Aerodynamic considerations for a speed plane design

Aerodynamic considerations for a speed plane design
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Aerodynamic considerations for a speed plane design - 3/30/2008 5:20:10 PM

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I want to start a thread about the aerodynamic considerations of speed plane designs.
It is my understanding that in pylon racing there are many limitations as to what you can do, we are going to ignore those limitations here.

This thread will focus on building an aircraft for the fastest time through the traps.

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RE: Aerodynamic considerations for a speed plane design - 3/30/2008 5:40:33 PM

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What type of power plant are we designing around? The RC speed world record is held by an airplane with no engine.

< Message edited by seanreit -- 3/30/2008 5:41:06 PM >

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RE: Aerodynamic considerations for a speed plane design - 3/30/2008 5:50:38 PM

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Well as far as powered airplanes we have several choices...

Perhaps we should break it down to IC engines, electric, or turbines.

But for the moment lets just focus on the basics of airframe, airfoil, control and drag reduction. Then we can tailor the airfame to match the power setup.
So a look at the record holder even if it is not powered would be important.

< Message edited by iron eagel -- 3/30/2008 5:52:22 PM >

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RE: Aerodynamic considerations for a speed plane design - 3/30/2008 6:01:30 PM

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Just look it up, it's a glider. Something like 300 MPH as I recall. Best a turbine could do was 45 lbs thrust in a 25 lb airplane somewhere around 260 MPH. The airframe there was a BVM Classic Bandit.

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RE: Aerodynamic considerations for a speed plane design - 3/30/2008 7:34:50 PM

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What I found was your basic sailplane or slope soarer, low drag design.
So I guess for the purpose of this thread lets work on the premise that we are looking at a powered airplane.

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RE: Aerodynamic considerations for a speed plane design - 3/30/2008 7:44:54 PM

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Well, according to your first post, you are taking Turbines out of the race because you indicate "Through the speed traps". Unless of course you are going to attempt this somewhere that the AMA is not involved. AMA rules indicate that turbine powered fixed wing aircraft shall not be flown through speed traps.

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RE: Aerodynamic considerations for a speed plane design - 3/30/2008 8:10:48 PM

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Perhaps then some other method to determine the speed of the aircraft has to be used...

Although I feel that it is a given that turbine powered aircraft would best suited for absolute speed, perhaps we should not use them as a method of power in this discussion.

What I want to focus on is the aerodynamic consideration of high speed designs, the power source is secondary to the primary consideration at this point.

So lets just look at what makes a speed plane, a speed plane.

< Message edited by iron eagel -- 3/30/2008 8:12:32 PM >

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RE: Aerodynamic considerations for a speed plane design - 3/30/2008 8:16:50 PM

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quote:

ORIGINAL: iron eagel

Perhaps then some other method to determine the speed of the aircraft has to be used...

Although I feel that it is a given that turbine powered aircraft would best suited for absolute speed, perhaps we should not use them as a method of power in this discussion.

What I want to focus on is the aerodynamic consideration of high speed designs, the power source is secondary to the primary consideration at this point.

So lets just look at what makes a speed plane, a speed plane.

-You are caught in a trap here -
better get your parameters figuredout
a very draggy looking setup with enough power may proove to be the fastest
consider a rocket powered model------
The slope setup which uses momma nature is easily the best scxample of drag reduction and maximization of lifting area.
Are you after an infernal powered setup- ?
what?

< Message edited by dick Hanson -- 3/30/2008 8:17:30 PM >

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RE: Aerodynamic considerations for a speed plane design - 3/30/2008 8:19:25 PM

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Since this is the aerodynamics forum and IE has said let's go for broke and DARN to the rules we can toss out the AMA restriction on turbines for whatever reason they put it into place. To a great extent a lot of this will be theoretical in any event.

There's no doubt that the power source is 95% of the equation on a speed model. The Extreme Speed Prop forum is full of models that fly very fast but do not have the best aerodynamics by any means. Brute power is obviously the cornerstone. But given two identical brute power sources what is needed to make one go a lot faster than the other? Now we come down to cleaning up the airframe so that the engine can spin a higher pitch prop and still unload enough to get up to the peak HP figure. And THAT is going to get us the extra speed.

< Message edited by BMatthews -- 3/30/2008 8:22:34 PM >

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RE: Aerodynamic considerations for a speed plane design - 3/30/2008 9:23:24 PM

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By Bm
"There's no doubt that the power source is 95% of the equation on a speed model. The Extreme Speed Prop forum is full of models that fly very fast but do not have the best aerodynamics by any means. Brute power is obviously the cornerstone. But given two identical brute power sources what is needed to make one go a lot faster than the other? Now we come down to cleaning up the airframe so that the engine can spin a higher pitch prop and still unload enough to get up to the peak HP figure. And THAT is going to get us the extra speed."

That is what I was thinking...

