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

SPEED DELTA - good or ...?

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Old 01-26-2006, 10:33 PM
  #1  
slowmo777
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Default SPEED DELTA - good or ...?

Hello folks!

Although delta constructions are not recommended for ambitious prop driven speed ships here we can see an example of an aerodynamically optimised “Laser Arrow”. Powered by a fully concealed 10 cc FIRE engine it is noticeably faster than the stock version.

If powering the pictured delta by a .90 ducted fan engine and a 9*9 carbon prop speeds of 170 mph are possible. So it is obvious that a delta design will never be as fast as a “regular” speed plane if powered by the same engine and matched prop.

A significant example for that is a “Whiplash” or “Diamond Dust” delta, powered by a F3D pylon engine versus a F3D pylon racer powered by the same engine. Guess who wins the straight in line speed?

Besides the high induced drag another basic drawback is, that deltas generally require a relative large prop diameter counterproductive for competitive speed.




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Old 01-26-2006, 11:27 PM
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Default RE: SPEED DELTA - good or ...?

That sure is a beautiful plane, SLOMO! For pure sport flying fun, it's hard to beat a 2.5 pound DIAMOND DUST, though. The early DIAMOND DUST advertisements claimed 200 mph speeds, there was even some sort of testimony by EDDY HILL, a top fuel drag racer. I wonder why no one at this forum has duplicated the same feat?
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Old 01-27-2006, 12:27 AM
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Default RE: SPEED DELTA - good or ...?

I don't understand. Exactly why will a delta not be as fast in a straight line speed as a conventional craft? I know why it will be slower in turns, but in straight line? Do tell.
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Old 01-27-2006, 02:16 AM
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Default RE: SPEED DELTA - good or ...?

well I'm definitely going to have to see about that..whiplash X + 60LX +tuned pipe with 8.8 x8.75..apc will do... not exactly in the ducted fan league but I think it might go close to pushing the 200mph.. but than again we'll just have to wait and see

I've already started the the enclosure/fairing that will conceal the engine, servos and probably the push rods... although I forget where exactly I was reading and amazed at how much drag is generated by the cyclinder head alone..so nomore open engines for me if i can help it

after the whip I'll try the zoomer , hopefully enclose the pipe..but cut the wing down to around 48"

cheers
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Old 01-27-2006, 07:22 AM
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Default RE: SPEED DELTA - good or ...?

ORIGINAL: combatpigg

…The early DIAMOND DUST advertisements claimed 200 mph speeds, there was even some sort of testimony by EDDY HILL, a top fuel drag racer. I wonder why no one at this forum has duplicated the same feat?
ORIGINAL: Lomcevak Duck
I don't understand. Exactly why will a delta not be as fast in a straight line speed as a conventional craft? I know why it will be slower in turns, but in straight line? Do tell.
Combatpigg gave already the answer – it’s good marketing, isn’t it?

Seriously, both statements do address the same problem.


As already mentioned in my first post we’re dealing with prop driven deltas. To get them successfully to the wanted speed is quite tricky.

Induced drag: A delta plane really does not like a pylon course because of the hard turns. So the speed pattern we do fly at the Speed-Cups is recommended. Meaning to perform a really high nose dive and a subsequent super smooooth pull out of the dive into the 200 m speed trap. Even here losing speed with a delta is barely preventible here – a major drawback.

Parasitic drag: Well there are certain “basic rules” for us speed lovers to be followed to make speed life easy. The main rule is: Reduce parasitic drag. So it is very very important to fully cover the engine and tuned pipe. But the dilemma is: All commercial prop driven delta designs don’t feature a full engine + pipe cover (DD, Whiplash, Laser Arrow etc.). BTW, the pictured modified Laser Arrow has a reduced airfoil of only 6 % which is comparable to the relative thickness of Whips and DDs. The original 10 % wing is not practical for adequate speed.

Which is the best prop size for deltas?
Sadly the small props usually used for “conventional” speed planes don’t match deltas any more. That’s not theory. Deltas need bigger props – often too large to gain satisfactory speed. To be able to turn a bigger prop at the rpm the engine needs to run (HP/torque peak) you have to reduce the prop pitch. So here’s another dilemma. Reducing the pitch reduces the top end speed and also the ability to unload freely during a dive – a second major drawback.
From experience the speed prop sizes used for well designed conventional speed planes (not pylon planes), characterised by a higher pitch than the diameter, don’t work with deltas. A “squarish“ prop like 7*7, 8*8, 9*9 etc is the maximum in terms of effectivity. These prop sizes only work for aerodynamically super well designed deltas. A further increased pitch will make even these deltas slower again.

