Tilt Rotor Performance

[sonty]

hello
I'm student seeking information for my project of tilt rotor design...
i've many question...and tried hard to ask all my teachers but they don't know
questions::confused:
1. from hover to cruise altitude tilt rotor climb like and aircraft or rotorcraft...
i'm trying to find maximum rate of climb..and only have equation for aircraft
mode...
2. I'm given cruise speed of 450 kts and greater... how to ensure it is achieved
in design...means any formula or equation to verify...
3. speed for best range should be found...i don't know this either...
also it should be achieved at best altitude....i have also no idea how to find it

please help me to answer these question...i'm trying hard but nobody is explaining me...:{

[Gemini Twin]

No one can provide an answer because you have not supplied details of the design! Need basic configuration, max all up weight and power available at the very least. 450 kts cruise, that is really something and will need big engines even then not sure it's achievable with prop rotors (think of the drag!).
Here is the estimated performance of the AW609 (courtesy Wikipedia) which will provide you with a starting point:


Crew: 1 or 2
Capacity: 6 to 9 passengers or 5,500 lb (2,500 kg) payload
Length: 44 ft (13.4 m)
Height: 16 ft 3 in (5.0 m) nacelles vertical; 21 ft 10 in (6.7 m) nacelles horizontal
Wingspan: 38 ft 5 in (11.7 m)
Width with rotors: 60 ft 5 in (18.4 m)
Rotor diameter: 25 ft 10 in (7.9 m) each
Rotor area: 981.75 sq ft (91.2 m2)
Empty weight (http://en.wikipedia.org/wiki/Manufacturer%27s_empty_weight): 10,483 lb (4,755 kg)
Useful load: 5,500 lb (2,500 kg)
Max. takeoff weight (http://en.wikipedia.org/wiki/Maximum_takeoff_weight): 16,800 lb (7,600 kg)
Powerplant (http://en.wikipedia.org/wiki/Aircraft_engine): 2 × Pratt & Whitney Canada (http://en.wikipedia.org/wiki/Pratt_%26_Whitney_Canada) PT6C-67A (http://en.wikipedia.org/wiki/Pratt_%26_Whitney_Canada_PT6) turboshaft, 1,940 shp (http://en.wikipedia.org/wiki/Horsepower#Shaft_horsepower) (1,447 kW) each

Performance



Maximum speed (http://en.wikipedia.org/wiki/V_speeds#Regulatory_V-speeds): 275 kn (509 km/h; 316 mph)
Cruise speed (http://en.wikipedia.org/wiki/V_speeds#Regulatory_V-speeds): 260 kn (482 km/h; 299 mph)
Range (http://en.wikipedia.org/wiki/Range_(aircraft)): 750 nmi (1,390 km; 860 mi)
Ceiling (http://en.wikipedia.org/wiki/Ceiling_(aircraft)): 25,000 ft (7,600 m)
Rate of climb (http://en.wikipedia.org/wiki/Rate_of_climb): 1,500 ft/min (7.6 m/s)
Disk loading (http://en.wikipedia.org/wiki/Disk_loading): 15.8 lb/sq ft (77.1 kg/m2)

Probably you should spend more time on aerodynamics and aircraft and rotor craft performance studies before you get into the tilt rotor design. Your teachers should be able to help you with those subjects.

[Ascend Charlie]

Are there ANY prop-driven planes that can do 450kt??

Tip speed would be well over sonic, so blade stresses would be considerable, as well as drag changes along the length of the blade.

Go for something more sensible, 250kt.

[Gemini Twin]

Certainly not with a disc 25 ft in diameter! But remember to prop rotors don't turn any where near regular propeller RPMs.

[ShyTorque]

Ascend Charlie, the Tupolev Bear later variants were reportedly able to achieve slightly over 500 kits.

[riff_raff]

sonty-

A cruise speed of 450kts+ is probably not realistic with current tiltrotor technology. It would require far too much compromise in the overall aircraft design/performance.

In the US over the past 2-3 decades, NASA and other agencies have published a large number of technical papers covering performance of tiltrotor aircraft concepts, and any of these reports will provide you an analytical approach for estimating the performance of your tiltrotor concept. These papers are publicly available on the DTIC and NTRS websites.

[henry_crun]

Tough assignment. You can get a very approximate answer to prop-rotor thrust and efficiency by comparing mv (momentum and thrust) with half m v squared (energy and power) for your chosen disc area. I think I saw a full analysis by von Karman.

An important practical challenge is sorting out the blade twist, which is a compromise between hover and forward flight.

Sorry, can't help any more, way beyond my primitive academic level!

PS - here's a comparison chart I did many years ago, not sure how accurate it is:

http://mike-wsm.org.uk/zpp167.jpg