Jet Fighter vs. Propeller Fighter Turning Characteristics

[HoHun]

Hi everyone,

Since we've had serveral threads on jet fighter vs. propeller fighter turning battles on this board in the recent past, I thought a comparison of their basically different charactistics might be interesting.

The attached graph is the result of a simplified calculation for the turn rate fo two generic fighters, the jet fighter patterned loosely after the Heinkel He 162, and the propeller fighter loosely after typical US single-engined fighters.

I have not attempted to match the historical parameters accurately to avoid opening several cans of worms at once.

The basic difference between jet fighter and propeller-drive fighter is the thrust-over-speed function, with propellers yielding good thrust at low speed but dropping off at higher speeds, while jets provide roughly constant thrust over the entire speed range. In WW2, the absolute thrust of jets was not very high, so at low speed they compared unfavourably against the traditional piston-engine/propeller combination.

Regards,

Henning (HoHun)

[Soren]

A very good Idea Hohun,

But did you use similar CL figures and the right wing area figures ?

An important thing to remember also is that the jets will hold their speed in tight turns allot better than any of the piston engined fighters.

[Soren]

Btw, the thrust available to the He-162 should be higher above 450 km/h, and for this reason so should the turn rate. The BMW 003 provided about 805 kgf of thrust. At a standstill the average piston engined fighter has around 1,800 - 2,000 kgf of available thrust, this would decrease considerably at 450 km/h though and the BMW 003 should have a clear edge from thereon.

[davparlr]

Originally Posted by Soren

An important thing to remember also is that the jets will hold their speed in tight turns allot better than any of the piston engined fighters.

Could you expand on this some more? I would like to understand the principle behind this.

[Soren]

The jets are ALLOT less draggy Davparlr, and will therefore hold their speed in tight turns allot longer. This was a great advantage, one which is noted by both vet Me262 pilots as-well as British & US test pilots who flew the a/c. The He-162 would've been no different, except it didn't possess the same power to weight ratio.

Me-262's Allied POH, put together by US & UK pilot experience:
"(2) The airplane holds its speed in tight turn much longer than conventional types."

Luftwaffe test pilot, Hans fey:
"The Me-262 will turn much better at high than at low speeds, and due to its clean design, will keep its speed in tight turns much longer than the conventional type aircraft"

[HoHun]

Hi Davparlr,

>I would like to understand the principle behind this.

Here is the diagram again, indicating turns at constant specific excess power values (in 5 m/s increments) in addition to the turns sustained at Ps = 0.

The basic relationship between jet and propeller propulsion stays the same throughout the entire specific excess power range.

Regards,

Henning (HoHun)

[FLYBOYJ]

Ya know, I gotta agree with Soren's statement - in a jet you don't have scoops and cooling ducts, let alone that prop that although is producing thrust is also producing induced drag.

[HoHun]

Hi Flyboyj,

>in a jet you don't have scoops and cooling ducts, let alone that prop that although is producing thrust is also producing induced drag.

The dominating factors are the induced drag of the wing, and the higher equivalent power of the piston engine at low speeds.

A 8 kN jet provides 600 kW equivalent power at 75 m/s. A 1500 kW piston engine at 80% propeller efficiency provides 1200 kW.

However, at 200 m/s, the 8 kN jet provides 1600 kW equivalent power while the 1500 kW piston engine at reduced efficiency - say 75% - produces only 1125 kW.

That's the reason jets are better at high speeds, and propellers are better at low speeds.

For the generic example aircraft, the break-even between total thrust and total drag in a sustained turn occurs at about 580 km/h. Above that speed, the jet can turn at a higher rate than the propeller fighter, below that speed, the propeller fighter can turn at a higher rate than the jet.

Regards,

Henning (HoHun)

[Soren]

Hohun,

I have the thrust output figures for the different aircraft in Kgf, and from these the conclusion is that the average piston engined fighter in 1944 produced roughly 1,800 - 2,000 Kgf of thrust at a standstill. By comparison the BMW 003 produces a constant 815 Kgf throughout the speed range.

Knowing the above we can quite safely assume that at speeds above 450 km/h the He-162 will have a higher sustained turn rate than a piston engined fighter with a similar lift loading.

[FLYBOYJ]

Originally Posted by HoHun

Hi Flyboyj,

>in a jet you don't have scoops and cooling ducts, let alone that prop that although is producing thrust is also producing induced drag.

The dominating factors are the induced drag of the wing, and the higher equivalent power of the piston engine at low speeds.

A 8 kN jet provides 600 kW equivalent power at 75 m/s. A 1500 kW piston engine at 80% propeller efficiency provides 1200 kW.

However, at 200 m/s, the 8 kN jet provides 1600 kW equivalent power while the 1500 kW piston engine at reduced efficiency - say 75% - produces only 1125 kW.

That's the reason jets are better at high speeds, and propellers are better at low speeds.

For the generic example aircraft, the break-even between total thrust and total drag in a sustained turn occurs at about 580 km/h. Above that speed, the jet can turn at a higher rate than the propeller fighter, below that speed, the propeller fighter can turn at a higher rate than the jet.

Regards,

Henning (HoHun)

OK -

I could tell you that the jets I've flown are slow in building up airspeed at lower airspeeds (confirming what you say). At about 200 knots they seem be able to start to accelerate quicker as well as build up and retain airspeed. On the reverse end they don't want to slow down easily. On landings you're watching airspeed and anticipating that slow spool up should you have to go around and if you allowed too much airspeed to diminish. I'm talking T-33s, L-29s and L-39s.

As this was pointed out to me - the back end of the power curve.

The Jet Provost seems a little better on spool up.

In essence when flying recips and then jets, the jets "feel slicker," especially at higher speeds.

[Soren]

Remind me to come fly with you next I'm in the states FLYBOYJ! I've always wanted fly one of those L-39's

[FLYBOYJ]

Originally Posted by Soren

Remind me to come fly with you next I'm in the states FLYBOYJ! I've always wanted fly one of those L-39's

If we plan it right we could do and L-29 and 39!

[Soren]

Now that would be cool!

What kind of money do you guys take for a ride ?

[FLYBOYJ]

Originally Posted by Soren

Now that would be cool!

What kind of money do you guys take for a ride ?

In the 29 it's about $2000 for about a 45 minute ride. That guy is in California. The 39 is a little more. I do work for a guy with an L-39 here in Colorado and he does unusual attitude and spin recovery training for new jet owners. I don't know what he charges but I'm guessing its got to be abut $4000 for a "lesson."

[Soren]

Roger that, gotta start saving up some money then