Deltas for turbines and pulse-jets however are another animal. Here the delta platform offers nearly ideal boundary conditions: Fuel bags completely hidden in the wing, no fuselage, no heat problems, no exhaust pipe and BIG thrust available that overcomes all types of drag easily.




To conclude, the drag and especially the prop problem cannot be solved while trying to make deltas competitive.
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Old 01-27-2006, 07:32 AM
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Default RE: SPEED DELTA - good or ...?

ORIGINAL: HaveBlue
well I'm definitely going to have to see about that..whiplash X + 60LX +tuned pipe with 8.8 x8.75..apc will do... not exactly in the ducted fan league but I think it might go close to pushing the 200mph.. but than again we'll just have to wait and see
Hello HaveBlue,

please consider: With a 8.75 pitch you need something like 23000 to 24000 rpm to come close to 200 mph. I guess 175 mph are realistic with the fully enclosed JETT .60 LX FIRE + pipe and your prop choice.


…after the whip I'll try the zoomer , hopefully enclose the pipe..but cut the wing down to around 48"
While meticulously modding the Zoomer it should be no problem for you to make a NACA 0009 wing for that bird. The original wing comes with much too thick 12%. Angle of attack should be about 0.3 degrees. Wing span of 48” is a good value for a hot .60 FIRE. No landing gear recommended.

P.S. Fully concealing a .60 FIRE or RIRE engine & pipe will be much more difficult for a Zoomer than for a CURARE .40 fuselage for instance.

Good luck!
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Old 01-27-2006, 09:02 AM
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Default RE: SPEED DELTA - good or ...?

ORIGINAL: slowmo777

Hello HaveBlue,

please consider: With a 8.75 pitch you need something like 23000 to 24000 rpm to come close to 200 mph. I guess 175 mph are realistic with the fully enclosed JETT .60 LX FIRE + pipe and your prop choice.
Hi slowmo777,
your pretty close to the figures I got when I ran the rpm and pitch numbers through a calculator.. on paper this is good for 179 mph excluding the drag and other factors....then why did I write that I'll think it will come close to 200 MPH..well apperently a whiplash with a comparable engine to 60LX has been clocked at 188mph... I think I can work with that..and it's sort of getting close to 200mph


ORIGINAL: slowmo777

While meticulously modding the Zoomer it should be no problem for you to make a NACA 0009 wing for that bird. The original wing comes with much too thick 12%. Angle of attack should be about 0.3 degrees. Wing span of 48” is a good value for a hot .60 FIRE. No landing gear recommended.

P.S. Fully concealing a .60 FIRE or RIRE engine & pipe will be much more difficult for a Zoomer than for a CURARE .40 fuselage for instance.

Good luck!
thanks for the vote of luck..from what I have seen and heard about Zoomer/ pipe enclosures..I think I'm going to need it!!..I envy the pattern plane designs of the 80's everything tucked away very nicely indeed. I like this design pictured, but its for a .60 - .90 size engine ..a bit big... but IF I was going for pure speed than I would be looking at a glider fusealge modified just engough to squeeze everything in.. I'd try a wing built with a regressing airfoil probably around 55% of span and either a full on pylon engine or perhaps car /marine equivelants that CAN get some serious rpm.. but thats later on if I try a serious attempt at something.. the learning curve between now and then is surely needed
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Old 01-27-2006, 10:21 AM
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Default RE: SPEED DELTA - good or ...?

slomo... good job.

Having an aero-engineering background myself, its sometimes painful watching/reading some information brought forth. I for one appreciate the time you have taken with your posts.

There have been a few reported and documented 200 mph whiplash (delta) aircraft flown ...... but by enlarge those were not level flight, entered in a dive, and in most cases wind aided. Never the less, its nice to see the smile on someones face when they see the 20X mph number on the radar gun

Of note, I recall folks telling me of the USA FAI trials not long ago, guys practicing out in Phoenix, trying to get max speed on the radar in straight line speed. Most of those made it just over 200 mph. And we all know what sort of combinations are flying there to achieve that.
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Old 01-31-2006, 12:57 PM
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Default RE: SPEED DELTA - good or ...?

slowmo777: Have fast do u think your beautiful modified Laser Arrow is? (Straight and level, no dives)
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Old 01-31-2006, 02:25 PM
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Default RE: SPEED DELTA - good or ...?

