This article seems like a good 2018 read for market forecast returns:
Some sniglets:

Quote: I totally reject the notion that bonds have more risk than stocks. A broadly diversified stock fund has more risk in a day than a similarly diversified high-quality bond fund, such as iShares Aggregate Bond Fund (AGG), has in a year. Never forget that on Black Monday 1987, stocks lost over 20% in one day, which equates to six standard deviations (six sigma) of the AGG in one year, meaning it should happen no more often than once out of every 294,117 years.

seven-warning-signs-of-market-gurus-and-which-forecasts-you-can-trust

Well ... well ... well! What do we have here?
There are many ways to price the market. I can remember within the past couple of years Liz Ann Sonders of Charles Schwab use to tout the Rule of Twenty as being plenty. I have not heard her speak much on P/E Ratios recently.
Old_Skeet uses a blended P/E approach using both the TTM and FE. In this way credit is given for what stocks have done and are expected to produce. Then, I apply the Rule of Twenty as being plenty. My number computes to a P/E ratio of 20.7 as of market close 12/29/17. Still pricey at this number indicating the 500 Index is about 4% overvalued, by my p/e mythology.
The 500 Index Blended P/E ratio is one of the feeds I use in my market barometer.
And, so it goes ...

High valuations has never been a cause for bear markets.
This is weak gruel for Stewart, and it is incredible he links it in any way to the election (when the whole world has done the same), but has some good quotes:
https://www.nytimes.com/2018/01/04/business/market-dow-2018.html

I had to switch over my 401k at the beginning of 2017 as my employer was acquired by another company. Thinking that market is at a high and due for correction, I held 60-70% in stable value fund and invested the remaining conservatively in a bond fund, OAKBOX, and a few aggressive domestic and international funds. Though out the year, I moved the money to these funds from stable value fund, but still kept it at around 50% - a bad move in retrospect.
I brought down the Stable value fund to 30% of my 401k as part of 2018 adjustments, still relatively high but not getting the courage to go all stocks at this high of all markets. Added to OAKBX, FTBFX, GTDIX, and FIDKX.
In my IRA accounts, I moved cash to VIAIX - V'rd International Divident Appreciation index fund. Opened a position in PRLAX.

@DavidV
I must have been writing my comment above when you were posting your questions. The cash is left in her brokerage account for use as needed -- mostly for monthly release via checks to pay for living facility expenses and supplemental in-room care expenses. Her SS income takes care of food not provided by the facility, medications, insurance payments, clothing, hobby supplies, other day to day expenditures, and some of her in-room care expenses. I just finished replenishing the cash portion of her account as part of the year-end portfolio rebalancing process. The current withdrawal rate is approximately 8% of the start-of-year account balance. The account balance increased slightly during 2017 due to investment returns. When (not if) the markets get upset, the account will trend downward -- at least for some period of time. The rate at which it will trend downward will be in part dependent on whether there are significant future increases in the level of her required living facility expenses. The level of stocks in her account will probably get ticked up slightly following any substantial stock market correction if the level of her living facility expenses does not dictate more conservative positioning for her account at that time. I hope this helps.....

FYI: As the S&P 500 climbs higher and higher, its trailing 12-month P/E ratio continues to climb as well. And there won’t be much opportunity for multiple compression until the bulk of S&P 500 companies report Q4 numbers in late January.
As shown below, the S&P’s 12-month P/E is now at 22.88 — just a hair below 23.
Below is a chart showing the S&P’s P/E ratio going back to 1980. The line is red when the P/E ratio is above the level it’s at right now. As you can see, there have only been a few periods over the last 35+ years where the index’s P/E was higher. It didn’t once get above this level during the 2002-2007 bull market, but it was consistently above 23 during the final three years of the bull market that ended in early 2000. From 1998 to 2000, the S&P’s P/E expanded from 23 up to 30+ as the Dot Com bubble reached its zenith. Over this period, the S&P experienced a massive rally as the Tech sector soared. While valuations are indeed elevated right now, we always note that high valuations alone are not a catalyst for corrections or bear markets.
Regards,
Ted
https://www.bespokepremium.com/think-big-blog/sp-500-pe-ratio-approaching-23/

