Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

a new idea

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Old 01-16-2008, 08:18 AM
  #1  
HaveBlue
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Default a new idea

I have been toying with this idea for some time now..and if anyone cares to contribute all comments, ideas, or criticisims are welcome

after making a cowl for my Diamond Dust ..which turned out to be a little trickyer than expected ..I started thinking about not needing to cowl an engine..when in effect all you are doing is not so much removing drag ..but reducing drag..you still have a cowl that air must move around...

so what if you were to place the engine in a normally configured fuselage( this wouldnt work with a dust as such) but place the engine internally( I'm thinking somewhere towards, where a canopy usally sits and run something like an rc boat propellor shaft to the nose..

1) Wouldnt this be easier to balance an aircraft(CG)

2) A lot less frontal area required

3) Have a totally clean air frame

cooling would be ducted of course

side exhaust engines might not be so conforming but not altogether ruled out

what I need is criticisms or rather reasoning to why this wouldn't work


cheers
HB

P.S I have been out of the picture for a while here at RCU..did C4F ever fly the 60lx powered Phenom????
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Old 01-16-2008, 10:52 AM
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Default RE: a new idea

I've been thinking about it and sketching designs for a long time too, but long prop shaft extensions and vibration and other such thoughts keep me from going any further with it.
If you have the machine tools (I don't ) to make some nice bearing blocks, shaft, etc. and get everything aligned properly it seems plausable [8D]

Yeah, the cooling could be ducted similar to a ducted fan...small inlets directing air flow over the engine/pipe...maybe an augmentor (augmenter? ) tube exhaust?

I've had thoughts about marine cooling heads, and skin radiators, and using a Perry pump to pump the coolant, etc. etc.

Go for it man! See if you can make something work
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Old 01-16-2008, 11:06 AM
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Mike Connor
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Default RE: a new idea


ORIGINAL: HaveBlue

...
so what if you were to place the engine in a normally configured fuselage( this wouldnt work with a dust as such) but place the engine internally( I'm thinking somewhere towards, where a canopy usally sits and run something like an rc boat propellor shaft to the nose..

1) Wouldnt this be easier to balance an aircraft(CG)

2) A lot less frontal area required

3) Have a totally clean air frame
...
what I need is criticisms or rather reasoning to why this wouldn't work
cheers
HB
Depending on the airframe, it may be harder to balance.
I am not sure how moving the engine back would give you less frontal area. If you looking at it as the engine and canopy as being two frontal objects the just remove the canopy on a speed plane. You can see from this link to NASA just how important the shape is when considering drag.
http://www.grc.nasa.gov/WWW/K-12/airplane/shaped.html
There was a thread in the aerodynamics forums about drive shafts in a prop plane. Unlike boats, it was abandoned by most because of a series of complicated issues on prop planes.

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Old 01-16-2008, 11:52 AM
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Default RE: a new idea

The next page in that NASA series explains why.....
http://www.grc.nasa.gov/WWW/K-12/airplane/sized.html

frontal area is a key factor.

Where aerodynamic shapes come into play..... is once you punch a hole in the sky with that frontal area.... you have to put the air back together as the object leaves that hole. So quite often, it is not as much the smooth shape on the front of an object, but the shape towards the aft end of the object that determines its drag.

That is illustrated well in the example page Mike posted. The flat plate and the prisim have the same flat wind-facing surface. But notice the difference in Cd when you make at least an attempt to return the air to its original location and flow.

Also worth noting there the drag of a sphere or cylinder - compaired with an airfoild shape... significant difference. This comes into play when we speak of cowling in an engine on the speed plane, and also on wires/struts/landing gear.
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Old 01-17-2008, 12:58 PM
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Default RE: a new idea


ORIGINAL: Mike Connor


ORIGINAL: HaveBlue
2) A lot less frontal area required
HB
I am not sure how moving the engine back would give you less frontal area.
Oh, you were viewing frontal area as having to be on front of the aircraft. I did not realize that first time through. As Bob pointed out it is a 2D view from the front.
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Old 01-17-2008, 03:36 PM
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Default RE: a new idea

I don't know why you insist on having the engine upright. Lay it over on it's side, and you have a much cleaner airplane. The other thing is that the engine will also run better due to more favorable polar moments.
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Old 01-17-2008, 03:56 PM
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Default RE: a new idea



Hi all

There is a company out there making delta's (seen them on this section before) and i think that they hit the nail more or lesss right on the head by mounting the engine horizontally, recessing it into the wing, this way a load of drag must be reduced, the model that this is done with doesn't look to be too fast (the chord looks way to thick for the rest of the wing, but it think the principle could be there.



just drew this up in paint ( so it's not to scale and quite ugly ..... but the concept is there)

Henley
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Old 01-17-2008, 03:58 PM
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Default RE: a new idea

HighPlains, lol didn't see your post !

