rotax618

When I replied, I had a simple 3 cylinder radial replacement for the rotax 503 class in mind, the engine could be built extremely lightweight using nikasil cylinders, CNC’d crankcase and computer controlled injection, ignition and solenoid valves. Provided it had enough displacement to provide 50-60hp using direct drive it would be possibly lighter than the 2 stroke. Just a thought!

I agree that electric is the future, as soon as someone develops a better battery, alas IC engines in aviation will still be with us for a while yet. You could say that a hybrid also has all of the disadvantages of IC and electric.

I don’t think that a solenoid engine would be as efficient as a brushless outrunner electric motor. What is worth thinking about would be a conventional radial IC engine with solenoid operated valves. Aero engines using direct drive don’t have to be high revvers, and solenoid operated valves would eliminate all of the gears, cams, rockers and springs, saving lots of weight and complexity. A radial, because of its single throw crank could make the lightest engine.

Sorry, I should read the posts more thoroughly before commenting. Your design has merit, I have not studied the aerodynamics of box wing types, but I believe they have structural and aerodynamic advantages and there have been some successful examples. I built a Flying Flea many years ago to understand their supposed advantages, unfortunately I did not enjoy flying it, the delay in yaw/roll couple was very uncomfortable. Others find them acceptable. I don’t know how far you are in the design but I suppose a large scale RC model will give you the CG and a fair idea of any vices before you commit to any structural analysis. I look forward to hearing of your progress.

The bevel gears was in reference to contra-rotating props. If you are considering an arrangement like the HM100, all well and good, I retract my concerns, I erroneously thought that the boom was to be cantilever. Perhaps a sketch of your design might help.

If you wish to register your amateur built grand design in Australia it has to be less than 560kg TOW. There isnt a lot of wriggle room if you dream includes a couple of 100-150mm dia high speed bearings and a bevel gear system with torsional vibration dampening - I dont want to appear to be a troll or naysayer, I know how difficult it is to design and build an aircraft within the RAA regs. I wish you all the best and look forward to hearing of your design processes.

YEP

Good grief, the secret to success in aircraft design is finding what you can eliminate, a lightweight aircraft flies best. A prop around the boom adds enormous structural complexity and introduces vibration into the slender boom and tail structure for no real gain excepting maybe asthetics. Contra rotating propellers adds more complexity and weight as well as unknown torsional vibrations to the drive system. Contra-rotating propellers are rarely use except when connected to turbine engines because of destructive torsional vibrations, they certainly have no place on ultralight aircraft.

Before you start making blanket statements blaming these tragic accidents on poor training, it is wise to look at the circumstances of each accident. From all accounts at least 2 of those fatalities were the result of a structural failure of the aircraft, and without knowing the exact circumstances I think it is extremely presumptuous to apportion blame for any of the other accidents on the pilot’s training without knowing the exact cause.

That is not true, the 618 produced far more power than the 582, and would spin the same prop 1000revs more, it was in direct competition with the 912 80hp. The 618 was heavier than the 582 and all of the extra weight was in the crankshaft. The 618 was a de-tuned 670 which produced 107hp. The RAV valves were poorly understood by users and required an additional manual control to exercise them after warm-up and to lift them at density altitudes above 5000ft, also the carbs required different jetting berween the PTO and MAG carbs. The muffler was also larger than the 582. If you understood the the above the 618 was unbreakable and long lasting and the most power for weight.

Yes the Austflight WB 582 wing is certainly strong enough, it is the certified wing I was referring to, conversions of Amateur Built 19 category lightweight Drifters is not possible.

I watched Wayne Fisher build a number of 912 Drifters, and helped rebuild a crashed aircraft. The lightweight Maxair 503 wing is not strong enough for the increased weight and performance, you could put sheets of lead on the pilots seat to balance the extra weight of the engine, but I hardly think that would be acceptably. The pilot provides the balance weight on a pusher aircraft So how do you get the Weight and Balance of a pusher correct if you add 35 - 40 kg more weight to the rear of the wing? The weakest point of the Drifter boom tube is directly under the down tube from the rear spar, early Drifter booms cracked there, it is subject to the greatest bending moment when landing or taxying, being 1/2 way between the UC and the tail wheel. Wayne sleeved the boom there because of that. Sure bolt a 912 onto your Drifter if you like, but if you don’t take into account the extra stresses and the CG the results will be catastrophic.

There is really no practical way to convert a 2 stroke Drifter to 912 power. You could use the wings, provided that they had the certified spars and flying wires, same with the tails. You will need a new longer boom tube and pans, the pilot seat has to be moved forward to balance the extra weight of the engine, the fitting on the boom that attaches the down tube from the rear spar is wider to attach the new engine mount, the boom is internally doubled under that fitting. Not worth the effort.

The Savannah door is airfoil shaped, the back edge of the door is sucked outward when only fitted with the standard single latch. A 3 poin latch is an absolute necessity.

Just wondering if you have progressed far enough to do a preliminary W&B.

I would be careful if you don’t understand the stress paths, reinforcing random points on a thin alloy skinned structure can give unexpected results - remember the NOMAD tail disaster.

Would help a little if you move the engine forward and use the maximum prop extension. I am basing my opinion on my experience with my Boorabee design, which had a 2 stroke more forward under the wing, a lighter 1.6mmx 127dia tube boom and fabric covered tail. The Boorabee Rearward C/G was limited by a 70kg pilot sitting only slightly more rearward than in your drawing. I admire your concept but I would go back to the moment spreadsheet at this point you will have a pretty good idea of the moments of the remaining unbuilt bits.

Project is coming along well, but just looking at the elevation I can’t help thinking about the C/G without wing sweep. If you haven’t started the wing design yet I would encourage you to consider the possability.

I got to look at how Groppo vent their tanks, they have a tube from the top of the outer end of the tank, the tube goes out to the wingtip where it is connected to a forward facing U tube.

I’m sure that you have considered the problem that you will loose some volume because you won’t be able to fill the tanks higher than the bottom of the cap outer body ( probably a good thing to prevent overfilling) and the inner clamping ring will have to be made in 2 halves to go into the tank so will have to be rigid enough to clamp the uneven plastic tank using 3 screws in each half. I noticed that the Groppo next door has flush tank fittings that have a brass screwed cap you can open with a coin, I have no idea how they vent the tanks, the screw caps are only about 25mm.

They look good Mark, how are you going to fit the vents, doesn’t seem to be too much room on the top of the cap.

I think you may get some of that extrusion from Hughes Aircraft, looks the same as the Lightwing.