Chicken Wings Forum

Roost Air Lounge => The Classroom => Topic started by: Frank N. O. on October 12, 2008, 08:52:00 PM

Title: What's the biggest influences on an aircraft's speed/performance?
Post by: Frank N. O. on October 12, 2008, 08:52:00 PM: I was talking with Matt in the chat a few days ago and again the Commander came up and it was said it was a high-drag aircraft. After that I looked at airliners.net and found some specs of other similar aircraft and some were slower but didn't seem to have a larger cabin and while some were ok fast they couldn't climb that fast compared to others. For a car you have have wheel-alignment, gear-ratios, engine torque-curve characteristics, tire-types/sizes that vary in rolling-resistance etc. that all influence acceleration, top speed and fuel-economy but what goes for an aircraft? Is it basically just the fuselage/wings that have a say or can a different prop give a significant difference in top-speed/fuel-efficiency? What about RG planes without wheel-covers like the Commander, would a plate over the wheels give anything, or removing the grip handle on the outside where you step up?

Here's a list of data for aircraft with 4 seats, retractable gear and around 200hp engines.
Edit: Hmm, for some reason, in the forum the tab-spaces aren't working unlike in the editor so the data isn't organized in coloumns but I hope you can read it all the same.
Aircraft         Weight   Power   Max speed      Initial Climb
Beech D35 Bonanza      760kg   205hp   306kph/165kt   1100ft/m
Cessna C177RG Cardinal   800kg   200hp   290kph/156kt   925ft/m
Money M-20E      714kg   200hp   317kph/171kt   1120ft/m
Piper PA-28R-201T Arrow   786kg   200hp   330kph/178kt   940ft/m
Rockwell Commander 112B   804kg   200hp   277kph/150kt   880ft/m
SIAI-Marchetti S-205-20   760kg   200hp   270kph/146kt   826ft/m
Socata ST-10      723kg   200hp   280kph/151kt   1005ft/m

I must say though, the Arrow seems unbelievably fast, any idea how come? I can't remember if it's turbocharged/normalized but when looking at the Commander data in the next paragraph then it could be the answer.

There was a new version made of the Commander in the 90s where they listed some aerodynamic improvements, a new engine cowl for one. However looking at the data between the original Rockwell GA-114A and the new Commander 114B there doesn't seem to be much difference, although that would depend on which of airliner.net's speeds are correct, the kph or the kts. If it is the kts then the improvements could perhaps make the Commander 112 faster than a C177RG. However how come the TC model with just 10 extra horsepower is so much faster? Is that because top-speed usually is achieved at well above sea-level where the turbo would help keep the engine-power?

Rockwell Commander 114A   885kg   260hp   307*kph/157kt   1088ft/m   *) 157kts = 291 kph
Commander 114B      927kg   260hp   304kph/164kt   1070ft/m
Commander 114TC      1018kg   270hp   364kph/197kt   1050ft/m

During my research for these planes I also found a very special plane I hadn't seen before, a Ruschmeyer R90. Aerodynamically clean body made of glassfiber with Rohacell core, rain-tolerant laminar-flow wing, a 230hp flat-six (de-rated from 260hp) and a top-speed of 324kph / 175kts with an initial climb-rate of 1140 fp/m although 1650ft/m is listed as possible. Now here's the really interesting part, something I haven't seen on any other small GA plane before, a 4-bladed propeller. http://www.airliners.net/photo/Ruschmeyer-R90-230RG/1369794/M/

Frank
Title: Re: What's the biggest influences on an aircraft's speed/performance?
Post by: Ragwing on October 13, 2008, 01:00:55 AM: Frank,
A lot of things contribute.
Shape which affects parasitic drag.
Wheel pants, cowlings, hinges, protruding rivet heads.
I shake my head every time I look at the GA aircraft with round external head rivets instead of a countersunk rivet that leaves a smooth skin.