Well, I’ve already mentioned the speed of this delta plane:

“If powering the pictured delta by a .90 ducted fan engine and a 9*9 carbon prop turning 23000 in the air speeds of only 170 mph are possible.”

More prop pitch will reduce speed here!

The pictured one was the first “prototype” just powered by a .60 FIRE sport engine and a sport prop – a lame dog but still much quicker than the stock Laser Arrow.




However, this delta only has the name “Laser Arrow” in common with the genuine construction:

- 6% airfoil thickness instead of much too thick stock 10 %

- fully concealed engine + pipe (glass fiber cowl construction)

- carbon spars for improving strength

- fully balsa sheeted wing for improving strength

- landing skid made of glass fiber

- Glass fiber strip incorporated into the leading edge for better strength

- fully concealed linkages

- Sandwich construction of the vertical fins: 1 mm glass fiber plus 1 mm strong balsa at each side

- Altered fin geometry

- Weight with a .90 ducted fan engine and light non-muffled tuned pipe is about 2500 grams wet




So we do realise that 170 mph are very slow for a .90 ducted fan engine powered speed plane. These 170 mph have been measured in a 200 m speed trap after a very shallow dive. You’ll hardly find a prop driven delta being faster in a 200 m trap. Please remember: While flying a 200 m FAI speed trap it is much more difficult to obtain the wanted speed than by a radar gun measurement.



I would like to recapitulate:

Even if extremely modified, prop driven deltas are not suited for satisfying speed - a quite inefficient combo. I do explicitly include the DD and Whip which I’ve flown myself.



Sounds a bit harsh, but prop driven deltas just look nice.




[sm=sleeping.gif]


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Old 01-31-2006, 02:55 PM
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Default RE: SPEED DELTA - good or ...?

ORIGINAL: slowmo777
Which is the best prop size for deltas?
Sadly the small props usually used for “conventional” speed planes don’t match deltas any more. That’s not theory. Deltas need bigger props – often too large to gain satisfactory speed.
Why do they need bigger props? With a thin wing section, and cowled engine/pipe, why can they not use oversquare prop designs? Or is this based on experimental observations? Just curious. The only reason I can think of is higher overall drag, which I guess must be the case due to the inefficiency compared to a conventional aircraft planform.

MJD

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Old 01-31-2006, 05:02 PM
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Default RE: SPEED DELTA - good or ...?

Hello MJD.

Yes, the derivation

“oversquare prop size = mission impossible for deltas”

is mainly empirically based.

Let’s do some brainwork though and let’s talk pictures instead.





Let’s focus on an air molecule nearby a “conventional” airframe, just pulled by the propeller and moving nicely around the airframe. It is a spiral type of path. No major obstacles here – a (more or less) round fuselage and the spiral type of movement complements each other well.

Now look at the delta airframe sort of “Cutting” the propeller induced stream - if using tractor configuration. Seems to be a very disturbed path of the air molecules. That sure looks to be quite inefficient aerodynamically. Much of the engine peak horsepower is nullified here.

I forgot to mention that a pusher prop sounds much cooler but is less potent (don’t know why) – so no gain in terms of effectiveness here compared to a tractor setup. That’s empirical observation too.


A “conventional” prop driven speed airframe is so much better suited, you can use some real “unusual” prop speed sizes here – working effectively.



[sm=idea.gif]



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Old 02-02-2006, 01:19 PM
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Default RE: SPEED DELTA - good or ...?

ORIGINAL: slowmo777

Hello MJD.

I forgot to mention that a pusher prop sounds much cooler but is less potent (don’t know why) – so no gain in terms of effectiveness here compared to a tractor setup. That’s empirical observation too.
I suspect that turbulence upstream of the prop reduces its efficiency; perhaps portions of the prop are ingesting stagnant air, or air with a radial velocity component.

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Old 02-08-2006, 06:31 PM
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Default RE: SPEED DELTA - good or ...?

