LSA in USA • 15 years on (AFJ article).

[Garfly]

Light Sport Aircraft aren’t selling well, but the LSA rule has still worked | Air Facts Journal

[Student Pilot]

Interesting evolution. I can't understand why very basic aircraft aren't more popular, seems everybody has to have glass dash and at least 2 axis auto pilot.

[old man emu]

It's about time that administrators of aviation, CASA, FAA etc., had a good look at the physical appearance of the citizens of their countries. When was the last time you saw a crowd of 86 kg men? Try looking back to the early 1970's before the multi-national fast food mobs arrived here. Also, without allowing for these purveyors of calories, the quality of the food we eat is vastly improved since the middle of the 20th Century. As a result, the average height, and hence weight, has increased. Look at the CASA table of assumed weights in CAAP 235-1 235_1.pdf

 

I wonder how hard it would be to design a small aircraft with a MTOW that allows for a load of 250 kgs for two persons + fuel for 4 hrs at the engine's cruise usage rate.

[facthunter]

It's not hard at all and we've done it here many times in the past. Rule of thumb.. Factor your payload by 150% and add that figure and you get a ball park AUW figure. or go basic wt for two seat (about 320 plus Kgs) and add your payload Including fuel oil etc. You won't come out below 600 kgs. IF you build in exotics you might save 40 Kgs and add many thousands to cost. Nev

[old man emu]

IF you build in exotics you might save 40 Kg

 

FH,

I have plans for a 1930's metal tube fuselage. What's your opinion of using aluminium for the fuselage like the Morgans? My thought is that while it could be done, it would mess up the C of G, and you would have to stick a weight down the tail, thereby cancelling out the weight saving of aluminium.

[facthunter]

Shorten the front if you can. Lots of old stuff had the engine very close to the pilot and a longish moment arm to the tailfeathers. The weight down the back if far enough away doesn't need to be large but always makes spin recovery worse than if there was none . IF it's a high wing parasol the pilot can sit rearwards even though a variable weight. You need to, to have good cockpit access. Many don't and getting in and out is difficult.. That's why the DH 82 had angled top wings. Nev

[old man emu]

You need to, to have good cockpit access

 

I was going to add a couple of inches to the width of the fuselage and insert a drop down door panel.

 

But what do you think of replacing steel tubing with aluminium tubing from the rear of the cockpit back to the tail?

[facthunter]

The main part around the pilot has the engine mounts ,bulkhead, wing, seatbelt attach points and U/c attached. I favour welded steel tube there. Rearwards of that, you could do what you like. wood, alu, or glass It's a much less load carrying section. Naturally it needs to be joined carefully, (carry stresses to attach points well) but it's an idea with merit. Nev

[old man emu]

I was of the opinion that everything forward of the cockpit rear bulkhead should be steel, but Morgan has the fuselage longerons going all the way to the engine firewall, with the steel engine mount attached there. The main landing gear is attached to the steel engine mount.

 

Also, is aluminium tubing of about 50 - 75 cm OD used as wing spars? I was thinking that by using as much aluminium for framing and fibreglass for wing ribs, the MT weight would be reduced sufficiently to allow for more weight in the occupants while keeping fuel storage at the designed level.

[facthunter]

I don't like using Al tube for wing spars. Most of the load is in one direction (up( lots) and down( less)) A uniform section tube is equal in all directions and too heavy and how do you taper it off strength wise? Shear and bend are a maximum near the centre section. Your wing spar is a girder. Wood or Carbon fibre?. C section or I beam with spar caps. Load bearing integral fuel tanks. Foam filled leading edge with al skin fitted direct to spar. Nev

[Mike Borgelt]

Jim Bede did like using aluminium tube for wing spars. He used it on the BD-1 which became the Grumman AA-1 and later AA-5 and also on the homebuilt kit BD-4 and the little BD-5.

As usual what looks like it ought not to be a great idea, on closer examination, has some advantages. There are torsional loads to be taken out by the spar and a tube will take these. You can put lightening holes in the front and rear of the spar in the outboard area and the root fittings can be non precision and lacking in stress raisers. Jim reckoned this was important in a kitplane. The outboard area spar could also be replaced with a rolled, thinner 2024 sheet tube.

I've owned a BD-4 for 24 years and it is a great all round homebuilt. If you are looking for a 4 seat homebuilt you don't have a lot of choice but a new BD-4C kit with a 180 - 210 HP Lycoming or clone and CS prop is available and heaps cheaper than an RV-10. Not bad for a design that first flew in 1968. Nobody is forcing you to fit galss and autopilot but in the overall cost of an aircraft, the glass panel (if you stay away from certified) is likely cheaper than steam gauges and already has the autopilot built in. All you need are the servos.

As for LSA - one of aviation's really bad ideas. Relatively fragile, limited aircraft, often flown illegally, are a result with a much higher accident rate than standard GA. The only real advantage was the relaxed medical requirement for pilots. As the USA and UK have in the last few years become sensible about medicals, unlike Australia, the requirement there for LSA has essentially disappeared. I doubt they'll be missed.

[Raytol]

Hi OME, Why not come to Camden and have a look at the latest Sierra/ Cougar. CroMo frame from firewall to seat back. The aluminium tube spar is not the best use of material.

It is about the moment of Inertia of the material.

I think Bede used to chemically mill the tube to thin the wall at the tip. The best use of materials is a box, I-beam or C section.