Cruise Descents

[csfahey]

I have learned more in the last 3 months of Mooney ownership than I have learned in nearly 25 years of flying.  An article I just read by Jeff West in the IFR magazine regarding flight profiles brought up another question that I would like to get an answer to.

My question to other Mooney owners is how do you setup your Mooney for cruise descent whether it be in advance of shooting an approach or just a large altitude change?  Do you just push the nose over a little and pick up speed, or do you adjust the MP and Prop for a specific result?  If so, which ones do you adjust and how much? 

Despite having had enough complex training to obtain an endorsement, I was startled to find one of the techniques to descend is to decrease the RPM to decend but set the MP high.  I am still trying to find more information on this aspect of flying, complex operations,  but I am finding that there really isn't a lot of general information on technique, just theory on the mechanics.

[Earl]

IMO opinion the answer is it depends.  How high are you and how quickly do you need to get down.  Is it a smooth day or do you expect turbulence on your descent.  On a smooth day I usually nose over and try to descend near the yellow arc to recover all that potential energy I created with climb thrust.  If there are speed restrictions, turbulence or I am too close to the airport or waypoint with an altitude restriction I will sometimes use my speed brakes which are most handy.   What I try to avoid is reducing MP below 20" so the engine doesn't cool too quickly.  If 20" and speed brakes don't do the trick them I would bring the prop back to help slow you down.  In the APS course they recommended WOT descent and control airspeed with RPM and speed brakes. I generally don't do it that way but that's what they showed in the air work videos with a V35 Bonanza. 

[skyking]

I generally lower the nose and reduce the MP at 1" per minute to avoid cooling off too fast.

i try and keep it at 500-600 FPM desent.

[Parker_Woodruff]

Wide open throttle as long as it's not turbulent.

[wnl]

If it is smooth I usually nose over and don't touch the power. It's nice to see 180 knot airspeeds. I always target a 500 fpm descent as I find it is easiest on my passengers. For most of my destinations I have to descend well before the airport, so there is no risk of arriving too high. But when necessary I will estimate my minimum distance for top-of-descent and request a descent before reaching it. Closer in I will start reducing throttle and prop as needed.

Bill

 

[hansel]

Quote: skyking

I generally lower the nose and reduce the MP at 1" per minute to avoid cooling off too fast.

i try and keep it at 500-600 FPM desent.

[Cruiser]

I try for 350 fpm descents. The longer I can stay in a gravity assisted, low fuel high speed configuration the better. 

[KSMooniac]

Shock cooling is a myth, so you don't need to fret about cooling off the engine too fast.  If it were a problem, shock heating would also be a problem, and we would be cracking cylinders on takeoff.

I run WOT until setting up for an approach or within 5 miles of entering a pattern for a visual approach.

If I'm flying instruments and just need an intermediate descent, then I'll just reduce MP to maintain a constant-airspeed descent, and then restore MP when reaching the target altitude so I won't have to mess with trim.

[mooneygirl]

There are always exceptions to everything but, normally I lower to 20" MP, lower to 2000 RPM and the nose drops to achieve approx. 400-500 FPM.

[Jeff_S]

I program my altitude preselector for a 500'/minute descent rate and the target altitude. Then I take the number of thousands of feet I have to lose and multiply by three to figure out how many miles out to start the descent. I usually add a few miles to that since I pick up speed in the descent. Then I just reduce MP gradually to keep the same MP I had at cruise, or to keep from zooming too high if there's turb, etc.

 

[Ned Gravel]

This is my approach after about 500 hours on my E model.

Altitude hold - OFF.  

Reduce MP by 1" for every 100 fpm desired for the desent (doesn't really work beyond 5" for 500 fpm). No reductions below 20" in cruise descent looking for 350-500 fpm, depending on turbulence.  For approach descent I do not reduce MP below 18" and looking for 500 fpm. 

More turbulence, less MP to keep IAS out of the yellow arc.  No turbulence, IAS in yellow arc OK so long as I stay below redline. 

Prop stays at 2500 RPM.

[RJBrown]

The inch a minute is for TURBOs only. That is what Rocket reccomended and thats how I flew it.  On the normal Lycomings. I just nose over and keep the speed up as long as possible. Adjusting the mixture to keep from going too lean as I decend. Where I am based I land at 5880' so I am never real high on the power. At lower altitudes I keep it at 20" in the decent.

[Ned Gravel]

Quote: RJBrown

The inch a minute is for TURBOs only. That is what Rocket reccomended and thats how I flew it.  On the normal Lycomings. I just nose over and keep the speed up as long as possible. Adjusting the mixture to keep from going too lean as I decend. Where I am based I land at 5880' so I am never real high on the power. At lower altitudes I keep it at 20" in the decent.

[skyking]

Randy: I am also with Ned.

When i did my transition training to the Mooney, the instructor was quite adament about the 1"/ Min.

Much like the lean of peak VS Rich of peak there will always be a discussion about which is correct.

[csfahey]

As far as the 1" per minute goes, if I push the nose over and without pulling power back and pick up a lot of speed, it would seem that I am going to have a lot of cooling from the increased airspeed possibly to the same degree as decreasing the MP and descending while maintaining the same airspeed as cruise. 

