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RV-9A and density altitude

Bryan Wood

Bryan Wood

Well Known Member
Yesterday while coming home from OSH our 9A couldn't deliver the altitude that we were asking of her. This is the first time that this has happened and I thought other 9 drivers might like to know the conditions that humbled our plane and it's owner. Departing Kimbal, Nebraska the density altitude was 8,900' and the plane got off the ground nicely. It would not however climb to 14,500' which we badly needed for our leg to Elko, Nevada. Being loaded heavy and temps at 12,500' being in the 80's F the plane just wallowed along at 12,500' in a nose high attitude barely maintaining the altitude it had fought so hard to obtain. We ended up turning our heading to follow the direction of the mountains and cool down the oil while the range subsided slowly to a less threatening body. As fuel burned and temps came down the idea to use the slightest bit of flaps seemed to work and we got up to 14,500' and were able to turn back on our course. This plane has never appeared to have an altitude limitation when we have traveled, but yesterday the extremely high density altitudes really took their toll. When each tank had burned off about 5 gallons of fuel the nose came down at 14,500' and the view out the front was a more normal kind of attitude. Prior to that the ride was kind of similar to a boat that doesn't have enough power to plane out and just mushes along with the bow in the air. This same scenario happened again departing ELKO, Nevada when we were asking 12,500' out of her. Again, slight flaps and after burning about 5 gallons from each tank the nose came down and the ride was fine.

All in all a good day though making it from OSH to San Jose and landing in the daylight!
 
thanks

I guess mother nature can even humble the RV sometimes. You mentioned "heavy". Did you have an unusual load in the baggage compartment? And do you know how much? Just curious if that was a factor. I have noticed performance differences when pilot/passenger, fuel and baggage were at max. even at lower altitudes. Especially when hot and humid. Stills performs well, but with a noticeably different "feel".
 
High, Hot, and Heavy

12,500 at 80F is a density altitude of 16700 feet. Impressive performance at that altitude and weight.

John Clark
RV8 N18U "Sunshine"
KSBA
 
I guess that's close to right, Vans shows a gross weight ceiling of 19k' for a 9A with 160 hp, and minor differences in aircraft and atmospheric conditions can definitely account for the delta between book and actual performance.
 
Bryan Wood said:
Departing Kimbal, Nebraska the density altitude was 8,900' and the plane got off the ground nicely. It would not however climb to 14,500' which we badly needed for our leg to Elko, Nevada. Being loaded heavy and temps at 12,500' being in the 80's F the plane just wallowed along at 12,500' in a nose high attitude barely maintaining the altitude it had fought so hard to obtain.
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What engine and prop do you have? What leaning technique did you use during the climb? How did the performance on this flight compare to the heavy weight high altitude climb performance testing you did during phase 1 flight testing?

The speed for best rate of climb will decrease as the altitude increases. The speed for best rate of climb will increase as the gross weight increases. But these relationships should become known as a result of the phase 1 test program, so it is a bit of a puzzle why the aircraft's performance would have decreased since then.
 
Here are some of the particulars. 170 hp 0-320, the Hartzell spinning at 2700, leaned to peak and then rich about 1/8 of a turn. We were at gross weight and there were up and down drafts over the mountains. This was just simply the first time I found the edge of the planes ability when traveling. This is basically a "For what it's worth" kind of thread so 9 drivers know there are limits because the plane doesn't give hints that you'll ever find any. With the right coaxing the plane responded, but it wasn't pretty.

Edit... The real problem was the lack of cooling in the thin hot air. Trying to balance the oil temps and airflow over the engine and continue to climb was what proved to be a balancing act. Sure the nose could have been pulled up more but the result would have been higher temps very quickly. So all of this took place at 105 knots indicated or around 120 mph. Kevin, this didn't compare to any testing that I did initially because finding air this hot up this high didn't happen. After leveling off the oil temp came down to around 210F in twenty minutes or so. It took a long time to get under 200F, and eventually it came down to around 190F. Usually the temps down lower are steady at 180F and that is what I'm used to seeing.
 
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I'm a bit baffled that if the speed was at Vy or higher for flaps up, that extending a bit of flap would improve the rate of climb. If extending the flaps helped, this suggests to me that the speed was perhaps a bit low. This would also help explain the "wallowing" and "nose high" comments.

