Effect of Flaps

[pmccarthy]

My recently acquired Vixxen likes to fly but is reluctant to descend. I have found that rates of descent with one POB and half fuel at 50 knots end engine idle are:

 

No flap 200 fpm

1/2 flap 400fpm

full flap 400 fpm.

 

The flaps are actually flaperons. Idle at 50 knots is 2200 rpm which is a bit higher than I would like, my previous 912s idled at about 1800 on the ground, about 2000 in flight. This is all manageable but getting it down to 50 knots is critical. With a stall speed of 27 knots at MTOW the old 1.3 rule would suggest a speed on final of 36 knots but with low inertia 50 knots is safe, 45 over the fence. Then add a bit of power for the round out, pull the flaps immediately on the ground. 

 

I was expecting the full flap setting would have a higher rate of descent but have tested this several times. 

 

 

[facthunter]

More flap will give more drag at the same speed. Your wing is most efficient when unflapped. Flaperons  are different and may give you some unwelcome adverse aileron effects. Make sure you are fully used to them before getting very slow near the ground and low wing loading planes are not for gusty conditions.  Avoid and downhill landings can try you.   Nev

[RFguy]

There is probably still a bucket of thrust at 2200 RPM. Probably 1/7th the thrust compared to when at TO rotation.

 

descent - How about full flap and a slip ? I have , in a Vixxen, found that very effective.  The rudder is quite big. 

 

[facthunter]

I certainly would NOT recommend that. You are really sticking your neck out. Maybe after a LOT of practice at altitude  and that's a MAYBE. Nev

[pmccarthy]

24 minutes ago, RFguy said:

There is probably still a bucket of thrust at 2200 RPM. Probably 1/7th the thrust compared to when at TO rotation.

 

descent - How about full flap and a slip ? I have , in a Vixxen, found that very effective.  The rudder is quite big. 

 

Yes, I have been slipping it a lot. That is very effective.

[RFguy]

In a high cross wind, wing down, when you put one wheel down,  you will approximate that type of slip anyway. In fact at full rudder, max Xwind,  it would be similar.

 

Nev I do agree with a general 'warning symbol'    - a potentially hazardous manouver if performed without correct technique. 

 

WHen I was practicing EPs in the PA28, I could get > 2000 fpm . However- dont try that too close to the ground, there is a fair chunk of DOWN  inertia  with a 1 ton  airplane descending at >2000 fpm at 75 kts.  takes a while to stop going down once the slip is removed. I was made aware of this before doing it .

 

 

 

 

Edited July 21, 2023 by RFguy

[facthunter]

Being in ground effect makes landings less critical. When you "slip to the actual flare" and kick it straight you are d oing a very critical manoeuver. It's generally advised to not continue a slip  to near ground and some planes say "no slips permitted with flap extended" is placarded. Flaperons are another watch what you are doing or you'll be sorry, thing.  Nev

[skippydiesel]

My last aircraft, ATEC Zephyr, had many of the characteristics of a motor glider, particularly its fantastic glide capabilities. This often resulted in being to high on final, slipping with flap was permitted and resorted to often. I did not slip to flair/land.

[Blueadventures]

7 hours ago, pmccarthy said:

My recently acquired Vixxen likes to fly but is reluctant to descend. I have found that rates of descent with one POB and half fuel at 50 knots end engine idle are:

 

No flap 200 fpm

1/2 flap 400fpm

full flap 400 fpm.

 

The flaps are actually flaperons. Idle at 50 knots is 2200 rpm which is a bit higher than I would like, my previous 912s idled at about 1800 on the ground, about 2000 in flight. This is all manageable but getting it down to 50 knots is critical. With a stall speed of 27 knots at MTOW the old 1.3 rule would suggest a speed on final of 36 knots but with low inertia 50 knots is safe, 45 over the fence. Then add a bit of power for the round out, pull the flaps immediately on the ground. 

 

I was expecting the full flap setting would have a higher rate of descent but have tested this several times. 

 

 

I have not flown a Vixen, and not an instructor.  A mate has recently purchased a Vixen and he about to convert to RAAus and experienced GA pilot.

A good friend has explained to him that best to become very proficient with side slipping and the slower speeds in circuit as these are a must otherwise it will float and float and not land.  They are prone to brake noise as well I am finding out as I have been doing the annual on the aircraft and during taxi the other day I was concerned by the noise from the moving caliper.  There is a very good facebook group of Australian owner / pilots.  The idle on the ground is 1950rpm and will be further adjusted slower as the maintenance work progresses. Cheers and enjoy.  

[skippydiesel]

"...........the slower speeds in circuit as these are a must otherwise it will float and float and not land"

 

Never flown a Vixen however the ATEC Zephyr had a 30 knot stall, low wing and those who did not read the POH, understand the need for a slow late final, would float for ever BUT this is a failure of the pilot to follow the POH ,not the fault of the aircraft.

 

Those who have difficulty landing aircraft with a low stall, should practise slow flight, at altitude, become proficient and then apply their new found skill to the Final & Landing of the aircraft.

[Old Koreelah]

10 hours ago, RFguy said:

There is probably still a bucket of thrust at 2200 RPM.