You must have wrote it as i was drawing lol

Henley
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Old 01-17-2008, 04:16 PM
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Default RE: a new idea

ORIGINAL: paulhenley



Hi all

There is a company out there making delta's (seen them on this section before) and i think that they hit the nail more or lesss right on the head by mounting the engine horizontally, recessing it into the wing, this way a load of drag must be reduced, the model that this is done with doesn't look to be too fast (the chord looks way to thick for the rest of the wing, but it think the principle could be there.



just drew this up in paint ( so it's not to scale and quite ugly ..... but the concept is there)

Henley
That would be an Outlaw you are thing of. It is a very tidy package, but the needle valve now sticks down which can be an issue with landings.

No one has mentioned cooling drag yet, so I will. A lot of the drag reduction associated with cowling an engine is not reducing the profile drag (drag from moving a shape through the air), it is reducing the cooling drag by forcing air accurately and efficiently through the engine fins to cool it. The concept being discussed will have significant cooling issues and they must be dealt with or the overall drag may well be higher than the initial configuration.

Also, it's not really a new idea, the P-39 Airacobra had a mid mounted engine 50 years ago...


Mark
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Old 01-17-2008, 05:28 PM
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Default RE: a new idea

The Bugatti 100P and 110P were also envisioned with a mid mounted engine... They never flew though.
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Old 01-17-2008, 06:17 PM
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Mike Connor
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Default RE: a new idea

The drive shaft thread was in the Scratch Build forums. Here is the link if you care to read about it.
http://www.rcuniverse.com/forum/m_34...tm.htm#3432920

If anyone comes up with a good way to mount the engine horizontal on a 6% airfoil delta please let me know.
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Old 01-17-2008, 09:25 PM
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Default RE: a new idea

The long shaft with a third bearing is a HP eater.....an extra load on the engine. I have a friend who keeps bringing this idea up. He is an auto mechanic and should know better.
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Old 01-18-2008, 12:47 AM
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Default RE: a new idea


ORIGINAL: Mike Connor

If anyone comes up with a good way to mount the engine horizontal on a 6% airfoil delta please let me know.
C'mon, Mike. Same way you mount it vertical, except you just lay it over at 90 degrees to vertical...

It would require some creative work on the firewall and mount, though. Maybe I need to look at that when I pull my kit out.


Mark
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Old 01-18-2008, 02:10 AM
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ORIGINAL: mmattockx
C'mon, Mike. Same way you mount it vertical, except you just lay it over at 90 degrees to vertical...
It would require some creative work on the firewall and mount, though. Maybe I need to look at that when I pull my kit out.
Mark
The engine cylinder is much thicker then the airfoil so there would be more then just the needle valve in the grass on landing. The equipment compartment is the thickest part of the airframe so the engine in front of that would leave the least amount of frontal area.
But, send me pics if you try it.
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Old 01-18-2008, 02:41 AM
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ORIGINAL: Mike Connor
The engine cylinder is much thicker then the airfoil so there would be more then just the needle valve in the grass on landing. The equipment compartment is the thickest part of the airframe so the engine in front of that would leave the least amount of frontal area.
But, send me pics if you try it.
Yeah, I know. I was just kidding you. I think that the nicely cowled version by Speedy Gonzales (sp?) is probably the best way to go. On an Outlaw the engine sits nicely in line with the wing, but not on the Screamin Demon. It would require landing skids or something similar to keep the engine and needle valve out of the dirt with that thin airfoil.

Mark
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Old 01-18-2008, 06:28 AM
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Default RE: a new idea

A remote N.V. assembly is std. equipment on many engines...so dragging it in the grass is a non-issue.

I mentioned something about cooling drag in my first post...(words to that effect )
Actually bench tested the Perry pump idea by using 2 marine cooling clamps (octura ) around the cyl. fins and head of a K&B .40 (#8011 ) back in (IIRC ) '77 (maybe it was '78?)
Anyway...the pump didn't like pumping antifreeze, either because of it's chemical make-up, or the temp. (or both? ) because it crapped out quickly.

I was designing a skin radiator set-up or a tubular system similar to the Curtiss or Supermarine Schneider cup racers of the 30's.

Had a completely enclosed engine, except for a small hole for the carb inlet. The fact that it added weight and unnecessary complexity didn't seem to matter much then...I was 17-18 and nothing was impossable.
A&P mechanic's school and a girlfriend kinda took my time away from model airplanes about then though...


If you wanted to go air cooled, you could use a ducted spinner.
There are brushless outrunner motors built right into the spinner and the only cooling for the motor is a hole in the spinner...
The prototype FW-190 had something along those lines too.
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Old 01-18-2008, 06:30 AM
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edited.
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Old 01-18-2008, 10:14 AM
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Default RE: a new idea

ORIGINAL: Mike Connor

Depending on the airframe, it may be harder to balance.
point taken ..yes I could see this perhaps creating new problems

ORIGINAL: Mike Connor
I am not sure how moving the engine back would give you less frontal area.
OK perhaps not the best way to convey what I mean...more so as not having a cylinder /carb protruding to create drag,
I was refering to the point that the front reduced so the overall shape of the fuse would be sleeker without having to accommodate the engine


ORIGINAL: Mike Connor

There was a thread in the aerodynamics forums about drive shafts in a prop plane. Unlike boats, it was abandoned by most because of a series of complicated issues on prop planes.

