V Speeds (New Owner)

[blueldr]

CF-HEW,

Where in hell is MHV? I live live near MHR and fly out of O70.

Instead of airport identifiers, why don't we use names of places that the vast majority of readers are not likely to know?

MHR= Mather airport, Sacramento, CA
O70= Westover Field, Jackson, CA

[cessna170bdriver]

C'mon Dick! Get over yourself! MHV is only a half tank of 170 gas from you. If you'll take about 15 seconds and check airnav.com you'll see that it's Mojave Airport. Sounds like she's goin' to the boneya... er, uh, I mean, uh, "flyable storage" out here in the desert.

Miles

[c170b53]

604 is or was one of our better 200"s.

[dacker]

Going back to Brad's post (if I understand what you are saying), pull the power back with wings level and whatever the ASI says is best glide???
In that case, depending on your airspeed/trim combination your airspeed could do any number of things... it is not going to automatically go to 76 mph (which in my engine out practice is a good target speed). In my experience if I pull back to idle @ 118 mph, then my airplane noses over and tries to maintain roughly 118 mph, that certainly isn't best glide. Do I not understand what you are saying?
David

[dacker]

After I typed my last I realized that what Brad might be saying is to maintain the pitch attitude at what it was before pulling power while in level cruise flight, not necessarily wings level (to me that means longitudinally level, i.e. roll). Am I correct? I have heard this "rule of thumb" before, but I think that I personally prefer to use a target airspeed and adjust for conditions.
David

[CF-HEW]

I believe it's whatever the speed is with the trim all the way back. Speed is controlled by your elevator, not your throttle. Therefore if you are in level flight at 100 mph and your engine fails, you will continue to fly at 100 mph until you retrim. As far as I know if you trim full up and let everything go you should be at best glide.

[jrenwick]

There are things being said on this thread that I've never read before. I've boned up on aerodynamics pretty heavily within the last couple of years, and I haven't run into this about throttling back to idle and letting your airplane tell you what best glide speed is. If someone knows a source for this, like an aeronautical engineering textbook or something else in the aviation technical literature, I'd really appreciate a reference so that I could learn about it in detail.

Because if true, it certainly is interesting!!!!

Best Regards,

John

[Jr.CubBuilder]

As far as I know if you trim full up and let everything go you should be at best glide.

Haven't heard that one before. I think that could potentially lead to a stall depending on how the plane is loaded.

[dacker]

I agree about not trimming all of the way back power off... on my airplane in most conditions that will put me at somewhere around 50 mph, certainly not best glide and very close to published gross wt. stall speed. I have flown 172s that this works well on, but I don't think this has a relationship to "rules of aerodynamics" as much as it is an airframe/rigging thing. In other words a "technique" that may work on some C-172 models.

John, throttling back to idle and letting your airplane tell you what best glide speed is simply not going to work. My question about this was to Brad from an earlier post that I was trying to clarify. I don't think that I understood what he was trying to say, but I will let him answer that.

I learned to fly the numbers, and that is what will usually work as the most conservative technique. That being said, attitude flying (I think that is what Brad was talking about) is a part of our flying skills that should be developed, and I would think is certainly used by us all, i.e. set an attitude then cross check instruments etc. I assume this since our airplanes are mostly a VFR fleet.

This is the point where I borrow someone's saying about my opinion being worth what you pay me for it!

David

[flyguy]

Similarly, the seaplane speeds for those manuevers is computed at a wt 75 lbs heavier and might lead one to feel one could develop a guide or graph, but I believe that any such method might not be accurate considering that the seaplane has additional structural considerations lacking in the landplane. The AFM tells us that the seaplane Va is 105... regardless of Cessna's differing recommendations for those maneuvers...

With very limited time in a C170 on floats I had to smile. If most are like the one we ferried about 1500 miles, I suspect that a pilot would have to be in a very steep descent to get one of them up to 100mph!

On the "best glide" computation,with all other things taken into consideration, there is another factor that will increase the distance over the ground you can cover for altitude lost. That is a prop that is stopped! One spinning but not pulling is pure drag+. In a catastrophic engine failure it may not be pertinent, but if you run out of fuel and need to go as far as possible to a safe landing, the spinning prop adds a lot of drag. I don't know whether the altitude you would lose to stop the prop dead would sacrifice precious altitude for distance gained.

What about it "Resident Engineer" Miles?

[bradbrady]

I think that people are reading more into my post than is there....The rule of thumb that I learned was.....pull the power, Level the bottom of the wings to the horizon, hold whatever pitch it takes to keep the wings level to the horizon, allow the aircraft to settle down, the speed that is indicated on the airspeed indicator will give you best glide, in that aircraft at that weight. Being a firm Nonbeliever in rule of thumb.......I have tried this on 152's and 172's with a book value for best glide and it always works out close to book value. The ones that didn't, usually had rigging issues.......

[jrenwick]

...Level the bottom of the wings to the horizon, hold whatever pitch it takes to keep the wings level to the horizon...

Ah! That was the missing piece. Now it makes sense -- thanks!

John

[GAHorn]

What a convoluted discussion this has become.

If we are intent on disregarding what the factory test pilots and engineers already have tested and found.... then the simplest method to determine best glide speed is to fly the airplane (with prop rotating or stopped...whatever configuration in which you expect to need the best-glide-speed information)... and observe the vertical speed indicator. Best glide is the IAS which gives the least VS/descent.

While it may coincide with what appears to be a "level" lower surface of the wing... I doubt anyone here has an eyeball calibrated sufficiently accurate to determine what is exactly level, while observing the forward motion sufficiently to find a landing spot and miss the power-lines.

[lowNslow]

Best glide is the IAS which gives the least
VS/descent.

George, once again you are confusing "best glide" with "minimum sink". Glide would be determined by dividing your speed in ft/min by VS in ft/min. The speed which gives you the highest ratio would be "best glide" for that weight in no wind. I.E. 75kts = 7595ft/min divided by VS of say 700ft/min would give you a no wind glide of about 11:1. Minimun sink would be as you say the speed which gives you minimum VS.

All math aside tho and probably the best technique for a 170 would be trim it up 75 mph plus half the estimated headwind - you'll probably be close enough to "best glide".

[bradbrady]

George,
What is so convoluted about this discussion? If you have NO reference where do you start? The man that taught me this rule of thumb bought an aircraft in ST. Louis, in 1920 something, and taught himself how to fly it on his way back home to Kankakee IL. I'm not saying disregard the numbers that Cessna or others have come up with.........But if they don't give them to you...........how do you find them? this works.......anyway how does Cessna come up with these numbers?....Remember Xwind is at the time the aircraft was flown.......Everybody has at one time or the other exceeded these numbers!!!!!