wuzak
Captain
I went away for less than half a day and 4 pages were added.
Groundhog Thread Part Deux - P-39 Fantasy and Fetish - The Never Ending Story (Mods take no responsibility for head against wall injuries sustained)
- Thread starter greybeard
- Start date
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I went away for less than half a day and 4 pages were added.
Thumpalumpacus
Major
Most probably haven't noticed, but I think most of the likey-type things I've offered here have been the "informative" check-marks, because I'm learning so much about the capabilities not only of specific airplanes, but of the thinking in general that lays behind planning a flight, or -- gasp! -- a mission.
Shortround6
Major General
No, you can't do it that way.
It doesn't take into account the different internal friction and supercharger drive requirements.
Please look at the manual again.
Power level.............................HP .......................rpm.......................altitude....................fuel per hour.......................HP/hr/gal
MIlitary...................................1125......................3000.......................15,500.......................138...........................................8.15
Max continuous.................1000........................2600.......................14,000.......................109..........................................9.19
Economical max..................750.......................2280.......................14,000..........................74..........................................10.13
Minimum cruising (R).......600.......................2190........................14,000..........................52.........................................11.53
Minimum cruising (L).......600.......................2190........................14,000..........................48..........................................12.5
Please note that in above examples from the manual that in all but the Minimum cruise (L) the mixture was set to rich. All but the Military rating were at the same altitude.
Now when the engine goes from 600hp at 2190rpm to 1000hp at 2600rpm we have a 19% increase in rpm, a 60 % increase in power to the prop and a 209%increase in fuel per hour burned or about a 25% increase in fuel burned per HP hour.
I will throw it back at you.
Explain where the energy needed to over come the changes in internal friction and energy needed to drive the supercharger at the higher speeds come from, please.
Until you can then you are the one who is incorrect.
FLYBOYJ
"THE GREAT GAZOO"
I'm actually enjoying looking into performance data charts, brings back a lot of memories.
When I was working on my PPL I had an epic cross country experience. Darted thunderstorms, barely cleared the Tejon pass in SoCal, bucked 30 MPH headwinds, all in a C152 that survived a mid air, didn't fly straight because the eccentric wing bolts were installed wrong, and wanted to spin when stalled. Flew about 400 airmiles but the 3rd leg of the 300 mile requirement fell short at 298 miles. Because I was learning at a military 141 school (EDW Aero Club) one of my instructors reached out to a DPE and the FAA and I was given a "pass" on my cross country. The rest is History.
Fast forward several years later, I'm in Colorado working on my Commercial. Training at a 141 school and using the VA to finance my flight training, the chief instructor wanted me to re-do my cross country so "their records are clean". Rather then fight this, I decided to go along with it (at the recommendation of my father in law who was my instructor)
The quickest plane I was able to rent for this was a 180 HP C172 with a constant speed prop, all STC installed. It was a good flying bird and I felt comfortable flying it as I took it up several times locally. My plan was to do a short leg by my home airport and then go out 300+ miles into Kansas. Got the POH supplement, did all my calculations, good to go! More to come on that!!!!
All went well after take off but the plane was flying faster and using more fuel than what I calculated. After landing at Hays KS (it was a Sunday) it seemed like the whole town shut down including the airport FBO! After some quick flight planning, I pressed on to my alternate, Norton KS which was 90 miles to the north. I calculated that I would have about an hour of RESERVE fuel left. A bit frazzled about the situation, I took off out of Hays and while paying more attention to my charts rather to where I was going, I almost hit the town's church steeple right when services were letting out! I'm sure I got on someone's prayer list that day!
Arrived at Norton, no issues, but it looked like the FBO there was closed too! Right when I was starting to plan to sleep in the plane that night a pick up truck drove up and the airport manager saved me. I still noticed faster speeds and higher fuel burn.
Got on my way back to KBJC and continued to arrive at my check points 10 to 15 minutes early, WTF!!! Still not to worry, I had plenty of fuel to make it back home and I did.
