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IIRC, at low cruise they had comparable burns, but when they got up around 180-190mph, Tracy was crying 'uncle' due to fuel flow.
The problem is that Bernie's -6A was much, much cleaner than most RV's, with aftermarket cowl, pants, etc. He could flight plan a cruise speed as high as my 1st RV-4, but with almost 1 GPH lower fuel burn. That -4 was very clean for a stock early '90's era -4, running at ~ 190-195mph burning between 9 & 9.5 gph depending on altitude & speed. That's roughly 75% power on a 160 hp Lyc. (Bernie's -6A had a 160 also.)
Here are Van's numbers:
RV-6 Performance
150 hp 160 hp 180 hp
Speed - Solo Weight
Top Speed 198 mph 202 mph 210 mph
Cruise [75% @ 8000 ft] 187 mph 191 mph 199 mph
Cruise [55% @ 8000 ft] 169 mph 172 mph 179 mph
Stall Speed 49 mph 49 mph 49 mph
Speed - Gross Weight
Top Speed 197 mph 201 mph 209 mph
Cruise [75% @ 8000 ft] 186 mph 190 mph 198 mph
Cruise [55% @ 8000 ft] 168 mph 171 mph 178 mp
Fuel burn of the 160 hp at 75% & .45 lb/hp/hr is 9 GPH.
Fuel burn of the 180 hp at 75% & .45 lb/hp/hr is 10.1 GPH.
I think the cruise numbers above might be a little optimistic, but aren't that far off for Lyc powered RV's.
To get the typical RV builder's attention, the rotary's numbers need to at least come close to these figures.
I suspect that Van would publish an accurate report showing equal or superior performance by a rotary, but he's not going to endorse anything because he wants testimonials to how simple it is to build an RV.
Is anyone coming close to the Lyc numbers at 75% cruise?
Charlie
Ed Anderson wrote:
Charlie, I believe that Tracy Crook and Bernie Kerr have done side by side
comparisons. I don't recall all the details, but my recollection is that
they were very similar at some speeds and diverged a bit at others, but
nothing dramatic either way.
Of course, Tracy was in his 4 and Bernie in his 6 so was not quite a one for
one, but I think a reasonable comparison.
Unfortunately, I can't recall the Lycoming Bernie had installed. Perhaps
Tracy will jump in - although have not heard from him on the list recently.
Ed
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
----- Original Message ----- From: "Charlie England" <ceengland@bellsouth.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Sunday, July 11, 2004 9:01 AM
Subject: [FlyRotary] Re: Powersport RV8 in the RVator
DaveLeonard wrote:
Dave you need to write up an article for Rvator!!.
You bet I will. As soon as I install my intersection fairings and my new
Harmon rocket gear leg fairings and improve cooling and "borrow" an O2
bottle from the hospital. Perhaps even a bigger prop. That might be a
good
chance to go up into the flight levels and give Tracy Sailor a number to
work toward.
That would make a good article. :-)
Dave Leonard
A couple of questions/comments:
Tracy & Ed both seem to have respectable fuel burns at *low* cruise
settings. Unfortunately, other RV flyers seem to be quoting burns in the
10 GPH range at cruise speeds noticably lower than Lyc powered RV's at
the same burn (and 'reasonable' VFR altitudes).
10 GPH is the ~burn of a 180 Lyc at 75% power (full throttle, properly
leaned, 7k-8k feet). Is anyone able to match Van's published 75% cruise
numbers, both speed & fuel burn?
One of the biggest knocks against the rotary is the perceived excessive
fuel burn. I think that we need to see side-by-side flights with Lyc 160
& 180 HP RV's at commonly flown VFR cruise altitudes (6k-10k feet).
Until there are well documented comparisons showing similar fuel burns,
the fence sitters will remain on the fence or fall on the Lyc side.
Comments?
Charlie
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