Decalage angle

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

Eugene

Well-Known Member
HBA Supporter
Joined
May 26, 2017
Messages
1,100
Location
Merrill, Wisconsin, USA
Another idea is reshaping the fuselage nose to provide more normal positive camber. Sort of a drooped snoot adds positive camber.
Probably should do all this with a 1/4 scale RC model.
I was thinking about making nose sharper, but they tell me that this would be waste of time.

fullsizeoutput_145c.jpeg fullsizeoutput_1463.jpeg fullsizeoutput_1596.jpeg fullsizeoutput_1468.jpeg fullsizeoutput_1467.jpeg
 

BBerson

Well-Known Member
HBA Supporter
Joined
Dec 16, 2007
Messages
12,995
Location
Port Townsend WA
Sharper won't help.
Looking at that first photo (front view) the armpit area of the gear legs looks like a choke point for airflow.
Angles less than 90° are not good. That's not a normal design feature and unique to that design.
Could fill those armpits maybe to make it 90° to the fuselage. It is faired some but maybe not enough.
 

Eugene

Well-Known Member
HBA Supporter
Joined
May 26, 2017
Messages
1,100
Location
Merrill, Wisconsin, USA
If I was going to reduce drag, I would start at the landing gear. It sticks out the furthest from the centerline, so it has the strongest moment arm. The drag on the gear produces more than twice the moment arm of the fuselage.

It's just like weight and balance calculations, but turned vertical. The wheels clearly have the worst moment arm for their drag to cause a pitch problem.
Here is another stupid question -

- in level flight we are moving draggy object through the air. Drag of this object have center. We should try to install our engine inline with this center. If we don't = we will have moment arm = balancing drag.

So, moment arm has nothing to do with CG, when we are talking about drag? Were CG is located vertical is irrelevant.
 

poormansairforce

Well-Known Member
Joined
Mar 28, 2017
Messages
894
Location
Just an Ohioan
Its what I would call center of drag but since almost everything is below the thrust line then yes, there is a moment to consider. I said CG because most people understand that term better. When I design RC planes this is always something I consider.

If you had a small turbine mounted behind the cockpit pushing through the center of drag/mass then this thread wouldn't exist. Well, maybe for the turbulence/stability issues
 

Doggzilla

Well-Known Member
HBA Supporter
Joined
Jun 2, 2013
Messages
2,272
Location
Everywhere USA
Yes, CG has no effect on the moment arm of drag. They just use similar calculations, turned 90 degrees from one another. But are completely unrelated otherwise.
 

Eugene

Well-Known Member
HBA Supporter
Joined
May 26, 2017
Messages
1,100
Location
Merrill, Wisconsin, USA
From Peter Garrison -
"3. The flow over the aft portion of the fuselage is separated. This has the effect of immersing the stabilizer in a turbulent wake and reduces its effectiveness.
The model I created does not include the boom, landing gear, vertical fin, or engine, whose effects on lift and pitching moment are small."

So, nothing is black and white in aircraft design like I was thinking 3 years ago. Some very smart people still disagree on simple fundamentals. Like landing gear has small effect on pitching moment.
 

TFF

Well-Known Member
Joined
Apr 28, 2010
Messages
12,618
Location
Memphis, TN
One row of vgs will not help much. The whole back section should look like a windmill farm. VGs don’t stop the swirling as much as they suck it in , making the dead spot smaller. Or you could have little wings like German Touring Car Racing
 

Eugene

Well-Known Member
HBA Supporter
Joined
May 26, 2017
Messages
1,100
Location
Merrill, Wisconsin, USA
My designer doesn't like vortex generators at all. Sure there is time and place for them. In his mind they always producing more drag than doing good. VGs can be used as temporary band-aide. If you need to use them = you made some kind of mistake. Correctly designed aircraft normally should not need them at all.

I think by now we all agree that rear cowling on Skyboy was probably ok for 65 mph Quicksilver competitor with enclosed cabin. But for 100 mph aircraft I need to shape it differently.

What I am trying to say, is that most likely rear cowling eventually will be completely or partially rebuild in to different shape in the future. So why couldn't I drill some holes to find out pressure drop. I really like that Idea. I can also build up using foam different shapes and test fly to find out pressure drop changes.

Worst that can happened, that I will to fly to Oshkosh this year with 100 little holes in my airplane. So what! I can cut round 1" pieces of white tape to cover all holes. It will look cool! Nobody will ever know what is it. There is white tape on my airplane already everywhere you look!
 

poormansairforce

Well-Known Member
Joined
Mar 28, 2017
Messages
894
Location
Just an Ohioan
They are button head so will give a higher reading if there is good flow over the surface because they will expand the air over the head. If the flow is stagnant then its good. But you don't know that yet.

A hole that the tube itself can be squeezed into would work. It shouldn't protrude higher than the surface.
 

BJC

Well-Known Member
HBA Supporter
Joined
Oct 7, 2013
Messages
10,893
Location
97FL, Florida, USA
They are button head so will give a higher reading if there is good flow over the surface because they will expand the air over the head. If the flow is stagnant then its good. But you don't know that yet.

A hole that the tube itself can be squeezed into would work. It shouldn't protrude higher than the surface.
Static ports that have proven to be accurate on several airplanes are made with a hole in the center of a disc about 1 1/2” in diameter that is raised about 1/8” above the fuselage surface.


BJC
 

poormansairforce

Well-Known Member
Joined
Mar 28, 2017
Messages
894
Location
Just an Ohioan
Static ports that have proven to be accurate on several airplanes are made with a hole in the center of a disc about 1 1/2” in diameter that is raised about 1/8” above the fuselage surface.


BJC
Yeah, just like the ones I put on the Max. Thats why they are 1.5" diameter so the flow is straight across the hole. Well, as straight as can be on a small disk.;)

If we make the air do work by flowing around a curve then it changes the air pressure. The button heads will do that. That was for general info since I know you know that.
 
2
Top