@davfor, Thanks for your income recipe. I remember @rono always mentioning - "invest in what you buy". Your healthcare comments make me think that a health fund would serve almost all retirees well. My thought...add VGHCX or PRHSX to this recipe.
Also, you mentioned that you are managing this portfolio for your sister. This is as important as the income recipe - who will manage this portfolio? Even Warren Buffet has toiled with this concern (portfolio management) for his wife's portfolio and he suggests 90% SPY and 10% ST Bond (cash).
I believe she would take her yearly withdrawals from the cash side, then re-balance the portfolio once yearly.
KISS

~2y of cash (say) would leave ~$450k; how to get $24k/y out of that with a fine mix of fine bond funds? >5% is needed.
When I run 'money last' calculators, it does not show making it to age 70. (6% return, 2.5% inflation, 10% fed marginal bracket -- reasonable?)
$476k (1y cash) with the above data gets one to 30y, yes, but no farther.
Not seeing how such bond heaviness is going to work.

FYI: The Dogs of the Dow strategy suggests investors buy the blue-chip index's 10 highest-yielding names at the start of a given year with the idea that the stocks can potentially top the broader market in the year ahead. “Dogs” strategies are not confined to the Dow or U.S. stocks, as confirmed by the newly minted Arrow Dogs of the World ETF DOGS, +0.00% DOGS tracks the ex-U.S. AI Dogs of the World Index. The index selects the five worst-performing countries where a return reversal or move back toward the mean or average is anticipated. The index has a contrarian approach that looks for deep value among a universe of 44 countries,” according to Arrow Funds.
Regards,
Ted
https://www.marketwatch.com/story/a-howling-good-idea-country-dogs-in-an-etf-2018-01-04-10464722/print
ETF. Com: 1st New ETF Of 2018 Debuts:
http://www.etf.com/sections/daily-etf-watch/1st-new-etf-2018-debuts
Arrow Funds Website: DOGS
http://arrowfunds.com/default.aspx/MenuItemID/1450/MenuGroup/Arrow+Dogs+of+the+World+ETF+(DOGS).htm

FWIW
I have been handling the brokerage investment account for a disabled sister for almost 20 years. Periodic withdrawals from that account together with SS (previously SSDI) have been her only source of income since her husband passed away several years ago. (By income, I mean dollars available to pay for living expenses. This could include some withdrawals of principal as I think on a total return basis.)
My first thought is there needs to be a set-aside of CASH. At minimum, I would suggest a 1 year set-aside, significantly more if rapidly increasing medical expenses are a significant concern. That set-aside provides a cushion for emergencies and also helps you to roll with the punches through the decades as the markets churn.
The comments @bee made about VWINX make sense to me. That fund has been around since the mid-1970's and has successfully navigated both rising and falling interest rate environments as well as both bear and bull stock markets. The comments @LewisBraham made about the challenging current market environment also make sense to me. So, going 100% into VWINX does not currently seem advisable to me. My SWAG suggestion would be putting maybe 35% of the assets available for investment into VWINX.
The general idea behind the suggestions @LewisBraham make for an investment mix also makes sense to me -- for the remaining 65% of the assets available for investment. My sister's account has included both RPAGX and ZEOIX since January 2016 (January is when most portfolio changes for the year are made).
VWAHX makes sense to me with maybe a little VWEHX mixed in if medical expenses will keep taxes from being an issue. Taxes might not be an issue anyway given the new personal exemption limits. That's something to look into.
Including a multi-sector bond fund in the mix also makes sense to to me - @Mark suggested PONDX. That fund has significantly outperformed VWINX when viewed since inception in 2007 due to its relatively strong performance during the bear stock market. But, can it continue to perform that well? Perhaps mixing it 50/50 with PTIAX in this component of the portfolio would make sense. Lumping GTEYX into your thinking about multi-sector bonds might also make sense.
If rapidly rising medical expenses are a potential concern, including a conservative bond fund such as DLSNX also makes sense to me. Holding a fund like this can also be a comfort when the markets turn against the portfolio.
A final thought. There needs to be some flexibility to decrease the withdrawal rate in the years following a major market decline unless STRICT NECESSITY does not permit this to happen. Otherwise, accepting the strong possibility/probability of the portfolio being exhausted as some point in the future is necessary.
I hope these general comments are helpful.....

