Charlie's observations are right in line with what I have seen so far. Still, I would not want to give up the ability to do wheel landings comfortably. 74" is at the limit for my -4. The -8 or the -4 with the updated longer gear would not have this problem. The -8 I'm building will have nothing less than 76" prop and more if I can get it. As I accumulate more hours I clearly see the trend. Huge advantage at low speeds (acceleration & climb) but advantage diminishes as speed approached maximum. With the IVO prop (72" dia) I saw the same thing but the advantage diminished to zero at about 140 mph and then became negative above that. I still have not run the new drive & prop to top speed. I attempted to yesterday evening but the dreaded SAG (Sparkplug Attention Getter as Ed calls it) struck as I was approaching 220 MPH. My best guess is that the zero point (same performance as with -B drive) is right at this speed. Things may improve after I get the cuffs built (today's project). BTW, this -C drive stuff is very encouraging but it's way too early to close the books on this. One week of testing does not prove anything about long term effects. It's always the unexpected things that are the bane of the experimenters' life. The 13B tension bolt problem took over 1000 hours to show up. I'll be flying on "Orange Alert" status for hundreds of hours before I feel as comfortable as I did with the -B drive. Tracy Crook ----- Original Message ----- From: Charlie & Tupper England Sent: Tuesday, March 23, 2004 9:21 PM To: Rotary motors in aircraft Subject: [FlyRotary] Re: C mounting on a B plate?? Renesis & RD-1Cdrivetesting You guys with nose wheels shouldn't get too excited. One of the reasons
that almost all bush planes use tailwheels is that the nose gear is just
too fragile for rough field operation. Guess what the other reason is.
FWIW, I've flown a short-legged RV-4 with a 76" dia. prop. I didn't do
it very much (long story) but it can be managed by doing all takeoffs &
landings tail low.
RE: Tracy's radically improved performance, I'm now flying Chuck
Dunlap's old Lyc powered RV-4 (Hi Chuck). It's got a 62" dia 3 blade
climb prop because he flew out of high altitude gravel strips. Down here
in the lowlands of Mississippi, it turns about 2450 static & will turn
over 3000 rpm in level flight. I recently tried a prop originally made
for a 180 hp engine, originally 72", cut down to 68" dia., a very bad
prop because of the 'surgery'. It was about 5 mph faster at full
throttle & turned not quite as high an rpm as the 3 blade, but the
takeoff performance was radically different. The extra 6" of diameter
probably cut at least 30% off the takeoff roll. Vance Jaqua (sp?) posted
a prop efficiency chart on the 'other list' comparing optimized props of
various diameters. Bigger (dia.) was always better until speed got over
200, at which time the smaller props became as efficient as the larger
ones. I'm pretty excited that Tracy will have the Renesis & big prop
debugged by the time my -7 is ready for an engine. (Go for a 76" dia on
the RV-8. :-) )
Charlie
Ed Anderson wrote:
> Sounds like all around great news on the new gearbox and prop. Keep
> the reports coming.
>
> If such a "retrofit" of a B shell to C internals is possible and
> economical then that could move the trend toward the 2.85 even quicker.
>
> Shucks, if you used NA rotor housings it sounds like you wouldn't even
> need a muffler {:>).
>
> I am somewhat surprised that you can get the same airspeed with only
> about a 5% difference in rpm - sounds like my initial assumption that
> a higher rpm (and fuel burn)would be required to get the same
> airspeed is not valid. Perhaps the much greater pitch gets more work
> done per revolution. I wonder if possibly the fact that at higher
> rpm you not only get the benefit of more power strokes per second, but
> at the higher rpm the airflow in your manifold (assuming you are using
> the same dia tubes as before) is at a higher velocity and therefore
> great inertia for stuffing even more air/fuel mixture into the
> combustion chamber when the port opens.
>
> In any case, sounds like all pluses for us guys with nose gears {:>)
>
>
>
> Ed
>
> Ed Anderson
> RV-6A N494BW Rotary Powered
> Matthews, NC
>
> ----- Original Message -----
> From: Tracy Crook <mailto:lors01@msn.com>
> To: Rotary motors in aircraft <mailto:flyrotary@lancaironline.net>
> Sent: Monday, March 22, 2004 11:02 AM
> Subject: [FlyRotary] Re: C mounting on a B plate?? Renesis & RD-1C
> drivetesting
>
> The -C drive has very different internals but I will look at the
> feasibility of reworking the -B housing to receive the -C guts. I
> think it can be done. Yes, the -C bolts right up to the same
> adapter plate. I think you are right about the 2.85 becoming the
> preferred ratio, but only if you can handle the longer prop. You
> nose draggers have the advantage here.
>
> The more I fly it the better I like this setup. The higher rpm
> was very disconcerting at first but I acclimated rapidly. And
> now that I have digested the fact that the actual rpm difference
> at normally used throttle settings is only about 5%, I absolutely
> love it. Another good sign is that the manifold pressure is now
> more than 5% lower at any given airspeed that I've tested so far.
> Even if the wear rate is up 5% or so it would be a non issue.
>
> One more plus for the 2.85 is something I hesitate to mention.
> It's kind of like the "engine making oil so I have to drain some
> out" thing, kind of unbelievable. It makes sense that there
> would be less prop noise but I'm also getting less engine noise.
>
> I was getting tired of the increased noise with the Hushpower II
> muffler and was almost ready to put the Spintech back on even
> though it costs at least 5 - 6 mph in drag. But with the -C drive
> things have quieted down substantially. I think part of the
> credit for this goes to the difference in RPM moving the
> vibrations away from the resonance point of the sheet metal panels
> in my RV-4 but even observers on the ground have mentioned
> that the engine sounds quieter.
>
> I better shut-up now, this is starting to sound too good to be true.
>
> Tracy
>
>
> ----- Original Message -----
> From: Ed Anderson
> Sent: Monday, March 22, 2004 8:30 AM
> To: Rotary motors in aircraft
> Subject: [FlyRotary] C mounting on a B plate?? Renesis & RD-1C
> drivetesting
>
> Sounds great thus far, Tracy
>
> Imagine having so much thrust that you can't hold the
> aircraft still for maximum static, must be tough {:>). If you
> initial observations hold regarding fuel consumption and
> performance, then I predict the 285 will soon become the
> standard. If the fuel burn/performance is a wash then only
> engine wear from higher rpm might be a factor, but since the
> rotary seems to only have no/ minimum wear in any case, that
> probably will not be a significant factor.
>
> So how much are you given for 2.17:1 trade ins? Seriously,
> will the B model mounting plate accommodate the C model gear
> box housing (looks like you mount it the same way). I presume
> it would not be so simple as swapping out the internals as I
> am certain the internal mounting/housing is different in the
> two. Third, in case you consider getting rid of that old
> performance prop, put me on top of your list.
>
> Ed
>
>> Homepage: http://www.flyrotary.com/
>> Archive: http://lancaironline.net/lists/flyrotary/List.html
|