In general "Additional" Information is:

• In addition to that found in other documentation related to this product,
• Often reflects feedback &/or questions from users of the product.

Subject to the Conditions of Use, please review the attachments and related articles listed below. 

For those of you who may be wondering about flying a VMAR Bird Dog at High Altitude please see the general article on high altitude electric performance included further below.

---

In addition to the article included below, here is some feedback provided by a modeler flying a Bird Dog near Durango, CO at approximately 7000 feet above sea level.

He has equipped his Bird Dog as follows:

• AXI Outrunner 2808/24
• 3 Cell LiPo consisting of 2 x 2200mAh 3 cell packs in parallel for 4400 mAh total capacity.
• Using a Graupner Folding 10x6 Prop

Reports brisk reliable performance with this power system in the Bird Dog.

---

 

Question: I live at 5000 feet above sea level. What should I do to get my electric power system to perform at high altitudes as well as it does at sea level?

Answer: It's tough to get the same performance at 5000 or 8000 feet as you do at sea level but we do have a technique that will help you come close.

First of all it's important to understand a few things:

1) Unlike an internal combustion engine (i.e. glow or gas), an electric motor does not consume oxygen and hence could care less about oxygen or anything else that affects combustion.

2) An electric motor system that runs well at sea level will underperform at higher altitudes not because the air has less oxygen but because the air is thinner. Hot weather does the same thing... the air gets thinner. Hot and high together can really gang up and take a chunk out of the performance.

In order to get your electric motor system to perform in thinner air the same way it does at sea level, you may actually have to change the motor, speed control, battery pack and prop but before you go reaching for your credit card here is a technique that attacks the problem from the lowest cost component first.

1) Measure the watts that your power system consumes at sea level or other relatively low altitude location. Use a Medusa Power Analyzer or AstroFlight Whatt meter.

2) Better yet, if possible, use the Medusa Power Analyzer PRO thrust meter to measure the thrust generated and the watts consumed.

3) Now do the same measurements (1 & 2) at the higher altitude location. You will notice that your system consumes less watts and if you are able to measure thrust you will notice that you get less thrust at higher altitude than you do at lower altitude. This is because the air is thinner (less dense) at higher altitudes.

4) In order to get the thrust back up to where it was at lower altitudes you need the prop to move more of the thinner air. To do this, select a higher pitch and/or larger diameter prop for use at higher altitudes. Test again and try to find a prop that gives you the same thrust and/or watt values as you were getting on the original prop at lower altitude. If you can get the same thrust at 5000 feet as you got at sea level for example, you will have similar flight performance. Thrust is really the key here and it's best to work with thrust numbers but watts are a good relative indicator of thrust. Not perfect but still helpful!

Be cautious when testing to ensure that the motor, ESC and battery do not overheat with the new prop. Some compromising may be necessary to get good performance that does not overheat components.

In a perfect world, you would carefully select a specific motor, ESC, battery and prop to get the ideal combination for high altitude performance when installed in a particular model. Yup... perfect is best... but for those of us who can settle for a bit less than ideal and have limited budgets, changing the prop to generate similar thrust in high, hot & thinner air as you get in low, cool & thicker air is a good low cost way to go.    

Question: I have a VMAX #VMM-111B18VM VMAX Brushless Motor. What do I need in the way of mounting screws?

a) VMAX VMAX #VMM-111B18VM VMAX Brushless Motors that are supplied with VMAX Power Modules and VMAX Power Packs come pre-mounted with the appropriate screws for the motor.

 

b) The threads are 3mm and generally four 3mm x 6-12 mm machine hex head screws with washers will work.

 

c) We sell a Mounting Screw Set (#VMM-111B18MS) consisting of four 3mm x 10mm hex head screws. Hex head screws should be used with flat washers under the heads.

 

d) We also sell a Mounting Screw Set (#VMM-111B18MT) consisting of 16 mounting screws. Four screws in each of four different sizes/styles.

• 3 x 10 mm Hex head machine screws (4) (like VMM-111B18MS)
• 3 x 16 mm Hex head machine screws (4) (longer version of above)
• 3 x   6 mm Phillips countersink head screws (4) (for flush fitting)
• 3 x 10 mm Phillips countersink head screws (4) (for flush fitting) 

The four different sizes/styles allow for thicker firewalls, multi-layer firewalls where the screw heads must be countersunk between the layers, etc.

 

This set provides for a very wide range of different mounting methods.

 

Hex head screws should be used with flat washers under the heads.

Wrench and Socket Head sizes for the VMAR Bird Dog power module hardware are as follows:

For the Prop Nuts 7/32"

For the Power Module nuts (that fit on the four threaded studs that attach the firewall to fhe fuselage) 7/32" deep socket

For the four black machine screws that go through the firewall and thread into tapped holes in the motor mount (backing plate) 2.5mm Allen Wrench

For the 2 or 3 black grub screws that retain the motor into the backing plate are accessed via the slot between the motor the backing plate 1.5 mm Allen Wrench.

Question: When I am mounting wing servos in the VMAR Bird Dog, the wing strut attachment point washer is in the way of the mounting tab on one of the servos. What do I do?

Solution: This is easy to fix. Use a sharp #11 Xacto blade to knotch out the wooden washer as shown in the picture below. Takes about 15 seconds and you'll be good to go.

Note that this notching is only required where the strut washer and servo are in contact. This appears only to be an issue on production models up to November 2005.