PDA

View Full Version : Rocket Speed


smokyray
01-11-2010, 09:48 AM
To answer some performance and trim questions on the Matronics List I went out and flew yesterday! Thought I would share the data on my 15 year old HR2, FYI :)

I took my HR2 out yesterday evening during our unseasonably cool FL Swamp weather (34 degrees F) and made some speed runs specifically to look at my horizontal at various speeds. To compare, I know exactly where my RV4 was at different speeds in the 15 years I flew it and I changed the incidence based on several RV8R articles and Van's input to level it at high cruise. My fear at that time was the slow speed STOL characteristics would translate into a "float". None of this proved true and my RV4 actually trimmed and flew much better at high cruise after the change. I am approaching 1000 Rocket hours now, so I think I'm starting to get the hang of it too:)

My Rocket was documented in the logs that they set the horizontal based on John's plans and incidence settings which I believe is 2 degrees down incidence. It is a very early HR2 (1994) and has a stock RV4 tail with .020 tail feathers, stock HR2 cowling, 285HP Ly-Con IO540, 2 blade Hartzell D twist and One EIectroair Electronic Ignition running Automotive Denso L14U plugs, One Magneto running REM-37BY (hot) plugs, (my standard setup on my last two airplanes). I have larger tires (380 X 150 X 5) Van's Pressure recovery pants set high enough to clear 3" stones and a large size Aviation products dual fork tailwheel.

At 1/2 fuel, a 100 LB passenger 23 squared and 2000 MSL yesterday I was indicating 208 mph and showing 171 Knots GS, elevator trim level, elevator very slightly up. At 24 squared speed increased to 223 MPH indicated, 184 Knots GS. elevator trim 3 degrees down, elevator perfectly level. 25 squared yielded 235 MPH, 195 Knots GS, trim two full clicks down (5 degrees) and still a level elevator. Full throttle showed 29" MP, 2750 RPM, 252 MPH 209 Knots GS, 3 clicks (8 degrees fwd) and elevator level. The amazing part is I came back to my 1500 foot strip and my FAS was 63 Knots over the trees, touchdown at 58 Knots. What a great airplane!

Hope this data helps.

Smokey
HR2

rvmills
01-11-2010, 11:14 PM
Smokey,

Bring "Swamp Thing" out to some SARL races...we'd have some fun, brudda!

I know fast and low would be a whole new thang to you (ahem ;))...but I have a feeling you'd like it! :D

Not to mention...that's one fast mo-chine! Good Stuff!

Cheers,
Bob

Bob Axsom
01-12-2010, 01:37 AM
From the description it appears that you reduced the negative incidence of the horizontal stabilizer to favor high speed neutral trim and that appears to be an area for modification. If everything is "flat" back there at maximum speed it should result in minimum pitch trim drag and a higher maximum speed in level flight while shaving some of the pitch stability margin. Do you have the before change comparative speeds?

Another area that I could work on is the vertical stabilizer angle. It seems like an offset of the leading edge to the left could be determined experimentally to eliminate the wedge that I am currently flying with to center the ball. If everything was inline back there in max speed level flight some yaw trim drag could be eliminated under this condition and the max speed could be increased. The tail fairing would have to be modified to accommodate this change.

I am currently working on the molds for some 1/2" to 3/4" wing tips but I will keep these in my thoughts for the future. Thanks for the information.

Bob Axsom

pierre smith
01-12-2010, 05:05 AM
...is a good time for a coupla questions I've been wanting to ask.

Bob/Smoky, do you run your engine WOT and max revs during the recent races?

Secondly, do you lean at all, if so?

Dunno how fast my -10 is but I may just find out today:)

Best,

Bob Axsom
01-12-2010, 06:32 AM
...is a good time for a coupla questions I've been wanting to ask.

Bob/Smoky, do you run your engine WOT and max revs during the recent races?

Secondly, do you lean at all, if so?

Dunno how fast my -10 is but I may just find out today:)

Best,

I always run WOT and max rpm in races and I do lean the mixture in races.

Bob Axsom

F1Boss
01-12-2010, 07:36 AM
...is a good time for a coupla questions I've been wanting to ask.

Bob/Smoky, do you run your engine WOT and max revs during the recent races?

