Reply
 
Thread Tools Search this Thread Display Modes
 
Old 03-17-2017, 12:18 AM   #29
3 Rivet Member
 
aircampr's Avatar
 
2015 23' International
Lake Forest Park , Washington
Join Date: Nov 2010
Posts: 125
Images: 21
Correction to my earlier post:

"The work required to raise 1000lb up 1000ft of altitude is about .377 KWh. So my rig, at about 11,000lb would require 4,15 KWh to go up 1000' hill plus the level consumption of rolling friction and aero drag. For a 5% grade, traveling a distance of 3.78 mi, that would add 3.78X.87 = 3.29 KWh for a total of 7.4 KWh. Running only on electric motor, I would be limited to a pass that gained about 2400' or so. Of course, if the e-motor contributes only half of the energy, then I could tackle a 4800' elevation gain. "

I would be limited to about 1148 ft. But if battery supplies 1/4 of total power, I could tackle 4595 ft of elevation gain.
__________________

aircampr is offline   Reply With Quote
Old 03-17-2017, 09:57 AM   #30
3 Rivet Member
 
2017 22' Sport
North Bay , California
Join Date: Nov 2016
Posts: 214
Images: 11
Quote:
Originally Posted by aircampr View Post
I concluded the electric motor (which is built into the transmission) would consume about .5 KWh/mi, and I used your figures with the Tesla X and 22' Sport to guess the towing consumption would be 1.74 times higher, so .87 KWh/mi.
500Wh/mi would equate to a 7kWh battery (with the 14 mile electric range). Is your assumption that there is only 7kWh available in that battery? I assumed 8.5kWh, which is reserving just over 5% for bricking avoidance. That takes me to my number of 607Wh/mi. 1.74x for towing (assuming that ratio is applicable) would bring you to 1058Wh/mi. I would also argue that the efficiency curve is not going to be as favorable on the X5 electric motor compared to the Tesla electric motor. I base this on the fact that the X5 uses as much energy without a trailer as my X does witha trailer.

Quote:
Originally Posted by aircampr View Post
Correction to my earlier post:

"The work required to raise 1000lb up 1000ft of altitude is about .377 KWh. So my rig, at about 11,000lb would require 4,15 KWh to go up 1000' hill plus the level consumption of rolling friction and aero drag. For a 5% grade, traveling a distance of 3.78 mi, that would add 3.78X.87 = 3.29 KWh for a total of 7.4 KWh. Running only on electric motor, I would be limited to a pass that gained about 2400' or so. Of course, if the e-motor contributes only half of the energy, then I could tackle a 4800' elevation gain. "

I would be limited to about 1148 ft. But if battery supplies 1/4 of total power, I could tackle 4595 ft of elevation gain.
I think you need to tackle this again with revised numbers, but I also think the most important thing is figuring out how manageable the electric assist is. I believe you'd want to manually manage it, keeping it off until you absolutely need it. I worry that it will be a distraction while towing, but that may be unfounded.

I certainly don't want to discourage the purchase of a more efficient vehicle.
__________________

ohmman is offline   Reply With Quote
Old 03-17-2017, 04:40 PM   #31
jcl
Rivet Master
 
Currently Looking...
Vancouver , British Columbia
Join Date: Oct 2012
Posts: 1,787
This article has some information on the various charge/hybrid modes on the 40e.

http://insideevs.com/1200-mile-bmw-x...ance-delivery/

My earlier comment about half battery capacity wasn't in relation to plug in charging, when it can be fully charged, but to charging over the road using the gasoline engine. I had remembered reading about a 50% charge. Perhaps it is a function of which combination of modes is selected by the driver.

Jeff
jcl is offline   Reply With Quote
Old 03-17-2017, 05:08 PM   #32
3 Rivet Member
 
aircampr's Avatar
 
2015 23' International
Lake Forest Park , Washington
Join Date: Nov 2010
Posts: 125
Images: 21
ohmman, thanks for your input. I agree my numbers are likely conservative, and also I expect the Tesla would perform better. So your numbers are very helpful. I later corrected the 2400 ft estimate, in post above.

