On 3/28/2010 11:34 AM, Dennis Haverlah wrote:

Chris,

Your static is very low compared to mine!  My static is in the range of 5800 to 5850 rpm IIRC.  I'll confirm  static rpm soon.  Does the engine run smoothly at max rpm?  I didn't know your engine was a 4 port Renesis - I thought it was an  earlier RX-7 unit.

A question was asked about my exhaust system and Hp.

I do slightly better than my neighbor's 180 hp. Lyc, powered RV-7A.  He and I will try to make some more comparisons this spring.  I believe mine is in the area of ~190 Hp. but it is only a guess.  This is one reason I wanted to post performance numbers so we can compare similar and different systems.

My exhaust uses the Renesis exhaust manifold.  The exhaust is pointed forward toward the prop.  To reverse the flow, I used a 4" dia. stainless tube mounted horizontally and parallel to the prop.  The tube acts as a swirl tube - the flow enters parallel to the inboard end and exits parallel to the outboard end of the swirl tube and the exhaust is toward the rear of the aircraft.  The exhaust than enters a Hushpower II _Resonator_ and than out and down to the rear. The resonator is shorter than the normal Hushpower II muffler.  All my exhaust system is inside the cowl.  I used some stainless and some aluminum for heat shields. With 230 hours of total run time I have not had any problems.
See attached picture and the article in the current issue of Van's Rvaitor.

When I built the exhaust system "Swirl Mufflers" were the "in thing" on the list.  Also, I had trouble finding 180 deg. stainless tubing with a sharp enough bend radius to fit in the space available in the cowl.  If I were building it now I'd use a 180 bend stainless tube instead of the swirl tube.  Probably would make a little more noise and Hp!

Dennis Haverlah

Hi Dennis,

I pasted the numbers from Van's web site for the 7/7A and from your previous post below. Van's numbers are almost certainly for a constant speed prop, so your climb numbers would be in the ballpark for 180-200 hp. But the cruise numbers don't line up at all, so I'm trying to sort out the reasons for the discrepancies. Full throttle, fully leaned at 7500' with a Lyc 180 hp should produce a tad over 10 gal/hr (maybe 10.5 on a bad day) & a tad under 200mph. Many -6's & 7's have shown this to be a repeatable number. If you're showing 195, you'd be in the ballpark for speed, but the fuel flow is way higher than I would expect; a 5% penalty is understandable but a ~20% penalty is surprising. Was that 7500' run at full throttle and leaned to best power or full rich?

8-8.8 gph at 7500' should yield a speed slightly under the 160hp 7500' (75%) speed of 192 mph. Again, repeatable among multiple RV-x's.

If your neighbor's Lyc numbers are worse than yours, he's got something seriously wrong with either his plane or his operating technique (maybe afraid to lean the Lyc properly?).

Tracy & I (a rather dirty Lyc 160hp RV-4) have done a couple of same-altitude/same-speed cross countries together, & he's been about 5% worse (a reasonable, acceptable compromise #) than me both times, with both of us flying his low/mid altitude economy flight profiles. No one else flying a rotary seems to come anywhere near his fuel efficiency numbers. I'm curious about whether the variations from Van's numbers are due to major cooling drag differences, or tuning/engine setup issues.

Anyone have any thoughts?

Charlie

/Solo Weight 1400 lbs
Gross Weight 1800 lbs/ *160 hp* *180 hp* *200 hp*
*/Empty weight and performance measured with Hartzell 2 Blade C/S prop/*
*Speed - Solo Weight*
Top Speed 202 mph 210 mph 217 mph
Cruise [75% @ 8000 ft] 192 mph 200 mph 207 mph
Cruise [55% @ 8000 ft] 173 mph 180 mph 187 mph
Stall Speed 51 mph 51 mph 51 mph
*Speed - Gross Weight*
Top Speed 201 mph 209 mph 216 mph
Cruise [75% @ 8000 ft] 191 mph 199 mph 206 mph
Cruise [55% @ 8000 ft] 172 mph 179 mph 186 mph
Stall Speed 58 mph 58 mph 58 mph

*Climb/Ceiling - Gross Weight*
Rate of Climb 1,400 fpm 1,650 fpm 1,900 fpm
Ceiling 18,500 ft 20,500 ft 22,500 ft



Numbers from previous post:
Field elevation  900'
Climbed @  110 kts. indicated air speed  - Full throttle climb to 7500"
OAT 70 deg. at takeoff
Initial climb rate was 1800 - 1900 fpm
( I get ~ 2400 fpm with only 21 gallons in the tanks)

@ 4500" the climb rate was ~ 1400 fpm
Water 188 F, Oil 200 F

@ 6000' the climb rate was ~ 1250 fpm
Water 188 F, Oil 203 F , OAT 60 F

@ 7500' climb rate was ~ 1000 fpm
Water 189 F, Oil 204 F

I leveled off for about 5 minutes than went to full throttle again.

_Full throttle for about 3 ot 4 minutes @ 7500' _
MP 23.3 in.
Fuel flow - 12.1 gph
TAS 193 mph  - EM-2 data
Engine: 6660 - 6680 rpm
Water 184 F, Oil 205 F  OAT 65 F

When I fly at 7500' I _normally_ use 8 to  8.3 gph
TAS 157 mph
Water 160 F, Oil 180 F


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