wjmiller3
Well-Known Member
That is exactly the reason NOT to fly that 5 mile straight in final at full flaps and 65 kts..... That was my point.
Full flaps
- Thread starter Dazzler
- Start date
That is exactly the reason NOT to fly that 5 mile straight in final at full flaps and 65 kts..... That was my point.
tgrayson
New Member
No, I never said that. I said it's better to standardize on full flap landings; it improves pilot skill and it prevents the pilot from making irrational decisions on flap settings. If you ask people why they use partial flaps, you will hear all sorts of reasons:
- The aircraft is more stable.
- The aircraft is more controllable (which is the opposite of stable).
- The "wind" affects the aircraft less.
- The aircraft is less susceptible to gusts.
- The aircraft can fly faster.
Realistically, the diversity of justifications suggests they're simply regurgitating "hangar talk" and have no first-hand experimental or theoretical evidence that any of these things are true.
The one thing you will pretty much never hear is that it improves rudder authority and I was the first one to bring it up in this thread. There is theoretical and experimental justification for this, unlike the rest of the above list.
Neither did I say that. The assumption in this discussion has been an aircraft on approach at normal approach airspeeds which then loses an engine. In this situation, an aircraft is operating at a particular lift coefficient, say, oh, .7, and this lift coefficient is produced by a combination of the AoA and the flap setting. If you raise the flaps---and do nothing else---the aircraft will 1) drop, and 2) accelerate to the speed appropriate for the new lower lift coefficient of, say .3. If you increase your AoA to compensate for the loss of flaps and return the lift coefficient to .7, then you will not experience the drop and the aircraft will remain at the velocity corresponding to that lift coefficient. However, your induced and parasite drags will now be lower and the flight path will shallow out, which is synonymous with increasing the glide range.
Thank you for that. I think that asking for evidence is a more productive response to new information rather than rejection. I was actually already thinking about how I would put together such a video and how to show useful information. Realistically, the video would need to capture airspeed, VSI, the flap lever, and the visible attitude outside the airplane. I'm not immediately sure how to do all that.
Do you have acces to a sim of some sort that you could do demos in?
I am taking the liberty of updating you since you said you had only read page one. The original topic was about when, the deviation and the argument here is in a misunderstanding of how flaps actually work aerodynamically. So we are currently stuck on that and the statement was made that "raising flaps does not make you sink."
This came up when the discussion came of losing an engine with full flaps on short final and raising them to make the runway.
Back on topic here.
I think there has been much unnecessary stress in this topic because tgrayson is explaining something, which he is right about, but doing so with fairly complex aerodynamic situations which Mshunter and maybe some others are not understanding.
Maybe this will help, ignore going to a runway and flying it there for your first times. Take the plane, even if it is with a student for 2 minutes at altitude and try it. Lower the flaps and flight straight and level, bring the flaps up and pull back to maintain altitude, which done right will also maintain airspeed. Leave this new pitch attitude to keep the airspeed constant after the maneuver which will result in a climb from less drag without flaps now.
If you do it right you can have your student watch and the airspeed should remain constant (within 5 knots) and your altitude shouldn't change. Obviously once the flaps are completely up again if you keep pitching back to maintain airspeed you will see a climb. This would correlate to a reduced sink rate in an engine out approach, the aerodynamic concepts are no different, the only difference is in this case we are using engine power.
You can do this with the outside horizon and seat of your pants (what you think is 1g sitting environment) better then with the instruments though. Once you realize it can be done level there, then you should easily correlate that it works in any form of climb or descent as well.
Almost forgot, the pitch up needs to be gradual as the flap retraction is not instant a quick pull to 20 degrees nose up will not suffice. It takes finesse and you cannot expect to do it right if you have never done it before.
Tgray,
You can record that with a video camera taped to the glare shield for a good natural horizon view and a second person to recording the instruments. Good luck and I would love to see it too, I hope you include an at altitude demonstration for climbs, level flight, and descents if you go through the trouble to set up the video.
R
Roger, Roger
Guest
this thread is crizazy.
as previously stated, assuming the flaps are actually working, I prefer to land with them full all the time.
as previously stated, assuming the flaps are actually working, I prefer to land with them full all the time.
How do you plan on increasing the AoA when you raise the flaps? And what kind of approach speeds are you using (172's..?)?
