VNE speeds GA vs RA

[shafs64]

Hi

 

I started in GA flying then moved over RA. I have noticed on RA aircraft that the difference in cruise and VNE is very small compared to GA types.

 

 

[Ultralights]

they shouldn't have, the VNE is a result of design parameters. unless of course one model has a differing weight

 

 

[ayavner]

what's an example?

 

 

[Jabiru Phil]

Foxbat?

 

 

[ayavner]

No I meant for shaf's to give an example of the disparities - what are the numbers? just curious.

 

 

[aj_richo]

Sonex cruise 100-130 kts (depending on engine) VNe 171 Kts

 

 

[facthunter]

I can accept that generally Vne is lower on U/L's than aircraft that aren't built to weight limit. The closeness of flap speed to clean turbulence speed is common too. The required low stall speed dictates lower wing loading or a high lift wing section often too. Nev

 

 

[poteroo]

The closeness of flap speed to clean turbulence speed is common too

Nev, Are you coming from the fact that when flaps are extended - the max +ve load factor (3.8) is halved to 1.9? So once you extend flaps, the 'turbulence' speed is going to be considerably lower. In fact much so. Calculation sq rt of 1.9 x Vso = ? It looks like these LSA's with 85 KIAS Vfe numbers could do themselves some injury if they strike severe turbulence while manoeuvring with flap extended. The rougher it gets on approach, or flying at low levels - the less inclined I am to extend any flap at all....much prefer to know that my +ve LF is 3.8 Comment?

 

 

[facthunter]

I'm not suggesting that the flaps be lowered as a method of coping with the turbulence as the range of allowable airspeed is reduced, and as you point out the structural considerations are important also.

 

I relate to the situation during the approach and land phase in turbulent conditions, where the speed you should be at clean is above the flap speed so you fly a bit slower clean than I like to to ensure the flap extend speed is not exceeded..There is also the considerable increase in drag on some aircraft (like a Technam echo??) that requires a significant pitch change or increase in power on extending flap. Nev .

 

 

[shafs64]

At the moment I private hire a sling and have notice. that the VNO is 110. and the VNE is 135. that not a big difference. And a C172 is around 165 vno is 110

 

 

[poteroo]

At the moment I private hire a sling and have notice. that the VNO is 110. and the VNE is 135. that not a big difference. And a C172 is around 165 vno is 110

Different numbers to our C172N (1980 model with 160HP) - which are Vne=158, Vno = 126, Vfe = 86. The given Va is for a range 97 - 80 kts depending on gross wt. Now it's instructive to note that Vs is 42 (KIAS) but this equals 50 (KCAS). Using the rule of thumb that Va = 2x the stall speed, (just under), then 50 x 2 = 100, which is very close to the given Va of 97 for gross weight.

 

The 172 cruises around 105 TAS, so at lower levels, it's IAS is up around the 100-105 mark - which is higher than Va, so we are careful about operating it in rough air at power settings giving over 100KIAS. Given that mostly these C172's are often operated at much lower than max gross weight, (with a correspondingly lower Va than 97), you can see why an eye needs to be kept on IAS in rougher air.

 

Now I'm unfamiliar with the Sling, but if it has a positive load factor of 3.8 at gross weight, then you can calculate Va by multiplying Vs by 2. With a Vno of 110, I'd be wondering just how high its' Va has been stated? A few manufacturers seem to be using Vno as Va - which is incorrect.

 

cheers,

 

 

[shafs64]

VA for the sling is 91

 

 

[poteroo]

VA for the sling is 91

Correct, and that's as it should be - because it's Vs = 45, so 45 x 2 = 90. The POH that I've seen says Vno = 120 and Vne = 135, so not a big range of yellow arc there. However, Va of 90 is well under Vno, and it's pretty close to the quoted cruise performances in the high 90's for 5000 rpm, (75%). The POH for this aircraft shows there is only pitot error at 40KIAS, ie below the quoted Vs of 45.