What I discovered later was the flight manual supplement (for the 180 HP STC) was forged, someone took the amended performance pages and replaced them with copies of the stock pages so all my calculations were about 20% off. People been flying the plane like this for who knew how long! Least to say there was some ass chewing by the people who ran the FBO, the owner pleaded to me not to tell FSDO about this!
Love performance charts!!!!
When I was working on my PPL I had an epic cross country experience. Darted thunderstorms, barely cleared the Tejon pass in SoCal, bucked 30 MPH headwinds, all in a C152 that survived a mid air, didn't fly straight because the eccentric wing bolts were installed wrong, and wanted to spin when stalled. Flew about 400 airmiles but the 3rd leg of the 300 mile requirement fell short at 298 miles. Because I was learning at a military 141 school (EDW Aero Club) one of my instructors reached out to a DPE and the FAA and I was given a "pass" on my cross country. The rest is History.
Fast forward several years later, I'm in Colorado working on my Commercial. Training at a 141 school and using the VA to finance my flight training, the chief instructor wanted me to re-do my cross country so "their records are clean". Rather then fight this, I decided to go along with it (at the recommendation of my father in law who was my instructor)
The quickest plane I was able to rent for this was a 180 HP C172 with a constant speed prop, all STC installed. It was a good flying bird and I felt comfortable flying it as I took it up several times locally. My plan was to do a short leg by my home airport and then go out 300+ miles into Kansas. Got the POH supplement, did all my calculations, good to go! More to come on that!!!!
All went well after take off but the plane was flying faster and using more fuel than what I calculated. After landing at Hays KS (it was a Sunday) it seemed like the whole town shut down including the airport FBO! After some quick flight planning, I pressed on to my alternate, Norton KS which was 90 miles to the north. I calculated that I would have about an hour of RESERVE fuel left. A bit frazzled about the situation, I took off out of Hays and while paying more attention to my charts rather to where I was going, I almost hit the town's church steeple right when services were letting out! I'm sure I got on someone's prayer list that day!
Arrived at Norton, no issues, but it looked like the FBO there was closed too! Right when I was starting to plan to sleep in the plane that night a pick up truck drove up and the airport manager saved me. I still noticed faster speeds and higher fuel burn.
Got on my way back to KBJC and continued to arrive at my check points 10 to 15 minutes early, WTF!!! Still not to worry, I had plenty of fuel to make it back home and I did.
What I discovered later was the flight manual supplement (for the 180 HP STC) was forged, someone took the amended performance pages and replaced them with copies of the stock pages so all my calculations were about 20% off. People been flying the plane like this for who knew how long! Least to say there was some ass chewing by the people who ran the FBO, the owner pleaded to me not to tell FSDO about this!
Love performance charts!!!!
Charts? What are those? I don't calculate anything. I just hop in and go. I'm an expert.
FLYBOYJ
"THE GREAT GAZOO"
Besides, my instructor did not teach me anything. I taught him by golly.
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
The other factor that has to be taken into account, is that with large bomber formations, there is turbulence created by the lead bombers, so the ones further back are getting buffeted, causing constant flight attitude correction.
GregP
Major
Hey pben.
He gets it from the P-39Q manual, page 25, chart for 8100 to 7200 pounds ,with 75 gal external tank. First set of columns, there is an entry for 25,000 feet. It says 2600 rpm, 267 mph T.A.S., Full Throttle, 62 U.S. gallons per hour (max continuous power). The climb data from the same manual says it will climb at 750 fpm at 135 mph in a combat climb and 650 fpm at 140 mph in a ferry climb at 25,000 feet. Combat missions were at 3000 rpm and 44..5 " MAP. Ferry mission were at 2300 rpm, 31" MAP (page 23).
When he gets to 25,000 feet, the pilot has to reduce to max continuous (2600 rpm, F.T.), level off, and accelerate to 267 mph. He'd better be quick about it because the range is not much, so he has to turn around rather quickly.
Range is unknown because the range tables are at S.L. and 12,000 feet. Ain't much performance at 25,000 feet. An old Spitfire from 1941 could climb at 3 times the rate, was faster, and had better range.