R
Roger, Roger
Guest
My guess is...the same way you always increase AOA-up elevator.
I read the same thing that Roger does: Raise the flaps and as the flaps come up increase up elevator to hold the same AOA value as before the flaps were raised. What are you reading that I'm missing?
Did you read my post 124? Your speed does not matter, when you raise the flaps it is essentially lowering the AOA on 50 percent of the wing by some amount. Since Cl = 2 pi AOA (in radians) then your CL must be going down and since lift = 1/2 (p * v2 * s * cl) than your total lift must have gone down. To compensate for this you raise the AOA of the entire wing (using the elevator), your speed does not matter because done right it will not change ever and you will never stall even if you are a knot above stall speed.
You are simply raising the AOA of the entire wing to compensate for reducing the AOA of 50 percent of the wing when you raise the flaps. Go try what I said in post 124 next time you are flying at altitude, it will hopefully end this little debate.
This is the same concept as opening a window and using the rudder to coordinate the new drag then closing it and reducing rudder. The only difference is we are balancing vertical and not horizontal forces in this procedure.
I read the same thing that Roger does: Raise the flaps and as the flaps come up increase up elevator to hold the same AOA value as before the flaps were raised. What are you reading that I'm missing?
I am guessing he is saying you cannot use the elevator because you are close to stall, so hopefully my post ^there^ answered it.
So what I'm gathering from what everyone is saying here is that when the engine quits, and you are only a few knots from stall, raise the flaps, increase back pressure and all will be o.k.?
Arbitrary numbers here. Lets say that you are on approach with full flaps and an AoA of 10 deg. The airplane you are flying has a critical angle of attack of 12 deg. About a mile from the runway, the engine quits, and you are already only 2 deg from a stall. Now we decide to de-stabalize the approach because the engine quit and decided to raise the flaps....
IIRC, flaps do not necessarly change the AoA, they change the chamber of the wing, makeing the airplane think it has a different airfoil than it realy does, which may or may not have an affect on the AoA.
I want everyone to think of 3407, and what may have caused that airplane to go down. They were on approach, picking up ice. They added flaps, and let their airspeed get low (think of it as a sim engine failure for our purpose), then, the flaps were raised and they continued to pull, exceded the critical AoA, and crashed. Do you see my point. The last thing I want to do when the airplane is low and slow is to re-configure the airplane and increase my AoA beyond the critical point, putting myself into a stall when I am only a few hundred feet from the ground. I think I am finally begning to understand the reasoning behind raising the flaps when the engine quits, but I still disagree with doing it because I see a big red flag that tells me to keep flying the airplane exactly as I just was. I would rather no make the runway, and come up short at a few knots abouve stall speed, than raise my flaps, pitch up to maintain my AoA when the flaps were raised and stall from 200-400 feet up and hit the ground at 1000fpm.
As for speed no being a factor,wwwuuuuhhhhh? Airspeed is life, and altitude is life insurance. When you have as much as a 10kt difference in stall speed between full flaps and 0 flaps, I think that speed is the most critical part of this whole situation. I will try this again in a 172N today, and see if I can make it work. Last time, I tried to maintain speed exactly what it was when I "simulated" an engine failure. Today, I will try to just make the runway since some seem to think speed is not an issue. And I know this much, that when I pull to make the runway, I will loose airspeed and ground speed. I just hope that I make the runway the raiseing the flaps method.
Arbitrary numbers here. Lets say that you are on approach with full flaps and an AoA of 10 deg. The airplane you are flying has a critical angle of attack of 12 deg. About a mile from the runway, the engine quits, and you are already only 2 deg from a stall. Now we decide to de-stabalize the approach because the engine quit and decided to raise the flaps....
IIRC, flaps do not necessarly change the AoA, they change the chamber of the wing, makeing the airplane think it has a different airfoil than it realy does, which may or may not have an affect on the AoA.
I want everyone to think of 3407, and what may have caused that airplane to go down. They were on approach, picking up ice. They added flaps, and let their airspeed get low (think of it as a sim engine failure for our purpose), then, the flaps were raised and they continued to pull, exceded the critical AoA, and crashed. Do you see my point. The last thing I want to do when the airplane is low and slow is to re-configure the airplane and increase my AoA beyond the critical point, putting myself into a stall when I am only a few hundred feet from the ground. I think I am finally begning to understand the reasoning behind raising the flaps when the engine quits, but I still disagree with doing it because I see a big red flag that tells me to keep flying the airplane exactly as I just was. I would rather no make the runway, and come up short at a few knots abouve stall speed, than raise my flaps, pitch up to maintain my AoA when the flaps were raised and stall from 200-400 feet up and hit the ground at 1000fpm.
