Increase in Weight demands an increase in Power
Thread Starter
Join Date: Jan 2012
Location: Not far from the edge of the Milky Way Galaxy in the Orion Arm.
Posts: 510
Likes: 0
Received 0 Likes
on
0 Posts
Increase in Weight demands an increase in Power
To maintain cruise speed an increase in all up weight demands an increase in power.
So, if you cruise along at 2350 rpm at your usual indicated airspeed for the cruise then add fat and heavy friends plus several pounds of baggage to your max all up weight then your 2350 which you may normally cruise around at will be insufficient to give you the same attitude or anywhere near the same airspeed. Although this seems obvious it is rarely stressed in most training documents.
An increase in weight demands an increase in power.
So, if you cruise along at 2350 rpm at your usual indicated airspeed for the cruise then add fat and heavy friends plus several pounds of baggage to your max all up weight then your 2350 which you may normally cruise around at will be insufficient to give you the same attitude or anywhere near the same airspeed. Although this seems obvious it is rarely stressed in most training documents.
An increase in weight demands an increase in power.
Join Date: Jul 2001
Location: Belgium
Posts: 486
Likes: 0
Received 0 Likes
on
0 Posts
Higher weight means more angle of attack means more drag means more power required. What is so difficult about it?
Moving weight aft (while remaining in CG limits) will also help since the tail will have less downforce which means less weight to be carried by the wing. Speaking of conventional tail here, not canards.
Moving weight aft (while remaining in CG limits) will also help since the tail will have less downforce which means less weight to be carried by the wing. Speaking of conventional tail here, not canards.
Join Date: Aug 2007
Location: Melbourne
Age: 72
Posts: 774
Likes: 0
Received 0 Likes
on
0 Posts
"add fat and heavy friends plus several pounds of baggage to your max all up weight"
Doesn't adding to your maximum all up weight take you over the maximum all weight? More to worry about than power.
Doesn't adding to your maximum all up weight take you over the maximum all weight? More to worry about than power.
Join Date: Nov 2013
Location: Oz
Posts: 242
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by dirkdj
Moving weight aft (while remaining in CG limits) will also help since the tail will have less downforce which means less weight to be carried by the wing. Speaking of conventional tail here, not canards.
I thought moving weight aft, moved CoG aft and therfore you need increased elevator input to keep the aircraft level. Just found this: Effect of Load Distribution but I need to go digest it a little longer.
Join Date: Dec 2013
Location: Paso Robles
Posts: 261
Likes: 0
Received 0 Likes
on
0 Posts
moved CoG aft and therfore you need increased elevator input to keep the aircraft level.
If CG moves aft (within allowed limits) there is less need for elevator 'input' (or force).
Join Date: Apr 2009
Location: Oakland, CA
Age: 72
Posts: 427
Likes: 0
Received 0 Likes
on
0 Posts
Doesn't adding to your maximum all up weight take you over the maximum all weight?
Although this seems obvious it is rarely stressed in most training documents.
Join Date: Nov 2013
Location: Oz
Posts: 242
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by porterhouse
Just the opposite.
If CG moves aft (within allowed limits) there is less need for elevator 'input' (or force).
If CG moves aft (within allowed limits) there is less need for elevator 'input' (or force).
This is how my brain is seeing it. I though rearward CoG means plane pitches up, requiring elevator input to pitch it down. What am I missing? Is the CoG always forward of the CoP when in the envelope?
Here I was thinking all confident, hoping to be able to do my BAK exam in 3-4 weeks time!
Join Date: Apr 2009
Location: Oakland, CA
Age: 72
Posts: 427
Likes: 0
Received 0 Likes
on
0 Posts
I though rearward CoG means plane pitches up
requiring elevator input to pitch it down.
If the plane pitches up it means its nose goes up but its tail goes down. If the tail goes down what do we do to make the tail go back up? We lower the downward force on the elevator - which means less 'input. The force on the elevator is always down.
Yes, center of gravity is always forward of the center of lift in conventional (non-canard) airplane.
Join Date: Nov 2013
Location: Oz
Posts: 242
Likes: 0
Received 0 Likes
on
0 Posts
This is all on the first few pages of any aviation PPL textbook, really very elementary part of aeronautical knowledge.
Join Date: Apr 2009
Location: Oakland, CA
Age: 72
Posts: 427
Likes: 0
Received 0 Likes
on
0 Posts
OK, good luck with your study.
Your previous post confused me when you said your were 'all confident' hence my thinking you already spent a great deal of time studying the material.
Your previous post confused me when you said your were 'all confident' hence my thinking you already spent a great deal of time studying the material.
Join Date: Dec 2013
Location: Paso Robles
Posts: 261
Likes: 0
Received 0 Likes
on
0 Posts
Although this seems obvious it is rarely stressed in most training documents.
Join Date: Nov 2013
Location: Oz
Posts: 242
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by olasek
OK, good luck with your study.
Your previous post confused me when you said your were 'all confident' hence my thinking you already spent a great deal of time studying the material.
Your previous post confused me when you said your were 'all confident' hence my thinking you already spent a great deal of time studying the material.
I am confident I can do it in 3-4 weeks!! Don't worry, still think I can. I am going to do a practice BAK test tomorrow, that should isolate those area where I need to put in more effort. I did read my text book cover to cover a couple of months back so have the basics covered, but I have only really started to knuckle down into the study this week.
Pitch excursion (due turbulence, say) down, speed increases. Downward "lift" on tailplane/elevator increases. Mainplane lift increases. Plane pitches up.
Some types, like the PA28, are very stable longitudinally. You can see it easily by moving the tailplane through its full range on a preflight. So in stable trimmed flight there's quite a lot of downward force produced by the tail.
Friend and I flew a 181, 2 up, on a quick 30 mile trip. When I climbed into the back seat, and he re-trimmed to compensate, it was good for another 10kts IAS.
Join Date: Nov 2013
Location: Oz
Posts: 242
Likes: 0
Received 0 Likes
on
0 Posts
And the primary reason for that is longitudinal stability.
Pitch excursion (due turbulence, say) down, speed increases. Downward "lift" on tailplane/elevator increases. Mainplane lift increases. Plane pitches up.
Pitch excursion (due turbulence, say) down, speed increases. Downward "lift" on tailplane/elevator increases. Mainplane lift increases. Plane pitches up.
Anyway, I shall go away and study now, I have hijacked this thread enough. Thanks folks for the pointers.
Join Date: Sep 2006
Location: 23, Railway Cuttings, East Cheam
Age: 68
Posts: 3,115
Likes: 0
Received 0 Likes
on
0 Posts
Friend and I flew a 181, 2 up, on a quick 30 mile trip. When I climbed into the back seat, and he re-trimmed to compensate, it was good for another 10kts IAS.
Join Date: Jul 2001
Location: Belgium
Posts: 486
Likes: 0
Received 0 Likes
on
0 Posts
See How It Flies
This is an excellent on-line free book if you want to dig a bit deeper into Stability, Balance, etc. Will give you a much better understanding without excessive math.
This is an excellent on-line free book if you want to dig a bit deeper into Stability, Balance, etc. Will give you a much better understanding without excessive math.