Go Back  PPRuNe Forums > Aircrew Forums > Rotorheads
Reload this Page >

Manifold Pressure R22

Rotorheads A haven for helicopter professionals to discuss the things that affect them

Manifold Pressure R22

Old 2nd May 2014, 07:38
  #41 (permalink)  
Join Date: Sep 2007
Location: I am not sure where we are, but at least it is getting dark
Posts: 356
Received 19 Likes on 9 Posts
I was ask a question recently that really I couldn't answer:

How much does 1 inch of manifold pressure lift?
Those aren't scientific rules you can look up in a chart or in the pilots handbook. They aren't published by the manufacturer. They are rules of thumb or rules of experience.

Load up to 1300 lbs take-off weight, pull into a hover, you may see 22". Add 50 lbs, maybe it's 23" in a hover now, or something. So someone came up with the "X lbs per inch of MAP" rule.

That's where that comes from. It's not accurate, nor is it valid under all circumstances. Same goes for the temperature "rule". To find the answer for your question, assuming this is from a quiz that you got from a flying school, look in your notes that you got from the school. It's probably in there somewhere.
lelebebbel is offline  
Old 2nd May 2014, 13:51
  #42 (permalink)  
Join Date: Feb 2005
Location: Australia
Posts: 1,957
Likes: 0
Received 0 Likes on 0 Posts
I wonder if the troll who asked the question to get this thread going is still pondering the contradiction of his question. Certainly the latest question would be beyond his power management comprehension as would his handle, which requires finesse with power.

I have fiddled with MAP / weight and it depends entirely on how smooth the pilot is. With dedication in a '47 you will lift 100 pounds extra vertically for every 1" MAP HOGE which will equate to around 10 horsepower. That of course requires clear airspace around the blades vortices, not lifting beside a bulky willow for example where the distraction will cost at least 1/2" extra MAP.

So if you require 23" to HOGE plus you will need just a small margin to go vertical from there say .4", then say your redline (in a G5) is 27.4" you should be able to lift 400 pounds of freight vertically as long as you can climb far enough above your obstacles (10feet) to then gain ETL without hitting your obstacles - with practice you won't drop anymore than ten feet doing that whilst maintaining RRPM and redline MAP - and do it all before the expiry of your full throttle power time limit; then there is your load to calculate your contract on.

Do the same experiment in your own R22 to come up with the numbers. If your machine cannot lift vertically from HOGE at MAX AUW, it needs to go back to the doctor or it is an extremely hot day.

You should be able to gain ETL2GO from HOGE in a 47 with either 1, 10 feet of altitude maintaining RRPM and MAP, or 2, 5 RRPM bled off whilst maintaining altitude and MAP, or 3, 1/2" MAP bled off maintaining RRPM and altitude.

In technique 2 the discipline is airspeed - RRPM -airspeed - RRPM - airspeed - ahhh - translation where power requirement starts to diminish below redline as airspeed picks up to the A/S for Minimum power, which will be your climb out A/S.
It is a secondary manoeuvre of reclaiming the RRPM by entering a very mild quickstop procedure at or just before ETL but not by losing the airspeed thus gained and then perhaps repeating the same manoeuvre until RRPM is back (where your max power is) and hey presto you have ETL2GO.

In technique 3 of course as your A/S increases you can again increase MAP as the requirement for power lessens.

Doing the exercise with me in a R22 at MAX AUW I will allow less margins all the way, I.E. about 1/3", a couple of % RRPM and 10 feet, why that's a luxury. But of course you must first be able to hover precisely, smoothly.
topendtorque is offline  
Old 2nd May 2014, 17:52
  #43 (permalink)  
Join Date: Jul 2013
Location: -
Posts: 67
Received 0 Likes on 0 Posts
The question was asked by a DPE during a check ride, his example was that if you come to work and you have to take a customer out or transport a load you could quickly establish how much power you need versus how much power you have available,
I guess the bottom line is, you don't wanna have a customer sitting for half an hour waiting for you while you do all your performance calculation just to tell him: sorry the flight can't be done.

I told him the same, doing it while on the helicopter, but he told me a way to do it with the hover chart and a calculator, sadly the check ride went on pretty quickly and I didn't have time to write it all down nor to remember exactly how he did it.

Last edited by MitchStick; 2nd May 2014 at 20:44.
MitchStick is offline  
Old 4th May 2014, 06:11
  #44 (permalink)  
Join Date: Feb 2005
Location: Australia
Posts: 1,957
Likes: 0
Received 0 Likes on 0 Posts
Gees mate, the astute professional student would have this all worked out but just for you I'll suggest that;

1. You won't be carrying anymore than MAX AUW.

2. If you can HIGE at more than 1/2" less than Maw Power allowed for the prevailing conditions, then you should be able to get ETL2GO.(make sure you translation occurs in a clear area)

3. If you then cannot cruise at or above Min power A/S whilst maintaining Max Continuous, you should return and unload some weight.

4. You will have already worked out from your margins above HIGE how much extra weight you can carry per Inch of MAP, or you are in the wrong business.(I know that was the question, but you work it out)

5. It is what you have in hand on the day that counts, not some hypothetical from the book, which is a good guide to start with, ask your instructor if that is a fair call.

6. if you overpitch and crash - come back, I'll direct you to some training as in Technique 2 from my previous post. For the purpose of that exercise please do not allow the RRPM below 90% or the closest red line above that.

7. If you are in a tight spot just add another 2" to 3" for a Max angle of sustained climb T/O, (that is a technique seldom taught these days) or a bit more than 4" for vertical.

cheers tet
topendtorque is offline  
Old 7th May 2014, 06:23
  #45 (permalink)  
Join Date: Jun 2004
Location: Depends on the day!
Posts: 223
Likes: 0
Received 1 Like on 1 Post
A shame we digress... I am still interested to learn how one exceeds MAP without loading the disc? Even an overspeed wouldn't do it.

I was ask a question recently that really I couldn't answer:

How much does 1 inch of manifold pressure lift?

I can tell you quite accurately that the first 12 inches or so don't lift anything! Whoever said that 1 inch will lift 50lbs is a man with a large ball park!
bellfest is offline  
Old 15th May 2014, 01:20
  #46 (permalink)  
Join Date: Jul 2013
Location: -
Posts: 67
Received 0 Likes on 0 Posts
I'm not sure what you mean but every inch lift something in my opinion,
if you put a helicopter on a scale, you read the weight, then you raise collective a few inches, that might not be enough to lift the entire helicopter off the ground, but sure you'll read less weight than with the collective full down.
Is that what you meant?

If you meant the actual scale from 0 to 12 then you're right, I never saw the MAP gauge displaying 0 anyway...
MitchStick is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.