ACTUAL Glide Angle with Prop Stopped

[fodrv7]

Recently there has been the odd post regarding Engine Failure Glide Angle of RV Aircraft. Generating a lot of opinion, but little hard data.

Today, I flew a number of Climbs at various airspeeds and by selecting my GRT (Grand Rapids) EFIS to "Record" and was able to just concentrate on accurate flying. After landing, I ?Replayed? the flights whilst parked on the apron and casually wrote down the data! ????.. Oooh technology!

The GRT displays GMT, so recording the times through each altitude was a breeze.

After reaching 10,000' for the fifth time, I fondled the throttle closed, progressively, in order to sooth my glorious Aero Sport Power IO-360M1B, selected "Record" and when the throttle was closed, pulled the mixture lean, stopped the prop, trimmed for 80KT and let the GRT record the data.

Pushed the nose down and a windmill start had the fan turning at 120KT.

Back on the ground the data showed a decent rate of 882fpm and 902fpm timed between 8000' & 7000' and 7000' & 6000'

This equates to a glide ratio of 9:1.

So there it is.

Let the discussion begin.
Pete.

[Ironflight]

Great work Peter! I hope that you saved the data file, becasue you can run it through Carl Morgan's GRT Decoder and get even more precision and extract more info.

I might be slow, but are your two numbers (882 and 902 fpm) the values with prop stopped and prop windmilling respectively? And I forget your configuration - which prop?

I love it when folks post REAL data!

Paul

[Alex]

How did you get 9:1? Did you maintain 120 kts indicated for the data points you listed? If so, I get 15.5:1. Here's my math

882 fpm = 14.7 fps
120 kts indicated @ 8000 ft = 228.5 fps true

gamma = asin(14.7 / 228.5) = 3.688 degrees (flight path angle)

1/tan(gamma)=15.5

Thus I get 15.5:1


Also, can you estimate your gross weight when you conducted the glide test? Thanks.

Alex

[DGlaeser]

Originally Posted by Alex

How did you get 9:1? Did you maintain 120 kts indicated for the data points you listed? If so, I get 15.5:1. Here's my math

882 fpm = 14.7 fps
120 kts indicated @ 8000 ft = 228.5 fps true

gamma = asin(14.7 / 228.5) = 3.688 degrees (flight path angle)

1/tan(gamma)=15.5

Thus I get 15.5:1


Also, can you estimate your gross weight when you conducted the glide test? Thanks.

Alex

I believe the glide was at 80Kt (120 was to get the prop spinning).
Also, weight does not affect glide ratio. It does affect the speed for best L/D, so it would be good to see this done for a few other speeds.

Dennis Glaeser
7A - fuselage

[fodrv7]

Sorry, fellas. I was a bit vague with the details.

Previously I had found that the best glide L/D was around 70KT, but there is no way I would want to do a forced landing and cross the fence at 70KT as I am sure you would run out of airspeed in the flare.

So the figures were obtained at 80KT.

I would like to go and do it again with:
Prop full fine.
Prop full coarse
Prop Stopped
for comparasion.

Today was dead calm with DALR 0f 2?C. I will need to wait for another similar day.

I have already sent the file to Carl for decode and his amusement.

When I replayed the flight I was writing down the Altitudes and times from the PFD. I then selected ENG and there were all the Engine figures?. Except RPM which was zero.

Pete.

[Alex]

Missed the 80 kts number in your initial post. Sorry!

I see how you got 9:1 now, if you take Vtrue=Vindicated, or if the 80 kts figure was GPS speed. That comes out to 6.2 degrees flight path angle, which seems pretty good to me.

BTW if you use standard atmosphere and calculate Vtrue=90.3 kts @ 8000 ft, then you get 10.3:1.

[Kahuna]

Here is some actual data.
My Super 8 data

Best

[akarmy]

Hey Mike,

So could you elaborate a bit on your power-off to touchdown testing? I've done the 10K down to 2K glide tests with my 9a, but I'm wondering your setup to take it down to the ground. (runway size, preparation, etc?)

[Kahuna]

Circle to land approaches. 5k' runway at sea level. (I was at KPGD at the time)
Aim for mid field, and you might make the numbers. After a couple of tries, you get the hang of the tremebdous sink rate in a turn to rouchdown. Deployed flaps at about 50' agl.

Making a spot landing is quite a chore prop stopped, but you can do it with practice.
Now go pull that red knob out and try it. ( Oh my god he told people to shut their engine down). Yes I did. Its my advice and you can take it or leave it. All normal blah blah blah caveats apply. Practice high, work your way down to zero agl. If you think your nervous now to stop the engine, wait till it happens when you not fully prepared. Dont wait for that day to come. Being a glider is no big deal.
Idle (making some power) is not the same and not even close when you are on the last 500'.
Just my observation with my limited flight experience compared to some. And I have had an engine quite completely at the most unopportune time in an RV so I know it CAN happen to me .
Best

[alpinelakespilot2000]

Originally Posted by fodrv7

This equates to a glide ratio of 9:1.

So there it is.

Let the discussion begin.
Pete.

This is exactly what the cafefoundation reported for the RV8. So it sounds like you're about where you should be. They also reported 900-1000 fpm poweroff descent rate so, again, you seem to be in the ballpark.