Q-Jets and engine blocks query

[prfesser]

At our last launch one attendee flew a Big Bertha. No problem on a C6-5, but when he tried a couple of Q-Jets they wouldn't go the whole way in so that the hook could engage. They stuck out about 1/4" or a bit more and had to be friction-fitted.

I was wondering if the cardboard engine block had an i.d. small enough that the projection on the forward end of the QJet wouldn't fit through it the whole way. Is this a problem anyone else has had?

I guess it's possible that there was a glob of glue or something to keep the motor from being inserted the whole way. I didn't look, though.

Best -- Terry

 

[Antares JS]

I have gotten them the whole way in, but they are a tight fit through that block. You also need to rotate them so that the upper end of the hook falls on one of the flats in the hexagonal forward protrusion.

 

[DigBaddy]

No problems yet for me flying 18/24mm QJets or other AT SU motors where there's a hook/block. @Antares JS makes a good point about rotation.

 

[heada]

Not all blocks are created equal. Quest blocks seems to fit no problem. Estes blocks can be tight. The clearances are close enough that sometimes the engine hook will catch the ejection well.

I've started to break off the forward end of the engine hook and sand the ID of the thrust block on new builds to help ensure a good fit.

 

[Scott_650]

I’ve had to peel labels off of QJets occasionally to get them to fit and it can take some fiddling to get the ejection enclosure to fit into some engine blocks.

 

[jmasterj]

I had to file down the forward end of an Estes engine hook so that a Q-Jet end would fit past it.

 

[BEC]

It's not the block, it's the hook....as @Antares JS and @jmasterj says. And even then, you can't get the ejection charge well past the upper end of the hook. It depends on how much that end of the hook projects.

The early production As and Bs were also too large in diameter. They revised the case and all motors made past, I think, May of 2019 have the reduced-diameter cases so label-peeling should not be needed. All Cs and Ds are of the laster case size.

 

[AeroTech]

Like Bernard says, all current production for the last few years have no problem fitting in motor mount tubes. Regarding the motor hooks, rotating the motor slightly as it is inserted will usually allow the forward bulkhead projection to clear the hook.

 

[MidOH]

Ya'll still run motor hooks and blocks?

Only the rockets that I mean to launch with only Estes 18mm's get a block. Getting rid of the heavy metal hook is the easiest way to move CG forward, for no real negative trade off.

 

[lakeroadster]

Ya'll still run motor hooks and blocks?

Only the rockets that I mean to launch with only Estes 18mm's get a block. Getting rid of the heavy metal hook is the easiest way to move CG forward, for no real negative trade off.

Opinions vary.

Unless you're flying competition for maximum apogee, the "belt and suspenders" approach is a proven winner.

Run a simulation with, and then without, that "heavy metal hook". It only amounts to a few feet in performance. Same goes for the thrust ring.

 

[Scott_650]

Opinions vary.

Unless you're flying competition for maximum apogee, the "belt and suspenders" approach is a proven winner.

Run a simulation with, and then without, that "heavy metal hook". It only amounts to a few feet in performance. Same goes for the thrust ring.

lakeroadster you make a solid point there…

And I have a bunch of 24mm powered “legacy” rockets built before I started using threaded retainers along with 18mm rockets built with blocks/hooks that fly great on QJets - sometimes the olde fashioned waye works just fine

 

[MidOH]

I just use tape, on 18mm and 24mm paper rockets. Tape ring if needed, and friction fit. Heck, I'm still tempted to just use cabbage, for wadding again.

I've got retainers on my larger fiberglass rockets. And my 38mm motored rockets.

 

[Ronz Rocketz]

Sometimes the label gets bunched up in the tube.

Here's an example from today.

 

[AeroTech]

Sometimes the label gets bunched up in the tube.

Here's an example from today.

View attachment 502428

Maybe rub the label down with your fingers before placing the motor in the tube.

 

[Ronz Rocketz]

Maybe rub the label down with your fingers before placing the motor in the tube.

To insert, I press it down with my finger, pull out when it bunches up, press down again, pull out again, press down again, insert again. And this was into a Quest fin can. Fortunately, the lot number is still available so I can email the photo to Gary after the motor failed, not Cato, just non-nominal. I almost lost my AC cam but found it in the grass.

 

[neil_w]

I have a separate suggestion for the label (credit to @hcmbanjo for originally showing this in his blog): At the nozzle end of the motor, print the motor type a couple of times around the circumference. That way, when the motor is inserted in a typical rocket and sticking out a 1/4" - 3/8", you can see what motor it is in there.

Something like this (apologies for the horrific photochop):