The Lazair Ultralight

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n3puppy

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I wonder how many Fox .35s you’d need to line up along the leading edge to get a Lazair airborne. Enough that I bet you’d probably never notice if one quit…
Calculated Thirty eight Fox 35's required, each swinging a 10x6 prop.

38 ten inch props plus clearance will fit on Lazair 36 ft wing span. :)
 

Armilite

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I wonder how many Fox .35s you’d need to line up along the leading edge to get a Lazair airborne. Enough that I bet you’d probably never notice if one quit…
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I wouldn't try to Fly with the (2) 5.5hp Chain Saw Engines let alone Fox .35 RC Engines. The Rotax 185's were 184.2cc, and if they had just talked to some Snowmobile Race Shops, they could have made the Improvements to make a lot more hp. 184.2cc/7cc= [email protected]! The Lazair really only needed 13.7hp per Engine to Fly Well. Just a Carb Change, CR Bump, and maybe some Trail Porting would have probably made 13-15hp. If Stock CR is 8.0 a +3cr Bump = 3hp + 9.4hp = [email protected] A +2mm Carb bump can make 10% more hp = +1.24hp = 13.64hp, a +4mm Carb bump can make 20% more hp. So +2.48hp = 14.88hp. Put a Belt Drive on it and you can turn it Higher rpm and use bigger props. (4) Stock Engines = 9.4 x 4 = 37.6hp total. (2) 185 Engines fully modified with a Tuned pipe at 26.3hp x 2 = 52.6hp. (4) Engines at 37.6hp/2= 18.8 hp needed per engine. Not too difficult to do at 6500rpm.

Today, these Honda/Clone GX200/212 Engines are the way to go on a Lazair.

Stock Predator 212 [email protected] on a Dyno. When on Sale $99.99.

Episode 1. We put a $99.00 Predator engine in our Honda Insight. 39mph on 6.5hp.

Episode 3. We build a Stage 1 Predator 212 cc engine [email protected]

These Honda/Clones with a Belt Drive similar to what Peter Harrison used would be ideal. (1) 4 Groove Micro Vee Belt is go for 20hp, but for redundancy use (2) Belts, so 8 Groove Pulley. I paid $8.50 for this 8 Groove Pulley off eBay. It looks like he used 1.0" for the Back Plate which is overkill for 9.4 to 15hp. 3/4" is more than you need for up to 35hp. Still working on the Design. First concept. PTO Hole and Bolt Pattern is correct. At 5000rpm/2750rpm= 1.81 Ratio, so if Small Pulley is 2.370" x 1.8 = 4.266" for the Big Pulley. 5500rpm/2750rpm = 2.0 Ratio. 2.370 x 2.0 = 4.74" for Big Pulley. Rotax's Prop Bolt Pattern is based on a 75mm = 2.952747" Bolt Circle so you probably need a Big Pulley at least 4.0+" OD.
 

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Armilite

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(4) 4 Groove Mico Vee Belts are good for 80hp on another Belt Drive Design. So (2) are good for 40hp. (1) for 20hp. One 4 Groove Belt is actually good for like 25hp, but you never go up that far for AirPlane use. 25hp - 20% = 20hp.
 

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REVAN

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IMO: If you want to power a Lazair, there are a couple options that make the most sense.

1) If you want 4-stroke and are looking for economy over performance, go with Tillotson engines.
- For less than $1000 you can power it with 2 stock 212cc engines and Xoar 36x14 propellers.
This will deliver about 19 hp and about 100 pounds of static thrust.
- For $1500, use 2 Stage1 Tillotson 212cc and get maybe 21 to 22 hp total.
- For about $2000, get 2 Tillotson 225cc performance engines and derate them with 36x16 props.
This should deliver about 27 to 28 hp at 4800 to 5000 RPMs.

Tillotson Engines @ GoPower Sports

These are all direct drive setups. Be cautious of heat dissipation issues. The Tillotson engines have more cooling fin area than a Predator engine, and the 225, more than the 212. However, it is still something to watch out for. Just because you can get up to 17.5 hp from a Tillotson 225 doesn't mean that it can sustain that without overheating. I would not consider using these engines with a redrive. Direct drive, the disk power-loading is about right. With a re-drive, the engine will get expensive, heavy and may exhibit poor cruise performance with the lower powered engine options. With the added weight of a re-drive, these 4-stroke engines may very well push a Lazair over the US 254 pound weight restriction of Part-103 and throw the CG too far forward.

2) If you want the acceleration and climb performance of a big propeller, I'd recommend powering the Lazair with Radne Raket 120 Aero engines. The cost is similar to using performance Tillotson engines with redrive systems, but I think Rakets will work much better on a Lazair, having reduced cooling and CG issues. These engines are lightweight, already come with a reduction drive that is set up to accept a propeller, have the right power for a Lazair and they are pretty affordable (about $1500 each with electric start). With propellers and a tuned exhaust, it would likely end up costing around a total of about $4000 to maybe $4500, depending on prop selection and how much you spend on motor mounts. For this, expect to achieve a total of 27 to 28 hp on your Lazair, while turning props in the 120 cm (47 inch) range. I would expect a Lazair to have reasonable single engine performance with these engines, so low level flying, flying over water, or mountain flying should be both fun and relatively safe. It should perform well on floats as well.

Radne Raket 120 Aero ES-RD
 
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