Gang
:
God, don't ya just love these technical people, and you-all out there better listen up cause in my book, its Goapel!. That being said, and being the Devils advocate that I am, Slomo777, please add the conventional wing to the airframe to your drawing example. I think a 400 Sq. In. delta and a 400 Sq. in. conventional design powered by a given 40 motor, the delta airframe has a overall drag=speed advantage, to a given speed, say 75-100mph. Then things start to reverse to a point the streemlined conventional airframe gains a design advantage. That is by observation (empirical), not calculated. Wind resisance does seem to increase in pressures expodentially as the speed increases, (ie pressures are more than 2 X at 50mph than at 25 mph! Don't expect Slomo to calculate the thing out, just wondering if he has thought this reality through?
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Old 02-08-2006, 08:06 PM
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Default RE: SPEED DELTA - good or ...?

After reading that post, I could only flame.
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Old 02-09-2006, 04:40 PM
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Default RE: SPEED DELTA - good or ...?

Drag increases as velocity squared, whether at 25 mph, 50 mph or 175 mph. Drag coefficients may change as airflow patterns shift, but for the most part they vary little in these lower airspeed regimes. While deltas may often offer small frontal area, they suffer from inefficiency in other ways, the low aspect ratio being a major one when it comes to turns. And the whole wing isn't lifting either, there has to be reflex of some sort to provide stability. Think of the difference between a conventional layout and a delta as the difference between holding the hood of your car open by lifting at the front (conventional layout) and by lifting about 10" in front of the hinges (delta). Crude analogy, but works for me. All lift results in induced drag. Deltas have a bunch of induced drag and inefficiency due to low aspect ratio. I'm sure there are more details to the picture but that's a start.

That said, they are easy to build as the structural challenges are far less with the relatively short span and low aspect ratio wings. Plus, they look cool, and that has to count for something...[8D]

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Old 02-09-2006, 05:23 PM
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[sm=thumbup.gif]
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Old 02-09-2006, 08:27 PM
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Default RE: SPEED DELTA - good or ...?

I agree that a low aspect ratio wing has a lot of induced drag in a turn. That I cannot debate. I also agree that tractor as well as pusher props are further hindered by the disturbance of the wing. I cannot debate that either. I do have a problem swallowing the idea that a delta wing design is less efficient for high speed straight line flight than a high aspect ratio wing. (If propulsion was not a factor.0 Cite the world's fastest aircraft. All modern military fighters use a low aspect ratio wing. ( I well understand that these are not the same speeds with which we deal, and that they use turbines; see the propulsion disclaimer) And I know that when they execute hard turning manuvers they become very inefficient. I have seen the same videos of test flights going from mach .9 to a near stand still in only a few seconds by executing a high G manuver. But in straight line low G unaccelerated flight I propose that low aspect ratio wings are the ticket. The fastest manned aircraft in history had a super low aspect ratio. (X-15). And kelly Johnson would not have designed one of the coolest aircraft in history as a delta if it was inefficient (SR-71). Nor would the Concord have been a delta. So maybe it's not the wing that needs rethinking, but the powerplant? I am thinking (I don't know, just theorizing) that if you were to move the engine (prop driven) farther out in front of the LE that maybe it would be benificial. One thing that all of the above aircraft mentioned have in common is a long nose infront of the wing. I don't know if it was for stability or drag reduction, but there had to be a reason the Blackbird had a long nose. It wasn't for the engine, nor passenger/cargo storage. Had to be some aerodynamic reason. I do know that the chines had a lot to do with stability, and when they clipped them for the A-12 version they had to add two dorsal fins under the engines to sort it out. Just a thought. Well, maybe a couple.
-Steve
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Old 02-09-2006, 08:34 PM
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Default RE: SPEED DELTA - good or ...?

If deltas were so efficient, don't you think the full sized glider guys would be using one as the platform? They are working at about the same Reynolds number as fast RC planes. There is also a big drag penalty with the reflexed airfoils that deltas need. Swept wings and deltas work great in the transonic and supersonic range, which is far far away.
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Old 02-09-2006, 10:41 PM
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Default RE: SPEED DELTA - good or ...?