Terry Jantzi managed to climb his 180 hp RV-6 up to 26,000 ft. An RV-9A, with the longer wing span, should have a higher absolute ceiling than an RV-6, if everything else was equal. Terry was solo, with minimum fuel, so his weight was a lot lower, which is certainly a major factor. He did run into oil cooling issues between 12,000 and 18,000 ft, and had to increase his airspeed. And his altitude attempt was in Feburary, so the air was definitely a lot cooler.
 
Kevin Horton said:
I'm a bit baffled that if the speed was at Vy or higher for flaps up, that extending a bit of flap would improve the rate of climb. If extending the flaps helped, this suggests to me that the speed was perhaps a bit low. This would also help explain the "wallowing" and "nose high" comments.
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I've just been reading "Stick & Rudder" so bear with me, but wouldn't dropping flaps a little increase the effective AoA of the wing, meaning the nose could be lowered while keeping the same effective wing AoA, and increasing stall speed (so you can get away with the slow flight)? Please correct me if I'm off-target with my understanding...

Bryan, do you have any airspeed notes from the different phases of that flight?
 
Sensitive to leaning

My last long trip I flew at 15,500 eastbound. The density altitude was around17,500. Climb up the last bit was anemic, only 200-300 FPM at gross.

Also it seemed I needed to keep it leaned about right to get maximum performance. Once up it flew fine and I got decent cruise speed.
 
Some numbers

Kevin Horton said:
I'm a bit baffled that if the speed was at Vy or higher for flaps up, that extending a bit of flap would improve the rate of climb. If extending the flaps helped, this suggests to me that the speed was perhaps a bit low. This would also help explain the "wallowing" and "nose high" comments.
Click to expand...

Believe me, if the nose would have been lowered for more speed the plane would have decended. This thing was being babied to get it up there. (You may be assuming that everybody is setting their gross weight at the factory recommendations. Maybe we were legally at gross, but a tad heavy for what Van's would like to see.:rolleyes:)


The flap thing is a little trick my father in law taught me back when when I was still flying a Cherokee. Basically if ever in trouble and not able to climb without flaps or if one notch of flaps makes it worse he said to just put my airport guide or similar under the flap handle providing just a few degrees of flap. One time after departing Reno with a load this was the only thing that allowed us to climb. With this in the back of my mind I tried it on the RV Friday and it worked also. By applying flaps on the RV it was basically one quick toggle of the switch with very slight movement of the flaps. The climb immediately followed. I've seen it work twice now in two different airplanes and whether or not it makes sense in theory it works in the airplane. Seriously, go try it.

I'm familiar with Terri Jantzi's flight and can pretty much bet he wouldn't have wasted the gas to try and get to 26K with a load like we were carrying. Apples and Oranges. My wife chose to stay home on this trip and so everything that we would normally share had to be duplicated for my friend to have a place to sleep. This made us heavy!

Airspeed up there was really good. The wing didn't give up hardly anything for being high once we burned off enough gas to fly with the nose down in a more normal attitude. We indicated around 121 knots on the leg at 14,500", and around 122 or 123 knots on the leg at 12,500'. This gave trues around 155-157 knots. In cruise the prop was set at 2600 instead of 2700 just because it made me feel better to not totally wring its neck all the way home.
Considering the density altitudes involved the speed was terrific and the burns were just under, but we'll call 6 gph. We were actually going to land at Wendover near Salt Lake but the burns were so low and the air was so smooth we pushed on to ELKO.

Best,
 
Bryan - you mentioned being "heavy"... any chance you were a little heavier than you thought? Those pounds can sneak up on us! Especially (as someone asked) with the weight being a bit aft? That -9's still a remarkable aircraft.

DJ
 
Phyrcooler said:
Bryan - you mentioned being "heavy"... any chance you were a little heavier than you thought? Those pounds can sneak up on us! Especially (as someone asked) with the weight being a bit aft? That -9's still a remarkable aircraft.

DJ
Click to expand...

Yes, but I'm stickin' to "We were at legal gross." ;)
 
9A and density altitude

I was just going to post a similar message. I was flying my 9A out of Bridgeport, Ca on 01Aug08 at a DA of about 10000feet, OAT85dF. I could not use full throttle for more than a minute or CHTs started going way too high. Engine is stock roller tappet O320D1A new from Lyc, with 100 hours on the clock. At full throttle and 1680 lbs I could get 500 FPS climb, but had to significantly reduce throttle to keep CHTs down. Then I could only get 100-200 FPS climb, which was not acceptable at all.

