Lockheed C-130 Hercules (oz13999)
About this Plan
Lockheed C-130 Hercules. Free flight scale model for electric power with 4x KP-01 motors. Wingspan 1393 mm.
Direct submission to Outerzone.
Update 18/7/2023: Added article, thanks to RFJ.
Quote: "STEPHEN GLASS developed his F/F Lockheed C130 for four KP-01 motors andsingle battery packs
Multi-engined, free flight models have been a practical proposition for a number of years now - readers of the Aeromodeller (March 1994) may even recall Brian Waterland's 44 in span Lancaster when Brian argued that four of the Knight and Pridham KP-01 electric motor/gearbox assemblies, with a single battery pack, should provide controllable power for a handy sized model and that a multi should obey the same rules of aerodynamics as its single engined brethren.
Recently, Knight and Pridharn have introduced matched 6 in tractor and pusher propellers, which are very handy, because they can be configured for contra-rotation, thus balancing out any possible torque problems inherent in multi-engine set-ups.
Anyroadup, living on the flight path to RAF Lyneham, there was not too far to look for inspiration so, safe in the knowledge that there was nothing to fear from free flight multis, the C-130 Hercules it had to be!
Model No.1 - AUW 14 oz: The first attempt to build the Hercules had a built up wing, a profile fuselage roughly hewn from 2" white foam, Depron foam tail surfaces and a three-cell battery pack.
This model proved extremely difficult to trim. If trimmed for left or right circles under power, most flights ended in a spiral dive to the ground. Occasionally, perhaps one flight in five, she would keep her nose up and put in a flight of unsurpassed serenity - all very tantalising!
The book, 'Model Aircraft Aerodynamics' by Martin Simons, has a chapter on spiral instability that explained exactly what was happening to the Herc - if a model has small dihedral and a large fin area, it could be spirally unstable. When a model starts turning, this turn becomes bank, the bank becomes sideslip, the sideslip and the large fin will make the nose drop. If there is insufficient dihedral to right the situation the model will continue to sideslip into a spiral dive.
With this information thoroughly digested, the Depron foam, used for the fin, came into its own now it's very easy to cut and the fin was gradually reduced in size until the flying was stable and reliable.
Model No.2 -AUW 15.5 oz: The second attempt had a 3D fuselage, made from white foam and hot wire cut. A balsa fuselage had become too heavy and was abandoned.
This model also showed signs of spiral instability, even with the smaller fin. The change, from a profile to a 3D fuselage, must have given the fin more authority. The subsequent adjustments mean that the fin is now about 60% scale size, which is a pity because that great, towering fin is such a strong feature on the original, although nobody has actually noticed without being told. Perhaps someone ought to tell Lockheed that they got their sums wrong during the design stage of the tail?!
With the change to a heavier and craggier fuselage, the Herc had lost some of its earlier sparkle, so it was decided to add an extra cell to the battery pack. This meant totally retrimming the model from scratch. If anything, she was now overpowered but final detailing was sure to push the weight up another ounce or so.
If there are any others out there interested in free flight multis, it may well be worth using Depron, so that you can subsequently size the fin for stability, particularly with the B-17 and the B-29 bombers. In the 'olden' days, we would have experimented with pendulum rudders and elevators to overcome stability problems, but that ancient lore seems to have been forgotten - or has it?
Model No.3 - AUW 17 oz: By this time, Model No.2 was looking decidedly war-weary, landings on tarmac, spiral dives, collisions into immovable objects and trees all having taken their toll.
With that in mind, model No. 3 was built and it's this one that's presented in this article, so to I recap, here's a list of important features and lessons learned.
1. The wings are located positively in order to keep the engine thrust lines constant but can skew on a hard landing - very important for survivability.
2. The high wing and fat fuselage keeps the props clear of the ground during a belly landing.
3. Two props run clockwise and two anti-clockwise to balance the torque.
4. The model balances with the batteries in the wing centre section - this greatly simplifies wiring.
5. Power is supplied to the engines via 'bus bars' along the leading edge of the wings - they offer high current capability with low weight and they again simplify wiring.
6. The white foam fuselage is light and can absorb a huge amount of punishment, whereas a built-up wing provides the best strength to weight ratio.
How to Build a 'Fat Albert': Fuselage: The fuselage is made up in two halves from white insulation foam. The foam has to be laminated from 1 in and 2 in thick sheet in order to make the 3 in thickness required. You can use PVA glue, thinned with water and applied with a paintbrush. Allow the assembly plenty of time to dry. Make the blocks slightly oversize. Mark out the fuselage profile on each side and add the 1" foam U/C fairing shapes. Remember to make a left and a right side, as it is important to have the 1" lamination on the inside.
For ease of handling, it is best to cut each side into three, making the cuts either side of the U/C fairings. You should now have six rectangular blocks, two of these with U/C fairings on.
Hot-wire-cut the blocks to section. The U/C fairings are cut off at this stage - they can be roughly shaped and glued back on later. The nose and tail pieces can now be cut to profile.
You should now have the components to make a hollow tube with the correct profile shape and two U/C fairings. Glue it all together. The inner nose block can be made from the off-cuts. The hole at the back (where the rear doors would be) is just covered with Litespan on a 1/8 by 1/4 frame.
When dry the fuselage can be sanded down, firstly to the correct plan shape, and then rounded off. The nose is quite pointed for such a fat fuselage, so try to get a few pictures of the real thing if you can so that you get the general character of the aircraft right. Add F1, F2 and the 1/64 ply reinforcement..."
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