Not stalling not stalling. I can feel it's close. As long as you stick to DMMS the airplane won't stall.
Engine just died, okay. Uh pitch for best glide. And at this speed I can maneuver. Uh engine is dead, okay.
Check that side. Where am I gonna land, where am I gonna land? In this video I will thoroughly test the
DMMS in my aircraft by pushing it until it stalls to unequivocally determine if it is a foolproof
anti-stall system or not. What's up everyone I'm A Private Pilot and Aviation Enthusiast and this is
Let's Go Aviate. In case anyone isn't sure what DMMS is, it stands for defined maneuvering speed
It is a minimum speed at which an aircraft can be maneuvered without fear of stalling in the event
of an engine failure. And that includes accelerated stalls. To calculate DMMS for any aircraft you take
the stall speed in clean configuration or VS1 and multiply that by 1.404. While the DMMS concept
is not new it's revolutionary yet simple. It promises to be a foolproof anti-stall system
that can save pilots from inadvertent stalls at spins. Yet there are still Pilots all over
the world and keyboard warriors all over the Internet kicking against the concept. So let's
get into the air and find out firsthand if you can trust DMMS with your life.
Ok, so to demonstrate it we are going to slow down to 70 mph
which is the DMMS for this aircraft
no flap selected. So let's start by doing 30 degree turns trying to maintain 70
miles per hour maintaining height and see what happens okay let's start to the left
Clearly this is fine. Do one to the right
And just dipping below 70 actually there. We're not done testing quite yet but at this point it
seems like DMMS works. So why is it not a more established concept why is DMMS not taught
as a hard rule in all flight schools? There are several arguments against it and here
are some of the ones I see and hear most often. An aircraft's safe maneuvering speed it's different
that every flap configuration and a different weight so single speed cannot be correct in all
configurations. Well technically that is correct and that is why DMMS is calculated based on Vs1 or
stall speed in clean configuration. An aicraft's published stall speed should always be for the
aircraft at max all-up weight. So as long as you don't exceed it DMMS will be valid up to
max all up weight. Same thing for different flap configurations. Stall speed with flaps is always
lower than stall speeds in clean configuration. So if DMMS is valid for the airplane clean it
is also valid - with additional safety margin - at any other flap setting. Another argument I
is; you should not be flying on the airspeed indicator you should fly on feel. While I don't
agree that that is good advice for all pilots, I fully accept it as a way that proficient pilots
can fly small aircraft. Keep the follow in mind though. One can't expect student pilots or low hour
pilots to fly on feel alone. It takes many hours of training to build a reliable baseline. The same
goes for pilots who aren't currently proficient. But on the other hand any pilot can read an
airspeed indicator and understand it without needing to be proficient. Now the question I've
seen are related to what the limits of the DMMS are. Some are saying 30 degrees angle of bank
some are saying 60 degrees angle of bank, and how much tolerance is built into it? Will it prevent
stalling up to 60 degrees and stall at 61 degrees? How careful do you need to be when flying at DMMS?
Let's go back into the air and test it. Lets do it by maintaining the DMMS and doing a 60 degrees of bank
and lets see what happens. Okay so hopefully you can see my uh this ASI. Ok lets start to the left
Ok we got a bit below 70 there
let's do one do the right
So clearly the airplane isn't anywhere close to stalling flying at the defined minimum maneuvering
speed of 70 miles per hour at 60 degrees angle of bank and I think I know why that is
To calculate DMMS you use the clean stall speed multiplied by 1.404
Now the clean stall speed I use, that you should you, is the one stated in the POH
which for this aircraft is 50 mph. But the stall speed in the POH is
for your aircraft at maximum all up weight unless otherwise specified
But clearly I'm not at maximum all up right so I'm only one person on board, about half fuel and not
really any baggage. Some I'm way below maximum all up weight.
So my stall speed in clean configuration is
actually going to be a bit lower than it is a smaller way so to fully test DMs I need to
determine the store speed for the plane on the day then you multiply that by 1.404 and then retest
Lets see what the stall speed is for this aircraft, clean, at the current weight. So we're going to do a clean
stall and use that number to calculate the actual DMMS in this configuration.
