Any 310Q owners here with the Colemill Executive 600 conversion?

I am flying one now and noticed there is a placard on the glove box which limits it to 2850 RPM for takeoff and 26" MAP to give 260hp per side for 5 min. Or 2700 RPM and 27" MAP.

Of course the sales literature shows 300hp from the IO-520E conversion.

The flight manual I have is wrong. Somewhere it was switched to the 550 conversion flight manual for the Executive II conversion.

I have a email in to Mike Jones aircraft to order the correct manual but they did get back and say the placard is correct.

So how do they figure the increased climb rate and single engine performance from sea level if the engines are restricted to 260hp per side (same as original)? I guess the similar conversion for Barons have the same placard.

I do notice with these engines it is a long throttle pull from full throttle stop to where the manifold pressure starts to reduce as your setting climb power. Seems like a long way before there is a manifold pressure change. Throttle plates are rigged correctly and cables / linkage are in good shape. Unmetered fuel flows are right on.

I can understand the limitation being for lack of funding to rewrite the flight manual back in the 70s when the conversion came out but was it for any airframe limitation or just lack of paperwork. How would that be affected by the Micro Dynamics VG installation with the option to reduce VMC markings?

I am curious if the Riley Turbostream 310 with 350hp Navajo engines conversion has any takeoff HP restriction?

Thinking of recent accidents.
Performing VMC demos with new owner/ multi student.

Airplane configured with Micro VG kit, radar nose and boots.
left idle and right full power.

6500ft Stall warning and buffet before loss of directional control with me limiting rudder travel
5500ft stall warning and buffet before loss of directional control Maybe slight yaw just before
4500ft a bit more yaw but not much before stall Buffet begins. Will need to really limit rudder throw for a decent VMC demo simulation. Even without the placard Manifold pressure limits for 260hp max.

Even with the larger engines it appears VMC occurs very close to stall speed with this loading.
Two in front seats. 90 gallons fuel total in tips with empty aux and no baggage.

Aft CG would probably be different but won't go there.

310Q with 260hp Rudder travel 25 degrees each direction
Turbo 310Q and 310R with 285 hp Rudder travel is 29.3 degrees each direction

Interesting Colemill did not use the higher rudder throw of the 285 hp airplanes to make that available for takeoff.

Cessna Manual recommends adding power to the inside engine during spin recovery!!

The IO-520E has a 5 minute limitation for operation at 2850 RPM / 300 HP at sea level. 2700 RPM / 285 HP is max continuous power.

Colemill conversions are great mods, with performance exceeding book specs for 310’s and Barons. The 26” limitation on takeoff was necessary since Colemill did not do the expensive flight testing needed to rewrite the performance data in the POH.

The performance is not the issue, they could have simply stated "no worse than book" and left it at that like many other engine STCs. The FAA doesn't require new performance figures as long as you meet or exceed the stock performance.

The issue was elevating Vmc. If you have higher power, Vmc goes up. Elevated Vmc would trigger some certification rules that limit allowed Vmc values.

Easy way around that, just publish a limit that keeps Vmc the same.

Mike C.

I'm just grumbling about misleading advertising saying they are 300hp. Yes 300hp engines but not for low altitude takeoff with the airframe STC.

If the only aerodynamic difference between the turbo 310Q and normal aspirated airframe is rudder travel increased from 25 deg to 29.3 to be able to use 285 hp It seems like that would have been easy to copy. But yes the shortcut was taken back in the 1970s and never revisited.

With the prop low pitch stops now changed from original 2625 RPM to 2850 RPM for takeoff it seems like that would make VMC worse at the STC placarded 260hp. Just like the 3 vs 4 blade Kingair conversions and low propeller pitch settings.

But flying a VMC demo with the Micro VG kit and using full power (disregard MP placard) it is hard to get it to slide off in yaw to the left before the wing shows the first signs of stalling. (well below original VMC marking) Granted that is not loaded to aft CG limit. Too bad the combo of VG kit would not allow full 300hp to be legally used with this STC.

Of course there are no redlines on the manifold pressure gauge and I don't think anyone has paid attention to the placard since it was installed 1977 under the copilot yoke on the glove box door.

Is the later 550 Bearcat STC the same?

I found a sheet among all the stuff my previous owners gave me with the airplane. Not sure how logical it is. I also have a 310q with the colemill executive 600.