914 cruise performance

[MartinH]

Just completed first long-distance trip with new 914 powered CTLS.  Keen to know how the following numbers compare with the experience of other folk ...

FL 115

MAP 34.5 in

FF 28 lph

RPM 5250

TAS 140 kt

Experimented a bit but was unable to determine for certain whether higher RPM increases TAS or what the ideal MAP/RPM combination is at that altitude.

Any and all responses will be appreciated.

Thanks,

 

-- martin

 

[Anticept]

Do you have IAS?

TAS won't only be airplane specific, it will be based on atmospheric conditions too and that doesn't help us compare performance, unfortunately

[MartinH]

IAS 115 kt

[Ed Cesnalis]

When I got to cruise in the 914 powered Europa I always said it would translate to 140kts in my CT.

I find 140k TAS believable and expected with more speed available higher up.

[Madhatter]

Unless you can change prop pitch turbocharging does very little at altitude. You just run higher RPM in thinner air. 914 is good in countries that can use constant speed props. I wouldn't wast the money.

[Roger Lee]

I agree with Madhatter. The 914 does not produce the performance it should without an in flight adjustable prop. A fixed isn't the way to go with a 914, but with LSA your stuck with it unless the new rule change allows it, but that also doesn't always make it retro-active. 

[Ed Cesnalis]

Rog,

Here in Florence, elevation 50' I still have my prop optimized for best speed at 11,500 DA.  (WOT @ 5,500 @ 11,500DA).  I like it there because of the still great performance down low ( I do throttle back for cruise ) and I get 128kts TAS up high.  The same prop and the 914 would only give ,me much better performance at altitude with no penalty over what I now have.  In flight adjustable would be better but I would still get to cruise at 145kts above 11,500.  All cruise above 7,500 would improve some.

It would be a lovely upgrade IMHO
 

 

[Madhatter]

Greater prop bite,  would translate into higher cruise at altitude with turbo, however takeoff and climb at sea level would put too much load on the engine.

[Ed Cesnalis]

6 minutes ago, Madhatter said:

Greater prop bite,  would translate into higher cruise at altitude with turbo, however takeoff and climb at sea level would put too much load on the engine.

Not at all.  As I said just above I'm already pitched for it and my lowly 912 climbs too steeply to see much at sea level unless I'm fully loaded. I already can realize 128kts and that's in the 60hp range.  Bump that 32 hp! 

[Madhatter]

It's all about manifold pressure regardless of engine model. 

[Towner]

I would love to see 140 knts tas, no matter how I got it!

[Madhatter]

Easy, just point the nose down but it never ends well.

[MartinH]

Thanks for the responses. This aircraft is equipped with an in-flight adjustable prop. 
 

My question - assuming wide open throttle at 34.5 in manifold pressure … for max speed should I set the prop for max or min rpm?

 

— martin 

[Madhatter]

Years ago there used to be Aeromatic propellers for a large number of aircraft. These propellers act just like a constant speed propeller but are not controlled from the cockpit. They don't use a governor but pitch is automatically adjusted through centrifugal and Aerodynamic forces. The low and high blade pitch stops can be adjusted to match the engine and aircraft. I guess with modern constant speed propellers there was no need for them anymore. This would be a great prop for LSA as there is no pilot controllable mechanism. Probably not enough LSA aircraft in the US to make it worth while.

[Skunkworks85]

16 minutes ago, MartinH said:

Thanks for the responses. This aircraft is equipped with an in-flight adjustable prop. 
 

My question - assuming wide open throttle at 34.5 in manifold pressure … for max speed should I set the prop for max or min rpm?

 

— martin 

I see your information says Cape Town, I will assume your in Africa? I don't think you will get many people on this forum have experience with the inflight adjustable or with a 914, as the US regulations do not allow it. (the Inflight adjustable prop) 

[Tom Baker]

11 minutes ago, Madhatter said:

Years ago there used to be Aeromatic propellers for a large number of aircraft. This would be a great prop for LSA as there is no pilot controllable mechanism. Probably not enough LSA aircraft in the US to make it worth while.

it would not be allowable for LSA, unless they change the definition. They only permit fixed or ground adjustable.

[Madhatter]

Always killing my dreams

[kinoons]

3 hours ago, Tom Baker said:

it would not be allowable for LSA, unless they change the definition. They only permit fixed or ground adjustable.

My understanding is that single lever engine control for both rpm and prop pitch was/is under consideration for Sport pilots, as that would need the “easy to fly” moniker. 
 

 

[Anticept]

3 hours ago, Madhatter said:

Always killing my dreams

Believe me, if it weren't for that, several of us on this forum would have already had such propellers.

[Ed Cesnalis]

8 hours ago, MartinH said:

Thanks for the responses. This aircraft is equipped with an in-flight adjustable prop. 
 

My question - assuming wide open throttle at 34.5 in manifold pressure … for max speed should I set the prop for max or min rpm?

 

— martin 

You can't begin with 34.5" @ WOT and then adjust prop pitch because it will change your manifold pressure.

Begin with WOT.  Now adjust  prop to get maximum manifold pressure without exceeding 5,500 RPM.   More simply with WOT just adjust prop till you get as close to 5,500 as you can without exceeding and you are at best speed.

[Tom Baker]

4 hours ago, kinoons said:

My understanding is that single lever engine control for both rpm and prop pitch was/is under consideration for Sport pilots, as that would need the “easy to fly” moniker. 
 

 

Yes, but who knows when that will happen. 

[kinoons]

12 hours ago, Tom Baker said:

Yes, but who knows when that will happen. 

A man can dream, right?

 

I’m also expecting single lever control to greatly increase the cost of an aircraft that is equipped with one. As is frequently the case, if you want better performance you have to pay to play.  

[Madhatter]

Until any regulatory changes are made E Prop seems to be the way to go for me. Also cost of a constant speed prop retrofit is significant, around 7-9 thousand for those I have seen. And by that time that's what toilet paper may cost by the way things are going.

[ct9000]

If you use the numbers in your flight manual you can't go wrong. t/o max five min 5800 at 40" MAP

                                                                                                      Cruise max continuous  5500 at 35" MAP

                                                                                                      Normal cruise for me     5250 at 33" MAP

                                                                                                                                       or      5000 at 31" MAP

                                                                                                      Econo cruise                    1800 at 29" MAP

Speed will vary with altitude. At low levels I normally see about 118 to 125 IAS and TAS are close to same and at 8500/9500 i see about the same IAS or even a bit lower but TAS is 20 or so higher

[FlyingMonkey]

Sounds like a fun airplane.  I can hit 130KTAS+ at altitude, so 140KTAS sounds about right for the 914.  But that is at 5250rpm...I wonder what you'd get at 5500rpm...