Proof of USAF insanity - H-1 normal landing approach

[Sundowner.pl]

H-1 Pilot Student Guide

1550th Aircrew Training and Test Wing

USAF 1978

 

 

 

Yes, you read correctly, normal approach is 30°. NORMAL approach, from 300ft AGL and 60 kts IAS, 30° down to 4ft hover.

 

I dare anyone to try it! :joystick:

 

PS. Yes, there is a "steep approach" too... I don't think you want to know how it looks like :music_whistling:

[Vlerkies]

How long can you sustain a 30degree pitch at 60kts? I guess from recommended height of 300ft not very far before you bleed speed badly.

 

My mind is working overtime now, and I am at work and can't test this lol.

[Sundowner.pl]

It's not 30° pitch, its 30° slope to landing spot.

Nose pitch up shouldn't be above 12° as that's how you strike ground with the tail first.

 

I tried it, and the funny thing about this approach is - you loose sight of your landing spot just before you start your descent - you have to observe it through the chin bubble... while watching your rate of descent, speed, heading... a lot to do on the same time.

 

It's a wild ride first time you try it... and the second one... third one usually end in VRS... fourth probably long... :cry:

[walker450]

I thought the 30 degrees is the angle relative to the ground... not the pitch of the helicopter.

[Vlerkies]

:doh:

 

Ok gotcha

[TimeKilla]

looks easy for a decent real pilot when you think they were touching down in hot zones and went in fast and out fast.

 

"Army helicopter pilots are God's Own Lunatics."

[Sundowner.pl]

It's definitely doable, although in the civilian world - a normal approach is 10°.

 

If you do the math you'll see that average descend speed is above 1500fpm in that 30° approach. Plus you have only 600ft of air to slow down to a dead stop. Try that with no wind and max gross weight :pilotfly:

[doright]

It's definitely doable, although in the civilian world - a normal approach is 10°.

 

If you do the math you'll see that average descend speed is above 1500fpm in that 30° approach. Plus you have only 600ft of air to slow down to a dead stop. Try that with no wind and max gross weight :pilotfly:

 

Just to elaborate.

 

If you assume that you really fly a straight 30deg line down and linear deceleration, then it looks like this:

300ft / 60kts / 3036fpm (1500fpm average)

200ft / 40kts / 2024fpm

150ft / 30kts / 2508fpm

100ft / 20kts / 1012fpm

50ft / 10kts / 500fpm

25ft / 5kts / 253fpm

0ft / 0kts / 0fpm (hopefully!)

 

A 10deg approach would look like:

300ft / 60kts / 1054fpm

200ft / 40kts / 700fpm

150ft / 30kts / 527fpm

100ft / 20kts / 351fpm

50ft / 10kts / 176fpm

25ft / 5kts / 88fpm

0ft / 0kts / 0fpm

Edited May 6, 2013 by doright

[Sundowner.pl]

Yes, although those approaches always end up in a 4ft hover, so no cookie for run-on landing ;)

 

I have to practice those A LOT, so far I call that 30�° approach: "Master Caution Approach". It's a roller coaster ride - first rotor overspeed, then low rotor rpm buzzer sound off, and the ground effect is the only thing that doesn't allow me to smack flat on the runway numbers (aiming point). This needs a lot more finesse than my 16 hours of stick time provides.

[wess24m]

I think right now since the VRS is over modeled, when you flared at the bottom of the decent you'd be in trouble.

[Sundowner.pl]

I'm doing this with unarmed helicopter, with 50% of fuel. Plus my current approach is a bit curved so I'm ending up still with some forward speed and a bit short of the landing spot, so VRS is not a problem right now... lack of available power is.

 

But I'm hamfisting this approach, I think I'll let it go for now, and do the patterns with "shallow" 10° finals, try it again when I get more hours on this thing, as half of them so far is not real flight training.

[cichlidfan]

I will have to find the passage in 'Snake Pilot' where a group of Hueys were dropping troops, one chopper at a time, at 5 sec intervals on the same LZ.

[HuggyBear]

Holy crap! That's a pretty extreme approach.

 

Our 'steep' approaches were 8-12 degrees!

 

- Bear

[Sundowner.pl]

Well their "steep" approaches look like this:

 

 

 

:thumbup:

 

Although it's less eventful than the the 30° one, much lower average descent rate, better visibility (although still through the chin bubble), but also require a lot of power.

[Chelco]

It should be doable now that we have an improved FM. Anybody tried?

 

Off topic: that manual

 

H-1 Pilot Student Guide

1550th Aircrew Training and Test Wing

USAF 1978

 

Is it available from somewhere?

 

Cheers,

[Robert1983NL]

I don't think you should want to do this. I think it's an outdated procedure, or used for basic training only. 8 to 12 degrees is more normal for a steep approach like Huggybear said.

 

I've done these 30 degree angle steep approaches in the Huey, to get a slow and very controlled landing in situations where you have a very small power margin, like at high altitude and a pinnacle landing spot. That way you require less and more gradual collective inputs.

 

But it has nothing to do with tactical flying.

[Chelco]

Thanks, Robert.

 

Yes, I agree.

 

There is this report, which you can argue is rather old:

 

A momentum analysis of helicopters and autogyros in inclined descent, with comments on operational restrictions. Technical Report TN D-7917, NASA Langley Research Center, 1975.

 

In page 22 it says: "... power settling is unlikely to occur if the glide slope is shallow. Limiting glide slopes to 10 or 15 degrees avoids power settling at almost any forward speed".

 

Figure 12 of the same report is quite a descriptive plot of the conditions under which power settling occurs according to the momentum theory, and sure enough at glide slopes >30 degrees helicopters start settling with power at relatively high descent rates.

 

My point is that 30 degree descent slope in that manual could be related to that report.

[Sundowner.pl]

Actually the USAF "steep approach" at 45° is more likely as it has stated to not exceed 800fpm in descent.

 

The 30° was doable on earlier FM, although hard to maintain, and pinpointing the landing spot, now it's a bit easier. The thing is though - if you loose power during that descent* you will make it to that landing spot in auto-rotation. With 5-15° - you won't.

 

* engine failures are most likely to occur during power changes - during descents, climbs or high bank - altitude steady turns.

[fjacobsen]

Doing some math I think the drawing and explantion is a bit too simple.

Something simply isn´t right.

 

If You have to descend with max 800 ft/min and maintain a 45° descend angle (same distance covered vertical as horizontal), then Your airspeed should not be higher than:

 

800 x 0.305 = 244 m/min => 14.64 Km/hr => 7.9 Knots

 

If You would fly at 30 kts with 800 ft/min that would equal:

3036 ft/min forward speed at 800 ft/min descend.

That would equal appr. 15°

[Sundowner.pl]

You've calculated ground speed, helicopter doesn't care about ground speed, as far as there is air between skids and pavement ;)

In 800fpm descent at 45° (and no wind!) your airspeed vector is 11.2 kts, you're riding the ETL.

 

30kts ground speed is the speed with which you're entering the maneuver, then it goes down, all the way to zero at 4ft height above the landing spot.