Primarily for general aviation discussion, but other aviation topics are also welcome.
  • 1
  • 5
  • 6
  • 7
  • 8
  • 9
  • 10
User avatar
By MichaelP
#1778642
My post was an assessment of the strip with the addition of looking beyond the ends at places to go along the departure path.

a stopped prop causes significant extra drag,


My answer to this is a comparison between the idle RPM on the ground and that in the power off glide.
The additional RPM in the glide is due to energy taken from the airflow = drag.

Where you have a constant speed propeller or a variable pitch one, going min RPM or max coarse produces a better glide.
In the Katana glide situation pulling the prop all the way back power off produces the glide ratio in the AFM and it is a very noticeable difference. The Point Of Zero Movement moves way ahead!
Prop windmilling in the Katana produces a descent similar to the Cessnas.

It’s VERY important that the propeller is returned to max RPM, fine pitch, before applying power.
The robust Rotax is tolerant, but a Lycoming or Continental can suffer serious damage and give you a real forced landing...

The DA20-C1 with a toothpick propeller has a superb glide as long as you fly an accurate glide speed, 73 KIAS iirc; at 60 knots it doesn’t do so well.
Used to glide 8 miles from 3,000 feet AGL and then do a circuit to land at the airfield!
User avatar
By Dave W
#1778643
It's not just that. A windmilling propellor is still producing aerodynamic thrust, a component of which can be aft-oriented (and hence deliver drag effect).
Image
Top diagram is when prop being turned by the engine.
Lower diagram when engine not running and prop is windmilling in airflow.
(Images from here.)
flyguy liked this
User avatar
By MichaelP
#1778646
this is because the coefficient of drag on a windmilling propeller is calculated using the "disc" diameter of the spinning propellor


This is fundamentally correct!
The drag is higher, why an autogyro can fly, why a helicopter can autorotate.
Wouldn’t it be terrible if the drag reduced on a helicopter rotor after an engine failure....

It is easily demonstrated in an aeroplane, especially practicing engine failure in a twin. Feel the drag of the windmilling propeller, and why is it four hundred revs more than it showed at idle on the ground?

Windmills generating electricity are popular these days.
If they fall over, will they fall into the wind or out of the wind?

Because they rotate, their drag is reduced thereby producing electricity for nothing! Wow that’s a perpetual motion machine! [This is a deliberately silly statement by the way, not to be taken seriously.]
Last edited by MichaelP on Tue Jun 23, 2020 10:53 am, edited 1 time in total.
User avatar
By MichaelP
#1778652
It's not just that. A windmilling propellor is still producing aerodynamic thrust, a component of which can be aft-oriented (and hence deliver drag effect).


The aerodynamic thrust in this case is in the opposite direction to the direction of flight so a windmilling propeller adds to the total drag and acts like an ‘airbrake’.
User avatar
By JAFO
#1778696
Today I managed to have a good look at the fields I'd picked out following the Google Earth suggestion on this thread. I have to say that, even though they're further to the right than I would perhaps have previously looked, they are perfect if the worst should happen and the donkey should go quiet soon after leaving the most used runway at the strip I fly from.

I've definitely learned something from this thread and have more options if that worst day came than I would have before.
MichaelP, neilmurg, Charles Hunt and 1 others liked this
User avatar
By Miscellaneous
#1778701
JAFO wrote:Today I managed to have a good look at the fields I'd picked out following the Google Earth suggestion on this thread.

So can it be read that you would not contemplate a turn back? If so, is that as a consequence of this thread, or was it always so? :D
User avatar
By Miscellaneous
#1778766
JAFO wrote:I wouldn't turn back but I would never have turned back. That's not a consequence of this thread but may be a consequence of my belief in my ability, or lack of either of those.

I'm with you. :thumright: The chances of getting it all right on the night, so to speak, don't add up for me.

So, of those similar minded to JAFO and I, who, as a consequence, limit where you fly to based on the options, or lack thereof, ahead? :D
User avatar
By foxmoth
#1778905
rf3flyer wrote:I'd think twice about the Montrose pop-up strip in any wind with a westerly component.
Image

Thats what golf courses are for!
mick w liked this
User avatar
By Trent772
#1778919
Adding into the propeller debate - if you have a c/s prop and have an engine failure and the prop is still rotating - pull the prop to full coarse - it helps.

We took the RV7 up a year ago and did some tests.

5,000', mixture ICO, assess the glide rod with prop fine - it was around 700fpm. Repeat with the prop pulled full coarse and it was around 500fpm.

You need engine rotation and obvs no failure of the governor so don't start carping :pirat: :mrgreen:
CherokeePete liked this
By AndyWW
#1778932
Your RV7 must be a magic carpet! The engine-idle clean glide numbers on my RV6 with prop pitch fine are about 850fpm at 78mph for best time aloft, and about 1000fpm at 87mph for best glide range (nil wind). As you say it glides better with coarse pitch, but still not great. No turn-backs for me below 700 feet, and even then I might make it back to the airfield but not the runway (ok at White Waltham).
Andy
User avatar
By Miscellaneous
#1778984
rf3flyer wrote:I'd think twice about the Montrose pop-up strip in any wind with a westerly component.

Seeing that pic, I'm surprised they get permission.

I wonder if action in case of EFATO is one of those subjects which lends itself to being discussed on forums, but with very little influence on an individual's actions in reality? :wink:
User avatar
By Rob P
#1778987
When it all went quiet my overriding thought was

"Don't stall, spin! Don't stall, spin!"

Where this came from I'm not sure. My flying instructors, AAIB reports, You-Tube case studies and forum chat I guess.

If this led me to get the nose down more aggressively than was necessary, if this led to the aircraft sustaining more damage than had it been flown with more finesse I will never know, but often wonder.

However I'm alive and largely undamaged which would not have been the case had I spun in.

I think forum discussions are valuable, but they just make up part of the whole of your personal knowledge base. We will each have different takeaways from the same discussion.

Rob P
Last edited by Rob P on Fri Jun 26, 2020 8:46 am, edited 2 times in total.
kanga, rf3flyer, Rob L and 1 others liked this
  • 1
  • 5
  • 6
  • 7
  • 8
  • 9
  • 10