# Decalage angle

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#### Eugene

##### Well-Known Member
If you can picture the airflow in front of the props you are probably as baffled as I am to why they did this.
They talking speed of 500 MPH!!!!!?????
At that speed this prop will get 0% airflow!!!
The clearly know something we don't! And they have much better sponsor than I have!!!

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#### Doggzilla

##### Banned
HBA Supporter
View attachment 86053

I was told this morning that this is correct explanation, but at wrong speed. They think, that this effect is only big enough above 200 km/hr to worry about. Engine cowling at speeds below 100 mph = 160 km/hr on engine sitting on backside of the wing and behind BRS will give you at best 3 mph. It will improve airflow to the prop at 20-30%. That area on your prop not doing much anyway.

Searay designer tell me same thing - "waste of time and effort with no speed increasing at all"
Honestly, since their advice conflicts with other engineers (one who hold a world record) the only thing you can do is test.

It doesn't take much. Literally anything that moves the drag forward of the wing will work. Even a plastic barrel. When I say anything I mean anything. As long as it can be secured safely.

It doesn't have to be any more aerodynamic, just shift the pressure forward.

That will quickly determine how much interference drag you really have while leaving the parasitic drag mostly intact.

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#### Eugene

##### Well-Known Member
Honestly, since their advice conflicts with other engineers (one who hold a world record)
It is very interesting to me how they think. They split this in 3 ways:

#1 - ultralight world of 65 MPH = nothing to worry about. You can do anything you want.

#2 - LSA world of 100-120 MPH - 100 HP, needed different thinking. If you don't pay attention to details = your creation will fly like Skyboy only 80 MPH and you will not make any money.

#3 - Speed world/world record 160-220 MPH = every little thing can have very big effect on your performance.

#4 - All you need is  money!!!

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#### Eugene

##### Well-Known Member
Pretty soon my Skyboy will like Pokemon

#### Eugene

##### Well-Known Member
With a little practice you should easily be able to create a cowling. The real question is how you want to attach it. Forward hinges? Forward sliding rails like a cabinet?

I was thinking, looking at this picture, that engine cowling can be made as one unit, that you will be able slide in from the front. It will hug wings on top and bottom, but only for about 2" or so. This way it will not brake away in flight. What we have on this picture , is non- removable or maybe structural part. I think.

#### Doggzilla

##### Banned
HBA Supporter
That looks great, and will assist lift due to its shape.

But if you want to do a test to see how much interference drag is present you can test with anything that extends the drag forward.

And I would definitely add hidden nylon straps, as they are about 100kg/cm strength. Loss of new components is very common during tests. Lots of cowling suffer vibration failures. If the mounts become loose for any reason the nylon will catch it before the prop.

#### Eugene

##### Well-Known Member
But if you want to do a test to see how much interference drag is present you can test with anything that extends the drag forward.
I love to do experiments, as you know, but not sure that I have clear picture in my head about how this supposed to look like. Sorry! Pictures working better for me than words.

#### Eugene

##### Well-Known Member

So, fuselage shape on the bottom looks like my Skyboy! So, nothing wrong with this approach ?

#### BBerson

##### Light Plane Philosopher
HBA Supporter
The Skyboy fuselage is much lower below the wing.

#### Eugene

##### Well-Known Member
The Skyboy fuselage is much lower below the wing.

Yes, I see that, and they use T-tail.

#### Doggzilla

##### Banned
HBA Supporter
The issue is that it's wide and flat. It probably won't add more than a few knots depending on how much drag is actually from that or if it's interference drag from the landing gear or engine.

#### birdus

##### Well-Known Member
I think someone said that Seeker was the worst airplane he ever flew (TFF?)
1300 pounds is a heavy two seater.
I am tempted to do another pusher, but not expecting top performance because of the intersection drag.

edit, yep TFF beat me by 2 minutes!
Have you thought about the Osprey 2? George Pereira's designs are fantastic.

https://www.ospreyaircraft.com/osprey.htm

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#### Eugene

##### Well-Known Member
Have you thought about the Osprey 2? George Pereira's designs are fantastic.

https://www.ospreyaircraft.com/osprey.htm

I did looked at them all for education only. They all look cool to me. But for some reason I never want to lend on the water. Someday I will be looking at my Skyboy and I wouldn't know what else to do. Then I will look at different airplanes. But that is not going to happened for this year. On top of that turning around and start going another direction will cost more money. I will play with what I got.

This time at Oshkosh I will be going around trying to find cool looking horizontal tail for me to copy. For next winter project.

#### Eugene

##### Well-Known Member
Here is another question:

On passenger side window I taped small level that represents 4° AOA to the bottom of the wing. With decalage of 6° and 80 MPH I know for sure now that AOA = 4°and horizontal stabilizer at negative 2°. But elevator depending on CG location anywhere from neg. 5°to neg. 7°.
They tell me that stabilizer at 2° is perfectly normal, but elevator at 5-7° is telling us that this area needs attention and improvements.

Things that will improve horizontal tail effectiveness on Skyboy:

- clean up airflow from fuselage

- increase horizontal tail volume to 0.45 - 0.5

- convert flat deck to symmetrical 8% - 10% airfoil

Did I forget anything?

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#### Eugene

##### Well-Known Member

Was flying today, but really didn't feel difference at all. Elevator position about the same as well.

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#### Aesquire

##### Well-Known Member
Kitplanes magazine,July & August issues, have Wainfan's "Wind tunnel" articles on tail size & CG limits. Might be worth a perusal for you.