I avoided mentioning PONDX because I was trying to envision worst-case scenarios going forward. I concur in the take that the longterm future is unlikely to be like the bull past we have enjoyed. Looking chiefly at GOs' UI in Premium, I still think trying to achieve the $24k/y would entail over half but hopefully not two-thirds in DODIX or Vanguard equivalent, with the rest --- as much as comfort-bearable --- in TWEIX / SPLV / CAPE or a combo of them. 40% or more.
Else VWINX, though I do not think it will quite hit the almost 5%-withdrawal mark.
Or this might do best, since security is paramount:
https://personal.vanguard.com/us/funds/snapshot?FundId=1263&FundIntExt=INT&ps_disable_redirect=true
or
https://www.fidelity.com/annuities/immediate-fixed-income-annuities/compare

What about something like VWEHX or PONDX? VWEHX is risky to the principal I know but as long as the income keeps rolling in it'll recover given his stated time frame. PONDX is less risky for an almost equal effect. Have smaller amounts in Ted's 2 suggestions to absorb any excess distributions above his needs. It's 14 below zero outside (read: brain freeze) so show a little mercy if my thinking is way off base.

@DavidV- With respect to your question: "What would be optimal investment for consistent income return of 4%", I think that @bee, above, gives you a pretty good insight. Both @Ted and @bee are well regarded with respect to financial matters; because they both mention VWINX perhaps you should give that fund particular attention.
The problem which all of us face is that all data sets for financial calculations are backward-looking: forward-looking data sets are very hard to come by. @LewisBraham, immediately above, expands on this.
@MikeM, above, makes an excellent suggestion with reference to on-line "Monte Carlo" sites which can be very helpful in analyzing individual retirement schemes. The Monte Carlo simulators have long been championed here on MFO by another poster, @MJG.
I've used the "Search" feature to go back and find a few of his references and links to such sites:
MJG Post #1 provides this Monte Carlo link.
and MJG Post #2 provides this Monte Carlo link.
You mentioned that "He will get help in portfolio management." Perhaps it would be helpful if you could expand a bit on this aspect- will he have the benefit of a professional manager of some sort?
We all wish you well in your efforts to help.

@AMatFO.
Your welcome! I am not sure what the initial minimum investment amount is at Fidelity (probably $2,500 like most other funds offered?), but it cannot be less than Scottrade's $100 plus T/F of $17 to purchase it.
Incidentally, I purchased CNRYX in my Scottrade account prior to establishing a CNRYX account with the transfer agent. I made an initial investment of $100 with the agent with no problems.

The other problem is this. VWINX is an excellent fund because of low fees and good management. These facts will likely continue into the future. But to project its past performance into the future is a mistake. Consider the author of the aforementioned seekingalpha article's premise regarding backtesting. He looks back to January 1, 1992.
These were the conditions for the market in January 1992:
Dividend yield of the S&P 500: 3%
multpl.com/s-p-500-dividend-yield/
10-Year Treasury yield 7%
macrotrends.net/2016/10-year-treasury-bond-rate-yield-chart
10-year Shiller P/E ratio 19
https://dqydj.com/shiller-pe-cape-ratio-calculator/
Here is where we are today
S&P 500 Dividend yield: 1.77%
10-Year Treasury yield: 2.4%
10-year Shiller p/e: 34
To back-test and assume the past from January 1992 is prelude for the future today based on these numbers I think is a mistake. We have lived through a historic period of falling interesting rates and rising stock valuations from 1982 onward. That period as far as interest rates goes is over and I'm not sure how much longer the rising valuations will continue. Creative thinking is necessary.

