Thread: Improving CTSW Speed?

Any advice on improving CT speed performance? Had the VP 3-bladed prop installed by Flight Design together with a 2-axis autopilot. On PPL there are no speed restrictions. Currently average between 105kts and 115kts TAS, at -12 deg flaps, no wind and engne RPM (Rotax 912S) of 4700 to 5000rpm. VP prop is not constant speed and for ideal performance, I find that setting one notch above fully coarse is best. On autopilot, if I trim the nose to a slight downward attitude, it steps up speed about 3kts.
Am doing a lot of X-country destination flying and an extra few knots would be great...well psychologically at least.

This may have been dealt with already, if so kindly direct me to the forum page,

Kind regards...Ron (ZU-ELZ)

Over here most of the CT's have their props set to give 5500 RPM, full throttle in level flight at the altitude you most often fly. I cruise at 5000 to 5200 RPM which gives me a TAS of about 120 knots at 3-5,000 feet MSL. We only are allowed -6 flaps. Minus 12 flaps, like you have should increase speeds 3-5 knots. I don't understand why you are so slow. Must be your prop pitch and the lower RPM's you run. Have you measured speed over a known course?

Originally Posted by Ron

... of 4700 to 5000rpm. VP prop is not constant speed and for ideal performance, I find that setting one notch above fully coarse is best.

Your best speed is at 7,500' density altitude, flaps reflexed, and your prop pitched so that you get 5,500RPM at Wide Open Throttle.

"one notch above fully coarse" sounds like the biggest issue, for speed you want to be flat not coarse.

I"m pretty sure you could find 125-130kts true air speed while being kinder to your engine but it will be a lot louder.

cruising @ 4,700 to 5,000RPM doesn't tell the whole story, you have to consider mainfold pressure too. 5,000RPM @ WOT will be faster then 5,000RPM @ 50% throttle.

Sounds a bit slow. I think most of us in the States are seeing 115-120 knots TAS or maybe even a few kts more. Is the TAS value straight from a Dynon or calculated based on indicated A/S and OAT? Is your groundspeed consistant with what you expect from the TAS values you stated? We use fixed pitch props in the States pitched for between 5400-5500 at WOT. Its a good balance between climb and cruise, and as mentioned before is better for the 912.

Eric

I think with a variable pitch prop that I could control in flight, I would set it when I levelled off, so that wide open throttle gives 5200 rpm at cruise altitudes near 5-6000 feet, and I would criuse with wide open throttle. That should be easy enough on the engine, and fast. At higher altitides I would run at slightly higher rpms. Cruising below 5000 rpm is too slow per rotax and many posts on this forum. - WF

I know this sounds like a lie but seriously, I get about 112-115 with just 4800 rpms, my prop must be out of adjustment. Also plane is quite noisy...@5500, I blow right past 120. I really don't feel safe going any faster than that at this point in my skill level. Usually fly it about 3000' MSL.

Hi Guys..... thanks for all the feedback - and apologies for my late reply (I normally get an inbox notification on Outlook to tell me there is a foru reply...but it is not doing this for the past three weeks?). OK... my main thing here is that I am running below 5000rpm. This is due to the fact that we fly mostly hot and high. Johannesburg sits at 5500 feet plus. I was told to keep the manifold prssure at 22 ideally, so the rpm of 4700 to 5000 equates to this at my general altitude. It is almost impossible to get as low as 7500 alt density, except on the coldest of winter days here. South Africahas a very temperate climate, seldom dropping below 15 deg celcius on a mid-winter day. Am I running too low RPM? At 5200 plus, am I harming the engine on long hauls. ?

I need to get this right, because I would like to do CT proud with the following just published local challenge.....

"...The ultimate air race – from Robin Spencer-Scarr
Dear Fellow Air Racers,
You have heard whispered rumours around the paddock, at the fuel bay or even in the pub.
You may have heard it through the grapevine or even on AVCOM.
Well now it is official. The Ultimate Challenge Air Race is on again!

The race will be held at the Witbank Airfield on Saturday 21 August and is NOT a handicap race. It is open to anybody and any aircraft that can take-off and land on the Witbank runway. The format and rules are simple and easy to understand:
• GPS' are to be used
• The course is straight out from a flying start for 250 kilometers (135nm), a quick U turn and back again over the windsock
• Jets, turbines, superchargers, turbochargers, diesels, petrol types, two-strokes and rotaries - all are welcome
• Categories are all based on the gross weight of the aircraft and its means of propulsion
Ok, so what does this mean?
It means that a Turbo Saratoga that weighs about the same as a 210 and both internal combustion engine driven, will race against each other. Now we know this is not fair because the Saratoga is obviously much faster than the 210 and will easily win but, maybe the 210 is faster than all the other 210s as well as the Bonanzas in the same category. Also, one wonders, is a Cherokee 235 faster than a 182? Last year we had some amazing performances from some awesome Jets (including a Boeing 737 with remarkable speeds attained by the likes of Pat Hanley in a Mooney and Chris Briers in the TBM 850. Perhaps a PC 12 or two this year?

The next exciting item on the agenda is the fact that this race will be recognised by the FAI as an official event. This means that, as we will be covering 500 kilometers, the category winners qualify for an official record in the both the 100 kilometer and 500 kilometer closed circuit fastest time. The entry fee is R500 per aircraft and that the pilot as well as the co-pilot must be SAPFA members (this is not negotiable). Please enter on-line on the SAPFA website:
Ultimate Challenge Air Race Entry | South African Power Flying Association
Office: 014 597 3652 or mobile: 083 3102850...."

PS - how do I switch the message notification thingy back on?

Regards...Ron

If you have a ground adjustable prop and you set it for 5500 rpm as I posted above, I do not think you need to worry about running a constant 5200 in cruise. Many of us in the US have our props set that way and I have not heard of any problems. Some run 5500 in cruise and all seems OK.

How involved in the prop adjustment? We have the 3 blade Nuform our our 2005 CTSW (bought earlier this year) and I get about 4,900 to 5,000 WOT in the 3,500-5,500 altitude range. So I know we need to flatten it out a bit (and plan to do so soon).