Secondly, do you lean at all, if so?

Dunno how fast my -10 is but I may just find out today:)

Best,

Lean for best power mix, which as I am told is about 125F rich...keep an eye on those CHT readings to see if your cooling is up to the job.

Good luck!
Mark

pierre smith
01-12-2010, 07:40 AM
...I'm getting more and more familiar with my Dynon EMS and CHT's run fairly consistently at 1430, Peak EGT, so it'll be simple to subtract 125. (1300). I was concerned about fuel burn for over an hour at WOT as well, because without leaning, it's way up there.

Best,

Toobuilder
01-12-2010, 11:36 AM
...I'm getting more and more familiar with my Dynon EMS and CHT's run fairly consistently at 1430, Peak EGT, so it'll be simple to subtract 125. (1300). I was concerned about fuel burn for over an hour at WOT as well, because without leaning, it's way up there.

Best,

Just remember that peak EGT is not a stable number... It varries with conditions. I'm thinking the Dynon has a "Peak" function which allows you to find any value from peak without doing any math.

Also, I'm thinking that 125 rich is a bit on the fat side for best power, but I could be wrong... It's been a while since I looked up the Lycoming data.

pierre smith
01-12-2010, 02:44 PM
....in the D-120 EMS and a separate little box appears next to the EGT temps that shows degrees LOP.

Best,

rocketbob
01-12-2010, 02:53 PM
Another area that I could work on is the vertical stabilizer angle. It seems like an offset of the leading edge to the left could be determined experimentally to eliminate the wedge that I am currently flying with to center the ball. If everything was inline back there in max speed level flight some yaw trim drag could be eliminated under this condition and the max speed could be increased. The tail fairing would have to be modified to accommodate this change.


Over the summer I put a new RV-8 VS/rudder on my -6 to replace the old one which had rivets coming loose and cracks in the rudder skins. Previously I had a trim wed on the rudder approx. 7" long, 1/4" wide to get the ball centered in cruise. When I installed the new VS I offset it to the left 3/32" in the hopes the offset would eliminate the wedge. It did, ball centered perfectly, and the fairing fit with no modifications. There was a slight speed loss going to the new taller tail, surprisingly did not feel any lighter but it is more effective.

rvmills
01-13-2010, 01:47 AM
...is a good time for a coupla questions I've been wanting to ask.

Bob/Smoky, do you run your engine WOT and max revs during the recent races?

Secondly, do you lean at all, if so?

Dunno how fast my -10 is but I may just find out today:)

Best,

Pierre...Hmmmm, asking a couple fighter pilots if they run balls to the walls...kinda like the "Bear in the Woods" question, aint it? :D

My caveat is that this info is from just two races and some speed testing, and I'm sure guys like Ax, John Huft, Tom Martin, Wayne Hadath, Boss Mark and SARL Puba Mike Thompson have much more data.

The Black and Blue knobs of course never move (well backwards anyway...till landing) :)

I also wondered a lot about leaning at high power, not wanting to get into the red zone down low. Turns out my first race in Pagosa was at 7-8K, so it matched what I do my speed testing at here in Reno, and I felt I could play with it without doing harm. My numbers from those tests are much like yours.

At 8500' last summer (so it was warm, and about 10-11K DA), at peak EGT, EGT's were 1450ish, CHTs were 380ish, and FF was 14.5 GPH. At "best power", EGTs were 1325ish, EGTs were still 380ish, and FF was 18.0 GPH.

Therefore, I planned to use 18 GPH for the race, and when I talked it over with Tom before the race, I believe that's what he was looking for +/-. Ran the whole race that way (richened up a little during the lower leg), and CHTs stayed cool throughout.

In Taylor, at 500' MSL, I was more cautious...just leaned a bit, and looked for low 1300's and 380ish CHTs. Turned out to be about 23-24 GPH, if memory serves. Given my CHTs and oil temp stayed pretty cool, I may be able to reduce my exit area and tweak my inlets a bit to decrease cooling drag. This piece (cooling drag and race leaning) is still something I am learning about. I think TB is right...temps do seem to vary a bit with OAT and varying condistions, so I need to get more data at lower DA's to find what a good best power is, while not running the engine to hot and hard.

