Best Glide in an RG

[labbadabba]

Hi all - Flying a 172RG for a checkride coming up. Looking thru the POH, it has numbers listed for best glide and emergency landing airspeeds. What it doesn't indicate is if best glide is calculated with the wheels up or down. Through experience, the plane is VERY draggy with the gear out so I'm thinking no. But I was hoping to have an explanation for the DPE why I'm flying best glide with the gear up because the POH doesn't say either way.

 

[Grum.Man]

Best glide is just that, the airplane configuration that will give the longest horizontal distance per loss of altitude. If you are in a situation where best glide is required you would keep the airplane as clean as possible until the last moment, or if you are going to overshoot your planned touchdown point and need to slow it down.

 

[labbadabba]

Best glide is just that, the airplane configuration that will give the longest horizontal distance per loss of altitude. If you are in a situation where best glide is required you would keep the airplane as clean as possible until the last moment, or if you are going to overshoot your planned touchdown point and need to slow it down.

That was my feeling as well, I just wanted to make sure since it could be asked in an emergency landing scenario

 

[dmspilot]

What it doesn't indicate is if best glide is calculated with the wheels up or down.

Yes it does. There is a chart in Section 3 that specifies the configuration.

 

[labbadabba]

Yes it does. There is a chart in Section 3 that specifies the configuration.

You're absolutely right, under the amplified procedures for Engine Failure.

Thank you!

 

[SoCal RV Flyer]

Does the RG's POH list different best glide speeds depending on load?

 

[labbadabba]

Does the RG's POH list different best glide speeds depending on load?

Yes, but all under the same configuration. Would be really nice to figure out best glide with the gear out but it seems 80KIAS is where it's happiest flying power off 180s.

 

[MBDiagMan]

When doing emergency landing in a retractable, when to put the gear down is an important decision. In some situations, putting the gear down soon after power loss could be a good thing, like when you’re close to your chosen landing area and you need to get the plane down. That decision is an important part of your landing.

 

[luvflyin]

Hi all - Flying a 172RG for a checkride coming up. Looking thru the POH, it has numbers listed for best glide and emergency landing airspeeds. What it doesn't indicate is if best glide is calculated with the wheels up or down. Through experience, the plane is VERY draggy with the gear out so I'm thinking no. But I was hoping to have an explanation for the DPE why I'm flying best glide with the gear up because the POH doesn't say either way.

I’m looking at C172RG POH, 1980. It says propeller windmilling, flaps and gear up, zero wind. Page 3-11, Figure 3-1. That gives you the ‘angle’ of descent, how far you can go from a certain altitude. There is also the Best Glide Speed. The speed you should be at to get the best ‘distance.’ That changes based on weight. To the best of my knowledge, flaps and gear do not change what best glide speed is. But they will certainly change the ‘angle.’

 

[luvflyin]

Does the RG's POH list different best glide speeds depending on load?

Yes. See post above

 

[dmspilot]

To the best of my knowledge, flaps and gear do not change what best glide speed is.

Configuration changes will result in different lift/drag characteristics of the airframe. Best glide speed will be lower with gear extension due to higher parasite drag. I believe the same is true of flaps. As you noted, glide ratio will also be reduced even if the speed is compensated.

 

[Witmo]

Wouldn't best glide be a function of the airfoil and be a specific angle of attack? That angle of attack would be the same gear up or gear down. The speed for that best AoA would be the same but the actual glide distance would be less with the gear hanging due to extra drag. Changing the flap configuration changes the wing shape so the best glide angle of attack might change for different flap extensions but the best glide overall would be for a flaps and gear up configuration. Speeds would change for any given AoA at different weights.

 

[dmspilot]

Wouldn't best glide be a function of the airfoil

No, it is a function of the whole airframe, not just the airfoil.

and be a specific angle of attack?

For a given configuration, yes.

That angle of attack would be the same gear up or gear down.

It wouldn't, for the reason I described in the previous post. Extending the landing gear will add parasite drag which is zero at an airspeed of zero and increases at the rate of airspeed squared. Reducing airspeed will reduce the adverse effect of the extra parasite drag.