the key factor here inregards to deltas is the prop size used on our deltas..as slowmo said..with a turbine which has the thrust to overcome these factors allows for the deltas high speed... but the point was that the smaller racing props just dont work to achieve the speeds we would like to see...but then again that doesnt mean we can get some really good speed...I am sure speed freaks everywhere have tried many different configurations to achieve high speeds and if the delta planform is capable of efficently acheiving high speeds it would be used more than what it has been... though I dont have the knowledge that you guys have, I can understand slowmo's point in regards to effiency of prop selection for maxium speed

other than that we cant use full scale plane forms to argue out speed effiency of RC models
which real prop plane has an engine that turns 17,000, 18,000 or 22,000 rpm to fly very fast...none..... we can scale an aircraft but we cant scale the power plants or props and achieve desired results especiallywhen it comes to speed.. I dont claim to know alot so if I am misguided here please correct me
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Old 02-10-2006, 12:22 AM
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Default RE: SPEED DELTA - good or ...?

If deltas were so efficient, don't you think the full sized glider guys would be using one as the platform? They are working at about the same Reynolds number as fast RC planes. There is also a big drag penalty with the reflexed airfoils that deltas need. Swept wings and deltas work great in the transonic and supersonic range, which is far far away.
Point taken. I am not an engineer, nor do I have a degree in aerodynamics, so I will not claim that my ideas are any more than that: ideas. I would like to propose another idea to you, however. Full scqale glider guys are not trying to achieve high speed efficiency. They are trying to produce as much lift as possible while giving up very little in drag. They need to simply stay aloft as long as possible, and (except for the racing gliders) do not desire top end high speed flight. They do need to avoid induced drag during turns and acceleratied flight. Military jets focused on high speed flight (lets examine my favorite again, the SR-71) have a lift quota to fill, and do not mind so much giving up penalties in induced drag as they can easily accelerate out of slow flight, and are much more concerned with top end speed. The Blackbird was designed with a purpose in mind. It was designed to operate at 85,000 feet at Mach 3.2. It was given a wing that would fulfill this need, and nothing more. At max cruise speed it had a turning radius (at standard rate) of 100 miles. It had a LOT of induced drag in accelerated flight, and was never meant to pull more than 3Gs in a manuver, but in a straight line nothing on the planet could touch it. Had it been designed with the idea in mind of flying slowly with little or no engine power and not to have much induced drag, it would have had a high aspect ratio, long and tapered, but unswept wings. Oh! Wait- there was another fantastic plane designed like that; the U-2.
Not trying to start an argument, just throwing out ideas with legitimate historical and seemingly logical backings.
-Steve
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Old 02-10-2006, 12:32 AM
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Default RE: SPEED DELTA - good or ...?

which real prop plane has an engine that turns 17,000, 18,000 or 22,000 rpm to fly very fast
All powered aircaft use propellors of some sort except for rocket motors. Even turbines use a type of propellor, and they can spool upwards of 100,000 RPM. No, no prop plane with a piston or turbo prop hits anything close to this. At least, not that I have ever heard of.
-Steve
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Old 02-10-2006, 02:04 AM
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Default RE: SPEED DELTA - good or ...?


ORIGINAL: Lomcevak Duck


Even turbines use a type of propellor, and they can spool upwards of 100,000 RPM.
-Steve
technically I think this statement is incorrect..they use compressors , inpart with impellers , diffusers and stator vanes..but I do not think it can be called a TYPE of propeller even though they perform similar functions ..but I could be wrong..just my opinion

I have started an technical course in maintence of particular series of jet/turbine engines predominately used in helicopters .. I have looked extensively through all maintenance and service procedures and there are no referrences to propellors until I get to turbo prop engines
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Old 02-10-2006, 05:54 AM
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Default RE: SPEED DELTA - good or ...?

Dear Lomcevak Duck

I would like to suggest taking several hours of internet search: Please do some google work for:

- Reynolds Number (reason: we can’t compare full scale planes to our small scale model planes. Do we model pilots use the full scale airfoils for instance?)

- subsonic vs supersonic aerodynamics (SR-71, Concorde, X-15 etc. layout is very inefficient in subsonic environment)

After that search many questions should be resolved.

Greets
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Old 02-10-2006, 08:40 AM
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Default RE: SPEED DELTA - good or ...?

HaveBlue, no, you're not wrong.. You are exactly right as a matter of fact.. I went to school for aviation mechanics myself (A&P).. Ended up a computer geek somehow but that's another story. A turbine engine, whether it be a turbo prop, turbo jet, or turbo fan all work the same... Compression section, hot section, power section....
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