Good point, RF. It took me ages to get my Jab 2.2 idle set properly. Too low and it would stop on late final as airspeed dropped off. A couple of hundred extra rpm kept it running, but made the landing considerably longer.
Getting the idle screw right was the key.

[MattP]

9 hours ago, RFguy said:

WHen I was practicing EPs in the PA28, I could get > 2000 fpm . However- dont try that too close to the ground, there is a fair chunk of DOWN  inertia  with a 1 ton  airplane descending at >2000 fpm at 75 kts.  takes a while to stop going down once the slip is removed. I was made aware of this before doing it .

 

 

 

 

~2000 FPM is about the ROD at best glide in a PA28 isn't it 😇 At least it makes forced landing practice easy. 76KIAS - look right down, we're not going anywhere else 🙂!  

[Area-51]

2 hours ago, MattP said:

~2000 FPM is about the ROD at best glide in a PA28 isn't it 😇 At least it makes forced landing practice easy. 76KIAS - look right down, we're not going anywhere else 🙂!  

Excellent demonstration here 😃

 

[skippydiesel]

Wow!!!! Not only an extraordinary hard landing but look at that nose wheel shimmy - no up elevator? 

[facthunter]

You can't keep the nosewheel off the ground and brake at the same time. Fair chance the nosewheel was damaged. That was an extremely HARD landing and the plane would require a thorough inspection ( and more)

[Area-51]

Watch the Right Prop rpm fluctuating afterwards; expensive badness; big fat invoice 😊

[facthunter]

It would not be beyond possibility that plane is close to a write off. and it's quite likely the occupants would have been injured. Nev

[Old Koreelah]

Landing with about ten knots tailwind, on what is probably a short strip.
Maybe terrain precludes an approach from the other end.

[facthunter]

Landing with a tailwind gives you a bit of extra airspeed near the ground.  That plane was doing a full flap with power off  and HIGH RoD approach and didn't have enough airspeed to flare and arrest the sink rate.  Nev

[RFguy]

I was doing crosswind practice on the weekend at a variety of different ADs (Young >> cootmundra >> , temora into a medley to keep me on my toes) ) 

wing down method, abotu 7-10 kts pure Xwind,, not much but I need practice.

The first 6 were pretty good. . remarkably easy, and I did a left wheel down, right wheel down, left wheel down and my coordination is much better with wind on my right.
One the last I did at Temora, getting a bit tired AND  I had a bunch of glider people standing at the threshold watching me, I let it get too slow in the wing down flare and it dropped the high wing. oops . which caused a bounce and on 2nd bounce where airspeed got too low for positive control, triggered an immediate go around.  nosewheel never touched the ground. plenty of elevator still left.  Looked terrible I guess. fortunately the wing that was into the wind was only a foot off the ground.......  The telltale of it coming was that the aeleron control started to disappear and the rudder started to dominate. anyway, now I know the limits and not to reduce power too much  (I reduced power too much and didnt arrest the falling airspeed) . ... How do people stay current on this stuff and only fly once a month in perfect condix ?

[Old Koreelah]

2 minutes ago, RFguy said:

How do people stay current on this stuff and only fly once a month in perfect condix ?

Most of us probably don’t. Few have the luxury of a quiet strip which they can use when the wind is just right. Then there’s the landing fees, which seem to have reduced circuit training.

 

I know one bloke who does hundreds of circuits, just to perfect his skills. Must be expensive.

[facthunter]

You kept going too long and your attention/ concentration dropped off.   Nev

[facthunter]

It's highly coordinated  controlling.  Nev

[johnm]

On 21/07/2023 at 10:51 AM, pmccarthy said:

My recently acquired Vixxen likes to fly but is reluctant to descend. I have found that rates of descent with one POB and half fuel at 50 knots end engine idle are:

 

No flap 200 fpm

1/2 flap 400fpm

full flap 400 fpm.

 

The flaps are actually flaperons. Idle at 50 knots is 2200 rpm which is a bit higher than I would like, my previous 912s idled at about 1800 on the ground, about 2000 in flight. This is all manageable but getting it down to 50 knots is critical. With a stall speed of 27 knots at MTOW the old 1.3 rule would suggest a speed on final of 36 knots but with low inertia 50 knots is safe, 45 over the fence. Then add a bit of power for the round out, pull the flaps immediately on the ground. 

 

I was expecting the full flap setting would have a higher rate of descent but have tested this several times. 

 

 

I think that's your problem - motor is idling to high - that's why the plurry thing won't come on down

 

- on the ground what does it idle at - I'd suggest 1500 - any other bidders please 

[Area-51]

The rotax 912UL will happily idle smoothly all the way down to 1200 before gearbox starts chattering and if really well tuned 1000; my 80hp will idle at 650rpm happily all day if allowed to. The ULS manages 1500 ok as it has slightly hotter cam. In the air they both windmill down to 1500 off power at around 50kt. Had the same float problem with aircraft after purchase, idle was set at 2000 and thing just floated right down the 900m strip in ground effect; handed controls over to more experienced right seat and was not an issue.

 

Higher nose up attitude while above the stall speed also helps on round out but requires sufficient experience and practice of flying power on stalls at safe altitude beforehand.