VansAirForceForums  
Home > VansAirForceForums

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

- Today's Posts | Insert Pics


Go Back   VAF Forums > Main > Safety
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
  #41  
Old 01-02-2019, 11:29 PM
skylor's Avatar
skylor skylor is offline
 
Join Date: Aug 2009
Location: Southern California
Posts: 882
Default Speed

Quote:
Originally Posted by RV7A Flyer View Post
A couple of these tests seem to stop just when it's getting interesting...just a tiny bit below Vs0 or Vs1, when they had to add a touch of power to slow further. Why not keep going? Increase pitch further while adding power, and continue until either you're uncomfortable with the pitch attitude (it'll be very nose up) or run out of power to give.

It's an interesting flight regime, just keep your turns coordinated and don't stall a wing!
50-51 KIAS was about as slow as I could consistently fly whithout stalling. This was already at the point of buffet (which is much less pronounced with flaps than without) and at one point I got a hair under 50 and had a clean stall break and had to restart the test.

Please note that I updated the data with a correction in the 55 kias run.

Skylor
Reply With Quote
  #42  
Old 01-02-2019, 11:47 PM
RV7A Flyer's Avatar
RV7A Flyer RV7A Flyer is offline
 
Join Date: Jul 2013
Location: US
Posts: 2,251
Default

Quote:
Originally Posted by skylor View Post
50-51 KIAS was about as slow as I could consistently fly whithout stalling. This was already at the point of buffet (which is much less pronounced with flaps than without) and at one point I got a hair under 50 and had a clean stall break and had to restart the test.

Please note that I updated the data with a correction in the 55 kias run.

Skylor
Now I gotta go do this again (been a few years since I did it during a BFR) and see what I can get! I'll give it a whirl this weekend, weather permitting. Gives me another excuse to go flying LOL!
__________________
2019 Dues paid!
Reply With Quote
  #43  
Old 01-03-2019, 07:31 AM
BJohnson's Avatar
BJohnson BJohnson is offline
 
Join Date: Jun 2005
Location: Federal Way, Wa
Posts: 264
Default

Quote:
Originally Posted by RV7A Flyer View Post
A couple of these tests seem to stop just when it's getting interesting...just a tiny bit below Vs0 or Vs1, when they had to add a touch of power to slow further. Why not keep going?
I was thinking the same thing. It?s going to be a bit tricky maintaining zero sink at the edge of stall with full flaps.

Does anyone have experience with power on stalls with full flaps? I imagine it?s going to pretty high pitch angle with lots of power.
__________________
Brice
RV-9A 90897 FLYING
Reply With Quote
  #44  
Old 01-03-2019, 09:23 AM
andrewtac andrewtac is offline
 
Join Date: May 2014
Location: Friendswood TX
Posts: 218
Default

Quote:
Originally Posted by RV7A Flyer View Post
A couple of these tests seem to stop just when it's getting interesting...just a tiny bit below Vs0 or Vs1, when they had to add a touch of power to slow further. Why not keep going? Increase pitch further while adding power, and continue until either you're uncomfortable with the pitch attitude (it'll be very nose up) or run out of power to give.

It's an interesting flight regime, just keep your turns coordinated and don't stall a wing!

I could keep going, my intent was to show my RV8 has typical backside behavior. The trend was obvious to me, and from qualitative analysis (flying the plane in slow flight before) I suspected this to be the case. The data does not lie, but sometimes our perception is not reality (specifically verifying my qualitative analysis and assumptions matched what was actually going on). I have done plenty of backside flying, when I began flying and even for years into flying it would always make me nervous; it felt like the plane was going to fall out of the sky. At some point it didn?t bother me anymore and I do find it interesting and fun. I?d suggest everyone get comfortable with it and listen to what the plane is saying in those regimes. It has made me a better pilot, and hopefully helped me recognize when the plane is getting there. I am a believer that you should always expand your own envelope, that way when you need to do something a little bit crazy you are more likely to know what to expect. However when expanding, use build up, don?t go right to the end points.
__________________
Mark Andrew Tacquard

RV8 N189DK
RV10 in progress
Reply With Quote
  #45  
Old 01-03-2019, 11:09 AM
506DC 506DC is offline
 
Join Date: Jun 2010
Location: Fresno, CA
Posts: 38
Default

The power required curved has nothing to do with engine power. Gliders have power required curves associated with them, just like airplanes, even though they have no powerplant. Power can be considered as a force times velocity; therefore, the power required at any given velocity can be determined by multiplying the drag times velocity. The power required curve is somewhat similar in shape to the drag curve, but skewed a bit due to additional velocity term that it contains. Like the drag curve, the power curve has a minimum point. More power is required at speed more than and less than the speed associated with minimum power; however, the speed at which minimum power is required is not the same as the speed for minimum drag. The term power required actually refers to the power required for level flight.

The important thing that Van is trying to point out is that you don?t want to unknowingly get behind the power curve. There is an airspeed that at full power you will not be able to climb and if you are low enough, you will most likely impact objects that are in your direction of flight. If you continue to reduce speed without having more power available, you will stall, spin and most likely kill yourself. I have seen this happen many times. This is especially important on twin engine airplanes where there is a point that you will not be able to maintain directional control (the blue line) even though you may have enough power to remain airborne on one engine.

