How slow can a 65hp LSA go? What about 50hp?

[N918KT]

I'm just curious on how slow an LSA can go with regard to maximum speed in level flight (in knots) with a 65 hp engine if the plane weighs, let's say 1,220 lbs? What about an LSA with the same max gross weight but with a 50 hp engine?

[MovingOn]

.......

[drseti]

An Aeronca 7AC Champ has a maximum gross weight of 1220, as it happens. The one I used to fly had a 65 HP engine. Many have been upgraded to 75, 85, 90, or even 100. The climb performance improves with more power, but the cruise speed seems to stay relatively constant, no matter what you bolt onto the firewall. I think the Champ is drag limited to 85 MPH cruise, regardless of engine.

[zaitcev]

Is this a trick question? Of course it depends on how much money you're willing to drop on it. With a high enough aspect wing it can probably putt along at 25 knots. Just add carbon fiber.

[dstclair]

I'd venture a guess most of us LSA drivers could slow flight with flaps at 40-45 kts which would allow my Sting to fly backwards with the winds of the last couple days.

[zaitcev]

Pitman Dragonfly, which was approved as S-LSA with 65 hp Rotax 582 in 2012, has Vne of 55 mph and cruises at 35 mph.

[drseti]

At the back side of the power curve, I would expect any LSA to be able to sustain stable slow flight, with flaps, at 40 KIAS or less. This figure is based upon the ASTM power-off stall speed limit of 45 KCAS, the ability of propeller blast across an airfoil to increase lift, and the fact that, at high angles of attack, the average airspeed indicator reads 15% low.

[CharlieTango]

My old Challenger, 50hp could cruise under 50mph.

[3Dreaming]

How slow an airplane can go and maximum speed are two completely different things.

[drseti]

two completely different things.

Of course. The OP posed the question in terms of engine power. In a car, a more powerful engine can result in higher speed. Not necessarily true in an aircraft, where top speed is drag limited, and minimum speed is related primarily to airfoil design and weight.

As far as minimum stable cruise speed is concerned, anything that meets the LSA stall speed limit will cruise safely at 40 KIAS or less in slow flight. Top cruise speed for LSAs is similarly defined for us, but that 120 knot limit is in terms of CAS, not IAS.

[drseti]

To further muddy the waters for Kevin:

Remember that a glider has a stall speed, a cruise speed, a Vne, and zero engine power. So, there must be no correlation between speed and power...

[MrMorden]

I'm a little confused about why we are talking about lower speed bounds related to horsepower. The two are independent, stall speed being a function of the aerodynamics of the airframe and overall weight, not the power of the engine. A Vari-EZ with 50hp will stall at probably 60 knots, a Xenos motorglider with 50hp probably stalls about 30mph. The power is not a factor here, if the weight were kept the same and the two airplanes were both bumped to 100hp, they would still stall at the same speeds. Same at 200hp, 500hp, 1000hp.

Maximum speed to some degree correlates to horsepower...stall speed does not.

[N918KT]

Hello guys. Sorry I guess I did not make my question clear. I know that 50 hp and 65 hp LSAs are slow, I just want to know how fast they can go anyways, maximum level speed, even though I know that they fly slower than other higher powered LSAs.

[MrMorden]

Hello guys. Sorry I guess I did not make my question clear. I know that 50 hp and 65 hp LSAs are slow, I just want to know how fast they can go anyways, maximum level speed, even though I know that they fly slower than other higher powered LSAs.

Ah, that is a much better topic for discussion!

Even the old 65hp Luscombe 8A can cruise at 105mph, and I think a 80hp CT2K or CTSW (there were a few made) cruise over 100 knots/115mph. The Sonex is experimental, but gets 130mph from a 76hp VW engine and is sport pilot eligible. I think with the right design you might get 115-125mph from 65hp. The trick would be designing it to keep the stall speed within the LSA limits. Others may have info about other specific airframes.

[3Dreaming]

Hello guys. Sorry I guess I did not make my question clear. I know that 50 hp and 65 hp LSAs are slow, I just want to know how fast they can go anyways, maximum level speed, even though I know that they fly slower than other higher powered LSAs.

That is kind of what I thought you were asking. There are a bunch of airplanes out there with 65hp to compare. A Piper J3 Cub is about a 65-70 mph airplane. An Aeronca Champ/Chief are 80-85. Ercoupe is 75-80, they didn't build many with 65hp. Taylorcraft is 85-100 depending on year and model. Luscombe is 95-105. I think Luscombe held a 100 mile closed course speed record for many years of 118mph with a 65hp airplane. Many of the 2 seat Rotax 65hp airplanes were slower than any of the production airplanes. Like many said before HP doesn't determine the speed, but airplane design does. I would think that you could make a 150-160mph airplane on 65HP pretty easy, but I doubt you could get the stall speed slow enough to call it a LSA.