My datapoint:
We flew our trusty 177RG for over 800hrs behind a 4-cyl lycosaurus. Propeller was dynamically balanced to 0.1ips at our cruise setting of 2500rpm, so very low vibration.
As was to be expected, at lower rpm vibration was higher, but our usual cruise and climb setting was 2500 so we preferred to balance the prop at the higher RPM.
We never had an issue with cracking on the exhaust or the cooling baffling in those 800 hrs…except for the one flight that we did long formation flying with slower aircraft. Rather than using an extremely low MP, also not good for other reasons, we flew for two hours at 2200rpm. Beautiful scenic flight across the Alps, back from EDNY!
An inspection upon landing back home revealed several cracks in the cooling baffling and in the exhaust that had to be repaired.
…but it was a lot of fun!
Incidentally, our friend’s airplane also had a mechanical failure on that flight when he lost the engine on the last leg and managed to land a few meters short of a nice runway, totalling the airplane but not hurting anyone. He had been flying WOT, fixed pitch, most of the flight. I do not think his failure was connected to the flight regime.
(sorry, could not help posting the photos, I prefer to keep the memory of the fun flight rather than the cracks…)
a COL4 at 100kts will be very nose high, so t/o flaps will make it more comfortable and safer.
Not an ideal plane for formation flying. Outlook is not great at the best of times and it is very slippery. Why not get hold of a plane suited for the task?
Short answer: no, I definitely wouldn’t. A Columbia 400 simply isn’t made to be flown at 100 kt for an extended period of time.
Jenny (Lancair 320)
I wouldn’t fly in such slow formation with aircraft which should normally cruise at least 150 kts. Since slower aircrafts would probably need more frequent refueling why not just jump ahead of them to next airport, prepare nice welcome, help in dispatching them and then just catch up during next leg.
I have flown in a C400 (N400UK) and as an experiment we set up 11.5 USG/hr and peak EGT/LOP to see what speed it does, and as I have posted previously it did the same speed as the TB20 does at that flow rate: 139kt IAS.
So for 100kt the flow rate would be, I would guess, around 8.5 USG/hr.
Like I said above, it will work, of course, otherwise you could not land the plane if it could not do slow flight, but over hours is likely to bung up the piston rings, and it could take some messing about to sort it out. As I wrote in that long thread, been there and done it 
The poh does not list any performance figure bellow 136kts (30% rated power), I don’t think 100kts will be a good idea.
Yes, any SEP airframe should be able to fly at 60kts even the fastest ones, engine mp/rpm is another story…
Flyingfish wrote:
for several hours.
What about dividing it into two groups, one slow and one fast ?
Tell her to fly her aircraft at the standard cruise speed. It is OK to join friends for few pics but after that she should fly her different aircraft at her different speed.
Two points:
The aircraft can be flown for extended periods on the forward side of the power curve. Sustained flight on the back side of the power curve should be avoided for cooling concerns. So, if you’re having to add power to fly more slowly, don’t do it for long. If the aircraft has been flown slowly, though still on the fast side of the power for a longer period, a higher power, leaned run would be nice for the engine.
Formation flying must be well planned, and briefed. It is hazardous, and not to be taken lightly. I would not fly formation with untrained (in formation flying) and pilots I had not briefed. The topic of safe formation flying is beyond the scope of internet discussion.
Pilot_DAR wrote:
Formation flying must be well planned, and briefed. It is hazardous, and not to be taken lightly. I would not fly formation with untrained (in formation flying) and pilots I had not briefed. The topic of safe formation flying is beyond the scope of internet discussion.
While true, the amount of briefing/training depends if we are talking about a PPL flyout? or an air display?
For the former, you need a radio for calls + comm failure protocol + nice camera for pictures and PPL who can fly a constant speed, heading and height?
For the latter, I don’t think you will able to do 3h of the latter without getting wet pants, especially when mixing different aircraft specs/crew mentality…