As far as gas goes, since the races are 30-45 minutes long, even at 24 GPH, you can launch with less than full tanks and still land with legal VFR reserves. On my first race I went way conservative, and had something like 30 gals on board (MIke T laughed at me!). Cut it to 24 in Taylor, and landed with 10ish. Airventure Cup is probably another story, but seems like for the average SARL race, gas management is figuring how light you can comfortably (and safely) go.

Fun stuff!

So how fast did you run? :)

pierre smith
01-13-2010, 04:58 AM
...since I had a couple of GPS/D-100 issues, after installing version 5.2, on the way home. VOR's were so-so but GPS magenta line wouldn't show on D-100 HSI and I fiddled with that.. Seems it's been corrected and I may try an approach at AGS and then go balls-to-the-walls:)

Later,

BTW...we'll be in Paradise, Ca. on Tue and Wed Jan 26th and 27th for a quickie visit to my parents.

rvmills
01-13-2010, 09:06 AM
Have fun Pierre! I'm home on the 26thand 27th, if you'd like to try to hook up. Short time with your folks though, so whatever works for you. Talk at ya soon!

Cheers,
Bob

Toobuilder
01-13-2010, 09:49 AM
....in the D-120 EMS and a separate little box appears next to the EGT temps that shows degrees LOP.

Best,

The GRT unit in the -8 shows the delta from peak (both fat and lean)... Does the Dynon ony show LOP delta?

Christopher Murphy
01-15-2010, 08:41 AM
The largest gain in speed I got with my RV-4 came from adjusting the Horizontal Stab. I made a change in the Vert. Stab too but that improvement was small compared to the horizontal. I may have mentioned the figures on this forum in the past but I am keeping them to myself now that the competition is heating up.

Here one for you... the large screen door tailwheel springs and chains costs me 3 kts at race speed.

Chris M.

vfrazier
01-15-2010, 09:19 AM
FWIW, another data point... I moved the leading edge of my VS 1/4" to the left on my Rocket. The ball says I should have moved it 0.260" instead. It's very close... to close to mess with... but not quite perfect.

Given that most RVs have the wedge on the left side, you'd think that Van would fix it. I recall asking him about it.... 20 years ago.

YMMV

pierre smith
01-15-2010, 12:30 PM
The GRT unit in the -8 shows the delta from peak (both fat and lean)... Does the Dynon ony show LOP delta?

....but it only shows degrees LOP in a separate box, next to the EGT's when you activate "Lean" mode. It doesn't show ROP in a separate box.

Best,

F1Boss
01-15-2010, 01:11 PM
....but it only shows degrees LOP in a separate box, next to the EGT's when you activate "Lean" mode. It doesn't show ROP in a separate box.

Best,

The Dynon shows the delta between the highest EGT temp and the current (lower) temp. It should show you this difference in temp regardless of rich or lean ops. The problem is that you do not know if you hit peak or not, unless you actually go to peak EGT, and you are monitoring the temp trending as you richen back up.

With the TCM brain dead injection system (close relative to a Hillborn system), the pilot is almost fanning the mixture lever into a blur while making throttle adjustments. The upside is there is no venturi to restrict MP, so the system makes a bit more power, if the pilot gets the mix right. At any rate, while getting all this TCM mixture control nonsense figured out, I noticed that MY Dynon will indicate ROP or LOP EGTs in the same manner, but to tell ya the truth, I can't say if the power percentage indicator shows ROP or LOP accurately...:confused:

Time for another test flight!:D

Carry on
Mark

Toobuilder
01-15-2010, 07:39 PM
The Dynon shows the delta between the highest EGT temp and the current (lower) temp. It should show you this difference in temp regardless of rich or lean ops. The problem is that you do not know if you hit peak or not, unless you actually go to peak EGT, and you are monitoring the temp trending as you richen back up. Mark

I think that once "peaked", the display will only show the delta for the remainder of the flight - therefore, no need for two boxes (LOP, ROP). With the GRT unit, it is easy to tell if it has peaked or not because if it is showing a discrete temperature for that chanel, it has not peaked. Once peaked, all you get is the -xx replacing the former temperature read out. Determining LOP or ROP is up to the pilot to keep track of (and I've found myself on the wrong side of the "hill" more than once while managing mixture on the letdown to landing).