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Slip necessary from Decision Height

cleve_thompson

cleve_thompson

Well Known Member
In my RV9A with O320 and fixed Sens. prop, I find that if I am doing an precision approach at 100-110mph that to get down anywhere near the TD zone, I have to slip. Just raising the nose to slow below 90 to lower flaps makes me gain too much altitude to get down short.

I find if I slow down from final approach fix to decision height, the plane is not stable enough for me.

Anyone have same or different experience.
 
Hey Cleve,

Not sure about what the best combo is for the 9 on a Precision approach. But I would not do anything that made me climb back up from DH as this may well pop you right back in the clouds and that is a bad thing at that point.

Very interested in the outcome of the issues you posted about on another forum. Have you found a solution to those coupling issues?
 
Similar but in a 7A

First, please see this thread with many interesting opinions:
http://www.vansairforce.com/community/showthread.php?t=29564
and this post:
http://www.vansairforce.com/community/showpost.php?p=220037&postcount=22
which lists what I suggest as criteria for correct speed.

Obviously, the 9/9A will have different answers to the same questions than a 7/7A. I suspect you will need to slow it down a little. But the 1000' touch down area is not a requirement for an RV-9/9A IMHO. The end of the runway is the issue, not the touchdown spot for jets.

That said, I had the same problem even at 100 kts. If you remember to completely chop the power at DH you will be able to pull the nose up pretty soon to get to flaps speed. YMMV. You can slip in the meantime.
 
Cleve,

I have the same setup as you do and I experienced the same as you do: raising the nose at that speed will make 9(A) climb (at least not descend). On an approach from OM I usually fly at below 90 kts and have at least 10 degree flap down (full flap at below 80 kts). Runway in sight, I lower all the flap and slow down. If I am too close, I slip if necessary. As a matter of fact I slip often during landing even in VFR. 7 is definitely different. I found 6 and 7 easier to land than 9: cut the power to go down, add power to go up. However, 9 is more stable at lower speed so you can fly slower than 6 & 7. With full flap I found it quite stable at 65 kts. Even so, I usually try to keep my AP on as much as possible. Checking the plate while hand flying in IMC is not easy for me.
 
Try a climbing slip or level slip. I find the climbing slip works quite well in the -4 to get down to flap speed without gaining much if any altitude. If gaining no altitude is your goal as it may be at DH then the level slip is almost as quick at dropping speed to get the flaps out.
 
cleve_thompson said:
In my RV9A with O320 and fixed Sens. prop, I find that if I am doing an precision approach at 100-110mph that to get down anywhere near the TD zone, I have to slip. Just raising the nose to slow below 90 to lower flaps makes me gain too much altitude to get down short.

I find if I slow down from final approach fix to decision height, the plane is not stable enough for me.

Anyone have same or different experience.
Click to expand...

If your doing a hundred at DH, your going way too fast.
If slower is not stable for you then you need to stop everything and figure out why that is.
Do you need slow flight practice? Maybe you need to verify your readings against actual? But if going slower than 100 actually produces an unstable plane, then something is amiss and you should stop flying low and slow until you resolve it. There are many things that could impact slow flight characteristics and cant be gone through here. But please figure out whats going on.
 
Oh and one more thing. If I read you correctly, at DH you are slowing to 90 then dropping flaps? That is absolutely not the correct procedure. You should be stable on the approach from FA all the way to DH, with flaps down. DH is not the time to be dropping flaps, gear, trim, speed ect. That will send your plane into a tizzy and you too if your in IMC.
 
grantcarruthers said:
Try a climbing slip or level slip. I find the climbing slip works quite well in the -4 to get down to flap speed without gaining much if any altitude. If gaining no altitude is your goal as it may be at DH then the level slip is almost as quick at dropping speed to get the flaps out.
Click to expand...

I've always been taught that a climbing slip is a recipe for stalling the aircraft, which is a bad thing to do at DH, IMHO.
Chuck Olsen
RV-7A
TSP
 
Forward slip to get down from Decision Height when at 90 knots

From all the helpful comments and the links, I think that I will continue to try to be at 100 MPH (90 knots) at decision height. Thanks to all! You have been most helpful!
Yes, Kahuna, the airplane is stable at much slower speeds but the coupled A/P is not and I like to fit under cat B for times etc. I can get her slowed and down from there by doing forward slip and I think that I will continue to do this. I, too, have been urged by the controller to keep my speed up and I will do this until I get to the FAF. How much speed I can bleed off by pulling throttle at FAF I haven't determined yet. I sometimes wish that I had elected to use a constant speed prop since I would have another way to bleed off speed.

