Pylons - Do they Affect Climb Performance at all?

[DarrenW]

It's pretty understandable that wing/fuselage pylons reduce maximum attainable level speed but I was wondering if they affect the maximum climb rate too? I'm thinking they might but not understanding the properties of lift vs drag in a climb situation I'm wondering if it's very noticeable at the optimum climb speed for a particular aircraft?

 

[swampyankee]

It's pretty understandable that wing/fuselage pylons reduce maximum attainable level speed but I was wondering if they affect the maximum climb rate too? I'm thinking they might but not understanding the properties of lift vs drag in a climb situation I'm wondering if it's very noticeable at the optimum climb speed for a particular aircraft?

Yes, as they increase drag, which increases the power required at any speed, which reduces the power available for climb.

 

[DarrenW]

Yes, as they increase drag, which increases the power required at any speed, which reduces the power available for climb.

Thank you swampy, I just wanted to make sure that the extra drag could have a noticeable effect on climb and now I know that it does.

 

[pbehn]

Thank you swampy, I just wanted to make sure that the extra drag could have a noticeable effect on climb and now I know that it does.

Well the pylons must have some effect but they hold bombs and tanks that the aircraft takes off with so not that much. I think they knocked 10-20 MPH off the top speed.

 

[DarrenW]

Well the pylons must have some effect but they hold bombs and tanks that the aircraft takes off with so not that much. I think they knocked 10-20 MPH off the top speed.

Yes, I should have not have used the word "noticeable", which can imply a large amount.

 

[Shortround6]

Some were better than others and of course you have one pylon/mount/rack vs 2 or more.

I believe the single rack under the Fw 190 was good for 4-6mph? out of about 400mph so it's effect on climb would be small.
A P-47 with 3 pylons/racks might see a rather larger difference.

 

[XBe02Drvr]

Practically all aspects of aircraft performance are a function of the operative ratio of lift over drag at any given moment in any given maneuver, as that determines how much power is required to continue the maneuver. When power required increases to match power available, you've reached the limits of performance.
I was a 1500 hour flight instructor, parroting this info to my students without intuitively understanding it, when I became a glider pilot, and true understanding dawned.
If you ever take up flying, I suggest you start with gliders. That's what Capt Sullenberger did, and look what it did for him. (Miracle on the Hudson, if by some slim chance you didn't know.)
Cheers,
Wes

 

[P-39 Expert]

wwiiaircraftperformance.org shows bomb racks for the 109 to reduce speed by 0-2mph, but underwing guns reduce speed by 7mph. Underwing bombs reduced speed 4mph. There is a climb graph but the tropical sand filter is also included so it would be hard to compare with the clean 109.

The racks only reducing speed 0-2mph seems like a stretch since the P-51 racks cost 15mph. And two underwing bombs only cost the 109 4mph. That must be one really clean installation.

 

[swampyankee]

wwiiaircraftperformance.org shows bomb racks for the 109 to reduce speed by 0-2mph, but underwing guns reduce speed by 7mph. Underwing bombs reduced speed 4mph. There is a climb graph but the tropical sand filter is also included so it would be hard to compare with the clean 109.

The racks only reducing speed 0-2mph seems like a stretch since the P-51 racks cost 15mph. And two underwing bombs only cost the 109 4mph. That must be one really clean installation.

It doesn't seem like a stretch; it seems very suspicious

 

[P-39 Expert]

WE NEED AN INVESTIGATION!!

 

[DarrenW]

A P-47 with 3 pylons/racks might see a rather larger difference.

The test data that I've seen of two different P-47Ds suggests around 300 fpm initially but the climb rates become much closer after an altitude of 16,000 feet is reached (when looking at 65" Hg of engine boost). The two aircraft had identical propellers and were ballasted at roughly the same weight (13,230 lbs vs. 13,260 lbs), with one in clean condition and the other with two wing pylons:

P-47 Performance Tests

http://www.wwiiaircraftperformance.org/p-47/p-47d-75035-fig2.jpg

http://www.wwiiaircraftperformance.org/p-47/p47d-44-1-climb.jpg

 

[Joe Broady]

I have no data at hand for WW2 aircraft, but do have performance data from the Vought A-7D flight manual. The A-7D has three pylons under each wing and a pylon on each side of the fuselage. The latter hold one Sidewinder each. In addition, I include the weight of a basic MAU-12 C/A rack in each wing pylon and a Sidewinder launcher in each fuselage pylon. The total is 1760 lb. Add enough fuel to bring the aircraft up to 29,000 lb (about 75% of internal fuel capacity). Time to height at military thrust:

10,000 1.1 minute
20,000 3.0
30,000 5.8

Now remove all pylons and add enough fuel to make up the weight difference:
10,000 1.0 minute
20,000 2.5
30,000 4.5

Finally, remove all pylons and do not add any fuel. In other words, we lose the drag of the pylons and about 1800 lb too:
10,000 1.1 minute
20,000 2.5
30,000 4.0

Clearly the drag of the pylons depresses climb performance more than their weight.