As for speed no being a factor,wwwuuuuhhhhh?
Airspeed is life, and altitude is life insurance. When you have as much as a 10kt difference in stall speed between full flaps and 0 flaps, I think that speed is the most critical part of this whole situation. I will try this again in a 172N today, and see if I can make it work. Last time, I tried to maintain speed exactly what it was when I "simulated" an engine failure. Today, I will try to just make the runway since some seem to think speed is not an issue. And I know this much, that when I pull to make the runway, I will loose airspeed and ground speed. I just hope that I make the runway the raiseing the flaps method.So what I'm gathering from what everyone is saying here is that when the engine quits, and you are only a few knots from stall, raise the flaps, increase back pressure and all will be o.k.?
Arbitrary numbers here. Lets say that you are on approach with full flaps and an AoA of 10 deg. The airplane you are flying has a critical angle of attack of 12 deg. About a mile from the runway, the engine quits, and you are already only 2 deg from a stall. Now we decide to de-stabalize the approach because the engine quit and decided to raise the flaps....
IIRC, flaps do not necessarly change the AoA, they change the chamber of the wing, makeing the airplane think it has a different airfoil than it realy does, which may or may not have an affect on the AoA.
I want everyone to think of 3407, and what may have caused that airplane to go down. They were on approach, picking up ice. They added flaps, and let their airspeed get low (think of it as a sim engine failure for our purpose), then, the flaps were raised and they continued to pull, exceded the critical AoA, and crashed. Do you see my point. The last thing I want to do when the airplane is low and slow is to re-configure the airplane and increase my AoA beyond the critical point, putting myself into a stall when I am only a few hundred feet from the ground. I think I am finally begning to understand the reasoning behind raising the flaps when the engine quits, but I still disagree with doing it because I see a big red flag that tells me to keep flying the airplane exactly as I just was. I would rather no make the runway, and come up short at a few knots abouve stall speed, than raise my flaps, pitch up to maintain my AoA when the flaps were raised and stall from 200-400 feet up and hit the ground at 1000fpm.
As for speed no being a factor,wwwuuuuhhhhh?
Not all flaps tilt down nearly as much as they go aft leaving the AOA change minimal, that is what the bold is about. Review what chord-line is and use a string, it will be visually obvious that the AOA has changed significantly for the portion of the wing that has flaps.
You cannot compare the aerodynamics of a delta wing aircraft to a rectangular wing the stall characteristics and propagation is completely different. Not to mention you are throwing icing into the mix which introduces issues with the tail stalling which requires opposite recovery than a typical stall (tail = inverted wing).
Go test what I said please, then apply that to what tgray said to test and please do that before you keep arguing this, I am sorry, but your wrong.
No vid to prove it but here are some bench marks for you I just did with a student an hour ago.
C152
1600 lbs
Vso - 35
Level at 35 knots, full flaps, 1900-2000 RPMs I reduced the flaps, pitched back about 5-10 degrees. We lost 20 feet in this demonstration and did not stall.
Descending at 35 knots, full flaps, engine idle, descent rate about 700 FPM. I did this two time, the first time I forgot to check what happened with descent rate and how it worked out, the second time I had my student make call outs on the VSI. Here were the results:
700 FPM, during flap retraction we fluctuated between 500-600 (for the 4-5 seconds of retract the altitude didn't change!!!) and then gradually increasing speed towards best glide. I didn't hold it long enough to stabalize after as I started letting the nose come back down so I didn't see the new descent rate at 35 knots which wouldn't even work as clean stall is 40, but that is besides the point.
Point is you can do this without stalling irregardless of how close your aircraft is to stall, go try it out at altitude to see.
Sorry no time for spell check got to teach ground school take care.
C152
1600 lbs
Vso - 35
Level at 35 knots, full flaps, 1900-2000 RPMs I reduced the flaps, pitched back about 5-10 degrees. We lost 20 feet in this demonstration and did not stall.