I agree with Ted Chang that a forward slip is a tool that I use in most of my VMC landings as well as instrument approaches with the RV9. You must remember that I only have 65 hrs. in my RV9A and before that I had 500 hrs flying a Tripacer or a Cherokee 140, both of which had plenty of drag and slowing down was not really something that one had to worry about.:D

I can "drag it in" and land short without a slip in my RV but I don't like to be in a position where I can't make the field if I have an engine failure, but this is another subject.
 
cleve_thompson said:
I sometimes wish that I had elected to use a constant speed prop since I would have another way to bleed off speed.
Click to expand...

The C/S and 320 go great together in a 9(a). Flying in mountainous country ( but not the rugged back country), we experimented with numerous steep approaches and different wind levels; including landing with the wind. Afterall, our state does have one way runways thanks to terrain issues. :)

The 9 will come down quite steep with a C/S but still reminds me of landing a 172; as it will easily float over the numbers with power off, and no tendency to drop through a flare.

L.Adamson
 
L.Adamson said:
The C/S and 320 go great together in a 9(a) ....
The 9 will come down quite steep with a C/S but still reminds me of landing a 172; as it will easily float over the numbers with power off, and no tendency to drop through a flare.L.Adamson
Click to expand...

Thanks for posting this - I'm nearly 1/2 way done (only 2 halves to go!) and I've not yet flown a 9A. These kind of posts provide great perspective. I've been leaning towards FP since it is way cheaper, way lighter, and less maintenance. May need to rethink this one. It's just hard to think about paying $6K for a prop and $1.2K for a governer!

dave
 
A really big help in slowing down for the 320/FP combo is keeping idle rpm as low as possible. I never pull the throttle all the way except on final. Down final I turn around 700 and far less on the ground. The airspeed keeps the prop turning and absorbing power. I usually add power on roll out just to keep things smooth. If I switch off the mag side and only run on the E-Mag while setting still, I can idle smoothly at 390rpm. Much rougher with the mag on, so I keep the throttle in about 1/8" except down final. Works for me and the difference is very noticeable.

Bob Kelly
 
Instrument approach

I'm going with Kahuna on this one. DH is not the place to be making configuration changes much less slipping the aircraft. If the AP is not stable as you get closer to the DH or MAP, either hand fly or have the AP fixed. The Navy was very particular about having the aircraft in the landing configuration (gear down, flaps down, on speed) by the final approach fix, AP or not. You might get away with slipping the aircraft in VMC conditions but it will get very "unconfortable" doing this in IMC conditions.

My .02 worth.

Marc
 
Hesitantly Disagree

marchudson said:
I'm going with Kahuna on this one. DH is not the place to be making configuration changes much less slipping the aircraft. If the AP is not stable as you get closer to the DH or MAP, either hand fly or have the AP fixed. The Navy was very particular about having the aircraft in the landing configuration (gear down, flaps down, on speed) by the final approach fix, AP or not. You might get away with slipping the aircraft in VMC conditions but it will get very "unconfortable" doing this in IMC conditions.

My .02 worth.

Marc
Click to expand...
I'm reluctant to disagree with the Navy, Kahuna or Marc, all clearly at higher skill levels than am I. That said, an RV is not a military airplane and it's not landing on a carrier. In my experience (limited), most ILS runways are 5,000' or more. I'll stick to my personal opinion that an RV should be in the missed approach configuration at/until DH, not necessarily landing configuration. Doubly true for those of us with electric flaps. I know it's different in a 9/9A, but certainly in a 7/7A there is no need to have the flaps down until below DH and good reason(s) to leave them up. I agree that the distance from FAF to DH/MAP should be in a stable configuration. But being ready for go around is safer. There's plenty of time and runway after the decision has been made to land. If I can do it at 100 -120 kts, a 9 should be able to do it at 100 mph. I've even done it without flaps to find out the limits.

Steps:
1. decide to land
2. chop the power
3. slip to lose speed and altitude
4. optionally stop slipping before next step
5. staying out of ground effect, lower flaps fully when able
6. land.

I see nothing difficult, let alone dangerous, about this in an RV. If you can do it in VMC for short fields then there should be no difference if you can see well enough to land.

My $0.02
 
What autopilot are you using?

Just out of curiosity, what autopilot are you using that isn't stable when flying slower? How about the rest of you flying IMC with autopilots? Do any others have a problem when slow?
 
Ok, I'm still trying to figure out why you are blasting along at those speeds when that close to the airport.