As far as prop settings go, MooneyGirl was the only one that mentioned this and stated that she uses 2000rpm.  Does anyone else use the prop during the descent or just push it forward for full?  If set to 2000 rpm now the intake risks of carburator icing come into play.

[Lood]

I usually plan to descend at 300 ft/min - mainly to protect my kids' ears. When cruising high, the descend starts quite far out from my home field. I normally trim the airplane for a 300 ft/min descend and then keep the MP at the cruise setting. This means roughly about 1" MP decrease every two and a half minutes. From 9500' for instance, I just keep it at 20" and once I am about 4 mins from the field, I start reducing power at 1"/min. This puts me in the circuit at 16-17" MP and also gets the speed down quite quickly once I start to level out. All temps stay put and I still get a good 150-160kt ground speed during the descend.

[MooneyMitch]

Whoops!  The Mooneygirl post was actually mine.  I didn't realize we were on her posting page at the time of the post.  That's actually my information of what I do in the R model.  I do normally turn the prop back to 2000 and reduce MP to 20" and trim down to achieve the 400-500 FPM decent.   This keeps my speed similar to cruise during the process.   I normally start all my decents far enough out from the airport to keep things smooth and gradual. 

Of course there are lots of other combinations using MP, RPM, gear and speed brakes.  Smooth air and fast, I'll leave all alone and just trim the nose to 400-500 FPM.  Rough ride, I'll slow things down us everything available to keep the manuevering speed.

[67M20F]

I to just trim it out for around 4-500, WOT, it makes up for some of the long climbs, and its cool to see the high ground speed.

Don't say that shock cooling is a wifes tale up here, they will get all rustled up by that, I am not saying it isn't or is, just many up  here think its a very big thing.

I was always told if you decend with a little power then its almost impossable to shock cool, and that is how I allways do it.

[Immelman]

If I am flying up high, I am usually ROP (because I lose too much power LOP). For descent, I simply go LOP on all cylinders which results in a nice power reduction, low fuel flow, keeps the engine from cooling too rapidly (my engine runs cool anyway), trim for 500 fpm descent, and take whatever airspeed I can get. My airplane (66E) has a low redline & top of green arc (189/150mph). I am comfortable with well-into-the-yellow descents but in smooth air.

Once down low I will back off on the throttle only when, say, 5000' or lower (mind you, I'm LOP all the way down, full throttle, making maybe 50% power).

Anyway this setup has worked well for me and results in minimal fussing around with the engine or worrying about temperatures.

[eaglebkh]

I have a different school of though on MP/RPM's for descent.  I have a 3-blade, so I usually keep the RPM's at 2500 for descent to increase drag and keep the engine warm.  Shock cooling or not, CHT's typically approach the bottom of green arc during descent.  Manage airspeed with MP and landing gear.

Also, do any of you keep your gear down throughout the entire approach phase, or just near the final approach?  I drop the gear just before the first step-down fix and usually leave it down.  I have problems keeping airspeed below 120kts during descents without the landing gear, and unless I am below 80kts, it's darn near impossible to retract the manual gear.

[jlunseth]

I usually drop the gear somwhere between the IAF and the FF depending on how far that is.  I may drop it before the IAF if the IAF-FF distance is short.  I want to slow to 90-100 at the FF, and the gear is the best way to do that.  Speedbrakes work dandy also, but a "speedbrake up" landing is not nearly as consequential as a "gear up."  I am killing two birds with one stone, getting the gear down (and then rechecking it during the approach), and using the gear as my speedbrake to slow down.

[Ned Gravel]

Brandon & Jlunseth:

I have a two blade Hartzell and it is very useful in acting as a speed brake on final, or just before the FAF, when the GUMPS check will push it to its max RPM.  So, Brandon, yours should be even better.

My gear also comes down between the IF and the FAF (or in the downind).  I have learned that dropping them as fast as 140 mph is not difficult and they are great as speed brakes too.  Have not had to do this very often and on bumpy days, I will generally drop them before crossing midfield when VFR prior to the turn on downwind.   With the MP as low as 18" to 20" with the gear down, my Mooney is as slow as 120 mph in descent/approach.

I need to drop MP to 15" or less to slow it down enough to deploy flaps at 100 mph. Then she is configured.  90 mph and stable for the remainder of the evolution.

[eaglebkh]

Quote: edgargravel

My gear also comes down between the IF and the FAF (or in the downind).  I have learned that dropping them as fast as 140 mph is not difficult and they are great as speed brakes too.

[FlyDave]

Quote: JimR

The forums are full of pilots that have never set foot in a Mooney that perpetuate this myth, and to an even greater degree the myth that tall people "can't fit" in a Mooney. The higher gear and flap speeds of the 201 might functionally be it's greatest, and least talked about, improvement over earlier models. It is hard to go down and slow down at the same time in many pre-201 Mooneys. Jim

[Lood]

Quote: JimR

Yes, I think that those low gear and flap speeds are largely responsible for the seemingly widely held misperception that Mooneys are "hot" airplanes that are hard to handle. Of course, nothing could be further from the truth, but perception seems to be reality these days. The forums are full of pilots that have never set foot in a Mooney that perpetuate this myth, and to an even greater degree the myth that tall people "can't fit" in a Mooney. The higher gear and flap speeds of the 201 might functionally be it's greatest, and least talked about, improvement over earlier models. Jim