and often much of it is perfectly fine to reuse. I often go home with more wadding that I arrived with that way.