Aircraft performing below book numbers

Antonio wrote:

both have been making a few knots better than book.

My Mooney was quite on the book figures in normal cruise, disregarding the bragging figures most books have at the time. Even though reaching book figures for a “C” is rare, I attribute it to the powerflow exhaust.

Antonio wrote:

again same as book as soon as we got our pilots to lean using the EGT gauges

Yea, that is it in many cases, ain’t it just.

Even if people do know how to read out some of the figures in the book, many don’t read the conditions for which the table was written.

And of course you get a lot of complaints that airplanes don’t reach “book speed”. You know what one of the more interesting “speed mods” is? Getting a TAS display like on an Aspen or similar! Because what those people were complaining about was IAS, not TAS, the difference of which they were oblivious to. They would not even notice that their GS on the GPS was constantly higher in zero wind and one guy in all earnest told me he was a blessed pilot because he always had a tailwind. I was not sorry to destroy that bit of confidence

I had a nice debate about that bit with someone doing a flight planning program and being a resident of a country where one hardly ever flies over 1500 ft MSL based the whole thing on IAS.

Antonio wrote:

What is the increase in HP due to it estimated at?

Difficult to say, particularly as I never owned the plane without it.

The previous owners actually did do a testimony for powerflow here

They say climb improved by about 200 fpm and they could reduce power by about 2" to achieve the same speed as prior install. I never was able to make much sense of that.

However, what I do know is that prior to the prop change, the airplane did true 150 kts on several occasions, something no stock C will do normally despite POH bragging rights. We also reached book values on most power settings, usually with a slightly better fuel flow. Take off performance always was better than book.

I did fly a stock C model at one occasion in the Netherlands and found it notably weaker in take off and climb. As it did not have a TAS indication I never got to check the speed on it.

Looking at Robins for sale when a Flying School was closing, several had a Factory statement that they could not meet book performance. We didn’t buy anything.

Maoraigh wrote:

several had a Factory statement that they could not meet book performance.

That is astonishingly honest. Particularly in older airplanes, POH’s at the time were quite optimistic, not to say marketing tools rather than honest information about performance.

While a lot of “underperforming” of airplanes is the result of pilots not knowing how to handle the airplane, e.g use of mixture, mistaking IAS for TAS, miscalculating TAS (which happens less now that there are nice TAS indicators such as in the Aspen PFD), not reading up on conditions for use of performance tables, some older POH’s are outright misleading in figures such as range and top speeds. And obviously, if those are taken directly into flight plan programs, this will result in garbage out and inaccurate flight plans as well.

When airlines get new airplanes, what they do mostly is to impose a 10% fuel penalty on them. Then they fly them on schedule and record the actual values until they get a performance factor which is consistent. That factor then is entered into the flight planning system. I recall a fleet of MD11’s I used to dispatch and they had performance factors from 1% up to 6% within the fleet.

Playing with POH’s is something I think far to few people do. Consequently they don’t know some rather interesting capabilities of their airplanes and often fly them sub optimum. There are sweet spots for range, speed and efficiency which can only be found when playing around with performance tables. Recalculating range is one item where lots of owners get rude surprises but at the same time honest values they can rely on.

Once that is done, flight verification is the next step. Again, it is vital to observe how performance is calculated so you are not comparing apples with oranges. And finally the result of all this has to be factored into your foreflight or sky demon or whatever flight planner you use. And of course the Final Reserve requirement introduced by EASA has to be factored into range calculations these days.

I find this one of the more interesting things you can do with an airplane used for touring. But something far too few people do.

Mooney_Driver wrote:

Recalculating range is one item where lots of owners get rude surprises but at the same time honest values they can rely on.

I don’t understand the point of the range tables in the POHs. They are completely worthless in practise.

Mooney_Driver wrote:

the Final Reserve requirement introduced by EASA has to be factored into range calculations these days.

Straw poll: How many EuroGA pilots flying under EASA regs are aware that since about three weeks the reserve fuel for non-commercial flights is final reserve fuel? That is, if it ever becomes apparent in flight that you will land with less that that amount, it is an automatic emergency (“MAYDAY FUEL”). You should now add contingency fuel separately to address any possible delays.

This is of course how CAT did it even before and also many private pilots, but it was not compulsory.

You cannot fly safely in that area of operations without a fuel totaliser, which almost nobody in GA has…