Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: PapaFox on March 19, 2010, 02:41:40 PM
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I've flown a Great Lakes biplane for 16 years and when the engine goes to idle that puppy is nothing like a glider. It can't even do a 7-to-1 glide ratio (seven feet forward for every foot of altitude lost). The reason for this dismal glide performance is all the drag from the struts, wires, and two sets of wings. Further, biplanes have relatively short wings. I'd expect the WWI biplanes to be even worse than the Great Lakes when it comes to gliding. Hitech needs to significantly tweak the glide ratio of our WWI biplanes to make them more realistic. The numbers are out there if he wishes to look at the glide behavior of World War I biplanes.
Papafox
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While we're at it, slipping in the Aces High WWI biplanes and triplanes needs to have more of a negative effect upon energy. For spot landings, I can hardly remember a time when I couldn't get down quickly enough in my biplane. A biplane descending at a rather steep angle plus some slip and the thing really came out of the sky. You certainly could get a descent rate that was too high for a comfortable flare, however.
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If the WWI plane engines are producing the correct amount of thrust, and the planes end up with the correct speeds in level flight, that means Hitech has the drag correct.
If the WWI planes have the correct power-off stall speeds, that means Hitech has the lift factor right.
If the drag is correct and the lift is correct, then the glide ratio will be right, as it is determined by lift/drag.
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This game is not always so self-checking....
P-38Gs met all the speed requirements, the climb, the acceleration, but it turned out their weight was 500lbs under normal.
P-40Es have issues with the engine settings, MAP might be wrong, WEP setup could be wrong, but overall they meet the right amount of dive acceleration and top speed.
Fw190A8s are almost 500lbs too heavy, both outboard weapons packs are way off in the weight department (hundreds of pounds), and yet it meets all the other specs. The Fw190F-8 is almost identical performance to the A-8, despite being a totally different plane with extremely heavy amounts of additional armor added.
So, it's complicated. It does not always self-check itself. One thing can be spot on, and the rest way outta whack. Look at the airflow model and 109s/190s, it used to snap-stall them even with the most gentle of inputs if you dropped below 250mph, and they fixed that. All the speed, climb, and other specs remained the same, but they fixed how the lift was being computed, and the result is night and day.
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Papafox, I also have always thought that they did not feel draggy enough. But remember to turn your engine off when testing these birds. They have a lot of torque at low throttle.
We are looking again, wish I could find some real glide ratio numbers on these planes. It could be as simple as the amount of power required for the prop to keep windmilling.
HiTech
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Did a bit of testing today, best I could arrange was using spawn point as a distance reference. After climbing to 1k, leveling, I few to 1k behind the spawn point. Flew with engine off in autoclimb until I reached about 1.4k in front of the spawn point, so aprox distance 2.4k total (in yards) for 500 feet of altitude lost.
Roughly giving you a 14- 1 glide ratio.
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Also take into account that most of the rotaries had little in the way of throttling.
Most rotary powered early WWI planes were draggy enough that they could be nosed down without too much engine overspeeding. The Sopwith Half Strutter had airbrakes, which was because the 110 to 130 HP rotaries only throttled to about 2/3rds throttle, and because the Half Strutter was more aerodynamically clean than say a Farman MF11. The early Sopwith Pup had real engine overspeeding issues with running the unthrottleable Gnome 80.
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Had a random thought as I was falling asleep last night, is it possible that while the area of the wires and bracing is calculating correctly, the vibration (and added drag) of those wires (while minor) is not being added to the calculations?
Just a guess :)
Steely
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HiTech have you seen this?
http://www.hq.nasa.gov/office/pao/History/SP-468/contents.htm
It has this table:
Aircraft..................... ......Engine......... ...................(L/D)max
Fokker E-III.....................Oberursel U.I.......................... .6.4
DeHavilland DH-2.........Gnome Monosoupape.................. ....7.0
Nieuport 17....................Le Rhone 9J........................... ...7.9
Albatross D-III................Mercedes DII.......................... ..7.5
Fokker triplane, Dr.-1.......Oberursel Ur II........................... 8.0
Sopwith F.1 Camel.............Clerget 9B........................... ...7.7
SPAD XIII C.1...............Hispano-Suiza 8Ba........................7. 4
Fokker D-VII.....................BMW IIIA......................... .......8.1
Sopwith 5F.1 Dolphin.......Hispano-Suiza............................9.2
Fokker D-VIII.................Oberursel Ur II........................... .8.1
Junkers D-I.......................BMW IIIA......................... .......7.0
Handley Page 0/400..........Liberty 12.N......................... .....9.7
Gotha G.V......................Merc edes DIVa......................... ..7.7
Caproni CA.42.....................Lib erty................. ................8.2
B.E. 2c........................... ...R.A.F.la.......... ......................8.2
Junkers J-I........................Benz Bz.IV........................ ....10.3
DeHavilland DH-4..................Liberty........................ ........8.1
And it also mentions the streamlined wires on the Camel.