I have to find this thread..cant see anything hard about mounting a shaft..boat engines are the same just no prop hub..only annoying aspect I can see
is trying to mount an apc to a threaded shaft..but then again I would probably mold my own CF prop with a precisely centered nut molded inside the hub
but I will still do a search to see what the problem is


ORIGINAL: HighPlains

I don't know why you insist on having the engine upright. Lay it over on it's side, and you have a much cleaner airplane. The other thing is that the engine will also run better due to more favorable polar moments.
upright or mounted on the side the fuse needs to be big enough to accommodate the engine..I want a very narrow front..of course the fuse naturally widens towards the canopy area of the fuse...hence mounting the engine there

ORIGINAL: Mike Connor

The drive shaft thread was in the Scratch Build forums. Here is the link if you care to read about it.
http://www.rcuniverse.com/forum/m_34...tm.htm#3432920

If anyone comes up with a good way to mount the engine horizontal on a 6% airfoil delta please let me know.
thanks for digging that out without reading it first I am struggling to see what is so complicated..but I'll get back to you on this

and as for my reference to the canopy as the place to mount the engine ..was merely to point out that, to me, would mean the wider part of the fuse which would accomdate the engine...if I was to build such a plane it would have next to no canopy at all, if any
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Old 01-18-2008, 10:16 AM
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ORIGINAL: combatpigg

The long shaft with a third bearing is a HP eater.....an extra load on the engine. I have a friend who keeps bringing this idea up. He is an auto mechanic and should know better.
I know that the shaft will rob power...but the shaft is not going to be that long, and without designing the plane yet, I am guessing 6 inches or less
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Old 01-18-2008, 10:20 AM
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ORIGINAL: mmattockx

Also, it's not really a new idea, the P-39 Airacobra had a mid mounted engine 50 years ago...


Mark
yes and so are most turbine engines..but I wasn't referring to full scale aircraft only model/RC aircraft
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Old 01-18-2008, 10:47 AM
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ORIGINAL: HaveBlue

ORIGINAL: Mike Connor

Depending on the airframe, it may be harder to balance.
point taken ..yes I could see this perhaps creating new problems
A narrow fuse with a drive shaft running through it would make that space useless for any equipment. With every thing mounted to the rear I see a very tail heavy plane. Of course the required support for the shaft may help balance the craft but it would be heavy. I agree that mounting the engine where the canopy is may make streaming lining easier but the frontal area would remain.
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Old 01-18-2008, 10:51 AM
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Old 01-18-2008, 11:47 AM
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Default RE: a new idea

HaveBlue, interesting thread. It is fun to think outside the box. I have been working off and on for a while on the concept below. Got a 60LX (black pipe) from Dub Jett a few weeks ago and picked up wing cores a couple of days ago. NACA 64A010 airfoil, Jett cg tanks in the wing and plumbed in parallel, minimized frontal area, internal linkages, fillets. At 500 sq in, it is not an outright speed plane but rather an aerobatic/speed/sport thingy to throw in the van with the other stuff when I'm headed to the field. Hoping for a legitimate 180 straight and level. I hope to get started soon, but I'm building in parallel with another project, so who knows.
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Old 01-18-2008, 12:03 PM
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Default RE: a new idea

hope you get it done bob..I dream of owning a 60lx..it's interesting to throw ideas out there and see what the other folk have to say about it..since I am by far no expert in aeronautics/aerodynamics..it can save you time when someone pops up with a valid point about a proposed cocept

as far as speed plane desig goes I am also think of using a diminishing naca foil approach ie. naca 8 at the root , progress thru to naca7 and finish at the tips with a naca6..but I have more ideas than I have time or money to do all of them
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Old 01-18-2008, 05:53 PM
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Default RE: a new idea

Funny to see this thread come up. I built a top flite P39 years ago and did just this, mounted the engine in the middle and made a long shaft to go to the front of the plane. The difficult part of that was that I had to make small universal joints to connect the shaft to the engine and then to the prop shaft. The way the line of the fuse ran, I couldn't make it a straight shot from the engine to the center of the nose without having the cylinder head stick way out of the fuse. The universal joints were basically robbed from an RC car axle (the dogbone) and the prop shaft was built into a bearing block in the front of the fuse. I was able to have a scale exhaust on the plane like this. I used a Supertiger 90. Cooling was the issue, I used the scale scoops for the cooling, but as the full scale (I assume) was liquid cooled, I didn't have enough airflow to keep the engine totally cool, this resulted in requiring very rich runs which were not that powerful. I'm sure the idea could be refined and made to work better, particularly if the airplane was designed around a model engine in this location. But you end up needing a fairly deep fuse to fit the engine, ducting, etc, I'd think you'd be adding more frontal area than if you stuck it in the nose with a really sleek streamlined cowl.
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