DME Arc approaches

[saracelica]

I hope we don't get much thread drift but I guess what fun is that on a web board.

So in IR training today my CFII made up a VOR/DME arc. We have GPS but no DME (thank goodness!) So he said "Follow the VWV - Waterville VOR with a 10nm radius" Once I found the Waterville VOR I got it nailed down pretty good. But I'm *concerned* that maybe it was luck. So for realistic scenerio...let's say you the reader of this post takes off from KTDZ and fly the 160 radial for 5-6 minutes and then your CFII says "Follow the VWV Waterville VOR" what would be the steps you'd do to figure out where you were and how to get there? Do you punch in VWV into the GPS and just hold when you're 10nm away?

 

[tonycondon]

I find it much easier to fly an arc with a real DME and a VOR receiver, but thats just me. With a real DME you can have the groundspeed readout and just keep it at zero as you incrementally turn.

 

[saracelica]

Our closest real DME is 23nm away. That's alot of expensive avgas blowing out just do practice.

 

[tonycondon]

No i mean DME receiver in the plane. and 23 miles is a nice distance to practice flying an arc

 

[bnt83]

Our closest real DME is 23nm away. That's alot of expensive avgas blowing out just do practice.

Microsoft Flight Sim X it then.

 

[N801BH]

No i mean DME receiver in the plane. and 23 miles is a nice distance to practice flying an arc

Sounds like the RNAV runway 01 into Jackson Hole. It is fun,,,, and we have terrain you have to miss too.

 

[tonycondon]

shot the DME arc into Ponca City on my IPC last week. It was a blast. held within .1 miles either side of the arc.

 

[alfadog]

shot the DME arc into Ponca City on my IPC last week. It was a blast. held within .1 miles either side of the arc.

How big do you make your turns or do you just kinda continually edge it around?

 

[tonycondon]

How big do you make your turns or do you just kinda continually edge it around?

incrementally turn towards the direction of the arc, usually in 10 degree increments, but really just depending on how fast and what direction the DME distance is changing. monitor location by centering up the VOR needle each time I turn.

 

[N801BH]

Our closest real DME is 23nm away. That's alot of expensive avgas blowing out just do practice.

23 nm is like 1 gallon of avgas...


Geez woman... ya got to spend a few bucks to get good...

 

[wsuffa]

I find it much easier to fly an arc with a real DME and a VOR receiver, but thats just me. With a real DME you can have the groundspeed readout and just keep it at zero as you incrementally turn.

Agree. I find it easier with a real DME, too. I can do it with a GPS, too, but the DME reduces workload.

Our closest real DME is 23nm away. That's alot of expensive avgas blowing out just do practice.

That's not far at all. By the time you get off the ground & set up, you'll be at the edge of an arc anyway. 10NM arc = 13 NM to fly.

 

[EppyGA]

We did an arc on my check ride. I almost always include it in my routing for practice. I usually end up flying 150+ miles on a practice day to keep current.

 

[poadeleted20]

I love the DME Conga:

Turn 10, twist 10, check your DME [kick]
Turn 10, twist 10, check your DME [kick]
Turn 10, twist 10, check your DME [kick]
Turn 10, twist 10, check your DME [kick]...

 

[SCCutler]

My last IPC, instructor cleverly had me fly a VOR-DME app to Pueblo, CO- at Ardmore, OK. The VOR's on the same frequency, and you fly the charted altitudes, because Pueblo is (most thoughtfully) so much higher than Ardmore.

Great training, and no magenta line.

Tony's "keep the speed at zero" play was coolest when I flew an A36 with the old King mechanical DME display, just keep it from moving at all, not even a tenth.

 

[TMetzinger]

I always just watch the dme and turn 5 degrees for every 1 tenth distance deviation.

If I'm supposed to fly a 13 NM arc, and I see 13.1, I turn 5 degrees towards the station. If it goes to 13.0 I take the 5 degrees out. If it goes to 13.2 I turn an additional 10 degrees. This works pretty well.

 

[jason]

I find it much easier to fly an arc with a real DME and a VOR receiver, but thats just me. With a real DME you can have the groundspeed readout and just keep it at zero as you incrementally turn.

