Silent Hunter,

Yup I am working on the fowler flap setup that will be cut into the aft wing section. I will post something on that when I get it worked out.

Cheers,
Eric B.

Here is a sketch for the fowlers on top of the airfoil.

Eric B.

Originally Posted by AirX

Still working thru the design of the plane so it can be cut on the CNC.
Here is a drawing of the naccelle and wing.

Eric B.

Hi Eric,

If you don't want the efflux to remain stuck to the top of the wing, you might be able to add a short extension to the thrust tube to keep the air from attaching itself to the top of the wing as it leaves the nacelle.

I've modified your drawing to show you what I mean. If you look at the top and side views of the wing, you can see the changes I made.

Dan

Hi Dan,

I am going to make a mockup as you have suggested to see how the the forces that the thrust line and Coanda effect produce. I might get into the thrust line more as you suggest.
Do you know what the ideal thrust line would be in this layout?

Cheers,
Eric B.

Neat Subject! I'll be watching as you go

Flew mine today, in about 15mph winds. A system such as Dan describes could really benefit the end result larger and more robust model you're creating.
In flight, mine will rise sharply with power...something normally denoting a swooper and the thrust line to be off, CG to be too far aft, I know that. However, these things don't work quite as expected. Under mild power, the aircraft will rise steadily, all predictable. Full power see's the coanda effect and gives massive lift, in comparison to that expected by a linear power input increase....like a switch being thrown !
Power off to glide and, with the strong undercamber evident on my little bird, it will float all day long. Today saw heights of about 70ft, power off and glides of at least 20 seconds, hands off the sticks, in adverse winds. Power back on at full and the aircraft gained height very well, not stalling (but forever fighting the oncoming wind at way less than an ounce in weight).
In Dan's drawings, we see an ability to direct the thrust conventionally, so increasing linear power availability in normal flight. Throwing the flaps right down will see the coanda effect and probable stunts that no other could reproduce.
Your tests will show the differences and i'd be very thankful to you for your notings, of what I can only term the 'switch throw' effect.

Hi Bob,

It will be fun and the largest plane I have built in 20 years.

Eric B.

Slider,

Thanks for checking in. I will have to check out your blog and see what you are up lately.

Eric B.

Originally Posted by AirX

Hi Dan,

I am going to make a mockup as you have suggested to see how the the forces that the thrust line and Coanda effect produce. I might get into the thrust line more as you suggest.
Do you know what the ideal thrust line would be in this layout?

Cheers,
Eric B.

Hi Eric,

I can't say I really know what it should be. I can only offer my experiences with other models that have offset thrust lines and let you learn from it.

It looks like you've already got about 2 degrees of down thrust set in the nacelles.

Whenever the thrust line is offset from the centerline of the model, like this or an airliner such as the 757, it will cause the model to react when under power.

In the case of my brother Daren's Airbus Beluga, we put 2 degrees of down thrust. In discussions with an airline pilot we know who flew the 757, he said that the the airplane had a strong nose-up tendency with power. We attributed this to the offset thrust line and adjusted that accordingly when designing the Beluga. It turned out to be the right thing to do. After finishing and flying his Beluga, Daren corresponded with a modeler in Germany who bulit his own Beluga, but didn't incorporate down thrust in the engine nacelles and his had a strong tendency to climb under power. He later added down thrust to his model and the problem went away.

Because your model will have the engines above the fuselage, I would expect it to cause down thrust all by itself, simply because of the location. But, because of how close the nozzles are to the wing, I would also expect it to produce lift due to the Coanda effect and that this life would probably cancel out the natural tendency for the location to want to push the nose down.

In the end, your best bet is going to test these assumptions with a test rig. At first, you may want to isolate the forces you're testing. The first thing I would test is whether the location of the nozzle to the wing is causing lift. I would make a simple rig that sits on a scale, but can't move forward or pivot downward. I would isolate the movement to a straight up and down. Measure the static weight, then run up the fan to see if weight decreases. If so, then you know that you're encountering the lift due to thrust. Then, adjust the thrust line or try to adjust the nozzle to shield the wing to keep the air from touching it. Once you can run the fan up without increasing or decreasing the weight, then you know that you've either eliminated the Coanda effect, or countered it.

This assumes that you want to eliminate the lift due to the Coanda effect. We already know it works. Personally, I don't like to have a model that climbs with power because then the model requires constant re-trimming of the elevator with every change in power.

Dan

Hi Dan,

Thanks for coming back with that information. I am about to build the test stand, my first thought was to let the engine push on a scale to see what rotation arround the center of effort would be and another scale with the engine nacclle mounted on a slide to measure thrust. I will draw up something to measure the forces you suggest and still get the thrust from the naccelle and post it later this week so you can see if I am going the right direction.

Eric B.

Hey Eric, can't believe you snuck so much work past me - looking good! Definitely seems like it will be a really unique model when it's done, and an interesting learning experience for sure.

-Matt

Hi Matt,

This will be a little larger than the F86D...
I thought of just leaving the interior without the ply bearing structure, I could have just glassed it but I did not feel my glassing skills are that good. The foam will be covered with WBPU and painted, lightweight and fairly durable.

I went to your blog yesterday thinking "what has he done lately"...
You are one of the people who have given me a lot of inspiration, just wish i had all the time and energy to follow up on those inspirations.

Cheers,
Eric B.

Well if you finish (or even fly!) one model this year, you will be way ahead of my 2009 zilchfest. I've got designs clogging up my hard drive but building 'em is a different story - no time, lots of excuses, etc. Can't crash a Rhino model, oh wait a minute yes I can!

I think the ply bearing structure will give you some advantages like easy repairability, modification, etc. plus you're building efficiently at such a large scale.

Admiring eyeballs on this one,

-Matt

My biggest worry is the Coanda effect and how it will manifest itself in this application. I saw Hokonghings Horten fly last weekend. He used an extended thrust tube to mitigate the problems associated with the flying wing and the Coanda effect. I need to spend some time drawing on a test stand as outlined by Dan Savage but just not had the extra time with the holidays and family. Maybe next couple of weeks i can get that going, besides i need to work thru the steps it will take to make the airfoil cutouts in the naccelles so they are set to the incidences i want on the wing/naccelle assembly.

Eric B.

This project is on the shelf for a while. I have had a couple of health problems that will keep me from spending the money on it. I think it will take most of this year to regroup and recoup the money that lack of health insurance has caused. It does not mean I will not be able to enjoy the hobby but it will reduce what I can do.

Eric B.