Descending at 35 knots, full flaps, engine idle, descent rate about 700 FPM. I did this two time, the first time I forgot to check what happened with descent rate and how it worked out, the second time I had my student make call outs on the VSI. Here were the results:
700 FPM, during flap retraction we fluctuated between 500-600 (for the 4-5 seconds of retract the altitude didn't change!!!) and then gradually increasing speed towards best glide. I didn't hold it long enough to stabalize after as I started letting the nose come back down so I didn't see the new descent rate at 35 knots which wouldn't even work as clean stall is 40, but that is besides the point.
Point is you can do this without stalling irregardless of how close your aircraft is to stall, go try it out at altitude to see.
Sorry no time for spell check got to teach ground school take care.
SpiraMirabilis
Possible Subversive
mshunter: 3407 doesn't have anything to do with this. The captain exerted enough back pressure to kick off the stick pusher. Thats 35+lbs of force.
Irrevelent, you had power applied.
Don't forget, the VSI is "special." 6-9 second lag on that thing. I see what you are getting at, and yes, at altitude it is benifical to retract the flaps, less drag. But when I am 1/4 mile from the end of the runway, I'll continue to fly the airplane as it is configured, at idle power with flaps where they are at. The way I teach the pattern is such that from anypoint from downwind abeam, regardless of flap setting/power setting, if the eingine quits, turn for the numbers and without reconfigureing the airplane, you will make it. And 40 deg. in a 150 IMHO is just no necessary unless you eff'ed up on your approach and need to get down in a hurry without building speed.
I have been trying to make this work for a while now(over a week and about 5 hours w/o students, on my own time/dime) and just can't seem to do it w/out wither loosing to much altitude and not making the runway or getting perrilously close to a stall and recovering before it gets to that point. I'll keep trying for another few hours, but I still don't know if I'll teach it after I figure it out. BTW, I'm no rookie pilot. I have been flying since I was 8, and am now 30, so it's not like I'm some freshly minted CFI with a narrow margin of an understanding of aerodynamics that I am trying to just get my head wraped around.
And to the person who sent me a PM about being "personal," no worries man. I'm sure my harsh demanor has made a few people get p.o'ed, but I am not trying to get personal either.
I don't think you understood the nature of why I was using 3407. It had nothing to do with anything other than in a panic situation, some pilots tend to, well, panic. And raising the flaps, and increasing your pitch att., some may pull too hard and induce a stall, similar to 3407. Please don't take it out of context. All that was meant by that post was pulling will induce a stall if you don't keep your head on striaght, and you just may pull through the stick pusher while in the middle of an engine failure.
SpiraMirabilis
Possible Subversive
And pushing down too much will cause you to crash into terrain, increasing bank angle too much will cause you to become inverted, floating down the runway too much will cause you to overun it, etc etc etc I don't know what your point is. That you shouldn't teach students how things actually work on the chance that they panic?
Slow your roll man. Name one thing that is wrong teaching a student to use power off approaches in a single engine airplane so if the engine quits they will make the runway. Need I remind you what the practical test standards are based off of? Do you remember the front of the PTS where it mentions the FAA-8083-**? Find me a place in any of those refrences that it says to raise the flaps when on short final and the engine quits. I did not mean to use 3407 as an attack on the crew, if thats how you thought I intended it. It was mearly a refrence to the classic stall spin scenario.
The bottom line is I am not going to try and re-invent the wheel. I am going to use tried and true methods that have worked for decades.
And for the panic comment. I can see a student panicing when they actually have an engine failure, and raise the flaps, and pull to make it to the runway, get slow, sink faster, pull more and stall, spin, crash. I have not been able to get this method to work, so untill someone can show me that it does, no I won't teach it..... kapeisch.
Wait I just want to see if I am understanding this right, you never let your students do power approach in case of an engine failure? They never use full flaps because they can't raise them if they need to?
I just don't understand what it is you do teach since you obviously have no idea the concepts behind what flaps are for on your airplane. You continue to come on here bashing first Tgray and now spiral when it is clear your understanding of the concepts in this situation need review.
You should be sitting on the computer here doing research on what has been discussed in this post so you can understand it. Run some of the numbers if that is what it takes for you to get it and then try it in the aircraft. That would be a better way to spend your time then continued rants on this forum that negitively attack members who have only been trying to help you.
Once you have done that you should come back apologize for being rude and if you have anymore questions about this topic ask them politely.