Effect of power loading on Vy ?

[Trolltuner]

Vy increases with weight, decreases with altitude. But what, if any, effect on Vy occurs with a change in power loading?

Example: A Cessna 182 w/MTOM of 3100 lbs and a stock, 230 hp engine has a power loading of 13.5 lbs/hp and a sea level Vy of 80 KCAS, decaying to 73 KCAS at 14,000 ft.

The stock engine is replaced with a 300 hp IO-550, and power loading becomes 10.3 lbs/hp. Obviously, the airplane will climb better at the same Vy. But is there also an effect to or change in Vy due to the power loading delta?

And a related question: Is there a way to reasonably approximate the correct decrease in Vy vs. altitude?

Thanks!

[Genghis the Engineer]

I don't have a pat answer to offer, but believe that the answers can be found in either Francis Hale's book "Introduction to Aircraft Performance, Selection and Design", or John Lowry's "Performance of Light Aircraft ".

If you can't get hold of either, or don't get an easy answer from anybody else here, PM me a postal address and I'll photocopy the useful pages for you.

G

[djpil]

John Lowry has some good stuff online at Propeller Aircraft Performance and The Bootstrap Approach (http://www.allstar.fiu.edu/AERO/AirPer-BA.htm) and more at the Avweb website where you can download the free spreadsheets - this link takes you to the Cessna 182 data (http://www.avweb.com/news/airman/182418-1.html).
A bit of tinkering with this should have your questions answered, Trolltuner.

[Trolltuner]

GtE, thank you - sent you a PM.

djpil, thanks as well. I've actually got his book - I'll try to become "less lazy" and do some studying. So far, it appears that power loading has very little, if any, effect on Vy.

Cheers ! :)

[Capt Pit Bull]

At a guess, I'd say its going to be more about the prop than the engine.

Since more power basically just stretches the power available graph upwards and leaves the power required graph untouched then the point with the most excess power isn't going to change very much.

But if you change the prop, then you may move the 'hump' in the power available graph left or right and therefore change Vy.

However, if you change the engine you'd probably need a different prop?

pb

[Trolltuner]

Capt PB, thanks, that sounds pretty good to me.

Yup, many of the engine upgrades demand a new prop - from different pitch, hub, balance, and sometimes two-bladed to three-bladed or more.

Anyone have a clue as to how to quantify the Vy delta? :)

Merry Christmas !

[Trolltuner]

djpil, reviewing some older posts it seems I neglected to thank you for your helpful info. So, THANK YOU! :ok:

Tom

[Jane-DoH]

What's Vy?

[Trolltuner]

Hi there, Jane-DoH.

Vy is one of many "V" airspeeds used to define aircraft performance, in this case the "best RATE of climb" airspeed. There are a bunch of others (Vx, for example, "best ANGLE of climb", etc.). HERE (http://en.wikipedia.org/wiki/V_speeds) is a longer list and explanation if you're interested.

Cheers,

Tom