Clean. Start pulling back.
42, 41. Want's to break.
Not braking. 40, 41.
40 miles an hour. 42 on that one.
And she's not breaking but let's work on 42. Okay so 42 times 1.404
that's about 59 mph if I'm not incorrect. So actually I should be doing the test at 59
miles per hour. Okay, 59 / 60, let's work around there. Lets do a turn to the right, 30 degrees
Seems to be okay let's go to the left
59, OK, 30 degree angles of bank.
So clearly, at 30 angles of bank at DMMS
the aircraft isn't showing in signs of stalling. So let's push this to
60 degree angles of bank. Because that's what DMMS was designed for
To be able to make turns at maximum all up weight, 60 degree angle of bank
Ok that's 59
59 / 60
to the left, 60 degree angles of bank
Very nice. Do one to the right
okay
60 degree angle of bank, 58 miles per hour, 59 mph
with load
not stalling
Okay so even at my true DMMS 59 miles per hour
60 degree angle of bank it's not stalling, so clearly DMMS works
but I want to actually push it to the limit. I want to see at what angle of bank I'm gonna
stall flying at DMMS. So I should be very close to the stall at 59 mph, 60 degree angle of bank
so at about exceeding that 65 / 70 degrees angle of bank
I should be stalling. So I'm making sure I've got plenty of height for this so I'm
actually going to push this till it's stalls. at 59 miles an hour. Let's start to the right
Not stalling, not stalling, I can feel it's close
We're about 70 / 80 degrees angle of bank
Okay uhm haha. So I...I don't really want to pull harder than that because I don't
want to put G's on this plane I don't want to go above 2G's
This plane is rated for 4G's but I don't like to go anywhere near the limit
Yeah so that was about 70 to 80 degrees angle of bank
you can maneuver that plane. You can maneuver it to whatever field you
want to as long as you stick to DMMS the airplane won't stall
Okay so say I'm getting an engine-out now. Engine just died...OK.
Uhm. Okay pitch for best glide, first thing to do. We're actually gonna have to stay below that
we're going to be a DMMS way below best glide. And at this speed I can maneuver uh engine is dead
let's look for a field, uh okay look that side, nothing there
where am I gonna land, where am I gonna land. Engine is dead.
Okay there's no field there, let's go that side.
I like this road below me. There might be a bit of a wall next to it though. Let's keep the speed up
let's keep the speed up. I'm actually going to, ah let's look at that field
I actually like that road better
In real life you're not going to maneuver like that when you have an engine-out. You're probably going to stick to
30 degree angle of bank, maybe even 45.
Point is if you stick to DMMS you're not gonna stall
Now, I am actually gliding nicely
Okay, definitely have it made lets abort.
Interestingly I couldn't get the plane to stall at DMMS
even exceeding 60 degrees angle of bank. Note that it is difficult to maintain
altitude at around 80 degrees angle of bank without pulling serious g-forces and I didn't
want to put abnormal strain on the airframe. If I had been able to maintain altitude exceeding
about 70 degrees angle of bank I am sure an accelerated stall would have happened.
Thus for me I would add the additional safety margin of restricting banks at DMMS to 45 degrees that way
if you get a little bit hard-handed on a stick or a yoke or go a few knots below DMMS by accident
you have that additional safety buffer before stalling. The last test I did by determining the
actual stall speed of the plane on the day was just for testing purposes. The DMMS concept is
simple so I suggest keeping it that way and using the clean stall speed published in your
aircraft's POH to determine your aircraft's DMMS. I also suggest taking a thin piece of
tape on your airspeed indicator so you don't even have to remember what speed DMMS is, it will be
on your ASI. As might be evident in the video I haven't flown the Bushbaby in quite a while so
I should probably have been a little bit nervous about bringing it in to land. But thanks to the tip
revealed in this video which is guaranteed to improve your landings it was a breeze.