Planes With the Best E Retention

[Die Hard]

That is strange, but "It seems that propeller drag, at either minimum or maximum pitch, is all over the place." is not strange in and of itself.

[moot]

It's not in and of itself, it's in this specific case.

[Die Hard]

It's not in and of itself, it's in this specific case.

Isn't that what I just said?

[moot]

It reads like you're trying to argue that there's nothing strange in the test results themselves or in what they imply.  I'm officially done trying to string coherent sentences together.

[BnZs]

Perhaps the efficiency of the Ta-152's high-aspect ratio wings reduces induced drag even in level flight enough to account for the effect?

Perhaps the fuselage of the Ta-152 is somewhat more streamlined than the D9, or you tested the Ta-152 with a higher gross weight than the D9 was carrying?

But these are only guesses.

I see, so that explains why there is a huge difference between the Ta 152H and Fw 190D-9 when they both have a Jumo 213 engine and the same propeller?

Guess not, huh?

Remember this equation: KE = (1/2)mv^   M=mass V=velocity. Velocity is the same. The difference in weight (mass) between the two is only about 400 lb, which should be offset for the most part by the Dora's much smaller wing (reduced flat plate area).


My regards,

Widewing

[Cthulhu]

I always think it's hilarious when people question WW's testing methods.

 

Man, I wish I'd seen this thread sooner.

Yeah, I dismissed the guy's argument when he essentially missed the point and simply started regurgitating the things he learned in Physics 101.  Chemical energy? What does that have to do with airframe energy retention?  E-retention is all about drag, parasitic, and perhaps more importantly the induced drag from performing maneuvers. If during the process of trading potential for kinetic energy (and back again), an aircraft losses less energy, then it has better E-retention.

Perhaps the efficiency of the Ta-152's high-aspect ratio wings reduces induced drag even in level flight enough to account for the effect?

Perhaps the fuselage of the Ta-152 is somewhat more streamlined than the D9, or you tested the Ta-152 with a higher gross weight than the D9 was carrying?

But these are only guesses.

I would expect the Ta-152's longer fuselage to have slightly less drag. I'm thinking you may be right about the Ta's higher aspect ratio wing. The lower induced drag certainly appears to outweigh the increased parasitic drag.
Of course this all assumes that HTC has modelled the Ta accurately. 


Widewing,

Have you considered a follow-on test where you recorded velocity loss following a constant g climb?  If one were to accelerate to 400 kts @ 5000ft, then measure the final velocity following a (power off) constant g climb (say 3g's) to a higher altitude (say 10,000ft), it might tell us something about E-loss due to induced drag at higher angles of attack (as well as due to elevator deflection).  Just a thought.

[Widewing]

Widewing,

Have you considered a follow-on test where you recorded velocity loss following a constant g climb?  If one were to accelerate to 400 kts @ 5000ft, then measure the final velocity following a (power off) constant g climb (say 3g's) to a higher altitude (say 10,000ft), it might tell us something about E-loss due to induced drag at higher angles of attack (as well as due to elevator deflection).  Just a thought.

I wish there was another viable method. One problem with a 3g climb... You can generate 3g as you maneuver into a climb. However, once you neutralize the controls...  1g. Actually, a vector of 1g. A continuous 3g climb would only be a climb until you pitched over inverted through the horizontal. Of course, the effect of gravity is a factor that will complicate the results.

We have very limited tools for measuring drag.

Nonetheless, thanks for the suggestion.


My regards,

Widewing

[Stoney]

I would fully expect the 152 to be better than the 190D9.  The 190 wing is one of the less efficient wings in the game, maybe equivalent to the Spitfire.  In this kind of test, wing efficiency is probably going to be the largest factor, especially over the full spectrum of speeds as the primary drag component shifts from parasitic to induced as the plane slows down.  190 wings suffer from both, parasitic at high speeds and high induced at low speeds.  It may be interesting to see the comparison in drag coefficients for the 190D vs. the 152.  I knew the P-51 would be the best since it won't suffer from nearly as much parasitic at high speed, and will have manageable induced at low speeds--especially considering this type of test keeps low AoAs. 

Cthulu, during my design process, I've found that generally the shorter the fuselage the lower the drag.  The longer fuselage may allow better trim drag characteristics that make it more efficient than the shorter 190D fuselage--we'd have to do the math to make a comparison.  Form factor, divergence angles, etc. considered...

[Cthulhu]

I wish there was another viable method. One problem with a 3g climb... You can generate 3g as you maneuver into a climb. However, once you neutralize the controls...  1g. Actually, a vector of 1g. A continuous 3g climb would only be a climb until you pitched over inverted through the horizontal. Of course, the effect of gravity is a factor that will complicate the results.

We have very limited tools for measuring drag.

Nonetheless, thanks for the suggestion.


My regards,

Widewing

On second thought, 3g's may be a bit extreme. What I'd hoped to describe was an arcing constant g flight path which would terminate at the target higher altitude (but not past the vertical). But in order for any comparison to mean anything, the flight path would have to be duplicated for all aircraft tested, which, as you say, is outside our ability.

Cthulu, during my design process, I've found that generally the shorter the fuselage the lower the drag.  The longer fuselage may allow better trim drag characteristics that make it more efficient than the shorter 190D fuselage--we'd have to do the math to make a comparison.  Form factor, divergence angles, etc. considered...

The reason I brought that up is that I've seen examples in autoracing (the old Porsche 935 "Moby Dick" comes to mind)



where lengthening the body reduced base drag more than it increased parasitic drag. Of course, making this comparison, an aircraft fuselage to an auto body, is a stretch at best. ( no pun intended)

[Stoney]

In Hoerner's Fluid Dynamics of Drag he discusses divergence angles and their effect on drag.  For example, the taper of the fuselage can't exceed a certain angle or the flow will trip turbulent and create boat-tail drag.  I think it was 8 degrees--I'd have to look it up.  He also stated his opinions on form factor (roughly stated, the width of an object versus its length) and found, IIRC, that approx 3.5 was optimal for drag reduction.  Apparently it was what encouraged the designer to craft the fuselage of the Quest Venture the way it is:

http://airventure.aviation.museum/collection/aircraft/Questair%20Venture%20200.asp

The biggest problem is that you add a lot of surface area as the tail is lengthened and it adds to the overall drag area.  As the tail arm gets longer, the size of the empinage control surfaces can become smaller, so there's a bit of optimization that's required to come to the optimal length.  Notice the Venture has extremely large control surfaces as a result of its extremely low form factor.

Sorry if I'm repeating something you already know.  Either way, you are correct, for any given configuration of height, width, and length, you can arrive at an optimal combination that gives you a lower total drag amount.

[Cthulhu]

Sorry if I'm repeating something you already know.

Not at all.    I usually learn something new whenever you and Widewing post.

I do have a question though:  Why does a guy in Reno have a Carolina avatar?

[Stoney]

Why does a guy in Reno have a Carolina avatar?

UNC, Class of '96.  Grew up just outside Charlotte.  After we win the National Championship next weekend, I'll swap it back to the old avatar of my namesake. 

[Cthulhu]

UNC, Class of '96.  Grew up just outside Charlotte.  After we win the National Championship next weekend, I'll swap it back to the old avatar of my namesake. 

Real sorry to hear that. I'll try to keep it civil, but no guarantees. 

Class of '78