RE: Light-Sport Aircraft Yahoo group Re: Cruising speed

I think its 120 KIAS at sea level, continuous maximum cruise speed.

 

From: Sport_Aircraft@yahoogroups.com [mailto:Sport_Aircraft@yahoogroups.com] On Behalf Of Bill C
Sent: Tuesday, March 09, 2010 6:01 PM
To: Sport_Aircraft@yahoogroups.com
Subject: Light-Sport Aircraft Yahoo group Re: Cruising speed

 

 

Here is an interesting post to another group concerning engine specs and how they effect this:

Re: Fastest Light Sport Airplane?
One thing is to remember is that top speed is limited to 120kts IAS NOT TAS. This is usually related to max continuous RPM of the engine. In other words, an LSA can have an IAS no higher than 120kts when running at it's max contious RPM. Therefore, the fastest LSA should be the one with an engine that can maintain max contious RPM (and thus 120kts IAS) at the highest altitude.

For example, a Rotax 912ULS has a Max RPM of 5800 and a max continous rpm of 5500. at 5500rpm the engine is running about 90% power. The highest altitude it can attain and still run at 5500rpm/90% power is roughly 3000ft. At that altitude, if IAS is 120kts, TAS should be roughly 127kts. If it flies higher than 3000ft it will not be able to maintain 90% power/5500 rpm and thus TAS will decrease.

Now a Jabiru 3300L has a max rpm of 3300rpm but a max continuous rpm of 2850rpm which is estimated at less than 75% of total power. As a result a Jabiru 3300L engine can maintain max continuous rpm of 2850 at and above 8000ft. At an altitude of 8000 feet, if IAS is 120kt, TAS is almost 140kts.

To take it a step further, the turbocharged rotax 914 can maintain its max continuous rpm to as high as 15,000 ft (although as of now, Sport pilots can not fly above 10,000 ft). At 10K ft with an IAS of 120kts, the LSA should be cruising at around 144kts TAS.

All this assumes that the airframe is clean enough to reach the 120kt IAS limit at it's max RPM. For example, a STOL 701 isn't coming close to that speed with any of the above mentioned engines. It is just too slow.

Hope this helps. My numbers are rough estimates.
Jon McDonald
Building Sonex #1287

 

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