If you have enough power available, you can actually climb at zero airspeed. In this situation the power curve would go straight up on the aft side. This is demonstrated quite nicely with high performance and what they call ?3D? aircraft flown by very experienced and talented Radio control pilots. These aircraft have thrust in excess of the weight of the airplane. Yes, propeller airplanes have thrust also but just at a percentage of brake horsepower. The power available curve in the diagram above is curved as a result of propeller efficiency. A very good example operating an aircraft below the power curve is demonstrated below. If you listen close enough you will hear the pilot adding power when he approaches a stall. He will also pulse the engine throttle. This is to maintain airflow over the control surfaces of the airplane which are very large compared to most aircraft. These large surfaces are affective at very low airspeeds. If you hang around to the very end of the video, you will witness a very unusual short field landing. Much like the STOL full scale aircraft use except the inverted part, he uses the aircraft power while operating behind the power while operating below the normal stall speed.

Enjoy.

https://www.youtube.com/watch?v=moQlvtHItg8
Reply With Quote
  #46  
Old 01-03-2019, 11:29 AM
skylor's Avatar
skylor skylor is offline
 
Join Date: Aug 2009
Location: Southern California
Posts: 882
Default "Departure Stalls"

Quote:
Originally Posted by BJohnson View Post
I was thinking the same thing. It’s going to be a bit tricky maintaining zero sink at the edge of stall with full flaps.

Does anyone have experience with power on stalls with full flaps? I imagine it’s going to pretty high pitch angle with lots of power.
Yes, I practice "departure stalls" with flaps in my -8 several times a year. At full power, the pitch is indeed quite steep. I'll have to do a couple and add them as a data point to my test data.

Skylor

Last edited by skylor : 01-03-2019 at 11:31 AM.
Reply With Quote
  #47  
Old 01-04-2019, 04:36 PM
RV7A Flyer's Avatar
RV7A Flyer RV7A Flyer is offline
 
Join Date: Jul 2013
Location: US
Posts: 2,251
Default

OK, the data don't lie .

Experimented with a co-pilot today. Half tanks, two big guys, around 40 pounds or so in the baggage area (steaks, smoke oil, what have you ).

Data logging via Dynon Skyview, observation by co-pilot on D6. I'll talk about calibration errors in a moment. 5500' altitude, RPM set to 2500 and unchanged throughout, full flaps.

Slow flight 1, into the stall buffet:
IAS 46 knots, observed IAS (D6) 41/42
AOA 72 %
Pitch 19.1 degrees
% Power 59
MAP 20.3"

Slow flight 2, full stall break:
IAS 46.2 knots, observed IAS (D6) 41
AOA 72 %
Pitch 19.2 degrees
% Power 47
MAP 18.1"

Looks like I could have given it a little more during the second run and gotten a bit slower, but the two are consistent.

My latest Pitot/Static/XPDR cert shows the Dynon reading 3 knots high < 50 knots (+1 at 50), and the D6 4 knots low < 50 knots, so splitting the difference would yield CAS of around 43 knots.

I suppose with some more practice and tickling the controls and such, we could have gotten a few knots slower, but that's still, IMO, pretty far on the back side of the power curve (normal Vs0 is 50 knots)...at least 10% if going by IAS, closer to 15% if using CAS.

Beat *that* .
__________________
2019 Dues paid!

Last edited by RV7A Flyer : 01-04-2019 at 07:23 PM.
Reply With Quote
  #48  
Old 01-04-2019, 06:01 PM
andrewtac andrewtac is offline
 
Join Date: May 2014
Location: Friendswood TX
Posts: 218
Default

Quote:
Originally Posted by 506DC View Post
This is especially important on twin engine airplanes where there is a point that you will not be able to maintain directional control (the blue line) even though you may have enough power to remain airborne on one engine.

https://www.youtube.com/watch?v=moQlvtHItg8
Blue line is VYSE
__________________
Mark Andrew Tacquard

RV8 N189DK
RV10 in progress
Reply With Quote
  #49  
Old 01-04-2019, 07:06 PM
rocketman1988 rocketman1988 is offline
 
Join Date: Jun 2010
Location: Sunman, IN
Posts: 2,189
Default and...

Vyse, as stated is the best rate of climb, single engine; it is the Blue Line

Vmc is minimum controllable speed and is typically noted as a Red Radial on the ASI of light twins according to FAR Part 23.
__________________
Bob
Aerospace Engineer '88

RV-10
Structure - 90% Done
Cabin Top - Aaarrghhh...
EFII System 32 - Done
297 HP Barrett Hung
ShowPlanes Cowl with Skybolts Fitted - Beautiful
Wiring...

Dues+ Paid 2019,...Thanks DR+
Reply With Quote
  #50  
Old 01-04-2019, 08:14 PM
andrewtac andrewtac is offline
 
Join Date: May 2014
Location: Friendswood TX
Posts: 218
Default

Quote:
Originally Posted by rocketman1988 View Post
Vyse, as stated is the best rate of climb, single engine; it is the Blue Line

Vmc is minimum controllable speed and is typically noted as a Red Radial on the ASI of light twins according to FAR Part 23.
Yep, what I was getting at. Flying with someone the other day; max conserve. Was below blue line (both engines at about 28% torque); he was worried if we lost an engine we?d depart. Well no because above vmc; and even if we were below vmc still wouldn?t depart with one engine failed and the other near idle.
__________________
Mark Andrew Tacquard

RV8 N189DK
RV10 in progress
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 08:05 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.