I have tried a different approach: forget the electric performance for now, and assess the towing performance using gas engine only. I want confidence that we can tow the 23D uphill in a headwind without stalling. And i want some feel for what speed, gear and rpm could be maintained on different grades.

I used the above numbers for 55mph to compute a thrust force (tires against the ground) of 436 lb. As rough estimates, I assumed this thrust force was 0 lb at 0 mph, and 850 lb at 80 mph. (I will not be driving at 80mph ground speed, but that would be the thrust requirement at 55 mph with a 25 mph headwind - and I can draw through three points with a French curve). For uphill grades, and an 11000 lb rig, the gravity component is for example 1100 lb on a 10% grade. So this lets me draw curves of thrust required vs mph for different grades. These curves may be shifted to the right for tailwind and to the left for headwind.

The spec for gas engine in the 40e shows 260 lb-ft from 1250 to 4000 rpm (which if true is quite impressive). For thrust available, I used final gear ratios and 28" rolling tire diameter to estimate thrust force at the max torque. I could then plot the available thrust in each gear as a flat line (simplified, I know) between the mph ground speed for each gear at 1250 and 4000 rpm.

Some example predictions (for no electric motor boost) from this: The car should do 55mph up a 5% grade in 5th gear at 2700 rpm, or possibly in 4th gear at 3465 rpm. It might do 55mph up a 10% grade in 3rd gear at 4290 rpm, but I would likely slow down for comfort and fuel consumption. It could manage 35 mph up a 15% grade in a 45 mph headwind.

So, if these numbers for gas only performance are in the ball park, I am willing to try towing with the hybrid. As for electric performance, the energy of a 1000' descent with 11,000 lb rig is 4.15 KWh. So the batteries could be fully charged at 80% efficiency, I would have 8.5 KWh after a 2048' descent. As mentioned an an earlier post, one reviewer said the cars software may stop charging at 50%. I don't know why they would do that, but I have a question in to BMW.

Charlie
aircampr is offline   Reply With Quote
Old 03-17-2017, 05:16 PM   #33
3 Rivet Member
 
aircampr's Avatar
 
2015 23' International
Lake Forest Park , Washington
Join Date: Nov 2010
Posts: 125
Images: 21
Thanks Jeff. Yes, I have seen that article. I am going to find a resource at BMW, or maybe get my hands on a manual.

I am tentatively convinced that the hybrid will work towing the 23D, and that we won't get stuck halfway up some steep mountain pass even if the batteries are depleted. That little 2.0 liter I4 twin-turbo appears to punch above its weight. It is no match for the 3.0 liter turbo diesel, but if makes it over the hill going slow, we don't mind.

Charlie
aircampr is offline   Reply With Quote
Old 03-17-2017, 05:35 PM   #34
4 Rivet Member
 
AirstreamCSH's Avatar

 
2016 25' Flying Cloud
Huntington , New York
Join Date: Jan 2017
Posts: 325
Images: 1
Perhaps I missed it but does the door sticker show you have the payload capacity to legally and safely carry the weight. One thing to tow, another thing to carry.
AirstreamCSH is offline   Reply With Quote
Old 03-17-2017, 06:46 PM   #35
jcl
Rivet Master
 
Currently Looking...
Vancouver , British Columbia
Join Date: Oct 2012
Posts: 1,787
Quote:
Originally Posted by aircampr View Post
I am tentatively convinced that the hybrid will work towing the 23D, and that we won't get stuck halfway up some steep mountain pass even if the batteries are depleted. That little 2.0 liter I4 twin-turbo appears to punch above its weight. It is no match for the 3.0 liter turbo diesel, but if makes it over the hill going slow, we don't mind.

Charlie
I have driven that engine in other BMW vehicles. I found it responsive. To put it in perspective for towing with that hp, compare the hp and tow vehicle curb weight to a Ram 1500 ecodiesel. Lots of towing reports here on those. Some payload caution may be warranted, but owners don't appear to get stuck on mountain passes due to a lack of power, with the same 240 hp, and a heavier Ram truck, pulling up to a 25 foot Airstream (and some, larger). Your torque would come in sooner than most current diesels; my 535 with a twin turbo pulled very strongly from the 1250 rpm torque peak.

