Max L/D, Minimum sink etc

Going to be flying an RV12 soon. Had a test flight with Van's and that was very, very nice....super actuarially. I also found the people there to be superb individuals who know their business and love it.

But now I want to nail down some knowledge. What is Max L/D at 1320# and what is Minimum sink at 1320#?

I assume normal "Vref" would be about 56 Kts or 1.3 Vso. If you thnk that's wrong please yell. But if it's true is that what I'd use on downwind, base and final with full flaps? I assume short final should be about 50 Kts.

I think I read that Va is 90 Kts. If not yell about that too.

Thanks a bunch
Ex Bonanza Bucko

Here's the POH

Good info here

http://www.vansaircraft.com/pdf/revisions/RV-12/User_Manuals/POH_SV.pdf

From the POH (page 6-10) link Previously given by Michael:
Maximum glide distance speed is 85 knots
Minimum rate of descent speed is 60 knots

These POH numbers are interestingly (to me at least) close to estimates previously given and very much doubted at the time.

http://www.vansairforce.com/community/showthread.php?t=50771

This link while esoteric and not necessarily correct does provide some interesting reading.

Note that the link estimates are in mph while the POH values are in knots.


-Dave

Ex Bonanza Bucko said:

What is Max L/D at 1320# and what is Minimum sink at 1320#?

Click to expand...

Your question is slightly vague. Are you referring to the values of max L/D and min sink, or to the speeds at which they occur? The values do not change with wing loading. They are always the same, determined by the aircraft's aerodynamic efficiency (shape). They occur at higher airspeeds as the wing loading increases. In theory (may be some slight variation but close enough) min sink equates to Vx, and L/Dmax to Vy.

X0ver0"
Sorry to be vague. I'm an old sailplane pilot and those numbers are among my religion. So please tell me what you think in terms that a dummy can understand....like airspeed.

EBB

A work of mine in progress

First, take a look at the various versions of my "TriangleTool" because it will help you get a set of numbers that will be able to be true at the same time. This idea will make more sense after you look at it.

But here's a problem: I've discovered with a high degree of probability that the speeds we are talking about are different with true zero thrust versus power versus dead engine (stopped and windmilling also differ). I am working on a new way to approximate zero thrust. But the really important numbers may be for "dead engine" and the rest may be academic. Beware: there can be very large differences.

Even more interesting, the speeds with power appear to be higher when you would expect them to be lower.

Testing and checking the numbers within the tool will help but the difficult truth appears to be that there is more than one correct answer. I would like to have an ongoing discussion of this, but for now, I just want to point out what you may run into in trying to nail down those numbers.

In a few days I will update the tool and post it on a public link for all to download and use. For now, the older versions are on my website.

Updated Tool

I posted the very latest version of my "TriangleTool" XLS at:
http://sdrv.ms/1a2fB7v
And it is a public link to a folder for this forum (or is supposed to be).

I got a well intended PM from a member who pointed out the 1995 work done by Jack Norris and Andy Bauer along with CAFE in testing a C152 sans prop. The links to those articles are on my website. They are worth reading over and over again.

If you compare the C152 emergency glide in the POH to the glide ratio that CAFE found you will see an enormous difference. I used the "true" drag curve of the C152 in analyzing the prop efficiency when combining that curve with POH data. That link is also on my site.

Jack validated that his zero thrust detection device duplicated a no-prop situation. CAFE used that device in about 4 airplane reports including the RV-6A. We also have zero thrust data for the C152 and Jack's Luscombe.

On my website are earlier versions of the tool with the data from each of those tests. There is also a link to the CAFE menu of reports. If one is interested, he can take the data from the old versions and plug it into the latest version which has more output information. The same basic math is in all of them.

The problem that I discovered is not in the tool but in the finding that the airplane is much different when propwash is hitting the fuse and wings. I am still working on revising my testing methods to deal with that, but the tool is based on zero-thrust drag curves. For now the bottom line is that the airplane has more than one "true" drag curve.

Changed speeds in the PoH

"Maximum glide distance speed is 85 knots
Minimum rate of descent speed is 60 knots"

These figures were quoted earlier from the PoH. The latest edition of the PoH, Revision 7, Dec 2013 quotes these as:

Maximum glide distance speed is 63 knots
Minimum rate of descent speed is 55 knots

Quite a difference!

The climb speed in the checklist at the front of the manual still says 75 knots, which I now assume is faster than the best rate of climb speed.

Cheers...Keith