For example, the Cessna 310 is a nice twin.
Cessna made it a little different shape, calling it the 320. AND it was faster.
It is believed that the extra curve in the top of the fuselage increased its performance.
It was not the reason for the change...... It was by chance.

The Cessna 170 (1948) complete with rag wings is faster than the Cessna 170A (1949) with metal wings and lower weight.

But a lot of what affects performance in GA will never be known.
The improvements are typically accidental and not design.
Cessna does not have stress analysis on it's singles (or did not as of 15 years ago).

Then we have all sorts of antenna's sticking out causing more parasitic drag.
Have you ever admired the NARCO antenna on the top of the older aircraft? That must take some wind out of those sails.
Title: Re: What's the biggest influences on an aircraft's speed/performance?
Post by: spacer on October 13, 2008, 01:56:20 AM: Drag is generally the biggest obstacle, as it increases four-fold when you double your speed.
There've been a few attempts at ultra-low drag aircraft using small powerplants and reaching
speeds that usually require copious amounts of power.

The challenge is balancing slipperiness with utility.
Title: Re: What's the biggest influences on an aircraft's speed/performance?
Post by: G-man on October 13, 2008, 02:18:19 AM: I cannot help but notice that everyone of the aircarft listed suck..

NOT ONE OF THEM CAN

HOVER
[/b]
Title: Re: What's the biggest influences on an aircraft's speed/performance?
Post by: Frank N. O. on November 11, 2008, 04:07:12 AM: Ok, I'd better reply to this now I got some time, and did some more investigating.

G-Man: No but they're a lot cheaper and since not many of us can handle the requirements to be a helicopter pilot we have to make so with less ;)
Although while on the subject, I do remember the CW strip with Chuck constantly bragging that his 500 could fly a lot faster than a JetRanger, is that due to weight, power, rotorblades or just aerodynamic drag? I also noticed that some helicopters have downforce-shaped aerofoils on the tailboom, is that to keep the tail down when flying forward at high speed which of course is done with the rotor tilted forward?

I still wonder a bit about the Commander being said to have an extra wide cabin but the data I see everywhere lists the interior cabin space as 46 inches with the Cardinal being 48 inches, much wider than both the Skyhawk and Skylane but no-one to my knowledge has ever said the Cardinal had a fat fuselage. As you know then sadly the Cardinal, apart from a grounded Caravelle, is the only airplane I've ever sat in but it's cabin was just fine, apart from the extremely high instrumentpanel (another reason the Commander is appealing since pictures seem to indicate it's panel is lower, but still with good placement of instrumetns and switches).

Frank
Title: Re: What's the biggest influences on an aircraft's speed/performance?
Post by: spacer on November 11, 2008, 05:41:01 AM: We don't get too many Commanders at our FBO, but one did stop in for a passenger this weekend. It did look nice and wide in the cabin.

Well, we do have one old Lark based here, but it's the one that looks like some Cessna factory workers had hit the weed a little hard before
coming to work. ::whistle::
Title: Re: What's the biggest influences on an aircraft's speed/performance?
Post by: ZK Kiwi on November 11, 2008, 08:45:23 AM: Biggest influence on speed / performance?.... easy.....

MONEY!!!!!!!!!!

(See Reno for examples)

:)
Title: Re: What's the biggest influences on an aircraft's speed/performance?
Post by: Mike on November 11, 2008, 08:42:02 PM: Quote from: ZK Kiwi on November 11, 2008, 08:45:23 AM
Biggest influence on speed / performance?.... easy.....

MONEY!!!!!!!!!!

(See Reno for examples)

:)

HA HA !!!
Good one !!! Love it!!! Sooooooooo true.....

::rofl:: ::rofl:: ::rofl::
Title: Re: What's the biggest influences on an aircraft's speed/performance?
Post by: Oddball on November 11, 2008, 10:33:24 PM: Quote from: ZK Kiwi on November 11, 2008, 08:45:23 AM
Biggest influence on speed / performance?.... easy.....

MONEY!!!!!!!!!!

