More LSAs Questions

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ktsai91

Well-Known Member
I've noticed that most LSAs are equipped with a Rotax 912 engine. I've noticed that it's RPM is higher than most conventional aircraft engine. For example, the RPM for a 912 can go from 5,000 to 6,000 RPM, whereas Continental O-200 engine can go from 2,000 to 3,000 RPM. Why is that? Both have the same 100 hp. Even 80 hp engine has a 5,000 to 6,000 rpm I think. How can the 80-hp engine have a higher RPM than conventional piston engines?

Second, why are some LSAs especially some modern LSAs measured in mph instead of knots? I thought knots was the standard measurement for airspeed? Is it possible to take a mph airspeed indicator out of an LSA and put a knots airpeed indicator in? Is there an option when buying an LSA to be measured in knots instead of mph?
 
ktsai91 said:
I've noticed that most LSAs are equipped with a Rotax 912 engine. I've noticed that it's RPM is higher than most conventional aircraft engine. For example, the RPM for a 912 can go from 5,000 to 6,000 RPM, whereas Continental O-200 engine can go from 2,000 to 3,000 RPM. Why is that? Both have the same 100 hp. Even 80 hp engine has a 5,000 to 6,000 rpm I think. How can the 80-hp engine have a higher RPM than conventional piston engines?

Second, why are some LSAs especially some modern LSAs measured in mph instead of knots? I thought knots was the standard measurement for airspeed? Is it possible to take a mph airspeed indicator out of an LSA and put a knots airpeed indicator in? Is there an option when buying an LSA to be measured in knots instead of mph?
Click to expand...


MPH looks faster!

DUH!
 
DPApilot said:
MPH looks faster!

DUH!
Click to expand...
Yeah, it makes the 120 knot restriction seem less lame. :D
As for the RPM, I think it's because engines like the 0-200 make their peak horsepower at a lower RPM, while the Rotax has to spin faster to make its peak horsepower. I could be wrong though. Wouldn't the engine having to spin at a higher RPM put more stress on it and shorten its life?
 
KLOU117 said:
Wouldn't the engine having to spin at a higher RPM put more stress on it and shorten its life?
Click to expand...

In short, Yes.

Anytime you are geting more power out of a smaller dispacment, you are going to suffer in reliability.

Rotax engine have a reputation of being less reliable than flat 4s. I don't know if it's real or just the reputation of their smaller non certified engines on homebuilts carrying over to the larger certified powerplants.
 
The Rotax 912 is a flat four, horizontally opposed engine, just the same as a O-200 is. However, the difference is in displacement 201 cubic inches for the O-200 and 82 cubic inches for the Rotax. The Rotax runs, in both of the planes I've flown with it, in cruise at roughly 4800-5300 RPM. While, it does sound like more, you must realize there is a gearbox with a ratio of around 2.4:1. So, it works out that the prop is turning roughly the same speeds.

In the cockpit, the Rotax is definatly louder, quite a bit infact. However, when a Rotax powered plane fly's over where I live on approach, you can't hear it, at all. So, its all a tradeoff.
 
The whole reason for the different RPM ranges and similar power production is that HP = (Torque x RPM)/5252.

Horsepower has no direct measurement and can only be derived from torque and engine speed. The smaller rotax produces less torque than the larger displacement O-200, so it needs to spin faster to produce the same power output.
 
OK...I am interested in LSA as well.

I would LOVE to get my medical and fly with no restrictions...but I am really nervous about getting denied. I can simply fly LSA (my medical lapsed, not failed) and I am torn right now. My idea is to fly LSA for a year or so until I know I can get a medical. I have been wondering about what kind of plane I would like if I end up having to fly LSA forever. Waco's, Stinson's and any of the other airplanes I want to fly would be out. Altough I love Champs, Cubs, Luscombes and T-crafts...I am not sure I want to only fly those forever. I want something a little more fun that the run-of-the-mill LSA, so here is what I am thinking:

  1. Pitts - not a firebreathing Pitts as seen everywhere, but something like this, a copy of the original Pitts (which had a 55hp Lycoming). Here is a Pirep, and it sounds like a great fun machine: http://www.airbum.com/Pitts/PirepPittsReplica.html The issue with this airplane is the stall speed - not sure if it is under 45 knots - then again, the airplane in the article is the only one and it is on static display...so if I build one, fly it and the plane stalls at 50, or 55 kts, who would know?
  2. Clip-wing Cub or Clip-wing T-Craft - these are fully aerobatic and fun, yet again, I am not sure what the stall speeds are with either with the shortened wings.
  3. Rose Parakeet - these are neat little airplanes and fully aerobatic. Also not sure of the stall speed, but I am not as worried about that with this airplane:
parakeet3.jpg
 
I see guys. Thanks for telling me that! Also, is it possible when buying an aircraft to have options of the airplane to be measured in mph or knots? I prefer the knots airspeed indicator. Can I also choose which type of engine that the plane could run on when buying an aircraft? In this case, I prefer the O-200.
 
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