DaveGee

Hi All: I am getting back into RC after a hiatus of about 5 years. I bought a couple of foamies to get started, a Dynam Hellcat, and a Corsair, too.

I am fixing up the Hellcat some, adding some flaps and I have an idea of making a retractable tailhook, mainly to use for low, dirty passes and then go around. I might use this in bigger aircraft in the future if this works especially for scale contests with larger planes.

The thing is I need to move the tailhook out of the fuse (it was carried internally on the Hellcat) about 4 inches or so.

I was wondering if anyone had any ideas on a mechanism, maybe a worm gear or something that could make the tailhook go out of the fuselage and hang down and then be able to retract it. I'm stuck on ideas of how to do this at the moment.

Any ideas?

Thanks,

davegee

abufletcher

Seems like a simple internal horn on the end of the tailhook would do the trick. A micro-servo (up front or perhaps even slaved with the gear servo) pushes and pulls a rod (music wire) that is attached to a vertical horn built into the tail hook.

DaveGee

Thanks, I'll start drawing something up!

davegee

scale only 4 me

My Feedback: (158)

I use a hs5645 to operate the tailwheel retract on my p-47,, I programmed it to 10% speed,

I'd probably do the same with the hook just use a digital mini.

good luck

N1EDM

My Feedback: (2)

If you're going to use the hook to actually 'catch the 3-wire', perhaps some kind of shock-absorbtion system (spring?) between the servo and the hook might be an idea, to keep the servo safe.

Just my $.02

Bob

DaveGee

Hi Bob: this idea of the tailhook is mostly just for show, especially for scale contests where one of the option maneuvers is a low, slow, dirty pass in front of the judges. I have not seen one where a tailhook is lowered for a "trap" but that doesn't mean someone else has already done this already. But in any case, I would just be using it for display passes, and then retract it for landing. I suppose if the hook itself was made of rubber or something, it might not get beat up too bad, but I don't plan to land with the hook down, at this point, anyway.

One concern I have is even with some sort of lever or arm I don't know if it will have enough play on the cable attached to it to push the tailhook out as far as I need it to go (about 4 inches out the back of the fuse.)

I might do a similar thing with my foamie Corsair where it is easier. On the Corsair, I just need to run a lever to the tailhook that is attached to the back of the tailwheel. I have already done this on a non-flying ESM plane that was built for a museum. But the principle is the same.

I appreciate any comments from anyone interested in voicing an opinion/help.

cheers

davegee

abufletcher

Ah, I see now what you mean about the Hellcat tail hook. It doesn't just swing down but rather really does extend quite a ways. And you're right that this extension would be greater than the movement on the servo arm. On a larger model some kind of small electric motor could maybe handle this task. But since you're talking about modifying a small foam model you need to be very careful about adding much mechanical weight to the tail.

DaveGee

Hi Abufletcher: yes, you are precisely on target! Although this idea is ultimately designed for use with bigger models someday, I'd like to test the theory at least on what I have right now, which are just small foamies. It still presents an interesting engineering challenge in that I have to get a lot of movement out of some mechanism that has to also be extremely light since a foamie isn't designed to take much extra weight.

If I can get the Hellcat to work, the Corsair will be a piece of cake, by comparison!

cheers

davegee

abufletcher

Maybe having a look around the ServoCity website might help you brainstorm a solution:

http://www.servocity.com/html/gears.html

On the Corsair type tail hook, the horn idea as seen in this drawing should work, just need to work out the geometry.

Chad Veich

My Feedback: (60)

Not only do you have to move the hook its entire length but also it has to swing down when it reaches the limit of its travel. I considered doing this on my 1/8 scale Hellcat but I could not come up with any light and simple solution. I will be interested in your results Dave.

Dean rcu

My Feedback: (5)

Use a 4" air cylinder to move the hook out and a mini servo with a delay switch attached to the air cylinder to move the hook down.

DaveGee

Thanks for the drawing. I was able to work out the geometry on the ESM Corsair, and a simple servo would move it up and down just like the real thing. For this smaller foamie, though, it will be a bit more of a challenge, but not unsurmounable.

I'll post my progress (or not) on this blog as I go about this project. If it works, then others can use it if they wish for their projects.
davegee

DaveGee

Thanks, Dean. I just got back from the hobby store with some other stuff to work on a possible plan before I saw your email. But the air cylinder sounds interesting, if I can keep the weight down. I'll post here what I come up with, whether successful, or not.

davegee

DaveGee

Hi Chad: thanks for chiming in. Hope those new knees are working out for you! I have no idea if this will work or not, but I got some stuff from the hobby store and will give it a try. If successful, I'll fly it at our Warbirds Over Denver in early June and take pics of it.

fred985

what p 47 ever had atail hook ?

fred985

whups, i missed your saying tail wheel.

scale only 4 me

My Feedback: (158)

No worries,

I was thinking for the little foamie one the mini servo to save weight, But for the larger scale model, a jack screw (lado or wingspan) retract actuator could both extend and retract the hook very well in a scale like manor

DaveGee

I agree. Probably could use two different mechanisms for smaller versus larger models. A jackscrew or some sort of geared worm gear I think would work on larger planes. I'm still looking into making a miniature version for the foamie, too, as well as a simple servo with a long arm that could push the arresting hook out of the fuse and then back in again.