(See Reno for examples)

:)

Phwoar Sea Furies, Bearcats, Mustangs MMMMMMEEEEERRRRRRRRRLLLLLIIINNNNNNNNNSSSSS *insert drooly smiley here* ;D ;D ;D
Title: Re: What's the biggest influences on an aircraft's speed/performance?
Post by: Mitchell99 on November 19, 2008, 08:30:04 PM: So true about the Money!!!! Just a side note; the picture of the Ruschmeyer R90, the tail number is G-UAPO. In Spanish Guapo is the word for "Handsome". Kind of ironic ::sleep::
Title: Re: What's the biggest influences on an aircraft's speed/performance?
Post by: Chopper Doc on December 31, 2008, 05:08:36 PM: Quote from: Frank N. O. on November 11, 2008, 04:07:12 AM
... I do remember the CW strip with Chuck constantly bragging that his 500 could fly a lot faster than a JetRanger, is that due to weight, power, rotorblades or just aerodynamic drag? I also noticed that some helicopters have downforce-shaped aerofoils on the tailboom, is that to keep the tail down when flying forward at high speed which of course is done with the rotor tilted forward?

The 500 flies faster than a JeBuggy due to slower rotorblade tip speeds. Since the 500 has five shorter blades turning at (I think) 384 RPM versus the two longer JetBuggy blades turning at about 324 RPM, you can see that the tip speeds are much greater with the longer Bell blades. Add this tip speed to the relative wind experienced by an advancing blade and you begin to push the airfoil into the early transonic regime, which the blade tip is not made for.

Also, the Hughes rotor system is fully articulated, which means each blade is free (ish) to flap up and down as well as lead and lag; this allows each blade to independently seek the position that aerodynamic/gyroscopic forces tend to displace it to. The Bell two-bladed, underslung, semi-rigid rotor system balances most of those forces with less complexity under most operating conditions: speed is not one of those conditions, so VNE is lower by design.

Some people confuse the characteristic "whop, whop" of a two-bladed Bell (iconic soundtrack to helicopters of any stripe in the movie world) with a sonic boom. This is not exactly what happens, but is rather caused by Blade Vortex Interaction. As every airman knows, there is a vortex formed at a wingtip where the high-pressure air beneath the airfoil is drawn around the tip into the low-pressure area above. Since this is a dynamic process occurring as a result of the airfoil's movement through a fluid, this results in a vortex forming at the trailing edge of the foil where the flows mix. So far, so good; now imagine the airfoil tip moving in a circle instead of straight ahead: the vortex describes a helix within the column of downward-moving air formed in the downwash of a hovering helicopter. Now add a vector of lateral motion to the helix. Looking down on at the path of one blade tip, one would see an endless pattern of loops - the path of a tip moving in a circle as the center of rotation is shifted forward. If one draws this pattern, there will be an intersection of the advancing tip with the trace from the previous rotation. This intersection is the site of BVI.

In most phases of flight there is no actual interaction as successive paths do not actually intersect in the horizontal: one can imagine that, just like in a hover, there will be vertical spacing of tip paths due to fluid movement in the vertical. Add to the fluid's movement the motion of the rotor system in a climb or forward flight and successive paths will be seen to not intersect, but when the aircraft's motion becomes very close to the downward displacement of the fluid the paths do interact. In this phase of flight, typically a low-rate descent, where the vertical and horizontal speeds are just right, the vortex from the previous blade tip passage is cut by the blade's next pass, and the impact causes the successive "crack" from each advancing blade: this is BVI. Nobody sneaks up on you in a Bell.

All rotor systems will experience this, by the way, but nobody else has the same tip speed, blade chord, and wing-loading characteristics that seem to make the Bell two-bladed systems into a perfect noise maker.

As far as the horizontal stab on the tailboom goes, you're correct: it is an inverted airfoil that creates a downforce in forward flight. This keeps the cabin somewhat level and reduces the drag you'd experience if you flew with the roof forward instead of the pointy end.
Title: Re: What's the biggest influences on an aircraft's speed/performance?
Post by: G-man on December 31, 2008, 10:51:50 PM: So Doc---is there a test??