Let's look at it for the P-39Q. Assume for the sake of argument we are on the drop tank from engine startup, to save arguments and get the best possible result.
87 gallons internal, 75 gallons aux tank. Total = 162 gals.
Climb to 25,000 feet at combat settings takes 13.1 minutes and eats up 39 gallons, leaving 123 gallons, per the manual. Assume we average about 140 mph (goes from 160 mph to 135 mph along the climb for best rate). That moves us forward about 29.5 mile. Let's call it 30 miles.
Assume we cruise at 25,000 feet at max continuous (2600 rpm, F.T., 62 gph burn). We have 36 gallons of aux tank fuel left. That's enough to go for a while 34.8 minutes at 267 mph T.A.S., if we instantly accelerate from the 135 mph climb speed to cruise speed. 34.8 minutes at 267 mph gets us 155 miles farther from home. We are now 155 + 30 = 185 miles from home and we drop the aux tank because it is EMPTY.
Sine we now have no external stores, we use the no external stores chart. Here's where it REALLY gets interesting. We don't change power because we are at full throttle, but our 267 mph T.A.S. with the external tank now magically jumps to 330 mph I.A.S. (if you believe the P-39Q manual). On a standard day, 330 mph I.A.S. becomes 498 mph! So dropping the 75-gallon tank somehow magically makes us accelerate from 267 mph T.A.S. to 498 mph T.A.S. , according to the P-39Q manual.
I think some marijuana was somehow involved in writing this manual. I'll make the assumption that they MEANT to say T.A.S. in both places. So, we now accelerate from 267 mph to 330 mph. Again, pretty doubtful, to me. But, let's run with it.
OK, we now run into our 10 minutes of combat at 25,000 feet and 62 gph and somehow, we manage to engage in this combat at 25,000 feet without losing any height and without getting any close or farther from home. Doubtful, but what the heck, let's ty it. The 10 minutes will eat up 10.33 gallons, leaving us 76.67 gallons of fuel, still at 25,000 feet and 330 mph T.A.S., which takes us 408 miles before we are a glider pilot.
But, suppose I want my half hour of reserve so I'm NOT a glider pilot. That means we only can use 45.6 gallons of the 76.67 gallons we have remaining, still at 25,000 feet and 62 gph, still at full throttle. That means we can only go 243 miles instead of 408 miles.
So, we went 185 miles, had combat for 10 minutes, and we now have 243 miles of range left. Our total distance we can travel will be 185 + 243 = 428 miles, so our combat radius range is now 214 miles and we end up over home base at 25,000 feet with 31 gallons of fuel remaining. Great.
We went from less than 190 miles range from my earlier post all the way to 214 miles range. We gained 24 miles * 2, or 48 miles. Nice.
But, to do that, we needed to be on aux fuel from takeoff (likely against procedures), needed instant acceleration from climb to cruise and instant acceleration from cruise with tank to cruise without tank, needed an instant turnaround at 214 miles, and we needed to have combat joined sometime AFTER we used up the entire aux tank, and also needed the combat to stay at 25,000 feet and get no closer or farther from home.
Offhand, I'd say we needed an absolutely ideal P-39Q mission to get a whole 214 miles from home. Definitely a niche airplane. And my earlier post with 170 - 185 miles of radius would be about right. And I don't think a P-39Q will cruise at 330 mph at 25,000 feet unless there really IS a flying pig somewhere in regular passenger service. At least you don't have to clear the plugs because you're already at full power.
This is futile, but was a bit fun, considering the 498 mph T.A.S. thing. A 498 mph P-39Q? Naahhhhhhhhh ....
Cheers.
He gets it from the P-39Q manual, page 25, chart for 8100 to 7200 pounds ,with 75 gal external tank. First set of columns, there is an entry for 25,000 feet. It says 2600 rpm, 267 mph T.A.S., Full Throttle, 62 U.S. gallons per hour (max continuous power). The climb data from the same manual says it will climb at 750 fpm at 135 mph in a combat climb and 650 fpm at 140 mph in a ferry climb at 25,000 feet. Combat missions were at 3000 rpm and 44..5 " MAP. Ferry mission were at 2300 rpm, 31" MAP (page 23).