I will check the technical manuals and see if there is more on the 40e.

Jeff
jcl is offline   Reply With Quote
Old 03-17-2017, 06:47 PM   #36
3 Rivet Member
 
aircampr's Avatar
 
2015 23' International
Lake Forest Park , Washington
Join Date: Nov 2010
Posts: 125
Images: 21
I don't own this vehicle yet, but the manual says:

curb wt: 5220
front/rear: 2391/2829
approved gross wt: 6570
approved front axel load: 2750
approved rear axel load: 3870
aircampr is offline   Reply With Quote
Old 03-17-2017, 06:56 PM   #37
3 Rivet Member
 
aircampr's Avatar
 
2015 23' International
Lake Forest Park , Washington
Join Date: Nov 2010
Posts: 125
Images: 21
Thanks, Jeff. I did just find a Owner's Manual online. I am feeling more comfortable about this car the more I learn. I am getting some guidance from CanAm RV, and I will be looking for a local shop to install the Curt class III hitch, then reinforce it, as well as a brake controller. I have some Volvo towing mirrors which I have modified to fit the 2012 X5 and they are very nice. I will have to modify them again to shorten the upper arms due to the wider hood of the 2017.
aircampr is offline   Reply With Quote
Old 03-18-2017, 07:39 AM   #38
Rivet Master
 
switz's Avatar

 
2014 31' Classic
2015 23' International
2013 25' FB International
Apache Junction , Arizona
Join Date: Sep 2012
Posts: 5,347
Images: 8
We use the Hensley Arrow hitch. When I took the 2007 Mercedes ML320 CDI to CanAm to have the hitch re-inforced, they also shortened the stinger (which required a new lock pin hole in the stinger) to bring the rig closer to the car for better control and pre-bent it to make loading the weight distribution happen in 3" of travel of the screw jacks versus 4 or more.

While we started towing a 25FB International Serenity with the 15" Michelin tires, we quickly decided that was too much and went to a 2012 Ram 2500HD Cummins that now tows the 31' Classic.

I kept the Hensley Arrow for some reason when the 25FB was traded in on the Classic , which has the ProPride hitch (second generation Jim Hensley design). The Hensley is now on the 23D which got a tire upgrade from the stock 14" tires and wheels to the same model 15" Michelins we used on the 25FB and using design matching SenDel wheels like on the Classic. Thus both trailers (25FB and 23D) were/are at the same elevation off the ground and all the Hensley settings from the 25FB are correct for the 23D. In 2017, Airstream is now installing the usual 15" GYM tires on the 23D.
__________________
WBCCI Life Member 5123, AIR 70341, 4CU, WD9EMC

TV - 2012 Dodge 2500 4x4 Cummins HO, automatic, Centramatics, Kelderman level ride airbag suspension, bed shell

2014 31' Classic model 30 twin beds, 50 amp service, 900 watt solar system, Centramatics, Dill TPMS, disc brakes, 16" tires & wheels
switz is offline   Reply With Quote
Old 03-18-2017, 11:24 AM   #39
3 Rivet Member
 
aircampr's Avatar
 
2015 23' International
Lake Forest Park , Washington
Join Date: Nov 2010
Posts: 125
Images: 21
I have been reading the users manual for the X5 Xdrive40e and it is a very interesting design which partners a modest but competent ICE with an electric motor and modest battery pack. The two are designed to work together, and can be used to achieve a wide range of driving performance or fuel economy according to how the car is driven. There are an array of instrument and control screen displays (configurable) which can aid (and train) the driver in this tradeoff.

For short trips at home or at a travel destination, a charged battery can provide very low fuel consumption (or fairly high driving performance with 308 hp). The battery is not large enough to drive great distance on epower, but can be charged to recover energy on the downhill, which can be used either to reduce fuel consumption or enhance performance.

I expect there is potential to significantly reduce fuel consumption by rethinking how we drive and how we travel. This hybrid is not a direct replacement for our diesel X5, and could be disappointing if I tried to travel and drive it the same way. But I see this as an opportunity to learn how to travel more fuel efficiently, driving more conservatively and in shorter hops.

