At our recent monthly club meeting it was agreed we will run a fun bomb-drop competition at our Xmas BBQ meet. The competition will involve two rounds of a run over a target marked on the ground - nearest to the target is the winner. Nothing too serious here - except there is a $50 voucher at stake for the winner.

There are no hard and fast rules. Contestants will use there favorite sport model rigged any way they like.

Query, I am looking for a simple design for a homemade bomb drop mechanism to install on the fuselage centre-line of my 65" span .46 powered low wing sport aerobatic model.

I intend to use one of those 'old' red plastic TopFlite bombs, but don`t currently have a release system for it. What I had in mind was to build a self-contained add-on box containing a mini servo connected to the retract switch to activate it.

Before I get out the pencil and paper and work something out, can anyone point me in the direction of a simple existing design or ideas for a simple unit that will do the job?

I did do a search prior to writing this up, but the only systems that came up were for expensive electronic multi-bomb scale systems which are way off the mark for what I am seeking.

Thanks,

Alan W

Alan,

A much simplier method would be to take a 6 to 8 oz (not sure how many cc's down under that would be ) and poke a popsickle stick through the bottom diameter so that two ends appear at each side of the cup. You can then take a rubberband, or two, to stap it to the nose (just ahead of the wing). You now have a container to hold a golf ball, egg, or flour ball to drop on target. To release the payload, fly inverted, or better yet, give a quick stab of down, being sure to follow up with up, and don't watch the bomb. Keep an eye on the plane after bomb departure, as it still might be heading for the ground after that stab of down input.

The most practical way to do it for an event is as Ed Stefan posted above. The problem with events getting people to do even simple mods to their airplanes just for a fun fly event is impractical and will severely limit the number of folks who will participate.

With the cup method the cup is on top of the airplane of course and the flour baggie is just dropped in. To drop the bomb you just roll the airplane or climb vertical or do a loops whatever, makes for a fun event with the antics.

The popsicyle sticks provide something to hold the rubber bands that hold the cup. Using the rubber bands makes it easy to strap the cups on just about any airplane. I once competed in a fun fly and did this event with my four engine Kaydet Senior, had a ball. Of course the accuracy with that airplane was great, being here in Arizona I actually got the bombs somewhere between the Pacific Ocean and Texas

John

I'll second that motion.

You find out that very few bring a plane setup for the event. Good thing about cups with popsicle sticks is they can be rubberbanded on anybody's plane.

The club gets a box of cups, box of sticks, and a pound of rubber bands. You can easily rubber band the contraption on any plane, even ones that don't have rubber band on wings. Link enough together to reach completely around the wing and hook the end to the stick. Masking tape helps greatly to hold the bands on the stick. It usually takes 2 officials to do the deed. Make sure to bring the tape or you'll be in a world of hurt.

Hi Guys,

Thanks for your replies. Our small club - 20 odd members ( and some are odd....) - holds an 'official' club day once a month in which we all participate in some simple competition. The type of competition is usually unknown until announced by the CD a few minutes before the start.

During the year we have had a couple of simple bombing competitions using gear pretty much as described above. The CD holds the bomb container and produces it on the day. We have found the ideal bomb to be a small rubber child`s balloon a little smaller than a tennis ball and containing water rather than air. Most guys can get within maybe 25 paces of the target. Best I have seen is within 10 feet. Last time out only one model rolled into the ground during the event.....

This next event in about 7 or 8 weeks time wil be much more keenly contested - after all there is 50 bucks up for grabs - and no restriction on the bombing gear.

I`m looking to make a conventional approach with a bomb in a rack held in place by the wing mount bolts. I`m thinking along the lines that the rack will contain a release servo operated from the currently unused retract switch.

If it comes to pass I might try and post a pic later.

Thanks,

Alan W

Sometimes with mechanical bomb racks The best method is the Kiss principle (keep it simple stupid). Even the old Vortac bomb and release mechanism that was avaliable for many years was subject to hangups on occassion.

Possibly the simplest servo actuated system possible is just a servo that lets go of a rubberband.
This is often done with highwing airplanes using an internal servo with a rod on the servo wheel that went out the side of the fuselage. A rubber band around the bottom of the fuse dead end hooked on one side and hooked on the rod on the other side. The bomb or cargo simply on the bottom of the fuselage.

Using a single external servo with an cross shaped output arm and doing the same thing on a frame would work well also. Just eliminate the wire rod out the side of the fuse and hook one end of the rubber band on the cross shaped output arm. Putting this simple frame under the wing bolts in your idea would be very nice.

Just my thoughts.

John

Hi John,

Thanks for your input - I like the sound of that and will push it around on paper and see what develops......

Alan W

Wish that was here and not in Australia....

Years ago I built a "dive " brake under my Kaos to use as a bomb drop. The back of the dive brake went up against a small wood dowel 1/4 " . For a bomb I used a large washer with a streamer on it and just droped the dive break, slid the washer onto the dowel and closed the dive break. When I made my bomb run i just hit the dive break switch and the washer released, at the same time the plane started a slight climb keeping ME out of trouble from watching the bomb. It worked great and I even held the record for getting closest to the target ( the washer stopped right against the nail holding the paper plate target ).

The method used with the cup was my first attempt at bombing and I could never get the bomb out of the cup ( I hadn't learned inverted flight yet). Being an OLD Navy guy I was up on
" LOFT " bombing and so I tried it and it worked Great for me. Fly toward your target and just before you get to it pull straight up then at the top push down QUICK. The bomb comes out and goes back toward the target, it takes some practice but it's a blast when you get it right. A buddy and I used to keep a track on his shop door as to who go the closest each time we played at his home field. By the way, the first time I tried it I watched the bomb and not the plane right to the point that everyone was yelling at me to watch the plane. I did save it. ENJOY !!! RED

On the strength of much of the above, I spent a couple of hours yesterday turning a rough sketch into reality. Not long back from a trial session and pleased to report the bomb drop gear worked flawlessly. The only problem so far is with the pilot - I got the lateral part of the drop OK, but my depth perception was way out and th ebomb was dropped further out than planeed. However, we still have several weeks for practise......

John`s idea above appealed most so I made up a small cradle with a rubberband release servo attached. The basic balsa cradle was glued to a simple 'bed' cut from .4mm plywood. This followed the contour of the bottom of the wing and was held in the front by a rubberband around the front wing dowels and held at the rear via the two mounting bolts. The servo was actuacted via the retract swith.

I`ll try and post a few pics. First attempt at this misfired. If this one fails I`ll try and post them separately.

Alan W

(pic posting won`t work today. I`m away to watch the Kiwis beat PNG in the League and will try again later....)

A little trick I learned about bombing was this : Practice your approach, get so you can fly straight down the runway, right in the center every time. Once you get that, pick a spot that should let your bomb drop where you want it and practice hitting the bomb release at that point each time. You don't need a bomb to practice, just the passes and release.

Once you practice a bit it will get easier to hit the same spot. One other thing I do, on my approach, I always start out far enough that I can line my plane up with my shoulder ( coming from the right, with my right shoulder) to start the pass. This helps with the line up and gives you time to think about what you need to do. ENJOY !!! RED