VAF Forums

VAF Forums (https://vansairforce.net/community/index.php)
-   RV General Discussion/News (https://vansairforce.net/community/forumdisplay.php?f=2)
-   -   Ground Proximity callout down to Touch Down (https://vansairforce.net/community/showthread.php?t=171059)

Ed_Wischmeyer 07-05-2019 07:48 PM

Quote:

On a normal approach, you should cross the threshold at 50ft. This should work just like the radar altimeter in the boeing.
Hmmm. A three degree glideslope is equivalent to 300 ft / nm. Crossing the threshold at 50 ft and three degrees means touching down 1,000 ft down the runway. That's fine for jets on an ILS but poor technique for, say, an RV landing on a 2000 ft runway with clear approaches.

The key point is that for GA, the term "normal" is really undefined, and at best misleading. After all, what's the "normal" runway length for GA? Normal winds? etc.

A key benefit of GA is the flexibility in so many aspects of operation. What the airlines seek to do is to standardize everything to minimize risk. Different styles for different goals.

Also, in jets it's common to reduce power to idle at 20 or 30 feet. In GA, throttle response is much faster, allowing for a variety of touchdown techniques.

And if you're counting on a voice callout for altitude and it only resolves to one foot, your landings in an RV aren't going to be all that gentle. There's better cues to use.

rocketman1988 07-05-2019 09:06 PM

Umm
 
I think you might get a nasty surprise pulling the power off at 20-30 feet in quite a few jets...

If you did that in a 727, you would open the cockpit door to find the rubber jungle...

In the 767, the landing can be hard enough to slow the earth?s rotation...:eek:

ChiefPilot 07-05-2019 10:58 PM

Quote:

Originally Posted by rocketman1988 (Post 1357428)
I think you might get a nasty surprise pulling the power off at 20-30 feet in quite a few jets...

If you did that in a 727, you would open the cockpit door to find the rubber jungle...

In the 767, the landing can be hard enough to slow the earth?s rotation...:eek:

...and if you did that in a CRJ200, you'd float waaaay past the touchdown zone while thinking that you were supposed to wipe the power off at the 50' callout ;)

rocketman1988 07-06-2019 07:31 AM

RJ 200
 
Never had the "opportunity" to fly the rj...though I get a kick out of some of the jumpseat briefings..."Don't worry, it going to look bad but we will be ok...":D

Peter Costick 07-06-2019 06:27 PM

[/QUOTE if you're counting on a voice callout for altitude and it only resolves to one foot, your landings in an RV aren't going to be all that gentle. There's better cues to use.[/quote]

I would hope no one would rely on this system instead of things like looking out the window, but nonetheless I have found it to be a useful addition to the all the other information I would take into account on landing. If the system resolved to inches it might get a bit verbose.

So out of interest how long should we take to descend the last 12 inches? At a stately 60 knots 1 second is 100 feet of runway, so at my strip at least I won't be waiting too long. 😁

rocketman1988 07-06-2019 06:59 PM

voice
 
It is kind of funny, once you get used to callouts the only time you will realize how accustomed you have become is when they aren't there...it usually ends with a firm landing!:D

EngineBridge 07-06-2019 07:06 PM

Quote:

Originally Posted by Peter Costick (Post 1357579)
I would hope no one would rely on this system instead of things like looking out the window, but nonetheless I have found it to be a useful addition to the all the other information I would take into account on landing. If the system resolved to inches it might get a bit verbose.

First, thank you Peter for your feedback and also for the many flights you made to checkout the various settings of the V3HP LIDAR. In particular, the ones you are waiting on hold line for your winter weather to get a break just to do one circuit :)

Yes, no one ever should rely on this or any other devices for landing. Not the intention of this system. Even for those who have been using it with a high-performance experimental pressurized airplanes and asked us if it can be used when there is fog on the runway.

The system gives a huge aid for the situations where one is used to 50ft wide runways for most of their flying then needed to go to a 150ft runway, also night landing, and also after a long VFR flight where the eyes are tired from scanning the sky or traffic. Basically, any situation where our eyes play tricks in regard to height.

Many said it helped a lot when transitioning to a higher-performance airplane. And also we got some feedback that it does give them an extra confidence and they developed their own technique to when to pull the power for perfect touchdown regardless if they came in bit faster or higher than usual.

Snowflake 07-07-2019 10:00 AM

Quote:

Originally Posted by rocketman1988 (Post 1357589)
It is kind of funny, once you get used to callouts the only time you will realize how accustomed you have become is when they aren't there...it usually ends with a firm landing!:D

I have to wonder if the real value in a GPWS is in larger aircraft where the pilot sits way up at the nose and the main gear is halfway (or more?) back on a 100' long fuselage. I've watched Q400's landing in front of my house recently, and they seem to vary widely from nose up to nose nearly level on touchdown. I have attributed this to differences in loading configuration, but i'm sure there are other factors. But the variation means a pilot could be 10 feet above the runway, or 20 feet, when the mains touch. With no aircraft structure in front of you or in your peripheral vision, the sight picture can't be easy to learn.

In the RV, we're right over the gear. We're always at the same elevation when the mains touch. Learning the sight line took a few landings, but I think I can already guess when i'm within a foot of the runway. What would be nice is something that could call out that "last foot" accurately. Maybe a tone that beeps increasingly fast until it goes "flatline" just when a wheel touches? It would need to know the difference between touching both wheels at once, or touching one first in a crosswind. This would be a much harder challenge technically, which is probably why nobody has done it.

F1R 07-07-2019 10:08 AM

For amphibs
 
Glassy water where you literally can not see if you are 100ft, 50ft or 5 ft

The LIDAR side of things needs a little more work yet before it is a useful / reliable tool.

For the time being conventional techniques (Sink rate of less than 80 fpm) or avoiding the hazard by waiting for ripples is the smart plan.
Formation approaches also work where #2 can see the reflection of the lead and call the altitude.

EngineBridge 07-07-2019 11:26 AM

Quote:

Originally Posted by F1R (Post 1357701)
Glassy water where you literally can not see if you are 100ft, 50ft or 5 ft

The LIDAR side of things needs a little more work yet before it is a useful / reliable tool.

For the time being conventional techniques (Sink rate of less than 80 fpm) or avoiding the hazard by waiting for ripples is the smart plan.
Formation approaches also work where #2 can see the reflection of the lead and call the altitude.

Agree, For amphibs LIDAR does not a little more work.

We have made a special version of the Controller just for that and currently working with a customer who did a few flights. That unit just logs everything that the LIDAR sees, we are waiting for the Logs to view and analyze. Some readings were correct and GARMIN tech guys did suggest some various settings to change within the LIDAR to improve this for amphibians.

It is expected for this specific LIDAR to work correctly when there are ripples. The ripples do reflect the beams back correctly. It's the glassy water situations where the beams tend to not come back. We did not give up on this yet and we are hoping to do more testing with an upgraded version shortly.


All times are GMT -6. The time now is 07:01 AM.