Power from fuel flow - looking for data

[RV3 Pilot]

Originally Posted by ghatch

Back in my Cirrus days we used a formula to calculate % Power which is directly proportional to Fuel Flow while LOP.

Formula: FF X 14.95 = HP, HP/Max HP = % Power

7.7gpm x 14.95 = 115.12HP, Assuming a 180HP IO-360, 115.12/180 = 64% Power. Sound about right?

I use that formula for an 310HP IO-550 but I believe the constant is constant for our internal combustions engines but, only while running LOP. Walter Atkins might chime in to verify.

Gerry

Might be a Misprint

[ghatch]

Yes, it should be gph... sorry

[Kevin Horton]

Originally Posted by ghatch

Back in my Cirrus days we used a formula to calculate % Power which is directly proportional to Fuel Flow while LOP.

Formula: FF X 14.95 = HP, HP/Max HP = % Power

7.7gpm x 14.95 = 115.12HP, Assuming a 180HP IO-360, 115.12/180 = 64% Power. Sound about right?

I use that formula for an 310HP IO-550 but I believe the constant is constant for our internal combustions engines but, only while running LOP. Walter Atkins might chime in to verify.

This is essentially what this old Lycoming method is doing, but it tweaks things to account for compression ratio (higher compression is more efficient, so you get more power from the same fuel flow) and rpm (less power lost to friction at low rpm, so more power from the same fuel flow). It also accounts for how far LOP you are - their data shows the efficiency dropping off if you go too far LOP. And, there is data to cover ROP too.

[Noah]

Originally Posted by Kevin Horton

I've got an old Lycoming document that describes a method to determine power during cruise performance testing, using fuel flow as the main input. It isn't usable real-time in flight, but it could be used in conjunction with flight testing to produce power setting tables for a handful of combinations of rpm, MP, altitude and fuel flow. I've played around with this power calculation method a bit, trying to figure out if it produced consistent, credible results. If it does, I'll document it in a Kitplanes article and produce a spreadsheet to use it. If it doesn't provide consistent results, then I'll drop it. I'll give an overview of this old Lycoming method in the next message in this thread.

The big question I need to answer is does this method produce a consistent power no matter what mixture is used. I will answer that question by plotting speed vs calculated power, with points at the same rpm, MP and altitude, but at several different fuel flows. I've got a bit of data from my RV-8, but it will be some time before I can get any more, and I am not completely satisfied with the stability of my fuel flow indication, which makes is difficult to draw solid conclusions from my data. Also, I really need data from more than one aircraft, with more than one pilot, to see whether this method is useable in the real world.

Kevin,

Where did this analysis end up? Ever do that Kitplanes Article?

[Kevin Horton]

Originally Posted by Noah

Kevin,

Where did this analysis end up? Ever do that Kitplanes Article?

I got enough data to satisfy myself that the method is valid. I started drafting a Kitplanes article, but never finished it. It is in the queue of a list of flight test articles I intend to write. I just need to get off TDC and crank them out. I'm hoping to take a few days off in the fall and get started.

[Noah]

Looking forward to it, Kevin!

[Ironflight]

Originally Posted by Kevin Horton

It is in the queue of a list of flight test articles I intend to write. I just need to get off TDC and crank them out.

Yes. You Do.