VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics


Go Back   VAF Forums > Main > RV General Discussion/News
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
  #21  
Old 09-11-2017, 09:15 PM
scsmith scsmith is offline
 
Join Date: Jan 2008
Location: Ashland, OR
Posts: 1,661
Default

Quote:
Originally Posted by flytoboat View Post
Steve,
A question on your comment about being over square at 2300 RPM with full throttle: My fixed pitch 0320 RV6A turns about 2300RPM on take off with full throttle. Other than not making full horsepower, what issues (damage?) do I face by running "over square"?
Thanks
The Lycoming performance charts in the Operating Manual show HP at various RPM and MAP combinations. At lower RPMs (below 2400), the power curves stop at various MAP, with a notation of "max pressure for continuous operation", presumably because Lycoming does not recommend operating at that low an RPM and high MAP. Its kind of like lugging your car in too high a gear. For reference, the chart for my IO-360-A1A shows 28 in. Hg limit at 2300 RPM. (figure 3-24 in my Operations Manual).

That being said, you make a good point about fixed pitch prop operation. The thing is, you open the throttle and start your ground roll, and although static RPM might be 2300, the RPM very quickly increases. And of course engine power increases with the increasing RPM, so by take-off, you are getting much higher RPM and close to max engine power. This takeoff transient is not what would be considered 'continuous operation.'

That is quite different from doing a go-around with a constant speed prop set at 2300 RM, where full throttle and 2300 RPM will be maintained for an acceleration and climb to some particular altitude where you may consider it safe to change engine settings, presumably either pushing the prop forward or closing the throttle some.

Of course, all this only has significance near sea level where there is enough pressure to be an issue.
Note also that the notion of "over-square" being a problem itself is disproved by the performance charts. The charts define the max MAP for each RPM and the boundary is WAY beyond the fake limit of 'square'.
__________________
Steve Smith
Aeronautical Engineer
RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet"
Hobbs 450 in 8 years
also LS-6-15/18 sailplane
Reply With Quote
  #22  
Old 09-11-2017, 11:45 PM
DNeufeld DNeufeld is offline
 
Join Date: Aug 2016
Location: Coeur d Alene
Posts: 30
Default

RV6 IO-360 CS Might not be text book but it works good for me.
Down wind I like be at 2300 rpm 90+ knots, throttle back before the perch, or just after abeam the no's. Start the flaps down turning base 87 to 90 kts. Pull power enough where I can run the prop full forward and the rpm stays down. Around 1800 rpm maybe less on base. Not so much engine breaking. If power is needed it'll be there. 80 usually to 85 max kts turning final and start rounding out just before the threshold bleeding off speed. Add a little power back in if needed for a wheel landing or throttle back for 3 point. Can't say I've ever looked at the AI at touchdown. I like fairly steep approaches for the good control feel or if the engine craps out.

I don't see the need to slow so much it feels mushy until almost over the runway? Why not keep good positive control feel? If the engine is set up to idle 600 or so rpm as mine is, (600 for landing not taxiing or holding) if I want to quit flying just pull the throttle all the way back. Speed bleeds off pretty fast. Landing short field would be different of course, slower on final.

Feel free to criticize.

I didn't do any transition training. Got my tail-wheel endorsement in a Scout and flew the RV6 home. My brother, HRII driver, helped me smooth things over a bit the next day along with advise from friends. I'll probly get it for admitting that! But that was probably the most fun I've ever had... just don't do it!
__________________
Dues paid 2017

Last edited by DNeufeld : 09-13-2017 at 06:37 AM.
Reply With Quote
  #23  
Old 09-11-2017, 11:52 PM
rv8ch rv8ch is online now
 
Join Date: Feb 2005
Location: LSGG
Posts: 2,048
Default oversquare myth?

