What is the weight for VH ?

[wantobe]

VH is defined as the maximum speed in level flight with the maximum continuous power at sea level. What is the weight of the aircraft for VH? Is it that of an empty aircraft with a skinny pilot and minimal fuel ? or MTOW(Maximum Takeoff Weight) ? or any weight between these two extremes?

[steveinindy]

The standard (if there is one) should be listed in the FAR. However, I believe (with the possible exception of the LSAs) it may be left up to the "manufacturer" to decide it as when I went looking quickly, I saw no reference to weights. However, I came across this one a site about the Sonex aircraft:

specifying that speed at Vh must be measured under the following conditions: speed in level flight with maximum continuous power (Vh) of not more than 120 kts (138 mph) CAS (Calibrated Air Speed) under standard atmospheric conditions at sea level.

SOURCE: http://www.sonexaircraft.com/ads/rx/index.html

There may not be a weight stipulation. Either way, it should be tested in all conceivable and rational configurations during initial flight testing (and during design calculations for the purposes of determining structural loads) Are you designing your own aircraft or building something from plans or a kit? Unless you're doing a clean sheet design or drastically altering a design, you probably don't have too much to worry about it.

The only time (other than regarding structural concerns) that Vh has any real concern is when you're talking about an LSA. Other than that, it's just bragging rights.

[FlyingRon]

I would assume it would mean at any permissible loading. If we're talking the LSA limits, there likely isn't going to be that much of a difference, the usable loads are usually pretty skimpy.

[steveinindy]

If we're talking the LSA limits, there likely isn't going to be that much of a difference, the usable loads are usually pretty skimpy.

That's the big problem (well besides the slow part) with the LSA concept: you have a large meal and you're over gross. "Sorry Bob, looks like you're going to have to walk home. If there is a headwind above five knots you'll probably beat me there." LOL

[Check 6]

Here is the definition per ASTM 2245-10c (LSA certification)


3.2.33
VH—maximum speed in level flight with maximum continuous power (corrected for sea level standard conditions)

[FlyingRon]

Here is the definition per ASTM 2245-10c (LSA certification)
That's exactly the same one from 14 CFR 1.1.

It doesn't answer the question though.

[Check 6]

That's exactly the same one from 14 CFR 1.1.

It doesn't answer the question though.

Tough crowd. :) Maximum gross weight (there is a tolerance).

[Check 6]

For clarification, the maximum gross weight is ultimately set by the manufacturer, but not to exceed the 1320/1430# per the FAA. The weight of course could be less.

[wantobe]

I asked around. The answer from two DERs was the lightest possible weight. Not the maximum gross weight. I am designing from a clean sheet. Some cautions here include possible power plant upgrade in the future and speed estimation errors, so add a few knots to give some margin. Vh is a speed used for all aircraft, not just LSA.

[Check 6]

I am addressing S-LSA. It is maximum gross weight. I confirmed this with a member of the ASTM S-LSA certification committee, plus it is addressed in 2245-10c. A minimum weight would be an open ended number, e.g. the certification would depend on the weight of the pilot and how much fuel was carried which is not very exact. Maximum gross weight is more exact.

[Tom brewington]

VH is defined as the maximum speed in level flight with the maximum continuous power at sea level. What is the weight of the aircraft for VH? Is it that of an empty aircraft with a skinny pilot and minimal fuel ? or MTOW(Maximum Takeoff Weight) ? or any weight between these two extremes?
VH is a limit not a spec. For a given airframe: A higher GW will normally give you a lower VH. So if you must exceed FAA Gross (may be legal on international ferry flights, etc.) then lower your VH. Check the data sheets for the airframe in question.

[Frank Giger]

Weight is only one factor in all speeds to be determined.

Leaving props and engines out of it, configuration and construction matter.

There is little design difference between the Airdrome Morane and the Airdrome Nieuport 11 - except one is a high wing monoplane and the other a biplane with a bunch of wires hanging out all over it.

With the same engine/prop combo the VH is going to be higher in the Morane, as the sustained continous power that is healthy for the engine isn't fighting all the drag of the biplane.

But let's not throw props out; the pitch of a prop (climbing versus cruise) really do matter. If one gets the prop carved for climbing it's at the sacrifice of cruise speed....

VH is one of those things that come out for real in Phase I testing....