My question to the group: What have you done to get better engine cooling? My oil temps are fine (180dF), but even at sea level, a warm day pushes the CHTs over 400dF which is where I start getting worried.

Best regards,
John Severyn
 
RichB said:
I've just been reading "Stick & Rudder" so bear with me, but wouldn't dropping flaps a little increase the effective AoA of the wing, meaning the nose could be lowered while keeping the same effective wing AoA, and increasing stall speed (so you can get away with the slow flight)? Please correct me if I'm off-target with my understanding...

I've done some testing of flap position on my Lancair during cross-country flights at high density altitudes, and when flying high or highly loaded, I change the amount of reflex to bring the nose down and increase the speed; I can see 3-4 mph change in going from -8 deg to -6 deg. When you put down the flaps, you change the airfoil camber, which, in turn, changes the position of the drag-bucket minimum relative to CL. The higher the camber, the higher the CL at which the parasite drag minimum occurs. What he did was spot-on!
However, I have a hard time believing that the OAT at 12,500' was 80F. That's 66F above standard, and in my limited flight hours at 11,500' and 12,500' I've never seen anything approaching that. Some of the testing I have done with RVs shows that there can be flow out of the cooling inlets which goes down the side of the fuselage and into the cabin inlets where so many place their OAT sensor. On one test the OAT showed almost a steady 15C from 4000' to 10,000'. That was changed by putting the sensor in the tailcone up and behind the elevator cutout.
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elippse said:
RichB said:
However, I have a hard time believing that the OAT at 12,500' was 80F. That's 66F above standard, and in my limited flight hours at 11,500' and 12,500' I've never seen anything approaching that. Some of the testing I have done with RVs shows that there can be flow out of the cooling inlets which goes down the side of the fuselage and into the cabin inlets where so many place their OAT sensor. On one test the OAT showed almost a steady 15C from 4000' to 10,000'. That was changed by putting the sensor in the tailcone up and behind the elevator cutout.
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Looking at the weather for today for Cheyenne, Wyoming it is going to be 90 degrees. I don't know what it was on Thursday, but it was really hot and this is the area we were in give or take 75 miles. Cheyenne is 6100' and will be 90, so dropping the temps by 3 degrees per thousand feet looks like it will be at least 72 degrees at 12K today. With an inversion, or higher ground temps it could easlily reach 80F and I can assure you it was. It was hot in the plane and the dumb thing didn't want to climb. Mabe your Lancair goes so fast thru this stuff that you can't feel the heat. ;)
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Bryan Wood said:
elippse said:
Looking at the weather for today for Cheyenne, Wyoming it is going to be 90 degrees. I don't know what it was on Thursday, but it was really hot and this is the area we were in give or take 75 miles. Cheyenne is 6100' and will be 90, so dropping the temps by 3 degrees per thousand feet looks like it will be at least 72 degrees at 12K today. With an inversion, or higher ground temps it could easlily reach 80F and I can assure you it was. It was hot in the plane and the dumb thing didn't want to climb. Mabe your Lancair goes so fast thru this stuff that you can't feel the heat. ;)
Click to expand...

Last Thursday, climbing out of Salt Lake City (4200' msl) in an RV9A at 7:00 in the morning, it was 71 degrees on the ground, but 85 degrees with a few thousand feet of altitude. In this case, an inversion was very possible.

L.Admason --- RV6A
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14,500 and higher

Bryan and all....
I have never had an issue climibing my 9 to any altitude. If you go to the link below and look at my performance you will see the 9 is more than capable. By using the information available on the screen view you can see the density altitude is at least 16,500. We were at gross...possibly 20lbs over. I think it would be very easy to exceed gross wt by 100lbs or more so I can see why your performance may be lacking and I don't think it is a fair statement to say the 9 would not give you what you were asking for when you were more than likely asking for more than what it was designed to give.

Please don't take this too seriously but I just have to say I have never had an issue with performance when operating within the specs. :)

As far as high CHT, I will climb out in the Phoenix area at lower altitudes with CHT around 450. As you can also see % of power at altitude is 52%. If airspeed is maintained for cooling CHT should not be a factor above 10,000ft. or for that matter above 5,000ft. I did some testing and if I maintained level flight at 4,000ft and allowed CHT to stabilize I was not able to reach high CHTs if I initiated a climb from 4,000ft.

