RV-9A and density altitude

[Phyrcooler]

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

[Bryan Wood]

Originally Posted by Phyrcooler

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

Yes, but I'm stickin' to "We were at legal gross."

[flyer46]

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

[elippse]

[quote=RichB;244388]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.

[Bryan Wood]

[quote=elippse;244599]

Originally Posted by RichB

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.

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.

[L.Adamson]

[quote=Bryan Wood;244656]

Originally Posted by elippse

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.

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

[R.P.Ping]

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

[Kevin Horton]

[quote=Bryan Wood;244656]

Originally Posted by elippse

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.

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:

-----------------------------------------------------------------------------
   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).

[Bryan Wood]

[quote=L.Adamson;244661]

Originally Posted by Bryan Wood

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

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.

[RV9798]

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.