Now given that most of us do not have access to the funds needed for turbines, my self included.
How do we take a glow/gas/electric powered airplane with a prop to the next level.
Some of the restrictions placed on pylon racers such as non tapered wings no fillets place severe limits on cleaning up the airframe.
I think that there some questions about different wing designs used for speed. In modern aircraft the swept wings and deltas of the 50's and 60's have been replaced by short stubby wings, at least for modern fighters. And concepts such as BWB are just now being explored in commercial and GA aircraft.
One would think that the BWB concept would lend itself to higher speeds where it could be setup to produce far less drag than the typical tube and wing designs now in use.
Another thought is regarding canards they seem to perfect for high speed flight but have never been mentioned as a possibility.
What I want is theoretical discussion on the subject, that perhaps some or all could be applied to building a aircraft that could exceed the present limitations, or allow someone to build a plane that may be a bit faster.

edit to add:
One comment in another thread regarding speed planes made by CP was, "Most of your speed plane designs look like model locomotives with wings". And they do indeed look much like the streamlined locomotives of the late 40's and 50's there has got to be a better way to build them...

< Message edited by iron eagel -- 3/30/2008 9:37:33 PM >

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RE: Aerodynamic considerations for a speed plane design - 3/30/2008 10:01:18 PM

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quote:

ORIGINAL: iron eagel

By Bm
"There's no doubt that the power source is 95% of the equation on a speed model. The Extreme Speed Prop forum is full of models that fly very fast but do not have the best aerodynamics by any means. Brute power is obviously the cornerstone. But given two identical brute power sources what is needed to make one go a lot faster than the other? Now we come down to cleaning up the airframe so that the engine can spin a higher pitch prop and still unload enough to get up to the peak HP figure. And THAT is going to get us the extra speed."

That is what I was thinking...

Now given that most of us do not have access to the funds needed for turbines, my self included.
How do we take a glow/gas/electric powered airplane with a prop to the next level.
Some of the restrictions placed on pylon racers such as non tapered wings no fillets place severe limits on cleaning up the airframe.
I think that there some questions about different wing designs used for speed. In modern aircraft the swept wings and deltas of the 50's and 60's have been replaced by short stubby wings, at least for modern fighters. And concepts such as BWB are just now being explored in commercial and GA aircraft.
One would think that the BWB concept would lend itself to higher speeds where it could be setup to produce far less drag than the typical tube and wing designs now in use.
Another thought is regarding canards they seem to perfect for high speed flight but have never been mentioned as a possibility.
What I want is theoretical discussion on the subject, that perhaps some or all could be applied to building a aircraft that could exceed the present limitations, or allow someone to build a plane that may be a bit faster.

edit to add:
One comment in another thread regarding speed planes made by CP was, "Most of your speed plane designs look like model locomotives with wings". And they do indeed look much like the streamlined locomotives of the late 40's and 50's there has got to be a better way to build them...

Aha- as I suspected - a model with a prop and an infernal combustion engine
a lot of streamlining may look pleasing but the smallest lightest one will do the most with a given amount of power.
Canards?
ferget it
build somethinglike a class A control line speed plane with aileron and elevator control - as a starting point.

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RE: Aerodynamic considerations for a speed plane design - 3/30/2008 10:13:38 PM

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Dick,
What about BWB?

As far as a canard, I was thinking along the lines of a twin wing mounted tractor setup, rather than the typical pusher setup. Round fuselage blended into the main wing, engines enclosed within wing mounted nacelles. The rudders also would be mounted on the wing as part of the nacelles. But that is going to be a interesting build in and of itself regardless of the speed it flies.

< Message edited by iron eagel -- 3/30/2008 10:19:34 PM >

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RE: Aerodynamic considerations for a speed plane design - 3/30/2008 10:29:28 PM

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A Captain in the US Airforce and his jump suit has that DS models' speed covered. I hear that by the time he landed, he had his orders for Major.
What did this DS model clock through an entire 1/8th mile level timing zone, after first flying through a 1/8th mile long leveling off zone?
I think the parameters are very important to establish first. The rules that are already in place at the European Speed Cup have been developed after many years of weeding out what the event should represent. They have set max wingloadings and I believe a 10cc limit. The planes are overpropped gliders that need to be dived to get the powerplant on step, then the timing zone is a very shallow slope that is about 200 meters IIRC. The planes enter the zone at 50 feet and exit at 15 feet ideally. I don't know if this is the FAI standard or not.
High Plains has extrapolated what the theoretic HP needs to be for these planes to do what they do.....the figure was pretty high. An equivolent wattage could be used for an electric plane discussion here.
One thing that High Plains has mentioned recently is that full length fairings probably have more drag than just a short wind screen for rear exhaust models. I'm all for that idea!

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RE: Aerodynamic considerations for a speed plane design - 3/31/2008 1:36:00 AM

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Well I guess the first thing to drop would be the 10 cc limit...
Lets say for a starting point we set 1.6 cu inches as a max displacement, or any combination of engines for that max. So we can look at building an airplane rather than an overpropped glider.
Lets try to set a few parameters, wing loading should be up to the builder, but for a max model weight lets say half of the AMA legal limit or 27.5 lbs dry, on a 8 foot max span wing. How does that sound?

Lets try to come up with something that can push the limits of R/C speed but be within the reach of the average hobby budget. If you have a better idea of what design should be used as a starting point then by all means join in. Keeping in mind this goes more toward an unlimited class than an FAI type of aircraft.

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RE: Aerodynamic considerations for a speed plane design - 3/31/2008 3:15:38 AM

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I'd stay at 15 cc or less or perhaps the big BVM .96 (made by Nelson). You need an engine that turns rpm so the props are closer to square.

The other thing, for maximum engine performance, make it a side mounted engine. I will leave it to you guys to figure out why.

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