if i drive a car steep downhill, there is a significant different in breakpower depending to the "throttle" position, despite the rpm is the same.
Probably. I think it would depend on the speed though.
Theoretically, if a plane is already reaching the terminal velocity limited by its drag characteristics, would adding in more power make any difference? The speed in which the plane is travelling is already much higher than the engine could manage, and whatever thrust available is already overshadowed by gravity and inertia.
If you put a WW2 aircraft in a straight 90 degrees down dive, and it is nearing its critical mach - in this case, I don't think adding more throttle is going to make the plane dive any faster, nor losing throttle will lower its falling speed.
So I think we should first determine just what kind of dive we are talking about.
In a full powered dive, with a flat angle, where the plane just reach 800km/h with full power(in rather low alt to stay outside the mach related problems), the propeller dont will create much thrust, but as long as the engine turn the blades, they dont create as much drag as if the windstream have to turn them around.
I remember HT saying that a propeller is basically the same thing as a plane flying around with a circular disk of the same diameter in front of it. The drag is always there.
When testing the P-51D at about 30k, I noticed that (even with a pretty shallow angle) once the speed reaches over 420 IAS, the RPM crawls above 3000 - the max permitted for P-51D in emergency power. 420mph is merely 676km/h. Since I observed it in IAS, the TAS was probably more close to 500mph.
The RPM crawling over the 3000rpm constraint of the prop governer is clearly an indication that the prop turned into a windmill. It's not the power of combustion that pushed it over 3000, but the airpressure which does so - and that sounds like a really, really heavy drag to me.
How big the breakpower would be, if the pilot reduce the power to zero??
Again, I'm but a layman, so everything is just pure guess. But that being said, I think it wouldn't matter much when the speed is so high.
800km/h is roughly 497mph, and if we assume no difference in between the IAS and TAS it is already a speed which the airpressure windmills the prop to higher levels of RPM than permitted.
Normally, when the pilot pulls back on the throttle the prop governer will flatten out the prop blades to make it turn faster, to compensate for the loss of power and maintain the set RPM. In the case of the P-51 doing 500mph the RPM is already spinning higher than the permitted levels, so the drag is going to stay constant.
I know some divetests with P51s, where the propeller got removed, but i dont know other power settings while dives and what was the result if somone didnt reduce power.
It wouldn't make any difference, I think.
The plane is already diving really fast. Whether the power stays on or not the speed is near the critical mach. Pulling back the throttle is not going to make the plane slow down.
I imagine the difference would be only when the pilot tries to pull out of the dive - in which case, the throttle at idle will help with faster decceleration only when the nose is pulled up and more drag is added via rudders or etc..
Currently the 109s in AH dont stop to accelerate in a dive, even without power, is that ok??
That's what gravity does. Gravitational forces accelerate an object down to earth - upto its terminal velocity. Unless something happens, so the physical characteristics of the object changes, no falling object - powered or not - cannot exceed the terminal velocity dictated by its drag.
When you look at the E6B, no matter how much more power you add, or pull off, you will notice the plane will always stop accelerating at the critical mach - until the physical structure cannot hold up to the pressure any longer and fails.
For instance, with a quick test I've observed the Bf109K-4 has a critical mach of 0.81. Even at the maximum possible throttle setting, the K-4 cannot exceed 0.81. Even when going straight down to earth at WEP, the plane stops at mach 0.81 and holds there. When you pull the throttle back, the change in the setting momentarily pulls down the speed to mach 0.80, until the freefall accelerates it back to 0.81.