When he gets to 25,000 feet, the pilot has to reduce to max continuous (2600 rpm, F.T.), level off, and accelerate to 267 mph. He'd better be quick about it because the range is not much, so he has to turn around rather quickly.
Range is unknown because the range tables are at S.L. and 12,000 feet. Ain't much performance at 25,000 feet. An old Spitfire from 1941 could climb at 3 times the rate, was faster, and had better range.
Let's look at it for the P-39Q. Assume for the sake of argument we are on the drop tank from engine startup, to save arguments and get the best possible result.
87 gallons internal, 75 gallons aux tank. Total = 162 gals.
Climb to 25,000 feet at combat settings takes 13.1 minutes and eats up 39 gallons, leaving 123 gallons, per the manual. Assume we average about 140 mph (goes from 160 mph to 135 mph along the climb for best rate). That moves us forward about 29.5 mile. Let's call it 30 miles.
Assume we cruise at 25,000 feet at max continuous (2600 rpm, F.T., 62 gph burn). We have 36 gallons of aux tank fuel left. That's enough to go for a while 34.8 minutes at 267 mph T.A.S., if we instantly accelerate from the 135 mph climb speed to cruise speed. 34.8 minutes at 267 mph gets us 155 miles farther from home. We are now 155 + 30 = 185 miles from home and we drop the aux tank because it is EMPTY.
Sine we now have no external stores, we use the no external stores chart. Here's where it REALLY gets interesting. We don't change power because we are at full throttle, but our 267 mph T.A.S. with the external tank now magically jumps to 330 mph I.A.S. (if you believe the P-39Q manual). On a standard day, 330 mph I.A.S. becomes 498 mph! So dropping the 75-gallon tank somehow magically makes us accelerate from 267 mph T.A.S. to 498 mph T.A.S. , according to the P-39Q manual.
I think some marijuana was somehow involved in writing this manual. I'll make the assumption that they MEANT to say T.A.S. in both places. So, we now accelerate from 267 mph to 330 mph. Again, pretty doubtful, to me. But, let's run with it.
OK, we now run into our 10 minutes of combat at 25,000 feet and 62 gph and somehow, we manage to engage in this combat at 25,000 feet without losing any height and without getting any close or farther from home. Doubtful, but what the heck, let's ty it. The 10 minutes will eat up 10.33 gallons, leaving us 76.67 gallons of fuel, still at 25,000 feet and 330 mph T.A.S., which takes us 408 miles before we are a glider pilot.
But, suppose I want my half hour of reserve so I'm NOT a glider pilot. That means we only can use 45.6 gallons of the 76.67 gallons we have remaining, still at 25,000 feet and 62 gph, still at full throttle. That means we can only go 243 miles instead of 408 miles.
So, we went 185 miles, had combat for 10 minutes, and we now have 243 miles of range left. Our total distance we can travel will be 185 + 243 = 428 miles, so our combat radius range is now 214 miles and we end up over home base at 25,000 feet with 31 gallons of fuel remaining. Great.
We went from less than 190 miles range from my earlier post all the way to 214 miles range. We gained 24 miles * 2, or 48 miles. Nice.
But, to do that, we needed to be on aux fuel from takeoff (likely against procedures), needed instant acceleration from climb to cruise and instant acceleration from cruise with tank to cruise without tank, needed an instant turnaround at 214 miles, and we needed to have combat joined sometime AFTER we used up the entire aux tank, and also needed the combat to stay at 25,000 feet and get no closer or farther from home.
Offhand, I'd say we needed an absolutely ideal P-39Q mission to get a whole 214 miles from home. Definitely a niche airplane. And my earlier post with 170 - 185 miles of radius would be about right. And I don't think a P-39Q will cruise at 330 mph at 25,000 feet unless there really IS a flying pig somewhere in regular passenger service. At least you don't have to clear the plugs because you're already at full power.