And while you're at it--explain the toroidal flow of air inside the combustion chamber, I have yet to be able to explain it withOUT the use of pictures or moving my hands. ::thinking:: ::thinking::

(http://i76.photobucket.com/albums/j35/helokat/funnies/n65p7q1186017833.jpg)
Title: Re: What's the biggest influences on an aircraft's speed/performance?
Post by: Oddball on January 01, 2009, 01:14:54 AM: If you cant do it with out models on sticks or using your hands its not educational.
Title: Re: What's the biggest influences on an aircraft's speed/performance?
Post by: Chopper Doc on January 01, 2009, 05:23:58 PM: Quote from: G-man on December 31, 2008, 10:51:50 PM
So Doc---is there a test??

And while you're at it--explain the toroidal flow of air inside the combustion chamber, I have yet to be able to explain it withOUT the use of pictures or moving my hands. ::thinking:: ::thinking::

Nope. Can't be done - I've got French-Canadian heritage and can't speak without my hands. Come to think of it, I've only ever tried to explain toroidal flow using my hands making this extension then inward-curving flexion motion, followed by fingers spread to reflect the nozzle config with the other hand's fingers moving past the windows in rotor-blade motion.

The blanker the look I get, the bigger the gestures get. It's the French-Canadian way of shouting.

Sorry if my explanations get long-winded, but a good audience is soooo hard to find.
Title: Re: What's the biggest influences on an aircraft's speed/performance?
Post by: G-man on January 02, 2009, 03:03:52 AM: Quote from: Chopper Doc on January 01, 2009, 05:23:58 PM
Nope. Can't be done - I've got French-Canadian heritage and can't speak without my hands. Come to think of it, I've only ever tried to explain toroidal flow using my hands making this extension then inward-curving flexion motion, followed by fingers spread to reflect the nozzle config with the other hand's fingers moving past the windows in rotor-blade motion.
The blanker the look I get, the bigger the gestures get. It's the French-Canadian way of shouting.
Sorry if my explanations get long-winded, but a good audience is soooo hard to find.

I finally figured it out and fully understood it two years ago.. 8)

I suspect that 99% of people in this site would give you the blank stares.. The "helicreature" types would understand ::whistle:: ::whistle::
Title: Re: What's the biggest influences on an aircraft's speed/performance?
Post by: TheSoccerMom on January 02, 2009, 03:49:24 AM: Quote from: Chopper Doc on January 01, 2009, 05:23:58 PM
I've got French-Canadian heritage and can't speak without my hands.
The blanker the look I get, the bigger the gestures get. It's the French-Canadian way of shouting.

I KNEW you were okay.

;) ;) ;)
Title: Re: What's the biggest influences on an aircraft's speed/performance?
Post by: Chopper Doc on January 02, 2009, 06:04:26 PM: Thanks, Mom, you say the nicest things.

Actually, there's lots about our aircraft that makes for fascinating cocktail knowledge. For instance, when you consider that a turbine engine is open at both ends (compressor inlet and exhaust) it's hard to imagine that the combustion chamber housing (in the middle between those openings as well as being between the compressor and turbines) might be containing over 100 psi at 100%N1.

Amazing things, our little forced air furnaces. A pressure drop of 100 psi from one side of the turbine wheels to the other results from the extraction of compressor power and shaft power. And the guts spin at up to 50,000 rpm. For hundreds of cycles over thousands of hours.

Wow. And the basic designs haven't changed since the '50s.
Title: Re: What's the biggest influences on an aircraft's speed/performance?
Post by: G-man on January 02, 2009, 07:09:17 PM: Quote from: Chopper Doc on January 02, 2009, 06:04:26 PM
Wow. And the basic designs haven't changed since the '50s.

Sometimes simple designs are worth keeping:

http://www.youtube.com/watch?v=AfTrBQFx1E0