The -9, or my RV-9 anyway, is VERY stable with full flaps and 65 MPH approach speeds. Should you hit the DH, in goes the power, up come the flaps and you are back in the clouds waiting for another shot at the approach.

Heck, 70 MPH w/ no flaps and the thing is still rock solid.

If you are uncomfortable flying at these slow speeds, find a good instructor who doesn't want to turn every stall into a spin entry and go do a lot of slow flight and stalls. It is possible to stall the -9 (or most any plane) at altitude and ride it down using the rudder to keep the wings level and then make a normal stall recovery.

What I'm trying to say is don't be afraid to fly the thing slow, that's what they are designed to do.
 
What Bill said...

N941WR said:
Ok, I'm still trying to figure out why you are blasting along at those speeds when that close to the airport.

The -9, or my RV-9 anyway, is VERY stable with full flaps and 65 MPH approach speeds. Should you hit the DH, in goes the power, up come the flaps and you are back in the clouds waiting for another shot at the approach.

Heck, 70 MPH w/ no flaps and the thing is still rock solid.

If you are uncomfortable flying at these slow speeds, find a good instructor who doesn't want to turn every stall into a spin entry and go do a lot of slow flight and stalls. It is possible to stall the -9 (or most any plane) at altitude and ride it down using the rudder to keep the wings level and then make a normal stall recovery.

What I'm trying to say is don't be afraid to fly the thing slow, that's what they are designed to do.
Click to expand...

65 MPH is the magic number, 1.3 x Vso. A 30 percent margin above stall is the conventional logic on a stable approach. As I said in a previous thread, it is just plain dangerous to be messing with configuration close to the ground in marginal conditions. VFR you can slip, s-turn or whatever you want but IMC, without much visual reference, you are putting yourself at risk.

In one of the earlier posts on this thread there was a comment about ATC "urging you to keep your speed up." If the conditions are close to your minimums, the response is "unable." The controller isn't flying the airplane, you are.

John Clark ATP, CFI
FAA FAAST Team Member
RV8 N18U "Sunshine"
KSBA
 
cbo111 said:
I've always been taught that a climbing slip is a recipe for stalling the aircraft, which is a bad thing to do at DH, IMHO.
Chuck Olsen
RV-7A
TSP
Click to expand...

Impossible at the speeds we're talking about. You'd have to pull better than 2 G's to stall getting down to the top side of flap speed. A -9 stalls under 50 mph so were talking more than 1.8 Vs.:eek: Pretty wide margin IMHO.

Cheers
 
Please explain....

hevansrv7a said:

Steps:
5. staying out of ground effect, lower flaps fully when able
Click to expand...

Can this be explained to me. EI not only can you explain why, but can I understand what you say (but I'll try).:confused:

When you are at some given height with X amount of energy (forward speed), why would it matter if you lowered you flaps before getting into ground effect as opposed to lowering them in ground effect.

Don't get me wrong I think by the time you get close to ground effect you should leave you flaps alone and land the plane. If you can't land the plane at that time then go around.

I am just curious about the theory behind the dissipation of the energy of the plane. I am overlooking something?

Kent
 
If shortening landing space required is your priority then you want to slow down before entering ground effect. A given amount of energy will bleed off faster out of ground effect than once into it thus you land shorter.
 
Any aircraft will have less drag in ground effect. Since the whole point is to slow down, ground effect is bad - you want the drag.
 
So you guys know, I have not flown actual IMC approaches in my RV9A, only under the hood. I think that in IMC with low minimums (which I hope I never have to make), I would not worry about floating some and landing a little long. Even under IMC, I don't think that I would want to do the approach at 85-90 MPH, the speed I could get the flaps down. I like to have more safety margin in case I get distracted. 100MPH seems to give me that. My A/P is a Tru-Trak Digiflight IIVSGV and it just doesn't seem to be able to manage a slow speed. I usually disconnect it when just above D/H and begin to drop the 20mph excess speed. To aid that I usually add a notch of flaps and slip.

This might change as I get more proficient but now I like the little extra speed during the approach, a forward slip to lose altitude without gaining speed, and then pulling the nose up to bleed off speed to land without too much float.
______________________________________________

Someone asked about whether a C/S prop would be worth the extra expense and maintenance cost. I don't know because I have only flown a fixed pitch prop during transition training and in my own bird. I think that the fixed pitch is fine in VMC. The bird lands well as long as you watch the A/S so in my humble and uninformed opinion, a C/S prop in VMC is not worth it. The only place I have wanted a little more drag has been practicing approaches to decision height and then trying to land without float. I still think that I can perfect my technique without putting an extra knob on my panel.
 
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