 

[somorris]

I fly an arc like Cap'n Ron described, in 10 degree increments. You can arc around any VOR. It doesn't have to be part of an approach. Last time I practiced, I went all the way around twice. It was fun trying to stay right on target. (Notice, I said "trying" . And by the way, I was arcing at 5 nm, not 10. Try that some time. Not easy .

 

[Banjo33]

My last (also my first) instrument student was struggling with the concept/procedures of flying a DME arc. After spending about an hour over a couple of flights, I found this app on the App Store: Radio Navigation Simulator. It only cost a couple of dollars, but much cheaper than practicing in the airplane! There's a "flight profile" that you can download free on their website too. Helps you to see what the aircraft is actually doing, in comparison to the instruments. My student passed his check ride about 3 weeks ago and is now on his way back to Mississippi from an IFR cross country flight to Arizona!

 

[Chip Sylverne]

Agree. I find it easier with a real DME, too. I can do it with a GPS, too, but the DME reduces workload.

.

I didn't have a dme, so preparing for my IR checkride my instructor had me use the brg and dist to waypoint on the GPS to simulate. Using those you can fly an arc around any waypoint.

I need to dust off some of those skills. Slipping into being a child of the magenta line.

 

[Jim_R]

23 nm is like 1 gallon of avgas...

Maybe in a powered parachute. What plane do you fly that does 115 kts on 5gph? Or are you flying 230 on 10gph?

 

[tonycondon]

Tony's "keep the speed at zero" play was coolest when I flew an A36 with the old King mechanical DME display, just keep it from moving at all, not even a tenth.

Brilliant.

 

[N801BH]

Maybe in a powered parachute. What plane do you fly that does 115 kts on 5gph? Or are you flying 230 on 10gph?

Hmmmm...

Just about EVERY experimental can get that kind of fuel burn.... Or better.. Well, except mine...

 

[dtuuri]

I fly an arc like Cap'n Ron described, in 10 degree increments. You can arc around any VOR. It doesn't have to be part of an approach. Last time I practiced, I went all the way around twice. It was fun trying to stay right on target. (Notice, I said "trying" . And by the way, I was arcing at 5 nm, not 10. Try that some time. Not easy .

I've never followed this logic. According to my understanding of what you guys say, you'd be on about a 2.5 mile arc instead of 5.0 after a complete circle.

If you "turn ten" when the CDI centers, you'll be inside the arc more and more with each turn.

If you wait 'till the DME is back on the arc, you'll need to "twist twenty" in a zero-wind situation.



dtuuri

 

[bobmrg]

I fly an arc like Cap'n Ron described, in 10 degree increments. You can arc around any VOR. It doesn't have to be part of an approach. Last time I practiced, I went all the way around twice. It was fun trying to stay right on target. (Notice, I said "trying" . And by the way, I was arcing at 5 nm, not 10. Try that some time. Not easy .

Note that the minimum arc distance in the real world is 7 nm. If you can do it at 5nm, 7 should be a walk in the park.

Bob Gardner

 

[John Collins]

Plus the tolerances required to follow the arc are the same as along an airway, stay within the same county.

 

[dtuuri]

Plus the tolerances required to follow the arc are the same as along an airway, stay within the same county.

That won't be good enough to pass a test:

8. Intercepts a DME arc and maintain that arc within ±1
nautical mile.​

dtuuri

 

[LDJones]

I've never followed this logic. According to my understanding of what you guys say, you'd be on about a 2.5 mile arc instead of 5.0 after a complete circle.

If you "turn ten" when the CDI centers, you'll be inside the arc more and more with each turn.

If you wait 'till the DME is back on the arc, you'll need to "twist twenty" in a zero-wind situation.



dtuuri

Now I'm confused. If you turn 10 deg. 36 times, allowing 10 deg. of the arc to pass between turns, how do you end up closer? The distance from the VOR only alters how quickly you move between the 10 deg arc segments. What am I missing?

BTW, twist 10, turn 10 has worked for me and my students for 33 years.

 

[alfadog]

Now I'm confused. If you turn 10 deg. 36 times, allowing 10 deg. of the arc to pass between turns, how do you end up closer? The distance from the VOR only alters how quickly you move between the 10 deg arc segments. What am I missing?

BTW, twist 10, turn 10 has worked for me and my students for 33 years.