Charlie
aircampr is offline   Reply With Quote
Old 03-18-2017, 11:32 AM   #40
3 Rivet Member
 
aircampr's Avatar
 
2015 23' International
Lake Forest Park , Washington
Join Date: Nov 2010
Posts: 125
Images: 21
Switz, it is a long way from Apache, AZ to London, ON. I guess I might be willing to do that, but CanAm has been very helpful and forthcoming. I am waiting to hear from Andy of a shop near Seattle which can install and modify the hitch. Clearly Andy Thompson has and continues to contribute greatly to the RV towing community, and the world is a better place because of him.

Charlie
aircampr is offline   Reply With Quote
Old 03-18-2017, 02:40 PM   #41
3 Rivet Member
 
aircampr's Avatar
 
2015 23' International
Lake Forest Park , Washington
Join Date: Nov 2010
Posts: 125
Images: 21
From my earlier post: "The spec for gas engine in the 40e shows 260 lb-ft from 1250 to 4000 rpm (which if true is quite impressive). For thrust available, I used final gear ratios and 28" rolling tire diameter to estimate thrust force at the max torque. I could then plot the available thrust in each gear as a flat line (simplified, I know) between the mph ground speed for each gear at 1250 and 4000 rpm."

I hope these back-of-the-envelope estimates are at least in the ballpark:

Click image for larger version

Name:	Thrust_40e.jpg
Views:	76
Size:	392.4 KB
ID:	281626

The estimates of thrust (tire force on ground) for an 11,000 lb rig, for different % grades, are overlaid in red over the estimates of available thrust from the X5 40e hybrid using only the ICE (with no electric boost).

The available thrust is a function only of ground speed. The required thrust is actually a function of airspeed. So the graph as shown applies to zero wind speed. The red thrust-required curves may be moved to the left by an amount equal to a headwind, or the the right for a tailwind.

The 8 speed gearbox offers very high leverage in the lower gears. This is what allows the 4 cyl twin turbo to move an 11,000lb rig up a 15% grade in 35mph headwind in 3rd gear at 35mph and 4000rpm. I am OK with that, and the diesels can pass me.

If anyone sees a flaw in my reasoning or calculations, I welcome comments.

Charlie
aircampr is offline   Reply With Quote
Old 03-18-2017, 03:23 PM   #42
jcl
Rivet Master
 
Currently Looking...
Vancouver , British Columbia
Join Date: Oct 2012
Posts: 1,787
I think it is a challenge to calculate theoretical performance given the number of variables.

I would go back to a comparable vehicle, the 240 hp (with no electric assist) Ram 1500 3.0 ecodiesel, which has the same hp, the same ZF transmission, and weighs more. That diesel truck won't be passing you up the hills, even if your high voltage battery is completely flat and you are just relying on the 240 hp gasoline engine.

Here is some BMW info on the vehicle. No service manual info found so far, but there is lots of press material such as this. This is the info that goes to those writing those magazine articles.

https://www.press.bmwgroup.com/globa...07284EN/360732

I read the entire owner's manual. Interesting. But no mention of towing, except in relation to tow trucks.

Jeff
__________________

jcl is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Hybrid tow vehicle? Eleganza Tow Vehicles 7 01-01-2017 02:50 PM
Anyone pulling a 19' with BMW X3? carydgeller Tow Vehicles 13 07-13-2012 06:58 PM
Anyone towing 5,000 lbs with a V8 BMW X5? adwriter73 Tow Vehicles 20 06-17-2010 01:14 AM
Chrysler Aspen Hybrid to tow 16ft int'l toaster ab Tow Vehicles 9 08-07-2008 06:53 AM
Looking at Hybrid and Vintage Tow Vehicles rec Tow Vehicles 16 06-28-2007 09:20 AM


Featured Campgrounds

Reviews provided by

Disclaimer:

This website is not affiliated with or endorsed by the Airstream, Inc. or any of its affiliates. Airstream is a registered trademark of Airstream Inc. All rights reserved. Airstream trademark used under license to Social Knowledge LLC.




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -6. The time now is 07:55 AM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.