One guy seems to believe that "oversquare" is an old wives tale:

https://www.avweb.com/news/pelican/186778-1.html
__________________
Mickey Coggins
http://rv8.ch
Reply With Quote
  #24  
Old 09-12-2017, 12:27 AM
DNeufeld DNeufeld is offline
 
Join Date: Aug 2016
Location: Coeur d Alene
Posts: 30
Default

Quote:
Originally Posted by rv8ch View Post
One guy seems to believe that "oversquare" is an old wives tale:

https://www.avweb.com/news/pelican/186778-1.html
Many people here run high compression pistons. I'd be cautious running oversquare if so equipped.

Another thing to consider FP verses CS is FP props are usually lighter which would reduce the load at low rpm and high manifold pressure with the FP.
__________________
Dues paid 2017

Last edited by DNeufeld : 09-12-2017 at 01:07 AM.
Reply With Quote
  #25  
Old 09-12-2017, 04:22 AM
rv8ch rv8ch is online now
 
Join Date: Feb 2005
Location: LSGG
Posts: 2,048
Default oversquare myth?

Another article. https://www.avweb.com/news/airman/184274-1.html

Quote:
"Oversquare" is Good

In fact, flying your engine oversquare can be very good for it. As long as you are using a power setting allowed by the manufacturer in the power setting tables, use the lowest RPM you can for the percent power you want and then select the corresponding manifold pressure. How is this good for your engine? The higher the RPM you use, the more often the pistons go up and down in the cylinders. More revolutions mean the metal changes position more often, which causes more friction and consequently more wear. Your propeller will also be more efficient at a lower RPM. The higher the RPM setting, the closer the tips of the prop blades are to the speed of sound and all the compressibility and high drag effects associated with operation in that regime.

You'll also find the lower RPM settings are quieter and easier on you and your passengers. Sometimes you'll find a legal power setting that just doesn't make your engine happy. This is caused by the particular airframe-engine-propeller combination and will usually result in increased vibration. Just change to another permitted power setting and all should be well.
__________________
Mickey Coggins
http://rv8.ch
Reply With Quote
  #26  
Old 09-12-2017, 09:01 AM
flion's Avatar
flion flion is offline
 
Join Date: Dec 2007
Location: Flagstaff, AZ
Posts: 2,435
Default

I just wanted to say that I hardly ever look at the MAP indication. Not much point at 7000 feet. On approach to downwind, I anticipate slowing down by reducing throttle and actually slow by making a fairly steep turn to downwind, then pitch for desired airspeed and manipulate throttle to maintain altitude and the prop full in. Well before abeam I should be stabilized. If I'm going to use flaps (you do practice no-flap landings, right?) then I add a click here and start trimming for my base leg speed. As I turn to base, I add the second click of flaps, start trimming for final, and use the throttle to correct descent rate as needed. Turning to final, I put in the last of the flap and then it's all throttle until flare or go-around. Airspeed is critical, throttle is whatever is needed to maintain the proper descent, which is not a number because it depends on too many things - how tight/loose is your pattern (not always in your control when you have to extend downwind for other traffic), did you hit a patch of sink/lift, flaps/no flaps, and so on.
__________________
Patrick Kelley - Flagstaff, AZ
RV-6A N156PK - Flying too much to paint
RV-10 14MX(reserved) - Fuselage on gear
http://www.mykitlog.com/flion/
EAA Technical Counselor #5357
Reply With Quote
  #27  
Old 09-12-2017, 07:27 PM
chrispratt's Avatar
chrispratt chrispratt is offline
Super Moderator
 
Join Date: Oct 2005
Posts: 562
Default

Quote:
Originally Posted by scsmith View Post
Chris, I'm interested in what in particular concerned you.
.........
Anyway, since my 75 kt is essentially the same as the RV7 85 mph recommendation, I'm wondering what concerned you and what speed/technique you use.
Well Steve, items like this concern me: "...while dropping nose and holding 70mph for the turn to base, half way in base full flaps, hold airspeed and 1800 rpm, turn final, point to threshold, begin nose up and cut engine (60 mph) over threshold...."

and then this: "...If you flare high - pitch down a little as if recovering from stall and re-flare. Once you've got it rounded out, ease back to slowly assume 3 point attitude.."

