Vr speed

[Bok269]

I've been thinking about how Vr compares across different commercial airliners. Since ie an ERJ and 737 cruise at similar speeds, do they rotate at a similar speed? Or does it vary because the ERJ is a smaller airplane requiring less lift?

[mikecweb]

I've been thinking about how Vr compares across different commercial airliners. Since ie an ERJ and 737 cruise at similar speeds, do they rotate at a similar speed? Or does it vary because the ERJ is a smaller airplane requiring less lift?

Similar is a pretty relative term so you could say yeah. But Vr speeds vary alot depending on weight. Our Vr speed will vary over 20kts depending on weight.

[gu.camargo]

For example.... in the flights from Brazil to Europe, VR of the most palnes is about 260 - 270 kts. In the domestics flight of here, 130 - 140 kts. Planes like 737, 767, MD-11 etc...

[Rjuncker]

For example.... in the flights from Brazil to Europe, VR of the most palnes is about 260 - 270 kts. In the domestics flight of here, 130 - 140 kts. Planes like 737, 767, MD-11 etc...

Hmm... Unless the Concorde flies from Brazil to Europe, I would have to disagree on VR speeds of 260-270 knots. It sounds like there's a confusion of speed there. On the jumbo I've never seen VR speeds at more than, say, 160. 260-270kts sound more like a best angle of climb speed to me (Vx) or it sounds like VR for a fighter maybe, but I wouldn't know about fighters, so others will probably correct me on that.

And for the original question. You can't really say that because two planes cruise at the same speed, they should have the same VR speeds. Those are two completely different things. Obviously cruise speed can vary a bit, depending on weight and what kind of speed the company wants (Long range cruise, Economy etc.), but the variation is very small.

As someone mentioned earlier in this thread, the VR speed can vary a lot for a lot of various reasons. Of course weight is a factor, but also consider the length of the runway, obstacles, contaminated runway, intersection take off, are you derating the engines (as happens most of the time) and so on and so forth. So you can see that there's no real comparison between the two.

Just for good measure, these things are correct for the planes I've flown. There might be some obscure Russian design out there that behaves differently, but I doubt it.

I hope this clarifies your question

[N9103M]

As someone mentioned earlier in this thread, the VR speed can vary a lot for a lot of various reasons. Of course weight is a factor, but also consider the length of the runway, obstacles, contaminated runway, intersection take off, are you derating the engines (as happens most of the time) and so on and so forth. So you can see that there's no real comparison between the two.

As far as VR is concerned, it varies dependent on weight and takeoff flap position.

All the contributing factors you described (Runway Length, Contamination, etc.) have more effect on V1 speed (Takeoff descision speed).

In preperation for a flight, you determine your Maximum Takeoff Weight using runway analysis which basically tells you the maximum weight you can take off on a runway given a certain temperature.

That weight takes into account runway length, temperature, climb requirements, engine out performance, etc.

You then compute V-speeds based on your takeoff weight. The heavier you are, the higher the speeds. Usually a greater flap setting (i.e Flaps 25 vs. Flaps 15) will lower your VR speeds due to the greater lift produced.

[Rjuncker]

As far as VR is concerned, it varies dependent on weight and takeoff flap position.

All the contributing factors you described (Runway Length, Contamination, etc.) have more effect on V1 speed (Takeoff descision speed).

I understand that, but since the original question was about Vr, then I used that as an expample. The thre V speeds (1,r,2) are all intertwined and the thus if you change V1 based on the things we both mentioned, you change them all (for all practical purposes).

[Bok269]

THanks everyone for clearing that up.

[AJ]

Here are some notes for you from the Boeing 767-338 Performance Limitations Manual:

Rotation Speed Vr
Generally must not be less than V1, 1.1 Vstall and it must result in a lift off speed which exceeds minimum unstick speed (Vmu) by 10%, or 8% if geometry limited.

The 767-300 is "geometry limited", that is tail scrape prevents it assuming a ground attitude which would seriously reduce ground acceleration. However, Vr exceeds 1.10 Vmu so the aircraft's certification does not rely on this characteristic.

Vr must also result in achieving V2 (engine out) by 35 ft height and it is this consideration which settles Vr for the 767 at medium to heavy weights. At lighter weights however V1 determines Vr.

All clear then?

[Rjuncker]

And so on and so forth. The 35 feet for V2 is only valid for non contaminated RWY. Contaminated RWY it's 15 feet. And so we could go on. I was just trying to keep it simple. I'm down route and don't have my books with me, so I think I did quite well, off the top of my head.

[AJ]

And so on and so forth. The 35 feet for V2 is only valid for non contaminated RWY.

Which would be 90%+ of all take offs in the Boeing 767-338

[Rjuncker]

Which would be 90%+ of all take offs in the Boeing 767-338

LOL. You don't give up easily do you? But, of course you're right. I just didn't think the initial question was limited to Qantas B767.

[AJ]

No, just my answer! It is great to be able to provide information from many different aircraft types...although we need a few Airbus convertees to balance out any discussion!

[Rjuncker]

No, just my answer! It is great to be able to provide information from many different aircraft types...

Yes, the answer is correct for a B767 operated by Qantas, but not for the aircraft type in general.

[/QUOTE]although we need a few Airbus convertees to balance out any discussion![/QUOTE]

And you're absolutelu right. Are there any Airbus pilots on the forum?

[AJ]

My post started 'Here are some notes for you from the Boeing 767-338 Performance Limitations Manual:' which sort of indicates that it was for a 767-338!

[Rjuncker]

My post started 'Here are some notes for you from the Boeing 767-338 Performance Limitations Manual:' which sort of indicates that it was for a 767-338!

There there, no need to get angry. I'm messing with you AJ. If you follow the thread continously, you started to talk about how 767-338 is operated on non contaminated RWY 90% of the time. Then in your next reply you on about how it's good to get info for different aircraft type. Since a type rating cover a B767 (in this case), then you can't say that the answer is true for the type.

Don't put too much into this. I jus like a good arguement and to play with the words andsentences being used in that arguement. I truly don't wanna upset anyone.

So, for all practical purposes: I fold and you're absoultely right.