This is futile, but was a bit fun, considering the 498 mph T.A.S. thing. A 498 mph P-39Q? Naahhhhhhhhh ....
Cheers.
SaparotRob
Unter Gemeine Geschwader Murmeltier XIII
A topic brought up earlier this thread. I just mentally scaled up the fleets of fighters to fleets of bombers. Great thread.
FLYBOYJ
"THE GREAT GAZOO"
Great post Greg!!!! It's funny, I came up with somewhat similar on a post about 70 pages ago!
I came up with a 140/ 150 mile range with out the drop tank. Amazing!
Great minds think alike!
Yep - Hempage was rampant during the development of this manual. I think a P-39 might make 498 MPH true while spinning to earth!
Groundhog Thread Part Deux - P-39 Fantasy and Fetish - The Never Ending Story (Mods take no responsibility for head against wall injuries sustained)
I felt like doing some math... So this is what I come up with, using those 2 charts posted and I used very conservative numbers except for take off weight, I used the fully loaded 8000 pounds, no wind condition to assume IAS will equal ground speed (for simplicity). Start with 120 gallons (per...
ww2aircraft.net
Last edited:
wuzak
Captain
Yep - Hempage was rampant during the development of this manual. I think a P-39 might make 498 MPH true while spinning to earth!
I was going to say that there were P-39s that could do 498mph TAS. They were known as Augers.
SaparotRob
Unter Gemeine Geschwader Murmeltier XIII
I do believe I understand it now. This post wasn't a bunch guys spitting numbers back and forth. Thanks GregP for explaining one side of the argument so I that I could understand the whole picture.
I haven't paid attention to the less dramatic aspects of aviation. I gave up on the jet fighter pilot fantasy when I got my first pair of glasses 60 years ago. That was after my dream of being a Coast Watcher. Studying flight plan prep was at the same level of reading tax codes. No reason to bother with it.
I started following this thread skipping past the numbers. The repartee is gold. That's how I got dragged into The Great Varmint's Burrow of Futility. I couldn't read the official reports posted. What was reprinted was too difficult for my eyes to focus on. So I started paying attention. I started learning (GASP).
Marcel, I am happy these guys keep coming back here.
FTL is right around the corner.
It seems almost all of the discussion is around miss prints and falsified tests. I couldnt understand how getting to 25,000ft was like getting into orbit for one particular aircraft, once there you can cruise at close to maximum speed using just a fraction of the fuel consumption used for climb or flat out runs.
buffnut453
Captain
And I still don't have an answer to my post #2746...and another page has been added since.
Mebbe I'll get an answer one day....but definitely not holding my breath.
FLYBOYJ
"THE GREAT GAZOO"
I think there's a few of you in the same boat here! LOL!
buffnut453
Captain
See? We suck you in with platitudes and then get you addicted on actual information. Come to the dark side...we have cookies!!!
At least that's how it's SUPPOSED to work but some people seem immune!
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
I've asked some honest questions during this protracted "conversation" that have gone unanswered, too.
It's aparent that the "authority" of Bell Products chooses to avoid engaging in a direct discussion that runs contrary to his beliefs for fear of having to acknowledge the short-comings of his diety.
So in short, yeah, don't hold your breath for a honest/truthful reply from the guy who would be the world's greatest used car salesman...
buffnut453
Captain
Sorry but I never buy anything from anyone who can't/won't answer basic questions about the item...and I would never deal with any salesperson who'd displayed such passive aggression.
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
And like you, there's about a dozen others here who aren't buying his shi...err...sales pitch, either.
But on the interwebs, there's quite a few sites where the uninformed would gobble his nonsense up as gospel (in essence, buying that low-mileage 1978 Gremlin that was only owned by a little old lady) and they wouldn't be the wiser.
But on the interwebs, there's quite a few sites where the uninformed would gobble his nonsense up as gospel (in essence, buying that low-mileage 1978 Gremlin that was only owned by a little old lady) and they wouldn't be the wiser.