These are things that if I did them in my -8 I would meet the ground very quickly and with less than satisfactory results. I can't imagine turning base at 70 mph or being at 60 mph over the threshold in my airplane especially with the power off. I understand the quoted aircraft is not an -8 and may or may not have CS prop, etc. and so that is why I caution about using a technique appropriate to the particular aircraft and not apply it to all RVs. I also suspect that even for a -6 this airspeed calibration looks a bit "iffy" to me (note it is in MPH). But again I don't fly a -6.

As to the second quote, my -8 is not a three point airplane. I've tried it and, especially with no power, it does not work well. The -8 just tends to be nose heavy and handles better as a wheel landing airplane. Yes, I've successfully landed it three point but usually with a passenger in back. Keep in mind -8s are tandem and that makes a significant difference in cg and handling conditions. As far as the flare recovery technique mentioned, I'm thinking that pitching down after a high flare had better be accompanied by adding a lot of power or else you'll have an arrival rather than a landing.

The 85 mph you mention in your technique is the speed I typically aim for on base and final with an over the fence around 80 mph. I enter downwind at about 120 MPH plus or minus, add 10 degrees of flap to slow the airplane down (RVs have drag flaps and they work well), then at about 100 mph (white arc) on downwind I add more flap depending on conditions (I use 20 degrees if very windy or 40 degrees for most landings). Then I aim for the 85 mph mentioned earlier. I basically disregard rpm and mp once in the pattern and use airspeed as my main reference. I advance the prop as I approach 85 mph. As I said my over the fence speed is about 80 mph (if I err it's to the high side of this); much less than that (in my airplane at least) and the -8 gets mushy, and starts to sink rapidly. Again this may be an airspeed calibration variance.

So I realize I am bearing myself to much criticism on technique and I'm sure I've left a few things out, but I've flown my -8 for more than 700 hours and the technique has let me "keep the shiny side up" as truckers say.

The original point of my comments, I repeat, was to caution people, especially newbies, to weigh the techniques that others publish (including mine) carefully as they may not work for your particular airplane and its airspeed accuracy. When in doubt find an instructor familiar with your model and seek advice.

Please keep flames on low

Chris
__________________
Chris Pratt (2017 VAF DUES PAID)
RV-8 Flying, 700+ hours
N898DK
Lycoming O-360-A1A, Hartzell CS
52F (Northwest Regional, TX)
Reply With Quote
  #28  
Old 09-13-2017, 01:03 AM
scsmith scsmith is offline
 
Join Date: Jan 2008
Location: Ashland, OR
Posts: 1,661
Default

Quote:
Originally Posted by chrispratt View Post
Well Steve, items like this concern me: "...while dropping nose and holding 70mph for the turn to base, half way in base full flaps, hold airspeed and 1800 rpm, turn final, point to threshold, begin nose up and cut engine (60 mph) over threshold...."

and then this: "...If you flare high - pitch down a little as if recovering from stall and re-flare. Once you've got it rounded out, ease back to slowly assume 3 point attitude.."

These are things that if I did them in my -8 I would meet the ground very quickly and with less than satisfactory results. I can't imagine turning base at 70 mph or being at 60 mph over the threshold in my airplane especially with the power off. I understand the quoted aircraft is not an -8 and may or may not have CS prop, etc. and so that is why I caution about using a technique appropriate to the particular aircraft and not apply it to all RVs. I also suspect that even for a -6 this airspeed calibration looks a bit "iffy" to me (note it is in MPH). But again I don't fly a -6.

As to the second quote, my -8 is not a three point airplane. I've tried it and, especially with no power, it does not work well. The -8 just tends to be nose heavy and handles better as a wheel landing airplane. Yes, I've successfully landed it three point but usually with a passenger in back. Keep in mind -8s are tandem and that makes a significant difference in cg and handling conditions. As far as the flare recovery technique mentioned, I'm thinking that pitching down after a high flare had better be accompanied by adding a lot of power or else you'll have an arrival rather than a landing.

