motor hook design issues

while there are arguments for and against the current design...I have found a couple of things. the current design makes it harder to get the motor into and out of some classic rockets(w/ bt50 airframes), example the Estes Alpha*, when built with the current design hook has a clearance problem by the time you get the hook pulled back far enough to insert or extract the motor you will have bent the aft end of the body tube. the old school design needed to be pulled back 5/32", new 5/16". on the other hand the current design does help keep the 'starter' plug from falling out (hook overlaps the plug).
*why yes I do happen to have both an old (1970) and new Alpha on hand, the hook on the old one does not distort the airframe when it is time to insert/extract motors. I will do some work on the new hook to reduce the clearance issue.
Rex

Let know what you come up with Rex.
I'm very interested in your findings.

Rex R said:

while there are arguments for and against the current design...

Click to expand...

I personally prefer a shorter "tab" on the end, and will modify hooks to my preference. (under normal or preferred working conditions, the only part that needs the motor in is the part that touches the engine case, and anything more can interfere with exhaust) The issue with a shorter tab on some hooks is that the tab on the end is not bent over 90 degrees resulting in a force that pushes the hook out when the motor ejects backwards. Masking tape solves this problem, though my solution is to use pliers to carefully bend the hook to figure 2. Bending too much can snap off the tab.

The standard way that I've seen is to bend the straight part of the hook, however that can result in crushed or deformed tubes and a larger ejection can still force it open. Bending the hook works better in my opinion.
____________________________

Figure 1: Unmodified hook)

Motor--------->
\_________________/ <Tab

Tab is angled to push away from the motor at ejection.

____________________________

Figure 2: Modified hook)

Motor-------->
a) \__________________\ < Bent tab

b) \__________________| <Slightly bend tab

a) Tab is angled to force hook towards motor at ejection, keeping it in place. Overbending may snap off the tab.
b) Tab is angled to not move during ejection.
There is more than enough room for the motor even with the bending.

____________________________

Estes hooks, the ones with the large tabs, already have (a) in place, so I'm not sure why the tabs are that size. Perhaps ease of manufacturing?

I haven't heard any arguments for that design except for that the tab helps little kids remove the motor. If you know of any others, I'd like to hear.

What I don't like with some versions is the distal tip is pointed downwards and has mildly sharp corners. While safety code prohibits trying to "catch" High Power rockets (sort of a Darwin Award Maneuver for larger HPR, obviously), I have seen kids and teenagers (and some adults who think they are teenagers) try to "catch" low power rockets before they hit the ground, and I have seen cuts on the hands from these engine hooks (also from some of the plastic fin cans, saw this from an AstroBeam.)

It is pretty easy to bend that tip upwards to prevent this, without interfering with the function of the hook.

BABAR said:

the distal tip is pointed downwards and has mildly sharp corners.

Click to expand...

Are you referring to the tips Estes used to use, or the bent less than 90 degrees ones?

I file mine to make the tips smooth(er)/rounded, but that's so it's easier on fingers while opening.

I've disliked the new Estes motor hook design after I one hang up on on the launch pad in 1994. The motor hook designs were introduced in 1993, IIRC. My solution involves a Dremel Tool with a cut off wheel and a bench vise. You can get classic style motor hooks (without the hang up on the launch pad finger tab) from either Apogee or Semroc.

I decided to order some from erockets.biz * note: use the search term 'engine hooks', the term 'motor hooks' only nets you hooks for mini motors.
*of course I couldn't just order engine hooks...also ordered centering rings and other assorted parts(no kits though) .
Rex

You know, I never actually noticed the difference since I just started build/flying a few years ago.
I just used pliers 'adjust' the hook when necessary

I'm not to keen on the redesign of the Alpha's motor mount centering tube either. since there isn't a groove for the hook...the mount tube tends to distort (which also makes inserting a motor difficult, just have to build me a new mount or three .
Rex

mwtoelle said:

I've disliked the new Estes motor hook design after I one hang up on on the launch pad in 1994. The motor hook designs were introduced in 1993, IIRC. My solution involves a Dremel Tool with a cut off wheel and a bench vise. You can get classic style motor hooks (without the hang up on the launch pad finger tab) from either Apogee or Semroc.

Click to expand...

Uncle Mikes Rocket Shack and Sunward also has them. UMRS advertises one with a little longer hook to go over the engine.

Incongruent said:

Are you referring to the tips Estes used to use, or the bent less than 90 degrees ones?

I file mine to make the tips smooth(er)/rounded, but that's so it's easier on fingers while opening.

Click to expand...

My bad, I guess I am talking about the old ones. Just looked at the ones on the web site and the distal tip is turned slightly out and up, so I guess they fixed my concern.

mwtoelle said:

I've disliked the new Estes motor hook design after I one hang up on on the launch pad in 1994. The motor hook designs were introduced in 1993, IIRC. My solution involves a Dremel Tool with a cut off wheel and a bench vise. You can get classic style motor hooks (without the hang up on the launch pad finger tab) from either Apogee or Semroc.

