Try this. I also added width & height to control images user adds. Image will always be that size. 150 is default on my board for avatars, thus allowing images to look correctly.
Change those to fit your needs.
Below is your code, rewritten
Code:
$template_hook[postbit_userinfo_left]
<!-- / helis and modes start -->
<td class="alt1" valign="center" nowrap="nowrap">
<if condition="$post[field10]"><img src="images/helicopters/$post[field10].gif" width="150" height="150"></if>
</td>
<td class="alt1" valign="center" nowrap="nowrap">
<if condition="$post[field7]"><img src="images/modes/$post[field7].gif" width="150" height="150"></if>
</td>
<!-- / helis and modes end -->
<!-- / motors start -->
<td class="alt1" valign="center" nowrap="nowrap">
<if condition="$post[field11]"><img src="images/motors/$post[field11].gif" width="150" height="150"></if>
</td>
<!-- / motors end -->
<!-- / radios start -->
<td class="alt1" valign="center" nowrap="nowrap">
<if condition="$post[field9]"><img src="images/radios/$post[field9].gif" width="150" height="150"></if>
</td>
<!-- / radios end -->