"... streamline wires were used for bracing on both the Camel and the Dolphin. (Streamline wires have a cross-sectional shape much like a symmetrical airfoil section.) Such wires were developed by the Royal Aircraft [29] Factory at Farnborough, England and were first flown experimentally on the SE-4 in 1914 (ref. 39). The Sopwith Pup and triplane, both of which entered service in 1916, also had streamline bracing wires. The advantage in drag reduction of using this type of wire rather than the usual round wire is great; there is a factor of about 10 between the drag coefficients of the two types of wire"
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Pretty amazing to see the Handley Page 0/400 bomber has one of the lower drag to lift ratios of all those planes in that list, considering it's got a forest of struts and miles of rigging wires. If I'm reading this correctly... :headscratch:
The airfoil used in the 0/400 is nearly flat bottomed and with a gentle radius entry, which would say to me that the chosen wing airfoil is at least as important as the rest of the airframe's drag inducing struts and rigging. It also has a generous aspect ratio, i.e. the wing's chord is quite narrow to it's span, gliders generally have quite large aspect ratios.
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Ok did some testing on the Dr1 and it does not appear to be out of range.
With engine off we got 7.94 glide ratio which matches nicely with the chart.
If you are testing throttled back, you are getting a fair amount of thrust do to the hi ideal speeds.
PapaFox, what may be different with the great lakes is the size of engine and prop creating a lot more drag. Also did you great lakes have a fixed or constant speed prop?
HiTech
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I tested the F1 and lost 10k in 2/3 of a sector. I don't know the distance exactly but I believe it's close to a glide ratio of 8.
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I think that's closer to 9? 8.8?
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Yes. If I went precisely 2/3 of a sector it would be 8.8.
I landed a little short.
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Maybe I wasn't short. I went across a sector in a Camel and Dr1 and got 9.4 and 9. Engine off, prop windmilling, glide speed 60 for the Camel, 58 for the Dr1.
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Rather then fly so far, just measure the time it takes do descend 500 or 1000 ft. Then do the math from your speed in TAS.
HiTech
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Thanks. It occurred to me to do it that way, I even grabbed my stopwatch, but I went with the slower less accurate route for some reason. :headscratch:
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Clocked it for 1000 ft, 3k to 2k, TAS 61-60, so I used the lower one.
Prop windmilling about 400 for F1, 380 for Dr1.
F1 9.1 Time was 1:44
Dr1 8.9 Time was 1:41
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An easy way to do it is to use your speed autopilot and the E6B. Get in the condition you want (idled, engine stopped prop stopped, engine stopped prop windmilling) and engage the autopilot speed. Use the .speed command to test at different speeds. Pull up the E6B display and record TAS and descent rate once a steady state is reached.
Convert your TAS and descent rate into the same unit, either FPM or MPH is fine. Remember that your airspeed is traveling along the hypotenuse of a right triangle. Your rate of descent forms one leg and you need to calculate out the last leg which is the distance traveled over the ground. The ratio between the ground leg and the descent leg is the glide ratio. So you need to calculate that leg using trig or geometry and divide the result by your rate of descent.
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That's pretty much what I did the second time Pyro. I assume I'm getting higher numbers because I didn't stop the prop. I had expected that windmilling would increase drag. I'll have to try it again with the prop stopped.
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FLS a STOP prop will glide better, but are you just throttling back or shutting the engine off.
HiTech
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I shut the engine off then waited a bit for the rpm to stabilize before I measured.
Pyro mentioned converting the distance traveled on the hypotenuse to the ground distance traveled and that's what I left out. I used TAS as if it was ground speed. I misunderstood what he was saying initially but it's clear now. Thanks for the help.
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I shut the engine off then waited a bit for the rpm to stabilize before I measured.
Pyro mentioned converting the distance traveled on the hypotenuse to the ground distance traveled and that's what I left out. I used TAS as if it was ground speed. I misunderstood what he was saying initially but it's clear now. Thanks for the help.
without wind, tas = gs
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Kvou75 that's true if you fly straight and level. The point Pyro made here is that I was descending, so the distance I traveled in the air between my start and end point was greater than their distance on the ground. Since I didn't allow for that my glide ratio was high. The F1 actually tested at 5.27 instead of 9.1, which shows the drag from the prop windmilling.
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Kvou75 that's true if you fly straight and level. The point Pyro made here is that I was descending, so the distance I traveled in the air between my start and end point was greater than their distance on the ground. Since I didn't allow for that my glide ratio was high. The F1 actually tested at 5.27 instead of 9.1, which shows the drag from the prop windmilling.
Oops, forgot time of flight. That should be 8.9 not 5.27. I still think I'm off though.
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I owned a Gere Sport Biplane for a couple of years, and that thing dropped like a rock after you cut power. A couple of pics:
In the cockpit:
(http://home.comcast.net/~dccowan/biplane/geredan1.jpg)
Flying just south of the US/Canadian border (Orcas Island to KBLI):
(http://home.comcast.net/~dccowan/biplane/gerecc.jpg)
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I owned a Gere Sport Biplane for a couple of years, and that thing dropped like a rock after you cut power. A couple of pics:
If you got a skinhead you'd probably add another 5 minutes to your glide time :D :neener:
Nice plane, must've been a blast tooling around in her :aok :aok
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Very cool plane Biggles!