Question: Hover @ MCP and TOP
Thread Starter
Joined: Aug 2004
Posts: 68
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From: NE
Question: Hover @ MCP and TOP
Hi
i'm working on a small database of helicopter performance, and i'm having a little trouble about HIGE and HOGE charts, with MCP and TOP
i've allready search on my books about this (Shawn's, until now whas the most informative), and i like to ask if anyone could give me some highlight about this and/or where i can find it written/explained (to me, and to show a couple of fellows ... )
i understand that the charts (for the given Temp/altitude) give the weight that is possible to HOVER with given ammount of power (MCP or TOP).
Now the questions
- imagine that i'm sling loading (OGE, in ths case...) (trees, water bucket, whatever..), and i want to find out, how much weight can i lift, should i go for the HOGE MCP, ou the TOP one??
* i'm ask this because i was thinking, that if it go with the TOP, it will allow to hover, but maybe will not have the power margin to takeoff (assuming that we aren't over clear area)
- since, my virtual helicopter has a limitation of takeoff power, (many do, right??) there will be a limited time that i can hover under this weight given by the chart (reduction of weight by fuel flow and/or paylod drop not in account)
thank u
i'm working on a small database of helicopter performance, and i'm having a little trouble about HIGE and HOGE charts, with MCP and TOP
i've allready search on my books about this (Shawn's, until now whas the most informative), and i like to ask if anyone could give me some highlight about this and/or where i can find it written/explained (to me, and to show a couple of fellows ... )
i understand that the charts (for the given Temp/altitude) give the weight that is possible to HOVER with given ammount of power (MCP or TOP).
Now the questions
- imagine that i'm sling loading (OGE, in ths case...) (trees, water bucket, whatever..), and i want to find out, how much weight can i lift, should i go for the HOGE MCP, ou the TOP one??
* i'm ask this because i was thinking, that if it go with the TOP, it will allow to hover, but maybe will not have the power margin to takeoff (assuming that we aren't over clear area)
- since, my virtual helicopter has a limitation of takeoff power, (many do, right??) there will be a limited time that i can hover under this weight given by the chart (reduction of weight by fuel flow and/or paylod drop not in account)
thank u
Joined: Apr 2003
Posts: 3,012
Likes: 1
From: USA
CS-hover,
Generally performance is stated at Take Off power, at the weight/performance limit for HOGE. While this is not practical if one must make a vertical takeoff in still air, it is the convention.
In reality, it takes about 1.5% more power (or less weight) to make a purely VTO that when near the HOGE performance limit, and even with that 1.5%, the climb rate is only about 50 to 100 ft/min. However, even 5 knots of relative wind makes a tremendous difference, as does even a few feet of run, should the zone permit it (because the first 4 to 6 knots is so powerful, and it only takes a few helo-lengths to get that.) So for most helo operations, HOGE weight is OK, but the first takeoff is a squeeze.
In many training exercises and tests I have hung at TOP at max HOGE weight, and there is no climb except that made by fuel burn. In one powerplant cooling flight, I set the power, hung in perfectly still air with fixed collective and slowly drifted upward, ending at 1500 feet about 1 hour after the "take off".
Generally performance is stated at Take Off power, at the weight/performance limit for HOGE. While this is not practical if one must make a vertical takeoff in still air, it is the convention.
In reality, it takes about 1.5% more power (or less weight) to make a purely VTO that when near the HOGE performance limit, and even with that 1.5%, the climb rate is only about 50 to 100 ft/min. However, even 5 knots of relative wind makes a tremendous difference, as does even a few feet of run, should the zone permit it (because the first 4 to 6 knots is so powerful, and it only takes a few helo-lengths to get that.) So for most helo operations, HOGE weight is OK, but the first takeoff is a squeeze.
In many training exercises and tests I have hung at TOP at max HOGE weight, and there is no climb except that made by fuel burn. In one powerplant cooling flight, I set the power, hung in perfectly still air with fixed collective and slowly drifted upward, ending at 1500 feet about 1 hour after the "take off".