Click to expand...

The only time I found Estes new hook design (with the finger tab) to be useful was when I discovered that having left mine unaltered on my Estes Mercury Atlas. I didn't remove the tab on my unfinished builds. When I had returned to building in 2013, I discovered that they had discontinued the short E motors (3.5"/89mm long), and increased the length of the E motors to the current (3.75"/95mm) dimensions. That extra bit of tab allowed me to carefully bend the hook out to accomodate the difference.

I do have kits that I've built, or are building, that have the finger tab intact, but mostly, I just use a couple of needle nosed pliers to snap it off. Since that results in an end that is rough, I use the factory edge on the other end as the bit that is exposed.

BABAR said:

My bad, I guess I am talking about the old ones. Just looked at the ones on the web site and the distal tip is turned slightly out and up, so I guess they fixed my concern.

Click to expand...

The current Estes hook is the middle one, the Apogee and Semroc kind without the finger tab is the bottom one, and the original Estes hook with the finger tab but also a puncture wound hazard is at the top. The top one is based off of other people's descriptions, I've never seen one.

So, to clarify, you are referring to the top one?

Incongruent said:

The current Estes hook is the middle one, the Apogee and Semroc kind without the finger tab is the bottom one, and the original Estes hook with the finger tab but also a puncture wound hazard is at the top. The top one is based off of other people's descriptions, I've never seen one.

So, to clarify, you are referring to the top one?

Click to expand...

The only motor hooks that I have seen like the top one were included in Quest, Custom, or MPC kits. The finger tab on the top picture was bent out towards the outside of the model. Estes used the bottom one from about the mid 1960s until 1992. The one in the middle was used starting in 1993 until the present day.

So the finger tab was bent not to make a 'tab' but to create a rounded end and make pushing the hook open easier?

I just found "THESE", I've bought from them in the past.
Good people. First one's I've seen you could buy separately.

erockets also stocks mini motor hooks.
Rex

They do, but by the drawing/pic they show they look more like a standard Estes hook.
Where Sharp Idea's (From Sunward I would imagine) has that straight leg with just a bit of a bend at the tip.

Carl worked on several designs to bend the hooks but the only thing that worked was to do one at a time. He really didn't like the newer ones with the finger hook. He wanted both ends to be a 90 degree angle but they didn't all come out like that.

Here's a recent engine hook install, a 18mm engine mount in a BT-50 sized tube.
The kit instructions said to make both tubes ends even (on left), but that doesn't leave much room for the engine hook to move.
I ended up gluing the engine mount with 1/4" of the tube extending out the back, shown on the right.
Now the hook can move outwards allowing enough clearance to slide in an engine.

I looked at this solution and decided the engine hook was wasted weight in the wrong place. Once you decide to extend the motor tube 1/4 inch aft of the main body tube, the use of 1/4 inch masking tape to create a shoulder on the motor and 1/2 inch masking tape to wrap around that shoulder and the motor tube works all the way up to 29 mm Estes black powder motors.

hcmbanjo said:

View attachment 308310

Here's a recent engine hook install, a 18mm engine mount in a BT-50 sized tube.
The kit instructions said to make both tubes ends even (on left), but that doesn't leave much room for the engine hook to move.
I ended up gluing the engine mount with 1/4" of the tube extending out the back, shown on the right.
Now the hook can move outwards allowing enough clearance to slide in an engine.

Click to expand...

Do you really need a hook? Motor can always tight fit into the body tube, right. And ejection chg never be able to push out, as the nose is much loose fit than motor

modeler said:

Do you really need a hook? Motor can always tight fit into the body tube, right. And ejection chg never be able to push out, as the nose is much loose fit than motor

Click to expand...

It's not just about pressure pushing the motor out. At the time the ejection charge goes off conservation of momentum (Newton's third law) is also pushing the motor out. Taping the motor in the motor mount usually works.


Steve Shannon

I just snip that funky end off, turn it over and put it on. Works great!

got my semeoc 'engine hooks' in the mail, they're nice.
Rex

Rex, can ya post a pick of them?
And what size(s) did you get?
I need to order up a bunch of all 3 sizes.
I've been looking at UMRS.

Rex R said:

erockets also stocks mini motor hooks.
Rex

Click to expand...

As does BMS

What does BMS's look like?
Side note: on the same page is launch lugs. How long do you know they are?

pic, no but here is a link. https://www.erockets.biz/semroc-engine-hook-standard/ I went for the 'standard 2.75" engine size' which will handle 75mm engines. are the same as the 1970 era hooks, no they are a bit wider (about the same as the current estes hooks). but since you don't have to pull them as far back they should work nicely in bt50 size rockets.
Rex

Woody's Workshop said:

What does BMS's look like?
Side note: on the same page is launch lugs. How long do you know they are?

Click to expand...

The BMS motor hooks are the old style Estes hooks that are a simple 90 degree bend at each end, as for the launch lugs the second number in the description is the length in inches, for example the 1/8" launch lugs are sold in 1.25" and 12" lengths.