The 85 mph you mention in your technique is the speed I typically aim for on base and final with an over the fence around 80 mph. I enter downwind at about 120 MPH plus or minus, add 10 degrees of flap to slow the airplane down (RVs have drag flaps and they work well), then at about 100 mph (white arc) on downwind I add more flap depending on conditions (I use 20 degrees if very windy or 40 degrees for most landings). Then I aim for the 85 mph mentioned earlier. I basically disregard rpm and mp once in the pattern and use airspeed as my main reference. I advance the prop as I approach 85 mph. As I said my over the fence speed is about 80 mph (if I err it's to the high side of this); much less than that (in my airplane at least) and the -8 gets mushy, and starts to sink rapidly. Again this may be an airspeed calibration variance.

So I realize I am bearing myself to much criticism on technique and I'm sure I've left a few things out, but I've flown my -8 for more than 700 hours and the technique has let me "keep the shiny side up" as truckers say.

The original point of my comments, I repeat, was to caution people, especially newbies, to weigh the techniques that others publish (including mine) carefully as they may not work for your particular airplane and its airspeed accuracy. When in doubt find an instructor familiar with your model and seek advice.

Please keep flames on low

Chris
I agree on all points. Sounds like our -8s are much the same. Although the issue with 3-pt landing the -8 doesn't seem to me related to it being nose heavy. I don't have any trouble getting the nose up. I can trim for 85 mph (75 kts) and just round out and hold it off. I can absolutely nail a 3-pt attitude, and just grease it on. Then the problems come. The issue is that it is still flying, even though all the wheels are touching the ground. It is squirrely and skittish, no weight on the wheels to brake, not much positive feel that it will go where you point it. One doesn't have much of a feeling of being in control. Rounding out to a wheel landing seems so much more positive.

I appreciate the affirmation that a few posts, like yours, has given me - I'm pretty comfortable with my strategy, and it is nice to hear others doing about the same. I sometimes have wondered if it is just me and/or my -8 that seems to want to land faster than some people quote.
__________________
Steve Smith
Aeronautical Engineer
RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet"
Hobbs 450 in 8 years
also LS-6-15/18 sailplane

Last edited by scsmith : 09-13-2017 at 01:09 AM.
Reply With Quote
  #29  
Old 09-13-2017, 09:56 AM
chrispratt's Avatar
chrispratt chrispratt is offline
Super Moderator
 
Join Date: Oct 2005
Posts: 562
Default

Quote:
Originally Posted by scsmith View Post
I agree on all points. Sounds like our -8s are much the same....

I appreciate the affirmation that a few posts, like yours, has given me - I'm pretty comfortable with my strategy, and it is nice to hear others doing about the same. I sometimes have wondered if it is just me and/or my -8 that seems to want to land faster than some people quote.
Amen.

I have a friend who always lands his -8 shorter than me. But he's quite aggressive on the brakes whereas I let the airplane bleed off speed until the tail wants to come down on its own before I touch the brakes.

Chris
__________________
Chris Pratt (2017 VAF DUES PAID)
RV-8 Flying, 700+ hours
N898DK
Lycoming O-360-A1A, Hartzell CS
52F (Northwest Regional, TX)
Reply With Quote
  #30  
Old 09-13-2017, 10:42 AM
AZtailwind's Avatar
AZtailwind AZtailwind is offline
 
Join Date: Nov 2005
Location: Flagstaff, AZ
Posts: 410
Default

Quote:
Originally Posted by scsmith View Post
I agree on all points. Sounds like our -8s are much the same.
I agree also.
I've flown with all the 2-place RV's of all types in formation and in the pattern. We all use the same speeds. Downwind- 87 kts(100 MPH). Base with full flaps 78 Kts(90 MPH). Final 70KTS (80 MPH). These speeds work well in all environments as far as I've experienced.

The 60MPH speed is way too slow unless the original poster has slow speed indicated errors that are way out of whack. That 60 MPH posted speed certainly grabbed my attention.
__________________

Brad Ransom
http://www.westcoastravens.com
RV-6A 180HP-purchased
Be V35
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 06:42 AM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.