 

[Shortround6]

we may have a slight problem with this comparison, which is detailed and well reasoned as far as it goes.

The problem, as I see it (and I could be wrong) is that the drag goes up with the square of the speed. Most of the Piston engine fighters had a best climb speed of 160-200mph?
A-7D had a best climb speed of ????????

 

[DarrenW]

The test data that I've seen of two different P-47Ds suggests around 300 fpm initially but the climb rates become much closer after an altitude of 16,000 feet is reached (when looking at 65" Hg of engine boost). The two aircraft had identical propellers and were ballasted at roughly the same weight (13,230 lbs vs. 13,260 lbs), with one in clean condition and the other with two wing pylons:

P-47 Performance Tests

http://www.wwiiaircraftperformance.org/p-47/p-47d-75035-fig2.jpg

http://www.wwiiaircraftperformance.org/p-47/p47d-44-1-climb.jpg

Question: why is there larger differences in the climb rate between the two airplanes at lower altitudes? Wouldn't there be be similar differences at most altitudes, with both airplanes climbing at what was deemed the P-47's optimum climb speed?

 

[Glider]

Practically all aspects of aircraft performance are a function of the operative ratio of lift over drag at any given moment in any given maneuver, as that determines how much power is required to continue the maneuver. When power required increases to match power available, you've reached the limits of performance.
I was a 1500 hour flight instructor, parroting this info to my students without intuitively understanding it, when I became a glider pilot, and true understanding dawned.
If you ever take up flying, I suggest you start with gliders. That's what Capt Sullenberger did, and look what it did for him. (Miracle on the Hudson, if by some slim chance you didn't know.)
Cheers,
Wes

Totally agree

 

[XBe02Drvr]

Question: why is there larger differences in the climb rate between the two airplanes at lower altitudes? Wouldn't there be be similar differences at most altitudes, with both airplanes climbing at what was deemed the P-47's optimum climb speed?

Air density affects all the variables of aircraft performance, and the differences with altitude are not linear, and will affect different performance aspects in different ways. A particular supercharger / turbocharger installation will not necessarily drive engine power in a linear relationship to ambient air density. A propeller won't convert horsepower to thrust at the same efficiency level at all air densities. We haven't even got into lift or drag yet. Get the picture?
Cheers,
Wes

 

[DarrenW]

A particular supercharger / turbocharger installation will not necessarily drive engine power in a linear relationship to ambient air density

That makes perfect sense to me and it's the most likely cause for the disparity. Thanks.

 

[swampyankee]

Propeller aircraft have, to a first approximation, constant power vs airspeed, so thrust is inversely proportional to airspeed. Turbojets and, to a lesser extent, turbofans have constant thrust vs airspeed. In either case, rate of climb is proportional to surplus power, so a jet aircraft otherwise similar to a propeller aircraft will have its best rate of climb at a higher speed. (SAAB 21/21R may be the best test case for this).

Pylons will also have a proportionately worse effect on a clean airframe, so the Bf109 (which had, reportedly, one of the highest [worst] zero-lift drag coefficients of any WW2-era monoplane fighter) would be harmed less by pylons than a clean aircraft, like the P-51 (which had, by far, the lowest*). The Swordfish (or its German equivalent, the Fi167**) would barely notice the extra drag


--------------
*The reports I've seen give the P-51 a zero-lift drag coefficient of about 0.017, with the Bf109 being between 0.027 and 0.029. Most fighters fell between 0.020 and 0.024. Of course, some versions of the Bf109 were much worse aerodynamically than others.

** Note that the Fi167 is yet another argument against the idea that the Bismarck's AAA couldn't target a Swordfish because it was so slow. The Germans were putting a biplane into service

 

[Glider]

I think I am right, when I say that the 109 with the underwing 20mm only lost about 8mph. However it did significant damage to its climb and handling