What would you recommend to maximize his investment income?

The investment should be safe as there is no other money to live on.

I think this is the crux of the problem when trying to give advice on this. These 2 "wants" are contradictions. Old_Joe made this point a couple times. Basically expecting to withdraw $24k and increasing each year for inflation and wanting it to last 45+ years has little probability of succeeding with any 60:40 or even 80:20 portfolio for that matter. The 4% rule I believe is based on a 25 or 30 year life span. Bee spelled it out in her post. Hate to be a wet blanket, but anything less than 100% equities probably can't last.
Maybe it is more realistic to plan 20 years and reevaluate circumstances periodically.
P.S., here is where Monte Carlo would be helpful at least for a realistic view of expectations.

@LB, by equity-aggressive I meant proportionally, not the holdings themselves. I would avoid foreign for this person.
VWINX looks like the choice, yes. Interesting its UI is high-ish (greater than VOOG and DSENX, e.g.).
If someone was 'managing' >1 fund, I would consider a mix of TWEIX and DODIX if FPURX dents comfort level. SPLV or CAPE could be the equity position instead of TWEIX, of course.

Thanks, @TheShadow. I did buy CNRYX few months ago at Scottrade with a transaction fee. Scottrade mutual transaction fees are lower than Fidelity, Schwab and TDA.

FWIW, a round trip will cost you $34 at Scottrade, $50 at Fidelity, and a whopping $100 at TDA.
Five purchases at Scottrade will cost you $85, but only $70 at Fidelity if you're willing to use their automated investment system and live with a lag of a day or so in getting your order filled. ($5/order once you have a position at Fidelity).
https://www.fidelity.com/cash-management/automatic-investments

FYI: Vanguard’s new chief executive has a challenge his three predecessors didn’t: How to how to grow a firm that is already the world’s second largest investment manager.
When Mortimer J. “Tim” Buckley started at Vanguard in 1991, the firm managed $77 billion and attracted $15 billion in new cash that year. It had 2,600 employees in one Malvern, Pa. office and was trying to grow with an unusual ownership structure—it is owned by its customers—and ultralow fees.
Regards,
Ted
http://www.cetusnews.com/business/The-Challenge-for-Vanguard’s-New-CEO--Keep-a-Behemoth-Growing-.HkBnTz9oQG.html
Vanguard Live Webcast January 4, 2018 at 7 p.m. EST:
https://pressroom.vanguard.com/news/Media-Alert-Vanguard-CEO-Tim-Buckley-And-CIO-Greg-Davis-To-Discuss-Markets-Economy-During-Live-Webcast-010318.html

FYI: The president of Fidelity Investments’ equity division is moving to a new role within the fund giant’s personal investing business later this quarter, leaving a post he has held since 2009.
Brian Hogan most recently led equity and high-income investing within the asset-management unit at Boston-based Fidelity. In his new role, he will be head of investment solutions and innovation within the company’s personal-investing unit, a Fidelity spokesman confirmed. The personal investing unit houses Fidelity’s brokerage platform, individual retirement accounts and other services for retail investors.
Mr. Hogan joined Fidelity in 1994 as a bond analyst. In 1998, he joined the stock picking unit and has held a number of roles including senior vice president of equity research. The equity division has faced scrutiny in recent months after The Wall Street Journal reported on a high-level firing there and allegations of sexual harassment.
Regards,
Ted
http://www.cetusnews.com/business/Fidelity-Moves-Brian-Hogan-Out-of-Equity-Division.rJANAA5Xf.html