BTW we did a 3:23 flight, most of it at 14,500ft, burned 21.5 gal, = 6.35gph average speed was 150 kts. 27 statute MPG. It just doesn't get much better than this!


http://picasaweb.google.com/rpping54/14500
 
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Bryan Wood said:
elippse said:
Looking at the weather for today for Cheyenne, Wyoming it is going to be 90 degrees. I don't know what it was on Thursday, but it was really hot and this is the area we were in give or take 75 miles. Cheyenne is 6100' and will be 90, so dropping the temps by 3 degrees per thousand feet looks like it will be at least 72 degrees at 12K today.
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Actual temperature variation with altitude is often quite different from the standard assumptions, especially if the temperature at the surface is far from standard. Actual upper air temperature data is taken with sounding balloons at a number of stations across North America. The closest data to Cheyenne appears to be Denver, CO. The data from 12Z today showed the following temperatures vs altitude:

Code: 
-----------------------------------------------------------------------------
   PRES   HGHT   TEMP   DWPT   RELH   MIXR   DRCT   SKNT   THTA   THTE   THTV
    hPa     m      C      C      %    g/kg    deg   knot     K      K      K 
-----------------------------------------------------------------------------
 1000.0     -6                                                               
  925.0    705                                                               
  850.0   1465                                                               
  836.0   1611   22.2    6.2     35   7.16    240      5  310.9  333.3  312.2
  820.0   1780   25.2    5.2     28   6.81    244      4  315.8  337.6  317.1
  802.0   1975   26.2    3.2     23   6.04    249      4  318.8  338.5  320.0
  760.3   2438   22.5    2.3     26   5.96    260      2  319.7  339.2  320.9
  734.1   2743   20.1    1.6     29   5.90    295      4  320.3  339.7  321.5
  700.0   3155   16.8    0.8     34   5.83    305      7  321.1  340.2  322.2
  659.5   3658   12.8   -1.8     36   5.12    255      7  322.1  339.1  323.1
  644.0   3858   11.2   -2.8     37   4.86    253      7  322.4  338.6  323.4
  612.5   4267    7.4   -3.5     46   4.84    250      7  322.7  338.9  323.7
  568.3   4877    1.7   -4.6     63   4.80    260     11  323.0  339.1  324.0
  539.0   5308   -2.3   -5.4     79   4.77    254     16  323.2  339.1  324.1
  520.0   5592   -4.1  -10.1     63   3.43    250     19  324.3  336.0  325.0
  500.0   5900   -6.5  -12.5     62   2.94    245     22  325.1  335.2  325.6
  487.5   6096   -8.0  -13.6     64   2.76    245     23  325.6  335.2  326.2
  457.0   6598  -11.7  -16.4     68   2.34    226     22  327.0  335.2  327.5
  454.0   6649  -11.5  -22.5     40   1.39    224     22  327.9  332.9  328.1
  442.0   6854  -12.7  -18.7     61   1.99    216     21  328.9  336.0  329.3
  433.1   7010  -13.9  -20.6     57   1.72    210     21  329.2  335.4  329.6
  429.0   7082  -14.5  -21.5     55   1.61    214     21  329.4  335.2  329.7

You'll note that the temperature at 3658 m (12,000 ft) was 12.8 deg C, or 55 deg F (ISA + 21.6 deg C). While the temperature at ground level increases significantly during the day, due to the sun's heat on the ground heating the low altitude air, the temperature at altitude doesn't vary that much. The data from 12 hr earlier showed 14.3 deg C at 3658 m (12,000 ft), or ISA + 23.1 deg C).
Click to expand...
 
L.Adamson said:
Bryan Wood said:
Last Thursday, climbing out of Salt Lake City (4200' msl) in an RV9A at 7:00 in the morning, it was 71 degrees on the ground, but 85 degrees with a few thousand feet of altitude. In this case, an inversion was very possible.

L.Admason --- RV6A
Click to expand...

Heading west on this leg we went right over Salt Lake City at 14,500 and it was really hot up there. I'm glad somebody else was there to see the inversion, or high temps that day. Thanks for sharing this.
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I like altitude

Hi Bryan,

On our way to OSH I had to climb in my RV9A over some weather. We went up to 17.5 K (temp 23F-19,440 ft DA). The camping gear loaded RV9A would still climb at 500ft/min. if needed. I had it up to 20K, but that is in cold Canada.

The engine (Lyc 320-160) does have a tendency to overheat. My CHT in hot weather does tend to go towards 450F and OT 210F+. So I tend to shallow my climb in hot weather. I am thinking about James Aircraft Plenum. Maybe this will help the cooling.