The fact that you make a 360d turn does not speak to whether you maintain a constant radius. Think of a spiral. It I center the CDI and fly 90d to the selected OBS course then I am flying at a tangent and will increase the radius. 10d of OBS further, I turn 10d in. Still on a tangent and still increasing the radius. If I continue doing that all the way around then I would have spiraled out markedly. No? Then why not? I don't have a CAD program on this computer but I will dl a free one and draw it out.

Edit. just did a quick calculation and if you actually did that method "perfectly", you would end up 55% further away than when you started, i.e. if you started at DME 10, you would end at DME 15.5 after 360d. Why don't you? Because you are constantly making additional corrections based on DME.

 

[dtuuri]

Now I'm confused. If you turn 10 deg. 36 times, allowing 10 deg. of the arc to pass between turns, how do you end up closer? The distance from the VOR only alters how quickly you move between the 10 deg arc segments. What am I missing?

If you turn 10, twist 20, you stay on the arc:

​

If you turn 10 when the needle centers after only 10°, you turn too soon. If you wait until on the arc, you need to twist 20, rinse and repeat. The way I figr it anyway...

dtuuri

 

[alfadog]

If you turn 10, twist 20, you stay on the arc:

View attachment 30467​

If you turn 10 when the needle centers after only 10°, you turn too soon. If you wait until on the arc, you need to twist 20, rinse and repeat. The way I figr it anyway...

dtuuri

If you were to turn 20d of heading every 10d of OBS, you would soon be heading too far inward. 10 for 10 is the formula, it just requires a bit of tweaking to get to the sweet spot. I am sure the old hands do it by feel but if you were to program it into a FMS that way (10 and 10), you would spiral in or out.

 

[alfadog]

Here is what happens if you precisely fly 90d to starting OBS setting and turn 10, twist 10.

 

[dtuuri]

If you were to turn 20d of heading every 10d of OBS, you would soon be heading too far inward. 10 for 10 is the formula, it just requires a bit of tweaking to get to the sweet spot. I am sure the old hands do it by feel but if you were to program it into a FMS that way (10 and 10), you would spiral in or out.

It's "Turn ten", not "twenty". You "twist" twenty:

​

Keeps you on/inside the arc, not outside it which is more difficult.

dtuuri

 

[alfadog]

It's "Turn ten", not "twenty". You "twist" twenty:

View attachment 30473​

Keeps you on/inside the arc, not outside it which is more difficult.

dtuuri

The included angle between those yellow lines is 160d. You can work that out easily enough from the equilateral triangles. You would have to turn 20d of heading to follow that line. Turn 20, twist 20. If you are not doing that then you are making corrections elsewhere.

My point is that turn 10, twist 10 is as good a method as any as you will make the adjustments to get to the sweet spot where that brings you right around. Looking at it now after drawing it out, I would try to hit my DME distance as the CDI centers, then turn 10 and twist 10.

 

[dtuuri]

The included angle between those yellow lines is 160d. ...You would have to turn 20d of heading to follow that line. Turn 20, twist 20.

Eureka! "Turn 20, twist 20!" Thank you for that! I never thought in these terms, I always turned perpendicular to the next 10° radial and advanced the OBS 20°. Doing it that way, only the first cut is 10° and the rest are 20°. So, it's really:

Turn ten,
Twist twenty,
Turn twenty,
Twist twenty, etc.​

I now see the light. Thanks again!

dtuuri

 

[denverpilot]

Some jerk failed my DG right when I intercepted one and I froze. Heheheh. He showed me how to fix it using a godawful mag compass at night in the dark, and timed turns.

But I was ****ed at myself for an hour for losing the picture and freezing up solid. Haha.

He lives in Nebraska and has a FlyBaby, a motorcycle, and a cool dog.

 

[Ghery]

The plane I did my IPC in Tuesday (and IR ride a couple years ago) has GPS and DME. I tend to fly DME arcs with the DME. Bigger numbers at a distance I can focus with my glasses when the foggles are on. And +/- 1 nm isn't hard. The VOR/DME 35 approach into OLM is a 15.3 nm arc. Not hard at all. And, I tend to just set the OBS on Nav 2 to the inbound heading for the approach. As the needle gets close, turn inbound. Of course, the GPS is giving me a countdown timer to the turn. Now, if I could just read it with the foggles on... When actually flying without those darned things, easy.