rotax618
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Everything posted by rotax618
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Which Savannah model did you get that dimension from? I used a CH701 2 stroke engine mount on my Classic Savannah and the bolt holes lined up perfectly, I compared the Savannah firewall with the early 701 drawings and found it to be almost identical. I later tried to fit an XL engine frame but found the angle of firewall to be different, about 6deg less, so the bolt holes were just a bit off centre.
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Soda blasting will take ages and cost lots if done out in the open (not in a cabinet). I used an organic citrus based paint remover, it fried up the paint and after it was dry the paint could be easily dislodged with scotchbrite, the silver base with clear came off cleanly but the Red 2 pack was a bit messy. Unless you are really concerned about weight just scotchbrite the surface and overpaint it, ask Danny, thats what he did. -
I get rotax exhaust springs from England on ebay, just search for rotax exhaust springs in th go-cart section, they are very cheap compared to Flood, you can buy them by the dozen.
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Great project Mark, from the outside the wing spars look to be bent where the outer spar extensions join, if that turns out to be the case the wing rebuild should be easy, unlike Danny's where someone took to the spars with a jigsaw. Will call up after Xmas and give you and Danny a hand now I have new knees.
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John, do you need them for a drifter? If not, similar ailerons are easily made from local drawn tubing, 32mmx1.6 for the main tube and either folded 0.6mm sheet or 12.5mm tube, as per Drifter, for the trailing edge.
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I will take my old 4 pin modules up to Roger next weekend, he may be able to work a conversion for the system to the new modules.
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The number on the side of my modules is, 966 721 992424. Thy may not suit your engine.
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These are the ignition parts. Consists of two 4 pin modules and trigger coils, two ignition coils, tachometer pickup.
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G'day Dan, I will take my old ignition setup up to Mark next week, maybe he and Roger (an expert friend) may be able to assess their usefulness for your purpose, if they recon they would be safe enough, make an offer and we could send the whole setup to you. They were working perfectly when they were replaced, and if the newer ignition hadnt become available they would still be in use. Cheers Tom.
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G'day Dan, from the look of it, the module you have is a very early one, the module Mark is experimenting with probably wont work with your pickups and coils. I replaced my old modules recently, it involved replacing the whole ignition, pickups, coils and modules. Unfortunately the later model second hand modules I got for replacements only lasted a matter of months before they required warming up before the engine would fire. I still have the old modules, I replaced them because I thought that the insulation on the wires had become too hard. There is fair bit work involved in setting up a whole new ignition system.
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Savannah nosewheel is connected to the rudder pedals. Castering nosewheels are usually fitted to aircraft with a high landing speed, the disadvantage is that they are more difficult to taxi in cross winds and direction is reliant on differential braking of the main wheels. The disadvantage of direct steering of the nosewheel is that it can effect the directional trim of the aircraft, leading to a wing heavy situation that can be miss diagnosed as a wing trim problem and is is incorrectly cured by fixing a trim tab on an aileron, another disadvantage is if the aircraft is "dumped" on the nosewheel in a crosswind landing situation the aircraft can veer violently and the nosewheel can be damaged, but for low stall speed aircraft a steerable nosewheel is far more convenient.
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Rivets do weaken the tube, the best solution is to only rivet the fairing at the ends of the strut and use a high strength double sided tape where the fairing touches the strut tube top and bottom.
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Lightwing (Hughes Aviation at Ballina) still have strut material, the same as used on their Lightwing, not sure that they have the smaller size but I bought some of the larger section last year. The larger section has about a 32mm internal minor axis.
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Pushers are always noiser than tractor aircraft, particularly for the persons in front of the prop, pilot-passengers. I think that the noise of the engine and particularly the exhaust is being reflected from the propellor disk forward. I was going to test this by extending the exhaust outlet down and along the boom to exit behind the prop. Unfortunately all of the pushers I built had 2 stroke engines which dont perform well if you modify the exhaust. Another problem I encountered was a pulsing and vibration when I used a 2 bladed prop, this was caused by the prop blades passing through the wing wake in unison, three blades fixed this although 2 blades gave a better cruise.
