I had a look at the new video - looks like 30s acceleration to 90kts - jetguy should be able to give us a reasonably accurate HP value from this.

Thanks for the heads up.

Yeah that run matches very closely with the acceleration observed earlier. It

looks to take about 32 seconds to reach his 90 knot rotation. In the

previous episode it takes about 22 seconds to get from 20 knots to 79 knots.

In both cases I am starting to count only when I hear his engine at full power, and stopping when you hear him back off the power.

I spoke earlier about doing a more detailed calculation:

The simple reality is that there is nothing new and very little guesswork involved in performing very accurate aircraft performance analyses. This is always done when designing a clean sheet airplane and setting performance targets, as well as extracting those unknown numbers for a competitor aircraft.

So I have worked up a calculator that lets you compute the drag polar of any airplane for which you have

__accurate __data, such as from a POH. In the calculator I use the SR22 data to find the parasite drag coefficient Cdo, which then lets us put together the entire drag polar for the airplane. And also takeoff performance, cruise performance etc.

The same method can be used for any other airplane POH and I have run also the TBM 850 and Bonanza A36. It's very accurate.

Just a couple of notes on my earlier post, where I brought out some of the analysis methods: I had found a somewhat highish figure for Oswald Efficiency factor e, so it turns out that the Continental engine in the Cirrus actually makes a little more power than book. When I looked into it, I found that the new Contis are certified for rated power

__plus __5 percent, minus 0 percent. So they actually average a little more power than the factory number.

Using a figure of plus 3 percent, which works out to about 320 hp, we get an Oswald number of 0.85, which is very much in line with what we would expect [the C182 is 0.84, a technical paper on Oswald number

here].

Another article I found is about prop efficiency in Bonanzas in cruise, which is about 0.9, a very good propulsive efficiency. A couple of good articles from this Bonanza fellow, about the

IO550 power and the

prop efficiency.
Btw, Prof Rogers has a lot of interesting technical articles on his website, including a

DIY angle of attack indicator which would be dandy for flight testing experimental aircraft.

So here is the calculator with the Cirrus SR22 example worked out. The second sheet has the takeoff performance analysis. I also use the Raptor as a worked example, for an aircraft for which accurate data is

__not __known. The method lets us compute all the drag and thrust parameters as we did with the Cirrus, based only on the

__demonstrated __aircraft performance in its acceleration runs. You can use this with any POH for any aircraft.

Finally we estimate engine power, using the prop efficiency calculated for the Cirrus at 0.7 rotation velocity. This is the analytic method used when you are trying to

__predict __takeoff performance, and want to get an

__average __thrust number for the entire run. Plugging in the observed takeoff roll numbers from both the latest video and the earlier one gives pretty much the same results.

The engine power comes out to about 230 to 240 hp, which is more than I expected, but this is because of the high rotation speed, and thus the

__higher drag. __
Another interesting point is the fact that he needs to get to 90 knots before he can even rotate. This is because his rotation angle is severely limited by prop clearance. Peter mentions that he gets about 5 to 7.5 degrees, but this is only half of typical rotation angle of 15 degrees.

This has a very big impact on takeoff. This plane, at this weight at least, could rotate at about 77 knots if he had enough prop clearance. This is a disaster. It means a takeoff roll of 30 seconds plus and about 2,500 ft distance, at least. And this is with one guy on board and light fuel. If he loads the airplane even a little we may be looking at a 100 knot rotation, and a 3,000 foot run...and that's before we even take hot and high conditions into account.

This airplane is the epitome of failure. Any reasonable person would be greatly concerned at this stage and would call it off and start building the second prototype with lighter weight, a well proved engine with the required power, and all the improvements that are required in the aerodynamics, flight controls etc.

That's what a smart person would do. He or she would take these valuable

__lessons learned__ as an important stepping stone in reaching the ultimate goal of creating a decent airplane, and addressing all of the glaring shortcomings that are now absolutely telling you it's time to quit and start over.

About the Drag Calculator, if anyone would prefer an earlier Excel format let me know. Also any feedback or questions appreciated.

[Edit: the drag calculator may open on the second sheet for takeoff performance. you can click on the sheet tab at bottom to get to the drag analysis page.]