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I've just past the 20 hour mark of phase 1 flight testing and would like to solisit some advice from the group. Overall I'm very pleased with the plane, handles like a sports car, but the performance isn't what I was expecting. I have a Corvair and Warp Drive prop set to max 3050 rpm in cruise configuration and no wheel pants yet. Rate of climb is only about 500 fpm at 1300lbs and it flys nose high as I've read from others. I do have wing lockers and I have seen some lifting of the front corners so I have taped these down with duct tape to see if there was any difference but I didn't see any change.
Two potential fixes I see are 1) install Vortex Generators as explained here http://www.stolspeed.com/id/60 or 2) Wing Root Fairings as described here http://www.utdallas.edu/~klaus/Airplane/wing_root_fairing.html. Or maybe a combination of the two.
Anyone have any real world experience with either of these modifications and if so what were the results? Any other suggestions? What sort of performance numbers are others getting with their HDS's?
Thanks and hope everyone has a great Christmas.
The factory airspeed performance figures were grossly overstated for both the CH601HD & CH601HDS series. I suspect the whole reason for the development of the CH601XL/650 series was to meet the demand for higher cruise speed. The other customer driven demand was for the aluminium spring gear. There are several HDS owners on this site that have done some serious speed fairings and other changes, but the factory numbers are not attainable. My wing lockers also flutter "lift" a bit. They don't do anything bad so carpet the inside to keep the air from entering and forcing the sun heated air inside the wing down the lightnening holes and venting hot air under your butt in the cockpit. (don't paint your wings black). I did install stol speed VG's as per instructions supplied and found a very significant improvment in the handling of the HD series wing. Lower nose angle in cruise, "float" on landing instead of a sudden "plunk" arrivial, lower stall speed and easier to fly slower.
For the poor climb rate part of it, you might want to make the prop into more of a climb prop, set the blades to a finer pitch. If you are only gettting 3050 RPM on your Corvair at top cruise speed, you are guaranteed to not be making much power at low airspeeds. Since the airframe will only go so fast, get more climb performance out of the engine/prop combination and I bet you will not hurt the cruise speed at all. You might even improve it by letting the engine rev to a bit higher RPM and make a bit more power. William Wynne posted a discussion of this on his website a while back, pointing out that the Corvair can rev much higher than a standard aircraft engine and suffer no damage at all, and it makes more power at the higher revs. Therefore, you can have a climb oriented prop to get better climb rate and yet still get good top end because the engine prop combination make good power at the elevated RPM's. You loose a little bit of efficiency at those RPM levels as the prop starts loosing performance, but you gain so much power that you still end up with more power going to the air than you get at lower RPM's.
As suggested by Bob Pustell I reduced the prop pitch from 8.5° to 7.5° and then to 6° to bring up the full throttle rpms, each reduction in pitch did increase the rpm's finally achieving a tad over 3300 however each reduction in pitch also reduced the top end and with 6° pitch I could barely hit 90 mph.
Next I installed STOLSpeed Vortex Generators which reduced the stall speed and did lower the nose a little but the prop just didn't have enough bite at this reduced pitch as discribed in William Wynne's 601 Engine Manual. So I increased to pitch to 9° and took her for a flight today. Top end has been retored which has further lowered the nose, take off roll is reduced and climb is better than with the lower pitch.
Getting another 200 or 300 rpm's out of the engine might help but it would have to happen in conjunction with reducing the prop diameter as flattening the Warp Drive prop isn't the answer.
i have a 601hd . operating out of 6,200ft. the performance was nothing what i expected. had a IVOPROP variable pitch. and a Rotax912. cruise was 88-92mph and stall was never better than 42mph. most of the time i had to touchdown at about 48-50 as i have alot of gusting winds. it was rather sad after what i was told before i bought it. also under 55mph don't try any turn steeper than 30 degrees.. i found there is not enough aileron to get out of it without diving down.. was rather scary the first time as i was a few hundred feet off the ground . also the luggage compartments on the wing need reinforcement on the lids, as they do really pull up when flying, but they don't affect the performance as i have had them fly open in flight and they just flap around.
I realise this discussion is somewhat dated but I do have some relevant info to add. I've put a wing root fairing on my 601 HDS and the most noticable improvement has been a less nose high attitude in climb with no loss of climb rate.
Please see attached article that contains measured changes in performance to 601HDS after wing root fairings and the theory behind them.
What speeds and fuel burn are you seeing at cruise? (my HDS tail dragger is under construction - considering a 3.0L corvair/wing root fairings/VG's)