I'm thinking that at the top of the arresting tube or bar, I'd put a Robart hinge or something so that when the arresting hook mechanism comes out as far as the hinge, the weight of the hook would cause it to point down like on the real thing. A lot of testing needs to be done, and a successful mechanism is not certain, but I'll try.

davegee

scale only 4 me

My Feedback: (158)

I'm sure gravity is how the 1-1 worked too.

In my mind I see the actuator above the wing/servo area, so it's easy to adjust. Then the screw action transferring the push/pull action back to the tail via a push rod, maybe even nyrod since it likely has to go around the tail wheel retract mechanics.

Can't wait to see it work

abufletcher

I was thinking of gravity as well, but the problem might be that with a light hook (which you need) airflow might keep it from dropping down. But I agree that this is an interesting engineering challenge. Just brainstorming but I wonder if it might be possible to make the hook out of a straw and then have it slip into (and out of) a slightly larger straw. Maybe a thread could be attached to the forward end of the hook but exit out the rear end of the outside straw. Pulling on the thread (in some manner) would extend the hook.

Getting it back in would be a separate problem. BTW, is the interior of the foamie's tail actually hollow? How much space do you have back there?

abufletcher

At a larger scale a mechanical system would definitely be the way to go. But I think with a small foamie, you're going to have to fake it with some sort of trick.

Edwin

My Feedback: (2)

How about a 2.25" tiller with a 180deg servo connected about 1/2" from the hinge point. That should get you close to 4". You would need a short guide tube at the exit of the plane since the catch hook arm would be hinged about that point. When the hinge on the catch hook exits the fuse, it will hang down. I dont see how you could reduce the size enough for a small foamy though.
Clear as mud?
Edwin

Chad Veich

My Feedback: (60)

Keep in mind that the 4" measurement is for the small scale foamy. The larger the scale the longer the distance becomes. On my 1/8 scale Hellcat the distance would be ~5.25 inches and on my 1/6 scale Hellcat I would need 7 inches of travel.

DaveGee

Hi All: I appreciate all the interest and great suggestions on this thread. I worked a lot on it today, and I think I am making progress. I have a mechanism using a servo with a long arm on it that brings the tailhook out of the fuselage to straight down, and then retracts it completely into the fuselage. In the process I had to cut into the foam in some places and ruined the gears on a little servo that gave its life to the cause.

I'm going to get a new servo tomorrow and try to put the whole thing together. If it works I'll take some pics and let you see where it stands. I think a larger plane would work better than this little foamie. It is really tight quarters in there, and although it is not the best arrangement to be had, I think it might just work!

More tomorrow!

davegee

DaveGee

SUCCESS!! Hi all: I worked another few hours on it today, and it is now working like it should. Really the typical snags/issues/problems that you would expect with a scratchbuilt system with nothing really to go on but trial and error.

Basically, I used a Hitec HS-81 micro servo, this time with metal gears as I stripped out the one with plastic gears during testing. I added an additional 1/2 inch of arm by gluing a Popsicle stick onto the arm and extending it to the point where it would bring the tailhook right up to the endplate of the fuselage, as on the real thing. I used a simple flexible steel cable in a plastic tubing, and then also in a guide tube to keep it from "snaking" and not completing the full distance needed to move the tailhook in and out of the fuse. I glued the servo onto the foam side of the fuse, and buttressed it with foam on either side to dampen out any tendency of the servo itself to move while it is working. The arm moves freely without any problem, although I had to whittle and dremel down a little on the areas where it touched during its arc.

All in all, this rather crude first attempt at a working scale tailhook assembly came out pretty well. I also made the flaps operational, and I'll test all this gear in flight next week. I'm glad it went together, it was a little frustrating at times, but I thought that the concept would work eventually. For a larger scale plane, I would use some sort of gearing and motor that would drive the tailhook straight out and back. If you use a Robart hinge pin, or something like that at the point where it goes over the lip of the fuse, the tailhook will hang down like the real one. It is no problem retracting it.

I used about 1/2 ounce more weight in the nose, to compensate for the addition of two servos for the flaps and the tailhook gear, that weighs next to nothing. I'll attach a few pics here. Let me know any comments/questions.

davegee