My plane behaved differently with the gross load, hot weather and high winds. I had to get used to it.
 
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What you showed, Kevin, is that the typical summer temps at altitude are about ISA +21C, which is what I usually encounter, and is typical. Thanks for the tabular data showing how the temps rapidly fall off several thousand feet above a hot high-altitude airport! I have usually found that forcaste temps vs altitude are very close, and that a lot of planes with their OAT sensors in cabin inlet ducts will show much higher temps than exist since they often have airflow OUT-OF the cooling inlets that gets heated by the engine then flows down the side of the fuselage. Those people who are experiencing such high temps at altitude could have this problem, which also means that their cabin temps will be much warmer! Any one seeing such high temps at altitude should call EFAS on 122.0 and ask them for the forecaste temps in their area and altitude. If they have a large discrepancy, they should relocate their OAT sensor, preferably into the tailcone above and behind the elevator cutout where they will get much better true OAT without stagnation rise. 'Course, too, they may want to relocate their cabin air inlets to get cooler air!
 
Bryan Wood said:
Yesterday while coming home from OSH our 9A couldn't deliver the altitude that we were asking of her. This is the first time that this has happened and I thought other 9 drivers might like to know the conditions that humbled our plane and it's owner.
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Sounds like the very same thing was happening all over the Rockies this weekend. I was returning from Oshkosh with the same load of camping gear, full fuel, and 2 people. Leaving Riverton WY at 98 deg F on the ramp the highest I was able to climb was just shy of 13Kft heading south of Jackson hole. The wind would blow us down to 12K and then struggle back up to 13K, after 2 hours of full throttle climbing we crossed fine but similar to you had high oil temps and really worked to get over.

Interesting that in my previous 6 crossings (all up north where they are cooler and smaller) I never had to give much thought to plane performance. Good for all of us to respect the weather and rocks out there.
2705232564_9c8bd407fb.jpg
 
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Thanks Bryan, elippse, and Roger.
I was especially interested in Roger's numbers out of Phoenix at high temps. I have never had problems getting my 9 to climb as long as I can keep the CHTs in check. But last week I sure wish I had cowl flaps, or some other mechanism to increase the engine cooling while climbing. CHTs in the 450dF range are a little too high for my taste.

But it is good to know that you are seeing the same kinds of temps at similar altitudes. I will try the suggestion of using 10deg flaps to lower the nose, as I know that once I level off and get up to speed, the problem goes away compeltely. I'm sure that I just do not have enough air mass flow to carry away the heat. And Yes.....I have noticed the cabin-air vents seem to provide hot air in a climb. I guess that could be because the nose is high and pressurising the cowl outlet, causing backflow out the nose.....and roasting the engine.

Thanks for all the good info and suggestions.
 
High CHT

flyer46 said:
.
I have never had problems getting my 9 to climb as long as I can keep the CHTs in check.

But last week I sure wish I had cowl flaps, or some other mechanism to increase the engine cooling while climbing. CHTs in the 450dF range are a little too high for my taste.
backflow out the nose.....and roasting the engine.
Click to expand...

Is the high CHT a RV9 problem? I have to really watch my CHT on climb in hot places like Nevada, Arizona. I dont have this in cold Canada even in summer. It seems that Cyl #4 gets the brunt of the problem. Do you experience this?

Do you think a plenum like the one from Sam James will help? May be the holy cowl will increase airflow?
 
o-320 with SJ cowl and plenum

I have a 9A with the Sam James cowl and plenum. I love the look! But, I often push 450 deg. on number 4 on climb out. At 155 kts cruise I get temps fairly uniform amongst all 4 jugs at around 390 deg.

Duane
 
My Experience

Last Thurday, I flew a Diamond DA20 (Katana) from Provo to Vernal and back - 11,500 eastbound and 10,500 westbound. I know it was hot, but I didn't have any problems with those altitudes. I was getting about 450fpm cruise climb just about all the way up. Of course, the performance of the DA20 is nothing like that of the RV-9A. But my point is that I was seeing the climb performance that I've been accustomed to see.

Then Saturday I got my first ride in an RV-9A, Bill Lechter's new plane flying out of Bountiful Skypark. That ride was late afternoon, with the temperature on the ground in the mid 90's. But we didn't fly very high - had to stay under the Salt Lake class B airspace. It's a great plane, but I need another flight before I can really be sure that this is the plane I'd like to build.
 
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