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The concept looks good but I can see two problems, unless you have something very heavy to put in the nose or you are planning on sweeping the wings, I suspect that the pilot and pass are not going to bring the CG forward enough for stability. The second problem is getting smooth air to flow around the rear of the pylon into the prop. I have had some experience with this problem when I designed and developed the Boorabee, which is a tandem and therefore less of a problem, I finally solved the problem with vortex generators. Vortex generators can delay the separation of the boundary layer by re-energising it, wings equipped with VGs still stall but at a greater Angle of attack, typically 15-18deg, from the looks of your design the rear of your fuselage is 30-45deg taper. You will probably be better off tapering the pylon 15deg and chopping it off square before the prop ( Kamm tail) Please accept my criticism as an attempt to help. There a far too few people willing and brave enough to design and build their own creation.
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Sorry doubled up for some reason.
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There were nine Boorabees built in total. I gave the fuselage plug to Dave Donohoe who modified it for a rectangular boom tube. Dave's Shuttle shared the same wing but the boom, tail, undercarriage and controls were vastly different. I built two Mk1 Boorabees then made new molds and simplified the design for the Mk2. I loand the molds to persons I trusted, and gave them the CAD plans at no cost. No more Boorabees were built because it required a great deal of effort on my behalf for builder assistance and it became very difficult to get the 5" boom tube and necessary drawn tubing to build the wing. I still have the molds.
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I designed and built that aircraft in 1992, 24 years ago. The Mk1 Boorabees flew with a Rotax 503, that paticular aircraft has had at least 3 different engines and the last time I saw it had an HKS engine. That Boorabee has flown thousands of hours. I cannot comment on the condition of that particular Aircraft because I havn't seen it in 20 years. Boorabees are extremely docile aircraft with few if any vices. The Mk1s are really powered gliders without air brakes (better than 12:1 glide) they tend to float so it requires a special technique to spot land them. One of the owners of that Boorabee told me at Narromine that he had flown dozens of different types of aircraft and that the Boorabee was the most pleasurable.
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I would like to use your construction method on a project of my design, have you had a chance to proof load the wings to verify your calculations? The only concern I have is the disconnection of the wingskin with the spar, relying on the shear between the foam and spar flanges, I discounted this method because of this concern, my solution was to shape the foam to the top of the spar caps and form the glass wing skins using the Strojnik method (lay up the skin on a flat mylar sheet and before it is cured ,hang the mylar up by two edges forming an aerofoil shape) then vacuum the skin sections onto the foam and spar caps. Do you think this method would produce a stronger wing with less finishing?
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Could you share your method of producing such a smooth surface, do you cover the cured layup with micros and block sand the surface (very time consuming) or do you have a trick that makes the construction a bit easier?
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Very pretty little aeroplane. Am interested to know what the skin is over the foam and how you get such a smooth surface finish.
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Very interesting little aircraft, could you please post some photos of the construction method/materials. Are structural limitations or regulations limiting the MTOW?
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DooMaw - building a STOL
rotax618 replied to Head in the clouds's topic in Aircraft Building and Design Discussion
In my opinion wing folding should only be used for storage, removing the wings for transport is far safer, Bill Knight said that the G meter on his Hyperlight would regularly show over 10G following transport on a well sprung trailer, these unacceptable shock loads could easily cause structural cracking and premature fatigue to critical components of the wing attachments. -
G'day Deskpilot, I think I may have made a comment on another forum concerning your "Prop around tail boom" design. As I see it the additional complexity and weight of having the prop rotating around the tail boom negates any perceived advantages (are ther any?). Have you investigated the weight of a 5-6 inch ID bearing capable of the thrust, side load (belt tension) at 3000 RPM. A conventional pusher with a high boom like the Streak Shadow is not the answer as it limits the prop diameter and therefore its efficiency, most pushers have a low boom, Sapphire, Boorabee, Drifter etc. If you want to think outside of the box, how about a dual ducted fan or prop on a pylon.
